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Sample records for cofecu magnetic alloy

  1. First order reversal curve investigation of the hard and soft magnetic phases of annealed CoFeCu nanowire arrays

    NASA Astrophysics Data System (ADS)

    Almasi-Kashi, M.; Ramazani, A.; Golafshan, E.; Arefpour, M.; Jafari-Khamse, E.

    2013-11-01

    (CoFe)1-xCux (x=0.12-0.84) nanowire arrays were ac-pulse electrodeposited into anodic aluminum oxide templates. The electrodeposition was performed in a constant electrolyte while Cu content was controlled by off-time between pulses. Nanowires with 30 nm diameter and the certain lengths with the both bcc-CoFe and fcc-Cu phases were obtained. Magnetization and coercivity of the nanowires decreased with increasing the Cu content. Annealing improved the coercivity and a remarkable increase in magnetization of nanowires with high Cu contents was observed. A two-phase treatment was seen for annealed samples with high Cu contents. First order reversal curves showed a hard magnetic phase with almost constant magnetic properties and coercivity of ~2500 Oe. The results showed that main source of the various magnetic behaviors of the samples may be attributed to increase in soft magnetic phase. A single domain treatment with a narrow interacting field and coercive field distributions was also observed for the annealed samples with high Cu content.

  2. New magnetic alloys.

    PubMed

    Chin, G Y

    1980-05-23

    Three notable new developments in magnetic alloys are highlighted. These include rare earth-cobalt permanent magnets with maximum energy products up to 240 kilojoules per cubic meter; chromium-cobalt-iron permanent magnets that have magnetic properties similar to those of the Alnicos, but contain only about half as much cobalt and are sufficiently ductile to be cold-formable; and high-induction grain-oriented silicon steels that exhibit 20 percent less core loss as transformer core materials than conventional oriented grades. PMID:17772813

  3. Structural alloys for high field superconducting magnets

    SciTech Connect

    Morris, J.W. Jr.

    1985-08-01

    Research toward structural alloys for use in high field superconducting magnets is international in scope, and has three principal objectives: the selection or development of suitable structural alloys for the magnet support structure, the identification of mechanical phenomena and failure modes that may influence service behavior, and the design of suitable testing procedures to provide engineering design data. This paper reviews recent progress toward the first two of these objectives. The structural alloy needs depend on the magnet design and superconductor type and differ between magnets that use monolithic and those that employ force-cooled or ICCS conductors. In the former case the central requirement is for high strength, high toughness, weldable alloys that are used in thick sections for the magnet case. In the latter case the need is for high strength, high toughness alloys that are used in thin welded sections for the conductor conduit. There is productive current research on both alloy types. The service behavior of these alloys is influenced by mechanical phenomena that are peculiar to the magnet environment, including cryogenic fatigue, magnetic effects, and cryogenic creep. The design of appropriate mechanical tests is complicated by the need for testing at 4/sup 0/K and by rate effects associated with adiabatic heating during the tests. 46 refs.

  4. Magnetic properties of metastable Fe Pd alloys by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Yabe, Hiromasa; O'Handley, Robert C.; Kuji, Toshiro

    2007-03-01

    Metastable Fe-Pd powder samples with various Pd content were synthesized by mechanical alloying. Their fundamental properties, i.e., structure, magnetization and coercive fore are discussed. The saturation magnetizations of the metastable Fe-Pd powders gradually decreases with increasing Pd content. The coercive forces observed in as-milled samples are all less than 40 Oe. However, some of the heat-treated samples, notably, Pd content around 55 at% with L1 0 structure, shows Hc up to 1589 Oe.

  5. Production feature of soft magnetic amorphous alloys

    NASA Astrophysics Data System (ADS)

    Tyagunov, A. G.; Baryshev, E. E.; Shmakova, K. Yu

    2016-06-01

    Methods for making nanocrystalline alloys have been discussed. Temperature dependences of the surface tension (σ), electric resistivity (ρ), magnetic susceptibility (χ) and kinematic viscosity (ν) have been obtained. Comparison of the properties of amorphous ribbons obtained by the pilot and serial technologies has been conducted. Science-based technology of multi-component alloy smelting makes it possible to prepare equilibrium smelt, the structure of which has a significant effect on the properties of the amorphous ribbon before spinning and kinetics of its crystallization has been offered.

  6. Magnetic Damping of Solid Solution Semiconductor Alloys

    NASA Technical Reports Server (NTRS)

    Szofran, Frank R.; Benz, K. W.; Croell, Arne; Dold, Peter; Cobb, Sharon D.; Volz, Martin P.; Motakef, Shariar

    1999-01-01

    The objective of this study is to: (1) experimentally test the validity of the modeling predictions applicable to the magnetic damping of convective flows in electrically conductive melts as this applies to the bulk growth of solid solution semiconducting materials; and (2) assess the effectiveness of steady magnetic fields in reducing the fluid flows occurring in these materials during processing. To achieve the objectives of this investigation, we are carrying out a comprehensive program in the Bridgman and floating-zone configurations using the solid solution alloy system Ge-Si. This alloy system has been studied extensively in environments that have not simultaneously included both low gravity and an applied magnetic field. Also, all compositions have a high electrical conductivity, and the materials parameters permit reasonable growth rates. An important supporting investigation is determining the role, if any, that thermoelectromagnetic convection (TEMC) plays during growth of these materials in a magnetic field. TEMC has significant implications for the deployment of a Magnetic Damping Furnace in space. This effect will be especially important in solid solutions where the growth interface is, in general, neither isothermal nor isoconcentrational. It could be important in single melting point materials, also, if faceting takes place producing a non-isothermal interface. In conclusion, magnetic fields up to 5 Tesla are sufficient to eliminate time-dependent convection in silicon floating zones and possibly Bridgman growth of Ge-Si alloys. In both cases, steady convection appears to be more significant for mass transport than diffusion, even at 5 Tesla in the geometries used here. These results are corroborated in both growth configurations by calculations.

  7. Magnetic circuit design for miniaturized magnetic shape memory alloy actuators

    NASA Astrophysics Data System (ADS)

    Bolzmacher, C.

    2013-05-01

    Magnetic shape memory alloy (MSMA) is a relatively new kind of smart material. Upon application of a large magnetic field, it exhibits actuation strains up to 10% similar to thermal shape memory alloy (SMA) but shows significantly reduced response time in the millisecond range. Currently, application is restricted by the brittleness of the single crystal material, its nonlinear behaviour and the difficulty to generate and apply a magnetic field around 0.6T in order to exploit the full actuation potential. The focus of this work is on the design of miniaturized magnetic circuits for bulk MSMAs. Various circuit designs are compared such as toroidal and series-parallel shapes. Equivalent circuit as well as finite element simulation is used to increase the magnetic field in a characteristic air gap where the smart material is placed. A symmetrical toroid coil layout with the MSMA element at the center that allows easy integration of the actuator in various applications is described. Static characterization results of this actuator are provided. Using the described magnetic circuit and 5M - MSMA rods with dimensions of 20x2.5x1mm3, a peak displacement of 0.8mm and a blocked force of 4.5N was obtained. Further design guidelines for such miniaturized actuators are given.

  8. Microstructure and magnetic properties of Fe-Co alloys

    NASA Astrophysics Data System (ADS)

    Fingers, R. T.; Kozlowski, G.

    1997-04-01

    Fe-Co soft magnetic alloys exhibit high magnetic saturation, high yield strength, and moderate core loss. Use of such materials in cyclic high temperature high stress environments, such as generators and magnetic bearings, gives impetus to determining material properties. In particular, Hiperco® Alloy 50HS, provided by Carpenter Technology Corporation, has been a subject of our study. In order to fully understand the overall behavior of the alloy, both mechanical and magnetic properties must be investigated. Magnetic performance is a function of grain size, which varies with the annealing process. Fe-Co samples have been treated by various annealing recipes ranging in temperature from 1300 to 1350 °F and magnetic saturation along with hysteresis loop measurements made using a vibrating sample magnetometer. An etching and sample preparation process was developed and microstructural analyses were performed. The correlation between composition, heat treatment, microstructure, and magnetic properties of these samples is discussed.

  9. The use of amorphous boron powder enhances mechanical alloying in soft magnetic FeNbB alloy: A magnetic study

    NASA Astrophysics Data System (ADS)

    Ipus, J. J.; Blázquez, J. S.; Franco, V.; Conde, A.

    2013-05-01

    Saturation magnetization and magnetic anisotropy have been studied during mechanical alloying of Fe75Nb10B15 alloys prepared using crystalline and commercial amorphous boron. The evolution of saturation magnetization indicates a more efficient dissolution of boron into the matrix using amorphous boron, particularly for short milling times. The magnetization of the crystalline phase increases as boron is incorporated into this phase. Two milling time regimes can be used to describe the evolution of magnetic anisotropy: a first regime governed by microstrains and a second one mainly governed by crystal size and amorphous fraction.

  10. The use of amorphous boron powder enhances mechanical alloying in soft magnetic FeNbB alloy: A magnetic study

    SciTech Connect

    Ipus, J. J.; Blazquez, J. S.; Franco, V.; Conde, A.

    2013-05-07

    Saturation magnetization and magnetic anisotropy have been studied during mechanical alloying of Fe{sub 75}Nb{sub 10}B{sub 15} alloys prepared using crystalline and commercial amorphous boron. The evolution of saturation magnetization indicates a more efficient dissolution of boron into the matrix using amorphous boron, particularly for short milling times. The magnetization of the crystalline phase increases as boron is incorporated into this phase. Two milling time regimes can be used to describe the evolution of magnetic anisotropy: a first regime governed by microstrains and a second one mainly governed by crystal size and amorphous fraction.

  11. Understanding the magnetic anisotropy in Fe-Si amorphous alloys

    SciTech Connect

    Diaz, J.; Hamdan, N.M.; Jalil, P.; Hussain, Z.; Valvidares, S.M.; Alameda, J.M.

    2002-08-01

    The origin of the magnetic anisotropy in a very disordered Fe-Si alloy has been investigated. The alloy containing 40 percent at. Si was prepared in the form of a thin film in a DC magnetron sputtering chamber. Structural disorder was obtained from Extended X-ray Absorption Fine Structure spectroscopy. The uniformity and lack of inhomogeneities at a microscopic level was checked by measuring their transverse magnetic susceptibility and hysteresis loops. The orbital component of the magnetic moment was measured by X-ray Magnetic Circular Dichroism spectroscopy. The orbital moment was extraordinary high, 0.4mB. Such a high value contrasted with the relatively small uniaxial anisotropy energy of the thin film (2kJ/m3). This suggests that the cause of the magnetic anisotropy in this alloy was a small degree of correlation in the orientation of the local orbital moments along a preferential direction.

  12. A new class of natural magnetic materials - The ordering alloys

    NASA Technical Reports Server (NTRS)

    Wasilewski, Peter

    1988-01-01

    It is shown that tetrataenite (approximately FeNi), found in many meteorites, and Josephinite (approximately FeNi3), found in many serpentinized peridotites and possibly in Allende, are atomically ordered alloys. Data are presented, showing magnetic hysteresis loops, coercivity-temperature behavior at cryogenic temperatures, and thermomagnetic curves, that show that these ordered magnetic materials have unique magnetic properties and do not fit the conventional rock magnetism paradigms represented by Fe3O4 serpentinites. The ordered state is characterized by induced magnetic anisotropy, reaching the extreme for the tetragonal truly uniaxial anisotropy in FeNi. It is suggested that these ordered magnetic alloys should be considered a new class of natural magnetic materials.

  13. Pressure-induced magnetic instability in Pd-Ni alloys

    NASA Astrophysics Data System (ADS)

    Oomi, Gendo; Iwai, Sadanori; Ohashi, Masashi; Nakano, Tomohito

    2012-12-01

    The electrical resistivity ρ(T) of dilute Pd-Ni alloys has been measured at high pressure up to 3 GPa. It is found that the ρ(T) of the ferromagnetic Pd-Ni alloy shows an anomalous temperature dependence near the critical pressure Pc, where the ferromagnetism disappears. The results are analysed in the framework of quantum critical behaviour induced by pressure. The effect of magnetic field on the ρ(T) is also examined. Different behaviour of magnetoresistance against pressure was found depending on the alloy concentration and discussed in connection with an instability of ferromagnetism.

  14. Effect of Temperature and Grain Size on Magnetic Properties of Soft Magnetic Iron-Cobalt Alloys

    NASA Astrophysics Data System (ADS)

    Kozlowski, G.; Fingers, R. T.; Coate, J. E.; Rogacki, K.; Dabrowski, B.

    1997-03-01

    Two specific iron-cobalt alloys have been tested as part of the magnetic materials characterization program at Wright Laboratory. The first material is Hiperco Alloy 50HS from Carpenter Technology and the second is HS50 from Telcon Ltd. The planned use of such materials in cyclic high temperature high stress environments (generators and magnetic bearings) gives impetus to determining material properties. These soft magnetic alloys exhibit high magnetic saturation, high yield strength, and moderate core loss. In order to better understand the overall behavior of these alloys, both mechanical and magnetic phenomena have been investigated. Specimens of these materials have been heat treated by various recipes ranging in temperature from 1300 degF to 1350 degF and magnetic saturation along hysteresis loop measurements were made using a vibrating sample magnetometer and an a.c. susceptometer. Measurements of remanence, coercivity, permeabilities and saturation were made as a function of temperature. Mechanical testing was also conducted and these results were used in conjunction with the magnetic behavior to characterize the two specific alloys. Etching and sample preparation processes were developed and microstructural analyses were performed. The effect of composition and heat treatment of these two soft magnetic materials and how they may influence potential applications is discussed.

  15. Hyperfine magnetic fields in cobalt-based Heusler alloys

    SciTech Connect

    Yehia, M.S.

    1987-01-01

    Measurement of hyperfine interactions at Cd-111 and Sn-119 impurity nuclei in Co-based Heusler alloys Co/sub 2/YZ (Y = Mn, Ti, V, Zr and Z was Al, Ga, Ge, Si, Sn) were made within a temperature range 77 to 746 K using the time differential Perturbed Angular Correlation (TDPAC) and Mossbauer techniques. The hyperfine-field results in these alloys are discussed in terms of two models, the localized moment model and the Volume Overlap model. In the localized moment model a pre-asymptotic phase factor n = ..pi.. at distance r = a/2 was used to fit the experimental results on Co/sub 2/YZ (Y = Ti, V, Zr and Z = Al, Ga, Sn, Ge). In the Volume Overlap model the hyperfine field results in the series Co/sub 2/MnZ (Z = Ge, Si, Sn) was plotted against the lattice parameter of these alloys; a linear relationship was found, suggesting a non overlap term between the magnetic atom and the nonmagnetic impurity. A prediction of hyperfine magnetic filed less than 40 (kOe) on Sn-119 and of about -250(kOe) on Cd-111 in Co/sub 2/TiSi and Co/sub 2/TiGe is made. Temperature variation of the hyperfine magnetic field in the alloy Co/sub 2/MnSn with magnetic moments residing on two sites, has been studied. Results didn't show a dramatic deviation form the Brillouin function.

  16. Magnetic properties and magnetic hardening mechansim of Pt-Co-B alloys

    NASA Technical Reports Server (NTRS)

    Qiu, Ning; Flanagan, F.; Wittig, James E.

    1994-01-01

    The intrinsic coercivity is found to be maximized in the Pt42Co45B13 ternary alloy which is undercooled and rapidly solidified (quenched using a 70 m/s wheel speed after undercooling), and then annealed (800 C for 2400 min). The same alloy, processed at slower cooling rates and annealed in the same way, has a much larger scale microstructure and a much lower resulting magnetic coercivity. The microstructure which would optimize the coercitvity of this coercivity of this ternary alloy is a completely ordered L1(sub zero) Pt-Co matrix with a submicron magnetic single-domion Co-boride precipitate. The L1(sub zero) phase is highly anistropic magnetically while the Co-boride precipate is somewhat less so. Annealing treatments designed to produced single-domain Co-boride precipitates enhance the coercivity. This suggests that the refined microstructures is responsible for the high coercivities found in the rapidly solidified and annealed alloy. The magnetic domain wall thickness for a Co-boride precipitate is determined from both experimental observation and theoretical calculation in order to evaluate its influence on the coercivity of the alloy. The effects of the pinning of domain walls and the barrier to the nucleation of reverse domains on the coercivity are discussed. Both microstrucutral analysis and theoretical calculation indicate that the high coercivities in the Pt42Co45B13 alloy are due to the difficult nucleation of reverse magnetic domains.

  17. Thermomagnetic analysis of FeCoCrxNi alloys: Magnetic entropy of high-entropy alloys

    NASA Astrophysics Data System (ADS)

    Lucas, M. S.; Belyea, D.; Bauer, C.; Bryant, N.; Michel, E.; Turgut, Z.; Leontsev, S. O.; Horwath, J.; Semiatin, S. L.; McHenry, M. E.; Miller, C. W.

    2013-05-01

    The equimolar alloy FeCoCrNi, a high-entropy alloy, forms in the face-centered-cubic crystal structure and has a ferromagnetic Curie temperature of 130 K. In this study, we explore the effects of Cr concentration, cold-rolling, and subsequent heat treatments on the magnetic properties of FeCoCrxNi alloys. Cr reductions result in an increase of the Curie temperature, and may be used to tune the TC over a very large temperature range. The magnetic entropy change for a change in applied field of 2T is ΔSm = -0.35 J/(kg K) for cold-rolled FeCoCrNi. Cold-rolling results in a broadening of ΔSm, where subsequent heat treatment at 1073 K sharpens the magnetic entropy curve. In all of the alloys, we find that upon heating (after cold-rolling) there is a re-entrant magnetic moment near 730 K. This feature is much less pronounced in the as-cast samples (without cold-rolling) and in the Cr-rich samples, and is no longer observed after annealing at 1073 K. Possible origins of this behavior are discussed.

  18. 3-T MRI safety assessments of magnetic dental attachments and castable magnetic alloys

    PubMed Central

    Miyata, K; Abe, Y; Ishii, T; Ishigami, T; Ohtani, K; Nagai, E; Ohyama, T; Umekawa, Y; Nakabayashi, S

    2015-01-01

    Objectives: To assess the safety of different magnetic dental attachments during 3-T MRI according to the American Society for Testing and Materials F2182-09 and F2052-06e1 standard testing methods and to develop a method to determine MRI compatibility by measuring magnetically induced torque. Methods: The temperature elevations, magnetically induced forces and torques of a ferromagnetic stainless steel keeper, a coping comprising a keeper and a cast magnetic alloy coping were measured on MRI systems. Results: The coping comprising a keeper demonstrated the maximum temperature increase (1.42 °C) for the whole-body-averaged specific absorption rate and was calculated as 2.1 W kg−1 with the saline phantom. All deflection angles exceeded 45°. The cast magnetic alloy coping had the greatest deflection force (0.33 N) during 3-T MRI and torque (1.015 mN m) during 0.3-T MRI. Conclusions: The tested devices showed minimal radiofrequency (RF)-induced heating in a 3-T MR environment, but the cast magnetic alloy coping showed a magnetically induced deflection force and torque approximately eight times that of the keepers. For safety, magnetic dental attachments should be inspected before and after MRI and large prostheses containing cast magnetic alloy should be removed. Although magnetic dental attachments may pose no great risk of RF-induced heating or magnetically induced torque during 3-T MRI, their magnetically induced deflection forces tended to exceed acceptable limits. Therefore, the inspection of such devices before and after MRI is important for patient safety. PMID:25785821

  19. Magnetically driven three-dimensional manipulation and inductive heating of magnetic-dispersion containing metal alloys

    PubMed Central

    Calabro, Joshua D.; Huang, Xu; Lewis, Brian G.; Ramirez, Ainissa G.

    2010-01-01

    Fundamental to the development of three-dimensional microelectronic fabrication is a material that enables vertical geometries. Here we show low-melting-point metal alloys containing iron dispersions that can be remotely manipulated by magnetic fields to create vertical geometries and thus enable novel three-dimensional assemblies. These iron dispersions enhance the mechanical properties needed for strong, reliable interconnects without significantly altering the electrical properties of the alloys. Additionally, these iron dispersions act as susceptors for magnetic induction heating, allowing the rapid melting of these novel alloys at temperatures lower than those usually reported for conventional metal alloys. By localizing high temperatures and by reducing temperature excursions, the materials and methods described have potential in a variety of device fabrication applications. PMID:20194786

  20. Magnetic properties in MnBi alloy of small crystallites for permanent magnet devices

    NASA Astrophysics Data System (ADS)

    Sharma, S. K.; Prakash, H. R.; Ram, S.

    2016-05-01

    A rare-earth free alloy like MnBi is a potential candidate for developing small magnets and devices. In a commercially viable method, a MnBi alloy was prepared by arc melting Mn and Bi metals in a 1:1 ratio. In terms of the X-ray diffraction a single crystalline MnBi phase is formed of the as prepared alloy. FESEM images delineate thin MnBi layers (25 - 40 nm thickness) of average EDX composition throughout the specimen. A large coercivity 5.501 kOe (6.5 emu/g magnetization) observed in an M-H at 300 K is decreased to 0.171 (9.0 emu/g magnetization) at 100 K in decreasing upon cooling.

  1. Abnormal magnetization behaviors in Sm-Ni-Fe-Cu alloys

    NASA Astrophysics Data System (ADS)

    Yang, W. Y.; Zhang, Y. F.; Zhao, H.; Chen, G. F.; Zhang, Y.; Du, H. L.; Liu, S. Q.; Wang, C. S.; Han, J. Z.; Yang, Y. C.; Yang, J. B.

    2016-06-01

    The magnetization behaviors in Sm-Ni-Fe-Cu alloys at low temperatures have been investigated. It was found that the hysteresis loops show wasp-waisted character at low temperatures, which has been proved to be related to the existence of multi-phases, the Fe/Ni soft magnetic phases and the CaCu5-type hard magnetic phase. A smooth-jump behavior of the magnetization is observed at T>5 K, whereas a step-like magnetization process appears at T<5 K. The CaCu5-type phase is responsible for such abnormal magnetization behavior. The magnetic moment reversal model with thermal activation is used to explain the relation of the critical magnetic field (Hcm) to the temperature (T>5 K). The reversal of the moment direction has to cross over an energy barrier of about 6.6×10-15 erg. The step-like jumps of the magnetization below 5 K is proposed to be resulted from a sharp increase of the sample temperature under the heat released by the irreversible domain wall motion.

  2. The magnetic entropy changes in Gd 1- xB x alloys

    NASA Astrophysics Data System (ADS)

    Dunhui, Wang; Songling, Huang; Zhida, Han; Zhenghua, Su; Yi, Wang; Youwei, Du

    2004-07-01

    A series of Gd (1- x) B x alloys have been prepared by arc melting method. After introducing small quantity of B atom in Gd, the Curie temperature of these alloys increase while the magnetic entropy changes are almost same as that of Gd. The refrigerant capacities of these alloys are also greater than that of Gd. These results suggest that Gd (1- x) B x alloys may be utilized as refrigerant in household magnetic refrigeration.

  3. Electrodeposition and magnetic properties of FeCo alloy films

    NASA Astrophysics Data System (ADS)

    Zhou, Dong; Zhou, Mingge; Zhu, Minggang; Yang, Xu; Yue, Ming

    2012-04-01

    FeCo alloys thin films have been successfully electrodeposited on Ag films. The morphology, structure, composition, and magnetic property of the FeCo films were characterized by scanning electron microscopy, x-ray diffraction, induction-coupled plasma spectrometry, vibrating sample magnetometer and network analyzer. The use of reverse pulse current in the process of electrodepostion can reduce the surface roughness obviously. The effects of anodic current density and thickness are studied. The results show that the film fabricated under appropriate conditions has low coercivity and excellent high-frequency magnetic property.

  4. Soft magnetic properties of a ferritic Fe-Ni-Cr alloy

    NASA Astrophysics Data System (ADS)

    Jin, S.; Sherwood, R. C.; Chin, G. Y.; Wernick, J. H.; Bordelon, C. M.

    1984-03-01

    Technologically important applications may exist for magnetically soft alloys that possess, in addition to the appropriate magnetic properties, relatively high mechanical strength and corrosion resistance. Such an alloy can be used, for example, for certain types of telephone receiver armature applications. In the present paper, we report the magnetic and mechanical properties of the ternary Fe-3Ni-5Cr alloy. The soft magnetic properties of the alloy are significantly improved by heat treatment within the (α+γ) two-phase region. Exemplary properties after heat treatment at ˜625 °C for 2 h are Hc˜1.2 Oe, μm˜4700, yield strength ˜59 ksi, and elongation ˜30%. The alloy exhibits reasonably good corrosion resistance. Magnetic, mechanical, and electrical properties of the alloy as well as the acoustic performance of telephone receivers using it, have been found to be comparable to those of the 2V-Permendur alloy.

  5. First principles statistical mechanics of alloys and magnetism

    NASA Astrophysics Data System (ADS)

    Eisenbach, Markus; Khan, Suffian N.; Li, Ying Wai

    Modern high performance computing resources are enabling the exploration of the statistical physics of phase spaces with increasing size and higher fidelity of the Hamiltonian of the systems. For selected systems, this now allows the combination of Density Functional based first principles calculations with classical Monte Carlo methods for parameter free, predictive thermodynamics of materials. We combine our locally selfconsistent real space multiple scattering method for solving the Kohn-Sham equation with Wang-Landau Monte-Carlo calculations (WL-LSMS). In the past we have applied this method to the calculation of Curie temperatures in magnetic materials. Here we will present direct calculations of the chemical order - disorder transitions in alloys. We present our calculated transition temperature for the chemical ordering in CuZn and the temperature dependence of the short-range order parameter and specific heat. Finally we will present the extension of the WL-LSMS method to magnetic alloys, thus allowing the investigation of the interplay of magnetism, structure and chemical order in ferrous alloys. This research was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division and it used Oak Ridge Leadership Computing Facility resources at Oak Ridge National Laboratory.

  6. Magnetically driven magnetostructural transformations of shape memory alloys

    NASA Astrophysics Data System (ADS)

    L'vov, V. A.; Cesari, E.; Pérez-Landazábal, J. I.; Recarte, V.; Torrens-Serra, J.

    2016-03-01

    A conception of magnetically driven martensitic transformation (MT) has been put forward. The MT driven by the ferromagnetic-antiferromagnetic phase transition has been analysed in detail for the case of weak antiferromagnetic exchange between the magnetic sublattices. It has been shown that in this case the MT is characterized by (i) a strong dependence of the MT temperature on the external magnetic field; (ii) a pronounced decrease in the martensite volume fraction and the macroscopic MT strain under the increasing field; (iii) the ‘arrest’ of the forward MT on the cooling of the alloy in a strong magnetic field; and (iv) a drastic decrease in the entropy difference between the austenitic and martensitic phases on approaching the temperature of arrest of the MT. The assumption about the antiferromagnetic ordering of the martensitic phase is not crucial for the proposed model of magnetically driven MT, and so its applicability to other types of ordering has been discussed. The Ni-Mn-In-based alloys have been considered as a case for study.

  7. Tunable exchange bias in dilute magnetic alloys - chiral spin glasses

    NASA Astrophysics Data System (ADS)

    Hudl, Matthias; Mathieu, Roland; Nordblad, Per

    2016-01-01

    A unidirectional anisotropy appears in field cooled samples of dilute magnetic alloys at temperatures well below the cusp temperature of the zero field cooled magnetization curve. Magnetization measurements on a Cu(13.5 at% Mn) sample show that this anisotropy is essentially temperature independent and acts on a temperature dependent excess magnetization, ΔM. The anisotropy can be partially or fully transferred from being locked to the direction of the cooling field at lower fields to becoming locked to the direction of ΔM at larger fields, thus instead appearing as a uniaxial anisotropy. This introduces a deceiving division of the anisotropy into a superposition of a unidirectional and a uniaxial part. This two faced nature of the anisotropy has been empirically scrutinized and concluded to originate from one and the same exchange mechanism: the Dzyaloshinsky-Moriya interaction.

  8. Magnetic cluster expansion model for random and ordered magnetic face-centered cubic Fe-Ni-Cr alloys

    NASA Astrophysics Data System (ADS)

    Lavrentiev, M. Yu.; Wróbel, J. S.; Nguyen-Manh, D.; Dudarev, S. L.; Ganchenkova, M. G.

    2016-07-01

    A Magnetic Cluster Expansion model for ternary face-centered cubic Fe-Ni-Cr alloys has been developed, using DFT data spanning binary and ternary alloy configurations. Using this Magnetic Cluster Expansion model Hamiltonian, we perform Monte Carlo simulations and explore magnetic structures of alloys over the entire range of compositions, considering both random and ordered alloy structures. In random alloys, the removal of magnetic collinearity constraint reduces the total magnetic moment but does not affect the predicted range of compositions where the alloys adopt low-temperature ferromagnetic configurations. During alloying of ordered fcc Fe-Ni compounds with Cr, chromium atoms tend to replace nickel rather than iron atoms. Replacement of Ni by Cr in ordered alloys with high iron content increases the Curie temperature of the alloys. This can be explained by strong antiferromagnetic Fe-Cr coupling, similar to that found in bcc Fe-Cr solutions, where the Curie temperature increase, predicted by simulations as a function of Cr concentration, is confirmed by experimental observations. In random alloys, both magnetization and the Curie temperature decrease abruptly with increasing chromium content, in agreement with experiment.

  9. Impact of magnetic surface anisotropy on the precessional switching of magnetization in Pt-alloy nanofilms

    NASA Astrophysics Data System (ADS)

    Daniel, M.; Arun, R.; Sabareesan, P.

    2012-09-01

    Precessional switching of magnetization in CoPt and FePt nanofilms is investigated by solving the Landau-Lifshitz-Gilbert (LLG) equation analytically and numerically. Switching in these films occurs only above a critical value of the magnetic field, and it further depends on the magnetocrystalline anisotropy and saturation magnetization of the film. The presence of magnetic surface anisotropy in these films reduces the switching time significantly. Also, the switching time in the case of Pt-alloys of Co and Fe is low compared to that in the case of pure Co and Fe films.

  10. New Fe-Co-Ni-Cu-Al-Ti Alloy for Single-Crystal Permanent Magnets

    NASA Astrophysics Data System (ADS)

    Belyaev, I. V.; Bazhenov, V. E.; Moiseev, A. V.; Kireev, A. V.

    2016-03-01

    A new alloy intended for single-crystal permanent magnets has been suggested. The new alloy has been designed based on the well-known Fe-Co-Ni-Cu-Al-Ti system and contains to 1 wt % Hf. The alloy demonstrates an enhanced potential ability for single-crystal forming in the course of unidirectional solidification of ingot. Single-crystal permanent magnets manufactured from this alloy are characterized by a high level of magnetic properties. When designing the new alloy, computer simulation of the phase composition and calculations of solidification parameters of complex metallic systems have been performed using the Thermo-Calc software and calculation and experimental procedures based on quantitative metallographic analysis of quenched structures. After the corresponding heat treatment, the content of high-magnetic phase in the alloy is 10% higher than that in available analogous alloys.

  11. Soft magnetic properties of LaCo13 and La(Co, Fe)13 alloys

    NASA Astrophysics Data System (ADS)

    Huang, M. Q.; Wallace, W. E.; McHenry, M. E.; Chen, Q.; Ma, B. M.

    1998-06-01

    LaCo13 and La(Co, Fe)13 alloys have been prepared and studied as high temperature, high performance soft magnetic materials. The dc magnetic properties have been measured over a temperature range of 10-1273 K in fields of 0 to 5 T. Data obtained show that the dc magnetic properties (Hc,K1) of the La(Co, Fe)13 bulk alloys are comparable with Fe bulk alloy and Tc=1021-1297 K are higher than that of Fe and Hiperco; ac magnetic properties are first time reported in a bulk LaCo13 alloy, showing a reasonably higher power loss than that of commercial Hiperco alloy. The ac magnetic properties can be improved by making LaCo13 alloys as laminated thin sheets.

  12. Applications of the directional solidification in magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Huang, Y. J.; Liu, J.; Hu, Q. D.; Liu, Q. H.; Karaman, I.; Li, J. G.

    2016-03-01

    A zone melting liquid metal cooling (ZMLMC) method of directional solidification was applied to prepare highly-oriented Ni52Fe17Ga27Co4 magnetic shape memory alloys. At high temperature gradient and low growth velocity, the well-developed preferred orientation for coarse columnar crystals was obtained. Such a structure leads to a large complete pseudoelastic recovery of 5% at 348 K. Moreover, the pseudoelastic behaviours and the kinetics of the martensitic transformation (MT) are significantly affected by the intersection angle between the loading direction and the grain boundaries.

  13. Laser-induced magnetization dynamics and reversal in ferrimagnetic alloys.

    PubMed

    Kirilyuk, Andrei; Kimel, Alexey V; Rasing, Theo

    2013-02-01

    This review discusses the recent studies of magnetization dynamics and the role of angular momentum in thin films of ferrimagnetic rare-earth-transition metal (RE-TM) alloys, e.g. GdFeCo, where both magnetization and angular momenta are temperature dependent. It has been experimentally demonstrated that the magnetization can be manipulated and even reversed by a single 40 fs laser pulse, without any applied magnetic field. This switching is found to follow a novel reversal pathway, that is shown however to depend crucially on the net angular momentum, reflecting the balance of the two opposite sublattices. In particular, optical excitation of ferrimagnetic GdFeCo on a time scale pertinent to the characteristic time of the exchange interaction between the RE and TM spins, i.e. on the time scale of tens of femtoseconds, pushes the spin dynamics into a yet unexplored regime, where the two exchange-coupled magnetic sublattices demonstrate substantially different dynamics. As a result, the reversal of spins appears to proceed via a novel transient state characterized by a ferromagnetic alignment of the Gd and Fe magnetic moments, despite their ground-state antiferromagnetic coupling.Thus, optical manipulation of magnetic order by femtosecond laser pulses has developed into an exciting and still expanding research field that keeps being fueled by a continuous stream of new and sometimes counterintuitive results. Considering the progress in the development of plasmonic antennas and compact ultrafast lasers, optical control of magnetic order may also potentially revolutionize data storage and information processing technologies. PMID:23377279

  14. "Treasure maps" for magnetic high-entropy-alloys from theory and experiment

    NASA Astrophysics Data System (ADS)

    Körmann, F.; Ma, D.; Belyea, D. D.; Lucas, M. S.; Miller, C. W.; Grabowski, B.; Sluiter, M. H. F.

    2015-10-01

    The critical temperature and saturation magnetization for four- and five-component FCC transition metal alloys are predicted using a formalism that combines density functional theory and a magnetic mean-field model. Our theoretical results are in excellent agreement with experimental data presented in both this work and in the literature. The generality and power of this approach allow us to computationally design alloys with well-defined magnetic properties. Among other alloys, the method is applied to CoCrFeNiPd alloys, which have attracted attention recently for potential magnetic applications. The computational framework is able to predict the experimentally measured TC and to explore the dominant mechanisms for alloying trends with Pd. A wide range of ferromagnetic properties and Curie temperatures near room temperature in hitherto unexplored alloys is predicted in which Pd is replaced in varying degrees by, e.g., Ag, Au, and Cu.

  15. Frequency-dependent energy harvesting via magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Sayyaadi, Hassan; Askari Farsangi, Mohammad Amin

    2015-11-01

    This paper is focused on presenting an accurate framework to describe frequency-dependent energy harvesting via magnetic shape memory alloys (MSMAs). Modeling strategy incorporates the phenomenological constitutive model developed formerly together with the magnetic diffusion equation. A hyperbolic hardening function is employed to define reorientation-induced strain hardening in the material, and the diffusion equation is used to add dynamic effects to the model. The MSMA prismatic specimen is surrounded by a pickup coil, and the induced voltage during martensite-variant reorientation is investigated with the help of Faraday’s law of magnetic field induction. It has been shown that, in order to harvest the maximum RMS voltage in the MSMA-based energy harvester, an optimum value of bias magnetic field exists, which is the corresponding magnetic field for the start of pseudoelasticity behavior. In addition, to achieve a more compact energy harvester with higher energy density, a specimen with a lower aspect ratio can be chosen. As the main novelty of the paper, it is found that the dynamic effects play a major role in determining the harvested voltage and power, especially for high excitation frequency or specimen thickness.

  16. Multiscale theory of thin film magnetic shape memory alloy microactuators

    NASA Astrophysics Data System (ADS)

    Stoilov, Vesselin

    2007-04-01

    This paper investigates the nano-macro transition in magnetic shape memory alloy(MSMA) thin films using a recently developed sharp phase front-based three-dimensional (3D) constitutive model outlined by Stoilov (JSMS 2007), and originally proposed in the 1D context by Stoilov and Bhattacharyya (Acta Mat 2002). The key ingredient in the model is the recognition of martensitic variants as separate phases in a MSMA domain. Evolution of the interface between these phases is taken as an indicator of the process of reorientation in progress. A formulation of the Helmholtz free energy potential based on Ising model has been derived. The implications of the external magnetic field on the initiation of phase transformation are studied for various mechanical loading modes.

  17. Structural and magnetic dynamics in the magnetic shape-memory alloy Ni2MnGa

    NASA Astrophysics Data System (ADS)

    Mariager, S. O.; Dornes, C.; Johnson, J. A.; Ferrer, A.; Grübel, S.; Huber, T.; Caviezel, A.; Johnson, S. L.; Eichhorn, T.; Jakob, G.; Elmers, H. J.; Beaud, P.; Quitmann, C.; Ingold, G.

    2014-10-01

    Magnetic shape-memory Heusler alloys are multiferroics stabilized by the correlations between electronic, magnetic, and structural order. To study these correlations we use time-resolved x-ray diffraction and magneto-optical Kerr effect experiments to measure the laser induced dynamics in a Heusler alloy Ni2MnGa film and reveal a set of time scales intrinsic to the system. We observe a coherent phonon which we identify as the amplitudon of the modulated structure and an ultrafast phase transition leading to a quenching of the incommensurate modulation within 300 fs with a recovery time of a few ps. The thermally driven martensitic transition to the high temperature cubic phase proceeds via nucleation within a few ps and domain growth limited by the speed of sound. The demagnetization time is 320 fs, which is comparable to the quenching of the structural modulation.

  18. Unexpected magnetic behavior in amorphous Co{sub 90}Sc{sub 10} alloy

    SciTech Connect

    Ghafari, M. E-mail: skamali@utsi.edu; Gleiter, H.; Sakurai, Y.; Itou, M.; Peng, G.; Fang, Y. N.; Feng, T.; Hahn, H.; Kamali, S. E-mail: skamali@utsi.edu

    2015-09-28

    An amorphous alloy Co{sub 90}Sc{sub 10} has been prepared by rapid quenching from the melt. The results of magnetization measurements show that this alloy has the highest Curie temperature reported for any amorphous transition metal based alloys. Furthermore, for a Co based amorphous alloy, the magnetic moment is remarkably high. Moreover, the alloy exhibits soft magnetic properties. Based on the findings, amorphous Co{sub 90}Sc{sub 10} appears to be an attractive candidate for applications as a soft magnetic material. The temperature dependence of the reduced magnetization can be described by the Bloch power law. The results show that the B coefficient of the amorphous Co{sub 90}Sc{sub 10} alloy, which is a measure of the rigidity of spin waves, exhibits the lowest value observed until now for any amorphous alloy and is comparable to crystalline alloys. It is found that the Sc atoms in the Co{sub 90}Sc{sub 10} alloy lead to an increase of the itinerant spin moment of Co atoms, and, in contrast to this behaviour, to a decrease of the local 3d-electrons of Co.

  19. Novel pre-alloyed powder processing of modified alnico 8: Correlation of microstructure and magnetic properties

    SciTech Connect

    Anderson, I. E. Kassen, A. G.; White, E. M. H.; Zhou, L.; Tang, W.; Palasyuk, A.; Dennis, K. W.; McCallum, R. W.; Kramer, M. J.

    2015-05-07

    Progress is reviewed on development of an improved near-final bulk magnet fabrication process for alnico 8, as a non-rare earth permanent magnet with promise for sufficient energy density and coercivity for electric drive motors. This study showed that alnico bulk magnets in near-final shape can be made by simple compression molding from spherical high purity gas atomized pre-alloyed powder. Dwell time at peak sintering temperature (1250 °C) greatly affected grain size of the resulting magnet alloys. This microstructure transformation was demonstrated to be useful for gaining partially aligned magnetic properties and boosting energy product. While a route to increased coercivity was not identified by these experiments, manufacturability of bulk alnico magnet alloys in near-final shapes was demonstrated, permitting further processing and alloy modification experiments that can target higher coercivity and better control of grain anisotropy during grain growth.

  20. Novel pre-alloyed powder processing of modified alnico 8: Correlation of microstructure and magnetic properties

    NASA Astrophysics Data System (ADS)

    Anderson, I. E.; Kassen, A. G.; White, E. M. H.; Zhou, L.; Tang, W.; Palasyuk, A.; Dennis, K. W.; McCallum, R. W.; Kramer, M. J.

    2015-05-01

    Progress is reviewed on development of an improved near-final bulk magnet fabrication process for alnico 8, as a non-rare earth permanent magnet with promise for sufficient energy density and coercivity for electric drive motors. This study showed that alnico bulk magnets in near-final shape can be made by simple compression molding from spherical high purity gas atomized pre-alloyed powder. Dwell time at peak sintering temperature (1250 °C) greatly affected grain size of the resulting magnet alloys. This microstructure transformation was demonstrated to be useful for gaining partially aligned magnetic properties and boosting energy product. While a route to increased coercivity was not identified by these experiments, manufacturability of bulk alnico magnet alloys in near-final shapes was demonstrated, permitting further processing and alloy modification experiments that can target higher coercivity and better control of grain anisotropy during grain growth.

  1. Novel pre-alloyed powder processing of modified alnico 8: Correlation of microstructure and magnetic properties

    DOE PAGESBeta

    Anderson, I. E.; Kassen, A. G.; White, E. M. H.; Zhou, L.; Tang, W.; Palasyuk, A.; Dennis, K. W.; McCallum, R. W.; Kramer, M. J.

    2015-04-13

    Progress is reviewed on development of an improved near-final bulk magnet fabrication process for alnico 8, as a non-rare earth permanent magnet with promise for sufficient energy density and coercivity for electric drive motors. This study showed that alnico bulk magnets in near-final shape can be made by simple compression molding from spherical high purity gas atomized pre-alloyed powder. Dwell time at peak sintering temperature (1250°C) greatly affected grain size of the resulting magnet alloys. This microstructure transformation was demonstrated to be useful for gaining partially aligned magnetic properties and boosting energy product. Furthermore, while a route to increased coercivitymore » was not identified by these experiments, manufacturability of bulk alnico magnet alloys in near-final shapes was demonstrated, permitting further processing and alloy modification experiments that can target higher coercivity and better control of grain anisotropy during grain growth.« less

  2. Novel pre-alloyed powder processing of modified alnico 8: Correlation of microstructure and magnetic properties

    SciTech Connect

    Anderson, I. E.; Kassen, A. G.; White, E. M. H.; Zhou, L.; Tang, W.; Palasyuk, A.; Dennis, K. W.; McCallum, R. W.; Kramer, M. J.

    2015-04-13

    Progress is reviewed on development of an improved near-final bulk magnet fabrication process for alnico 8, as a non-rare earth permanent magnet with promise for sufficient energy density and coercivity for electric drive motors. This study showed that alnico bulk magnets in near-final shape can be made by simple compression molding from spherical high purity gas atomized pre-alloyed powder. Dwell time at peak sintering temperature (1250°C) greatly affected grain size of the resulting magnet alloys. This microstructure transformation was demonstrated to be useful for gaining partially aligned magnetic properties and boosting energy product. Furthermore, while a route to increased coercivity was not identified by these experiments, manufacturability of bulk alnico magnet alloys in near-final shapes was demonstrated, permitting further processing and alloy modification experiments that can target higher coercivity and better control of grain anisotropy during grain growth.

  3. Magnetic patterning using ion irradiation for highly ordered CoPt alloys with perpendicular anisotropy

    SciTech Connect

    Abes, M.; Venuat, J.; Muller, D.; Carvalho, A.; Schmerber, G.; Beaurepaire, E.; Dinia, A.; Pierron-Bohnes, V.

    2004-12-15

    We used a combination of ion irradiation and e-beam lithography to magnetically pattern an ordered CoPt alloy with strong perpendicular magnetic anisotropy. Ion irradiation disorders the alloy and strongly reduces the magnetic anisotropy. Magnetic force microscopy showed a regular array of 1 {mu}m{sup 2} square dots with perpendicular anisotropy separated by 1 {mu}m large ranges with in-plane anisotropy. This is further confirmed by magnetic measurements, which showed that arrays protected by a 200 nm Pt layer present the same coercive field and the same perpendicular anisotropy as before irradiation. This is promising for applications in magnetic recording technologies.

  4. Iron-Nitride Alloy Magnets: Transformation Enabled Nitride Magnets Absent Rare Earths (TEN Mare)

    SciTech Connect

    2012-01-01

    REACT Project: Case Western is developing a highly magnetic iron-nitride alloy to use in the magnets that power electric motors found in EVs and renewable power generators. This would reduce the overall price of the motor by eliminating the expensive imported rare earth minerals typically found in today’s best commercial magnets. The iron-nitride powder is sourced from abundant and inexpensive materials found in the U.S. The ultimate goal of this project is to demonstrate this new magnet system, which contains no rare earths, in a prototype electric motor. This could significantly reduce the amount of greenhouse gases emitted in the U.S. each year by encouraging the use of clean alternatives to oil and coal.

  5. Magnetic properties of doped Mn-Ga alloys made by mechanical milling and heat treatment

    NASA Astrophysics Data System (ADS)

    Brown, Daniel R.; Han, Ke; Siegrist, Theo; Besara, Tiglet; Niu, Rongmei

    2016-05-01

    Mn-Ga alloys have shown hard magnetic properties, even though these alloys contain no rare-earth metals. However, much work is needed before rare-earth magnets can be replaced. We have examined the magnetic properties of bulk alloys made with partial replacement of both the Mn and Ga elements in the Mn0.8Ga0.2 system. Bulk samples of Mn-Ga-Bi, Mn-Ga-Al, Mn-Fe-Ga and Mn-(FeB)-Ga alloys were fabricated and studied using mechanically milling and heat treatments while altering the atomic percentage of the third element between 2.5 and 20 at%. The ternary alloy exhibits all hard magnetic properties at room temperature with large coercivity. Annealed Mn-Ga-X bulk composites exhibit high coercivities up to 16.6 kOe and remanence up to 9.8 emu/g, that is increased by 115% over the binary system.

  6. Effect of chemically active medium on frequency dependence of magnetic losses in soft magnetic Fe-based amorphous alloys

    NASA Astrophysics Data System (ADS)

    Skulkina, N. A.; Ivanov, O. A.; Stepanova, E. A.; Pavlova, I. O.

    2013-03-01

    The effects of the electrolytic hydrogenation and oxidation and of the interaction of the surface ribbon with water and vapor on the frequency dependence of magnetic losses per magnetization-reversal cycle are studied based on the example of soft magnetic Fe81B13Si4C2 amorphous alloy, which exhibits a positive saturation magnetostriction. It was shown that, after the hydrogenation and oxidation of soft magnetic amorphous alloys, their frequency dependences of magnetic losses per magnetization-reversal cycle, which are reduced to unit induction, exhibit groups of hydrogen- and oxygen-related peaks in the frequency ranges of 35-55 and 55-80 Hz, which can be explained by the formation of O- A and H- A atomic pairs (where A are atoms of alloy components) and their reorientation in a magnetic field in the course of magnetization reversal at certain frequencies. The formation of analogous groups of peaks for samples of soft magnetic Fe-based amorphous alloys was observed after the interaction of the ribbon surface with water and vapor and after heat treatment in air. This fact confirms the possibility of the hydrogenation and oxidation of the alloys during the aforementioned processes.

  7. Magnetization curves of sintered heavy tungsten alloys for applications in MRI-guided radiotherapy

    SciTech Connect

    Kolling, Stefan; Oborn, Bradley M.; Keall, Paul J.; Horvat, Joseph

    2014-06-15

    Purpose: Due to the current interest in MRI-guided radiotherapy, the magnetic properties of the materials commonly used in radiotherapy are becoming increasingly important. In this paper, measurement results for the magnetization (BH) curves of a range of sintered heavy tungsten alloys used in radiation shielding and collimation are presented. Methods: Sintered heavy tungsten alloys typically contain >90 % tungsten and <10 % of a combination of iron, nickel, and copper binders. Samples of eight different grades of sintered heavy tungsten alloys with varying binder content were investigated. Using a superconducting quantum interference detector magnetometer, the induced magnetic momentm was measured for each sample as a function of applied external field H{sub 0} and the BH curve derived. Results: The iron content of the alloys was found to play a dominant role, directly influencing the magnetizationM and thus the nonlinearity of the BH curve. Generally, the saturation magnetization increased with increasing iron content of the alloy. Furthermore, no measurable magnetization was found for all alloys without iron content, despite containing up to 6% of nickel. For two samples from different manufacturers but with identical quoted nominal elemental composition (95% W, 3.5% Ni, 1.5% Fe), a relative difference in the magnetization of 11%–16% was measured. Conclusions: The measured curves show that the magnetic properties of sintered heavy tungsten alloys strongly depend on the iron content, whereas the addition of nickel in the absence of iron led to no measurable effect. Since a difference in the BH curves for two samples with identical quoted nominal composition from different manufacturers was observed, measuring of the BH curve for each individual batch of heavy tungsten alloys is advisable whenever accurate knowledge of the magnetic properties is crucial. The obtained BH curves can be used in FEM simulations to predict the magnetic impact of sintered heavy

  8. Interplay between magnetism and energetics in Fe-Cr alloys from a predictive noncollinear magnetic tight-binding model

    NASA Astrophysics Data System (ADS)

    Soulairol, R.; Barreteau, C.; Fu, Chu-Chun

    2016-07-01

    Magnetism is a key driving force controlling several thermodynamic and kinetic properties of Fe-Cr systems. We present a tight-binding model for Fe-Cr, where magnetism is treated beyond the usual collinear approximation. A major advantage of this model consists in a rather simple fitting procedure. In particular, no specific property of the binary system is explicitly required in the fitting database. The present model is proved to be accurate and highly transferable for electronic, magnetic, and energetic properties of a large variety of structural and chemical environments: surfaces, interfaces, embedded clusters, and the whole compositional range of the binary alloy. The occurrence of noncollinear magnetic configurations caused by magnetic frustrations is successfully predicted. The present tight-binding approach can apply to other binary magnetic transition-metal alloys. It is expected to be particularly promising if the size difference between the alloying elements is rather small and the electronic properties prevail.

  9. Magnetic viscosity in Ni/Cu compositionally-modulated alloys

    SciTech Connect

    Bennett, L.H.; Swartzendruber, L.J.; Ettedgui, H.; Atzmony, U.; Lashmore, D.S; Watson, R.E.; Brookhaven National Lab., Upton, NY )

    1989-01-01

    The existence of a magnetic aftereffect ( magnetic viscosity'') in Ni/Cu multilayered alloys was established using a vibrating sample magnetometer at room temperature and at 86 K. It was shown that the effect is strongly dependent on the step field, H{sub 2} (i.e., the value the field is reduced to after the magnetic moment has been aligned in high field) and exhibits a maximum relaxation rate for values of H{sub 2} around the reverse coercive field, {minus}H{sub c}. Aftereffect behavior of this type has been observed in other materials, though most often for systems composed of superparamagnetic particles, where the relaxation freezes out at low temperatures. In contrast, the relaxation in the CMA was shown to be enhanced at 86 K over its value at room temperature. New measurements over a wider temperature range show that the enhancement in this sample reaches a maximum near 120 K, but below that temperature the relaxation does freeze out. The temperature of maximum enhancement varies from sample to sample. 6 refs.

  10. Half-metallic alloys: electronic structure, magnetism and spin polarization.

    PubMed

    Dederichs, P H; Galanakis, I; Mavropoulos, Ph

    2005-01-01

    Using the state-of-the-art screened Korringa-Kohn-Rostoker Green function method we study the electronic and magnetic properties of NiMnSb and similar Heusler alloys. We show that all these compounds are half-metals, e.g. the minority-spin band is semiconducting and the Fermi level falls within this gap resulting in 100% spin polarization at the Fermi level. The total spin moment M(t) shows the so-called Slater-Pauling behaviour and scales with the total valence charge Z(t) following the rule M(t) = Z(t) - 18 for half and M(t) = Z(t) - 24 for full Heusler alloys. These rules are connected to the origin of the gap. Finally we show that the inclusion of the spin-orbit interaction in our calculations kills the half-metallic gap but the spin-polarization at the Fermi level can be still very high, approximately 99% for NiMnSb, but much lower for a half-metallic compound like zinc-blende MnBi (77%). PMID:16157642

  11. Microstructural and magnetic characterization of iron precipitation in Ni-Fe-Al alloys

    SciTech Connect

    Duman, Nagehan; Mekhrabov, Amdulla O.; Akdeniz, M. Vedat

    2011-06-15

    The influence of annealing on the microstructural evolution and magnetic properties of Ni{sub 50}Fe{sub x}Al{sub 50-x} alloys for x = 20, 25, and 30 has been investigated. Solidification microstructures of as-cast alloys reveal coarse grains of a single B2 type {beta}-phase and typical off eutectic microstructure consisting of proeutectic B2 type {beta} dendrites and interdendritic eutectic for x = 20 and x > 20 at.% Fe respectively. However, annealing at 1073 K results in the formation of FCC {gamma}-phase particles along the grain boundaries as well as grain interior in x = 20 at.% Fe alloy. The volume fraction of interdentritic eutectic regions tend to decrease and their morphologies start to degenerate by forming FCC {gamma}-phase for x > 20 at.% Fe alloys with increasing annealing temperatures. Increasing Fe content of alloys induce an enhancement in magnetization and a rise in the Curie transition temperature (T{sub C}). Temperature scan magnetic measurements and transmission electron microscopy reveal that a transient rise in the magnetization at temperatures well above the T{sub C} of the alloys would be attributed to the precipitation of a nano-scale ferromagnetic BCC {alpha}-Fe phase. Retained magnetization above the Curie transition temperature of alloy matrix, together with enhanced room temperature saturation magnetization of alloys annealed at favorable temperatures support the presence of ferromagnetic precipitates. These nano-scale precipitates are shown to induce significant precipitation hardening of the {beta}-phase in conjunction with enhanced room temperature saturation magnetization in particular when an annealing temperature of 673 K is used. - Research Highlights: {yields} Evolution of microstructure and magnetic properties with varying Fe content. {yields} Transient rise in magnetization via the formation of ferromagnetic phase. {yields} Enhancements in saturation magnetization owing to precipitated ferromagnetic phase. {yields} Nanoscale

  12. Thermal and damping behaviour of magnetic shape memory alloy composites

    NASA Astrophysics Data System (ADS)

    Glock, Susanne; Michaud, Véronique

    2015-06-01

    Single crystals of ferromagnetic shape memory alloys (MSMA) exhibit magnetic field and stress induced strains via energy dissipating twinning. Embedding single crystalline MSMA particles into a polymer matrix could thus produce composites with enhanced energy dissipation, suitable for damping applications. Composites of ferromagnetic, martensitic or austenitic Ni-Mn-Ga powders embedded in a standard epoxy matrix were produced by casting. The martensitic powder composites showed a crystal structure dependent damping behaviour that was more dissipative than that of austenitic powder or Cu-Ni reference powder composites and than that of the pure matrix. The loss ratio also increased with increasing strain amplitude and decreasing frequency, respectively. Furthermore, Ni-Mn-Ga powder composites exhibited an increased damping behaviour at the martensite/austenite transformation temperature of the Ni-Mn-Ga particles in addition to that at the glass transition temperature of the epoxy matrix, creating possible synergetic effects.

  13. Magnetic properties of Co2Fe(Ga1-xSix) alloys

    NASA Astrophysics Data System (ADS)

    Deka, Bhargab; Chakraborty, Dibyashree; Srinivasan, Ananthakrishnan

    2014-09-01

    Magnetic and crystallographic properties of bulk Co2Fe(Ga1-xSix) alloys with 0≤x≤1 are reported in this work. The alloys with x=0.75 and 1.00 exhibit L21 structure whereas the alloys with x=0, 0.25 and 0.50 crystallized in the disordered A2 phase. Unit cell volume of this series of alloys decreased from 189.1 to 178.5 Å3 as x was increased from 0 to 1.00. All alloy compositions exhibit ferromagnetic behavior with a high Curie temperature (TC) which showed a systematic variation with x (1089 K, 1075 K, 1059 K, 1019 K and 1015 K for x=0, 0.25, 0.5, 0.75 and 1.00, respectively). The saturation magnetization moment Ms for the alloys with x=0, 0.25 and 0.50 are 5.05μB, 5.23μB, 5.49μB, respectively, in accordance with the Slater-Pauling rule, but alloys with x=0.75 and 1.00 deviated from this rule. The effective moment per magnetic atom (pc) of the alloys was estimated from the inverse DC magnetic susceptibility data above TC. A comparison of Ms with pc reveals the half-metallic character of the alloys.

  14. Magnetic and magneto-optical properties of cobalt-platinum alloys with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Weller, D.; Brändle, H.; Gorman, G.; Lin, C.-J.; Notarys, H.

    1992-11-01

    Co1-xPtx alloys with Pt contents in the range 0.45≤x≤0.9 show sizable perpendicular magnetic anisotropy, 100% perpendicular remanence and coercivities in the range 160 kA/m. Thin films of this material are grown by electron beam evaporation onto fused silica or Si, at substrate temperatures between 150 and 350 °C. Spectroscopic investigations of the polar Kerr rotation show a significant enhancement of the Pt related UV peak. A comparison of the static signal levels R×(θk2+ɛk2)1/2 of Co/Pt multilayers and alloys shows an overall 50% enhancement in the case of alloys. Curie temperatures around 200 °C are observed for Co˜22Pt˜78 compositions. These properties, together with the potentially high chemical stability and ease of manufacturing make Co1-xPtx alloys very attractive materials for short wavelength magneto-optic recording.

  15. Magnetic Properties of Radiation Damage in Pu and Pu Alloys

    SciTech Connect

    McCall, S; Fluss, M J; Chung, B; Chapline, G; McElfresh, M; Jackson, D; Baclet, N; Jolly, L; Dormeval, M

    2005-03-31

    Among the many exceptional properties of Pu is its apparent lack of either local moments or cooperative magnetism. Lashley et al., have recently noted that little experimental evidence for the existence of local moments or collective magnetism has been found in over 50 years. Nevertheless the search for local moments in Pu and Pu-alloys continues, why? Plutonium's physical properties: resistance, magnetic susceptibility, and heat capacity, all support a system with an enhanced electron density of states. Pu sits on the edge of both magnetism and superconductivity and possesses one of the highest elemental Pauli susceptibilities, consistent with a highly correlated electron system. The low-density {delta}-Pu has eluded full first principles description and is both a challenge and an area of active investigation for theorists. The complex changes associated with the transition between the light and heavy actinides happen within the phase diagram of Pu, thus making Pu an intriguing and challenging solid-state system for continuing experimental and theoretical investigation. Recently, Griveau et al., observed the variations in the resistance and superconducting properties of Am metal as a function of pressure to 27GPa and T>0.4K. They postulate that the interesting features in the superconducting critical temperature, T{sub c}, vs. pressure, indicate a Mott-like, f-electron localization-delocalization transition as pressure drives Am towards a Pu and then a U-like structure. Hence, we posit that it would be reasonable to expect that dilating the Pu lattice will bring one to a similar transition. Experimental evidence supporting this point of view is given here.

  16. Magnetic, magnetocaloric properties and phenomenological model in amorphous Fe60Ru20B20 alloy

    NASA Astrophysics Data System (ADS)

    Boutahar, A.; Lassri, H.; Hlil, E. K.

    2015-11-01

    Magnetic, magnetocaloric properties and phenomenological model of amorphous Fe60Ru20B20 alloy are investigated in detail. The amorphous alloy has been synthesized using melt spinning method. The magnetic transition nature undergoes a second-order magnetic phase transition from ferromagnetic to paramagnetic states with a Curie temperature of 254 K. Basis on the thermodynamic Maxwell's relation, magnetic entropy change (-ΔSM) is calculated. Further, we also report a theoretical investigation of the magnetocaloric effect using a phenomenological model. The best model parameters and their variation with temperature and the magnetic field were determined. The theoretical predictions are found to agree closely with experimental measurements.

  17. Phase stability and magnetism in NiPt and NiPd alloys

    NASA Astrophysics Data System (ADS)

    Paudyal, Durga; Mookerjee, Abhijit

    2004-08-01

    We show that the differences in stability of 3d-5d NiPt and 3d-4d NiPd alloys arise mainly due to relativistic corrections. The magnetic properties of disordered NiPd and NiPt alloys also differ due to these corrections, which lead to increase in the separation between the s-d bands of 5d elements in these alloys. For the magnetic case we also analyse the results in terms of splitting of majority and minority spin d band centres of the 3d elements. We further examine the effect of relativistic corrections to the pair energies and order-disorder transition temperatures in these alloys. The magnetic moments and Curie temperatures have also been studied along with the short range ordering/segregation effects in NiPt/NiPd alloys.

  18. Spin-density-wave magnetism in dilute copper-manganese alloys

    SciTech Connect

    Lamelas, F.J.; Werner, S.A.; Shapiro, S.M.; Mydosh, J.A.

    1995-02-01

    Elastic neutron-scattering measurements on two samples of Cu alloyed with 1.3% Mn and 0.55% Mn show that the spin-density-wave (SDW) features found in more concentrated alloys persist in the limit of very dilute alloys. These features consist of temperature-dependent incommensurate peaks in magnetic neutron scattering, with positions and strengths which are fully consistent with those in the concentrated alloys. The implications of these measurements are twofold. First, it is clear from this data that SDW magnetic ordering occurs across the entire range of CuMn alloys which have typically been interpreted as spin glasses. Second, the more fundamental significance of this work is the suggestion via extrapolation that a peak in the magnetic susceptibility x(q) occurs in pure copper, at a value of q given by the Fermi-surface diameter 2k{sub F}.

  19. Design and development of novel MRI compatible zirconium- ruthenium alloys with ultralow magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Li, H. F.; Zhou, F. Y.; Li, L.; Zheng, Y. F.

    2016-04-01

    In the present study, novel MRI compatible zirconium-ruthenium alloys with ultralow magnetic susceptibility were developed for biomedical and therapeutic devices under MRI diagnostics environments. The results demonstrated that alloying with ruthenium into pure zirconium would significantly increase the strength and hardness properties. The corrosion resistance of zirconium-ruthenium alloys increased significantly. High cell viability could be found and healthy cell morphology observed when culturing MG 63 osteoblast-like cells and L-929 fibroblast cells with zirconium-ruthenium alloys, whereas the hemolysis rates of zirconium-ruthenium alloys are <1%, much lower than 5%, the safe value for biomaterials according to ISO 10993-4 standard. Compared with conventional biomedical 316L stainless steel, Co–Cr alloys and Ti-based alloys, the magnetic susceptibilities of the zirconium-ruthenium alloys (1.25 × 10‑6 cm3·g‑1–1.29 × 10‑6 cm3·g‑1 for zirconium-ruthenium alloys) are ultralow, about one-third that of Ti-based alloys (Ti–6Al–4V, ~3.5 × 10‑6 cm3·g‑1, CP Ti and Ti–6Al–7Nb, ~3.0 × 10‑6 cm3·g‑1), and one-sixth that of Co–Cr alloys (Co–Cr–Mo, ~7.7 × 10‑6 cm3·g‑1). Among the Zr–Ru alloy series, Zr–1Ru demonstrates enhanced mechanical properties, excellent corrosion resistance and cell viability with lowest magnetic susceptibility, and thus is the optimal Zr–Ru alloy system as therapeutic devices under MRI diagnostics environments.

  20. Design and development of novel MRI compatible zirconium- ruthenium alloys with ultralow magnetic susceptibility.

    PubMed

    Li, H F; Zhou, F Y; Li, L; Zheng, Y F

    2016-01-01

    In the present study, novel MRI compatible zirconium-ruthenium alloys with ultralow magnetic susceptibility were developed for biomedical and therapeutic devices under MRI diagnostics environments. The results demonstrated that alloying with ruthenium into pure zirconium would significantly increase the strength and hardness properties. The corrosion resistance of zirconium-ruthenium alloys increased significantly. High cell viability could be found and healthy cell morphology observed when culturing MG 63 osteoblast-like cells and L-929 fibroblast cells with zirconium-ruthenium alloys, whereas the hemolysis rates of zirconium-ruthenium alloys are <1%, much lower than 5%, the safe value for biomaterials according to ISO 10993-4 standard. Compared with conventional biomedical 316L stainless steel, Co-Cr alloys and Ti-based alloys, the magnetic susceptibilities of the zirconium-ruthenium alloys (1.25 × 10(-6) cm(3)·g(-1)-1.29 × 10(-6) cm(3)·g(-1) for zirconium-ruthenium alloys) are ultralow, about one-third that of Ti-based alloys (Ti-6Al-4V, ~3.5 × 10(-6) cm(3)·g(-1), CP Ti and Ti-6Al-7Nb, ~3.0 × 10(-6) cm(3)·g(-1)), and one-sixth that of Co-Cr alloys (Co-Cr-Mo, ~7.7 × 10(-6) cm(3)·g(-1)). Among the Zr-Ru alloy series, Zr-1Ru demonstrates enhanced mechanical properties, excellent corrosion resistance and cell viability with lowest magnetic susceptibility, and thus is the optimal Zr-Ru alloy system as therapeutic devices under MRI diagnostics environments. PMID:27090955

  1. Design and development of novel MRI compatible zirconium- ruthenium alloys with ultralow magnetic susceptibility

    PubMed Central

    Li, H.F.; Zhou, F.Y.; Li, L.; Zheng, Y.F.

    2016-01-01

    In the present study, novel MRI compatible zirconium-ruthenium alloys with ultralow magnetic susceptibility were developed for biomedical and therapeutic devices under MRI diagnostics environments. The results demonstrated that alloying with ruthenium into pure zirconium would significantly increase the strength and hardness properties. The corrosion resistance of zirconium-ruthenium alloys increased significantly. High cell viability could be found and healthy cell morphology observed when culturing MG 63 osteoblast-like cells and L-929 fibroblast cells with zirconium-ruthenium alloys, whereas the hemolysis rates of zirconium-ruthenium alloys are <1%, much lower than 5%, the safe value for biomaterials according to ISO 10993-4 standard. Compared with conventional biomedical 316L stainless steel, Co–Cr alloys and Ti-based alloys, the magnetic susceptibilities of the zirconium-ruthenium alloys (1.25 × 10−6 cm3·g−1–1.29 × 10−6 cm3·g−1 for zirconium-ruthenium alloys) are ultralow, about one-third that of Ti-based alloys (Ti–6Al–4V, ~3.5 × 10−6 cm3·g−1, CP Ti and Ti–6Al–7Nb, ~3.0 × 10−6 cm3·g−1), and one-sixth that of Co–Cr alloys (Co–Cr–Mo, ~7.7 × 10−6 cm3·g−1). Among the Zr–Ru alloy series, Zr–1Ru demonstrates enhanced mechanical properties, excellent corrosion resistance and cell viability with lowest magnetic susceptibility, and thus is the optimal Zr–Ru alloy system as therapeutic devices under MRI diagnostics environments. PMID:27090955

  2. Structural, thermal and magnetic investigations on immiscible Ag-Co nanocrystalline alloy with addition of Mn

    NASA Astrophysics Data System (ADS)

    Mondal, B. N.; Chabri, S.; Sardar, G.; Nath, D. N.; Chattopadhyay, P. P.

    2016-08-01

    50Ag-50Co (at%) and 40Ag-40Co-20Mn (at%) alloys prepared by ball milling up to 50 h and subsequent isothermal annealing at the temperature range of 350-650 °C for 1 h has been investigated systematically. Mn promotes early formation of the nanostructures and solid solutions of the alloys by ball milling. In contrast, annealing at 350 °C of Ag-Co alloy resulted the dissolution of hcp Co. Annealing above 350 °C decomposes the metastable Ag-Co alloy into the polycrystalline and segregated Ag and fcc Co. Enthalpy of mixing of both the alloy has increased with increase in milling time. Both the nanocrystalline alloys prepared by ball milling and annealing have been revealed the ferromagnetic behavior. The most significant improvement of magnetic properties is yielded in as-milled Ag-Co-Mn alloy obtained after annealing at 550 °C for 1 h.

  3. Ab initio predictions of the stability and structural properties of zincblende (III,TM)V magnetic semiconductor alloys

    NASA Astrophysics Data System (ADS)

    Caetano, C.; Pela, R. R.; Martini, S.; Marques, M.; Teles, L. K.

    2016-05-01

    First-principles calculations and statistical methods were combined to study electronic, magnetic, thermodynamic and structural properties of zincblende (III,Mn)V and (III,Cr)V magnetic semiconductor alloys, including both nitride and arsenide alloys. From phase diagrams it was observed that nitride alloys are much less stable than arsenide ones, although the former ones have more localized d-states at the Fermi level. It was observed that all alloys present an anisotropic behavior, with the strongest magnetic interaction in the < 110 > direction. The relationship between the structural properties of these alloys and their electronic and magnetic characteristics (i.e., their half-metallicity) was investigated.

  4. Temperature Dependence of AC Magnetic Properties of FeCo-Based Soft Magnetic Alloys

    NASA Astrophysics Data System (ADS)

    Xiao, J. Q.; Yu, R. H.; Basu, S.

    1998-03-01

    AC magnetic properties of soft FeCo-based alloys have been studied at different temperatures and frequencies. Samples of Fe_49Co_49V2 (Hiperco50), Fe_49Co_49V_1.7Nb_0.3 (Hiperco 50HS), and Fe_72Co_27Cr_0.5Mn_0.5 (Hiperco 27) were selected and heat-treated to obtain different microstructures. TEM observation reveals that the ordering parameter of the BCC phase in Hiperco 50 series vary with the cooling rate, and a high temperature disordered phase with a high density of defects can be retained through rapid quenching, whereas Hiperco 27 exhibits a disordered structure which is insensitive to the heat treatment. Toroidal laminated samples were used to measure AC magnetic properties. At low frequencies, all the samples either with ordered or disordered phases show low coercivity H_c, high magnetization and initial permeability μ. As the frequency increases, Hc increases and μ decreases due to the damping effect of the magnetic domain walls. In a certain range of frequencies, magnetic permeability spectra show a dispersion zone where the permeability sharply decreases near to zero. This magnetic permeability dispersion zone shifts to lower frequencies with increasing temperature and decreasing ordering parameter. The effect of microstructure, frequency and temperature on core losses will be also presented.

  5. Evaporated CoPt alloy films with strong perpendicular magnetic anisotropy (abstract)

    NASA Astrophysics Data System (ADS)

    Lin, C.-J.; Gorman, G. L.

    1993-05-01

    Co/Pt multilayers with large Kerr rotations at short wavelengths and the magnetic and material properties desired for magneto-optical (MO) recording have been studied extensively as potential future MO materials. Very good recording performance has been demonstrated.1 However, the typical constituent layers in Co/Pt multilayers are very thin, 0.2-0.4 nm Co layers and about 1 nm/Pt layers. To manufacture Co/Pt multilayers consisting of 10-30 periods of such thin Co and Pt layers is certainly quite a challenge. One would prefer to deal with CoPt alloys if the alloys can be made to have large perpendicular magnetic anisotropy and coercivity. Previously no one was able to directly deposit CoPt alloy films with large perpendicular magnetic anisotropy and saturated remanence. Here we will demonstrate for the first time that CoPt alloy films with large perpendicular magnetic anisotropy and coercivity, and saturated remanence can be directly deposited by e-beam evaporation onto heated substrates, at 200 °C or above. Furthermore, we will demonstrate that the perpendicular magnetic anisotropy of CoPt alloy films can be dramatically enhanced by well (111)-textured Pt underlayers. The key to this success appears to be in controlling the crystallographic orientation of these alloy films such that the CoPt(111) lattice plane is parallel to the film surface. CoPt alloys with wide composition range, e.g., 25-57 at. % Co, have been obtained with saturated perpendicular magnetic remanence, indicating that the perpendicular magnetic anisotropy obtained in these alloy films is not related to the ordered tetragonal Co50Pt50 phase. Further work, however, is needed to clarify the anisotropy mechanism in these CoPt alloy films.

  6. Creep deformation of a soft magnetic iron-cobalt alloy

    NASA Astrophysics Data System (ADS)

    Fingers, R. T.; Coate, J. E.; Dowling, N. E.

    1999-04-01

    The U.S. Air Force is in the process of developing magnetic bearings, as well as an aircraft integrated power unit and an internal starter/generator for main propulsion engines. These developments are the driving force for the new emphasis on the development of high saturation, low loss magnets capable of maintaining structural integrity in high stress and high temperature environments. It is this combination of desired material characteristics that is the motivation of this effort to measure, model, and predict the creep behavior of such advanced magnetic materials. Hiperco® Alloy 50HS, manufactured by Carpenter Technology Corporation, is one of the leading candidates for these applications. Material specimens were subjected to a battery of mechanical tests in order to study and characterize their behaviors. Tensile tests provided stress versus strain behaviors that clearly indicated: a yield point, a heterogeneous deformation described as Lüders elongation, the Portevin-LeChatelier effect at elevated temperatures, and most often a section of homogeneous deformation that concluded with necking and fracture. Creep testing indicated three distinct types of behavior. Two types resembled a traditional response with primary, secondary, and tertiary stages; while the third type can be characterized by an abrupt increase in strain rate that acts as a transition from one steady-state behavior to another. The relationships between the tensile and creep responses are discussed. Analyses of the mechanical behavior include double linear regression of empirically modeled data, and constant strain rate testing to bridge the tensile and creep test parameters.

  7. Microstructure and magnetic properties of soft magnetic powder cores of amorphous and nanocrystalline alloys

    NASA Astrophysics Data System (ADS)

    Liu, Yapi; Yi, Yide; Shao, Wei; Shao, Yanfang

    2013-03-01

    With the development of modern ferromagnetic technology, soft magnetic powder cores (MPCs) of amorphous and nanocrystalline alloys have been intensively studied for their excellent soft magnetic properties such as high flux density, low coercivity and reduced core loss due to amorphous state and nanocrystalline grains of 10-20 nm dispersed in a residual amorphous matrix. In this paper, the microstructures and soft magnetic properties, i.e., maximum magnetic induction Bm, effective permeability μe, DC-bias properties and volume power losses PCV of MPCs made from amorphous powder of gas atomization and nanocrystalline powder of pulverized melt-spun ribbon were investigated and also compared on the basis of the same level of μe. It is found that μe of both kinds of MPC keeps unchanged up to 1 MHz. The amorphous MPC has lower PCV at lower frequency range, while the nanocrystalline MPC has lower PCV at high frequency range instead. Also, the nanocrystalline MPC has better DC-bias property. Moreover, the DC magnetic properties and the changes of PCV of both MPCs with frequency and flux density are also studied. Furthermore, the electromagnetic characteristics, the microstructures and the mechanisms accounting for these phenomena of both MPCs are also discussed.

  8. Perpendicular Magnetic Anisotropy in Co-Based Full Heusler Alloy Thin Films

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Xu, X. G.; Miao, J.; Jiang, Y.

    2015-12-01

    Half-metallic Co-based full Heusler alloys have been qualified as promising functional materials in spintronic devices due to their high spin polarization. The lack of perpendicular magnetic anisotropy (PMA) is one of the biggest obstacles restricting their application in next generation ultrahigh density storage such as magnetic random access memory (MARM). How to induce the PMA in Co-based full Heusler alloy thin films has attracted much research interest of scientists. This paper presents an overview of recent progress in this research area. We hope that this paper would provide some guidance and ideas to develop highly spin-polarized Co-based Heusler alloy thin films with PMA.

  9. Atomic structure and magnetic properties of Fe1-xCox alloys

    SciTech Connect

    Nguyen, Manh Cuong; Zhao, Xin; Ji, Min; Wang, Cai-Zhuang; Harmon, Bruce; Ho, Kai-Ming

    2012-03-09

    Using genetic algorithm with first-principle calculations, we searched for low-energy crystal structures of Fe1−xCox alloys. We found that Fe1−xCox alloys are highly configurationally degenerate with many additional off-stoichiometric stable structures to the well-known B2 structure. The average magnetic moment of Fe atom increases with concentration of Co in the alloy, while that of Co atom is almost constant, which are consistent with experiments and earlier studies. The magnetic moment of Fe atom is strongly dependent on the number of Co nearest neighbor and it increases with this number.

  10. Iron cobalt boride and iron zirconium silicide-based nanocomposite soft magnetic alloys and application

    NASA Astrophysics Data System (ADS)

    Long, Jianguo

    Nanocrystalline composite soft magnetic materials, which consist of nanoscale crystalline ferromagnetic phases (typical 10 nm) homogeneously dispersed in an amorphous matrix are derived from crystallizing amorphous ribbons. The excellent soft magnetic properties, such as extremely low coercivities, high permeabilities, low energy losses, etc, have attracted the major interest and research activity in both academic community and industrial community in the past two decades. In this thesis, two classes of nanocrystalline composite soft magnetic alloys are developed from their amorphous precursors, accompanying the analysis on their sturctural evolution, thermal kinetics and variou magnetic properties. FeCoB based nanocrystalline composite soft magnetic alloy is developed, in collaboration with Magnetics Division at Spang & Company, for application in high frequency and high temperature. This class of nanocrystalline composite alloy has the nominal composition (FeCo)80Nb4[BGe(Si)] 15Cu1. The crystallization products are bcc FeCo for primary crystallization at 410°C and (FeCoNb)23B 6 for second crystallization. The average grain size is below 10 nm after annealed at 500°C for 1 hour. After transverse field annealing at its primary crystallization temperature, the core loss significantly decreased to the value which can comparable with other commercial soft magnetic alloy. Another class of nanocrystalline composite soft magnetic alloy is Fe based and Boron free alloy. This class of soft magnetic alloy with the nominal composition Fe79ZrxSi20- xCu1 was developed for low cost on raw materials. The nanocrystalline phase alpha-Fe(Si) with average grain size 10 nm was observed in this kind alloy annealed at 460°C for 1 hour. Cu acts as the nucleation agent for making the precipitated nanocrystals uniform and very fine. The measurement of core loss shows the alloy annealed at 460°C for 2 hour has the relatively core loss which can be comparable that of other commericial

  11. (Fe,Si,Al)-based nanocrystalline soft magnetic alloys for cryogenic applications

    NASA Astrophysics Data System (ADS)

    Daniil, Maria; Osofsky, Michael S.; Gubser, Donald U.; Willard, Matthew A.

    2010-04-01

    In this work Al and Si are substituted for Fe in a (Fe,Si,Al)-Nb-B-Cu alloy with the goal of improving its magnetic properties at 77 K. The x-ray diffraction patterns for a series of five alloys annealed at 823 K shows a Fe3(Si,Al) ordered phase with some residual amorphous phase. The lowest coercivity at room temperature was observed for the alloy with composition Fe68Si15.5Al3.5Nb3B9Cu1. At cryogenic temperatures, the saturation magnetization of 99.3 A m2/kg, coercivity of 0.45 A/m, and resistivity of 122 μΩ cm for the Fe63Si17.5Al6Nb3B9Cu1 alloy, compare favorably to commercial alloys at 77 K.

  12. Magnetic susceptibility of Inconel alloys 718, 625, and 600 at cryogenic temperatures

    NASA Technical Reports Server (NTRS)

    Goldberg, Ira B.; Mitchell, Michael R.; Murphy, Allan R.; Goldfarb, Ronald B.; Loughran, Robert J.

    1990-01-01

    After a hydrogen fuel bleed valve problem on the Discovery Space Shuttle was traced to the strong magnetization of Inconel 718 in the armature of the linear variable differential transformer near liquid hydrogen temperatures, the ac magnetic susceptibility of three samples of Inconel 718 of slightly different compositions, one sample of Inconel 625, and on sample of Inconel 600 were measured as a function of temperature. Inconel 718 alloys are found to exhibit a spin glass state below 16 K. Inconel 600 exhibits three different magnetic phases, the lowest-temperature state (below 6 K) being somewhat similar to that of Inconel 718. The magnetic states of the Inconel alloys and their magnetic susceptibilities appear to be strongly dependent on the exact composition of the alloy.

  13. On the magnetic properties of mechanosynthesized Co-Fe-Ni ternary alloys

    NASA Astrophysics Data System (ADS)

    Jartych, E.

    2011-01-01

    X-ray diffraction, Mössbauer spectroscopy and magnetization measurements were used as complementary methods to obtain structural data and to determine magnetic properties of the mechanically synthesized and subsequently thermally treated Co-Fe-Ni alloys. New, however approximate, phase diagrams were established on the basis of X-ray diffraction investigations. Mössbauer spectroscopy and magnetization measurements allowed to reveal practically linear correlation between the average values of the hyperfine magnetic field induction, < Bhf>, and the effective magnetic moments, μeff, of the alloys. The decrease in < Bhf> with the number of electrons per atom, e/a, was observed. Moreover, the dependence of μeff on the valence 3d and 4s electrons per atom follows the Slater-Pauling curve. Thermal treatment of mechanosynthesized Co-Fe-Ni alloys led to some changes in the phase diagrams, increase in the grain size and decrease of the level of internal strains in alloys. Dependencies of lattice constants, average hyperfine magnetic fields, effective magnetic moments and Curie temperatures on the number of electrons per atom have the same trends for mechanically synthesized as well as for thermally treated alloys.

  14. Magnetic properties of Fe-Cu alloys prepared by pulsed electrodeposition

    SciTech Connect

    Noce, R. D.; Barthem, V. M. T. S.; Magalhaes, S. D. de; Wolf, W.; Castro, A. C. de; Guimaraes, R. B.; Pires, M. J. M.; Macedo, W. A. A.; Givord, D.

    2009-11-01

    Fe{sub x}Cu{sub 100-x} metastable alloys were prepared by pulsed electrodeposition for 5alloys crystallize in the bcc structure of alpha-Fe and the Fe-poor ones in the fcc structure of Cu. The magnetic properties of the ferromagnetic Fe-rich alloys (x>50) are reminiscent of those observed in Fe-Cu alloys prepared by other methods. The Curie temperature decreases regularly with decreasing x. In the Fe-poor alloys (x<=30), the observed properties indicate that Fe-rich clusters form within a Cu-rich matrix. In the x=10 alloy, the Fe clusters are found to be superparamagnetic at room temperature, but a superferromagnetic order develops below a critical temperature of about 120 K. It is suggested that the intercluster coupling is mediated by Ruderman-Kittel-Kasuya-Yosida interactions which are predominantly positive due to the very short intercluster distances.

  15. Abnormal reduction of coercivity on magnetic cobalt platinum alloy films

    NASA Astrophysics Data System (ADS)

    Su, C. W.; Shern, C. S.

    2006-08-01

    Ultrathin Co-Pt alloy films as substrate were studied by the surface magneto-optical Kerr effect. As the growth of Ni, the films show uniquely high polar Kerr responses without any in-plane signals. The coercivity decreased until the thickness of Ni film was higher than 5 ML. A new surface structure was discovered at 7-10 ML Ni/Co-Pt films by the low-energy electron diffraction. Interestingly, polar Kerr signal and coercivity of the 10 ML Ni/Co-Pt(1 1 1) template film reduced rapidly as Co films were further deposited onto only about 1-2 ML. Then the films show a canted magnetization with a rollback hysteresis in the polar configuration during the growth of Co. Coercivity of the 7 ML Co/Ni/Co-Pt film was found unusually down to almost 100 Oe.The corresponding magic number at around 7 ML of Co in the abnormal reduction of coercivity may be attributed to the cluster formations of Co.

  16. Producing Low-Oxygen Samarium/Cobalt Magnet Alloy

    NASA Technical Reports Server (NTRS)

    Das, Dilip K.; Kumar, Kaplesh; Frost, Robert T.; Chang, C. W.

    1987-01-01

    Experiments aimed at producing SmCo5 alloy with low oxygen contamination described in report. Two methods of alloying by melting without contact with crucible walls tested. Lowest oxygen contamination, 70 parts per million achieved by dc arc melting on water-cooled, tantalum-clad copper hearth in purified quiescent argon atmosphere. Report includes photographs of equipment, photomicrographs of alloy samples, detailed descriptions of procedures tried, and tables of oxygen contamination and intrinsic coercivities of samples produced.

  17. Constrained non-collinear magnetism in disordered Fe and Fe-Cr alloys

    NASA Astrophysics Data System (ADS)

    Nguyen-Manh, D.; Ma, Pui-Wai; Lavrentiev, M. Yu.; Dudarev, S. L.

    2014-06-01

    The development of quantitative models for radiation damage effects in iron, iron alloys and steels, particularly for the high temperature properties of the alloys, requires understanding of magnetic interactions, which control the phase stability of ferritic-martensitic, ferritic, and austenitic steels. In this work, disordered magnetic configurations of pure iron and Fe-Cr alloys are investigated using Density Functional Theory (DFT) formalism, in the form of constrained non-collinear magnetic calculations, with the objective of creating a database of atomic magnetic moments and forces acting between the atoms. From a given disordered atomic configuration of either pure Fe or Fe-Cr alloy, a penalty contribution to the usual spin-polarized DFT total energy has been calculated by constraining the magnitude and direction of magnetic moments. An extensive database of non-collinear magnetic moment and force components for various atomic configurations has been generated and used for interpolating the spatially-dependent magnetic interaction parameters, for applications in large-scale spin-lattice dynamics and magnetic Monte-Carlo simulations.

  18. Magnetism in NiFeMo disordered alloys: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Banerjee, Mitali; Banerjee, Rudra; Majumdar, A. K.; Mookerjee, Abhijit; Sanyal, Biplab; Nigam, A. K.

    2010-10-01

    In this communication we carry out experimental investigation of the behavior of magnetization with temperature and magnetic field of six samples at different compositions of the disordered ternary alloy NiFeMo. We analyze the data using a fist-principles density functional based electronic structure method and a mean-field phase diagram study.

  19. Chemical, electronic, and magnetic structure of LaFeCoSi alloy: Surface and bulk properties

    SciTech Connect

    Lollobrigida, V.; Basso, V.; Kuepferling, M.; Coïsson, M.; Olivetti, E. S.; Celegato, F.; Borgatti, F.; Torelli, P.; Panaccione, G.; Tortora, L.; Stefani, G.; Offi, F.

    2014-05-28

    We investigate the chemical, electronic, and magnetic structure of the magnetocaloric LaFeCoSi compound with bulk and surface sensitive techniques. We put in evidence that the surface retains a soft ferromagnetic behavior at temperatures higher than the Curie temperature of the bulk due to the presence of Fe clusters at the surface only. This peculiar magnetic surface effect is attributed to the exchange interaction between the ferromagnetic Fe clusters located at the surface and the bulk magnetocaloric alloy, and it is used here to monitor the magnetic properties of the alloy itself.

  20. Structure and texture in Ni-30% Co alloy ribbons subjected to annealing in high magnetic field

    NASA Astrophysics Data System (ADS)

    Gervas'eva, I. V.; Milyutin, V. A.; Beaugnon, E.; Khlebnikova, Yu. V.; Rodionov, D. P.

    2016-05-01

    The structure and texture in the Ni-30% Co alloy subjected to cold rolling and annealings in strong dc magnetic field at the temperatures of above and below the Curie point are studied. It has been shown that, at all annealing temperatures, the average grain size after magnetic annealing is smaller than after annealing without filed. After the magnetic annealing of the alloy in the ferromagnetic state, the volume fraction of grains with cube orientation decreases and the volume fraction of the components of deformationinduced texture increases.

  1. Chemical short range order and magnetic correction in liquid manganese-gallium zero alloy

    NASA Astrophysics Data System (ADS)

    Grosdidier, B.; Ben Abdellah, A.; Osman, S. M.; Ataati, J.; Gasser, J. G.

    2015-12-01

    The Mn66Ga34 alloy at this particular composition is known to be zero alloy in which the linear combination of the two neutron scattering lengths weighted by the atomic compositions vanish. Thus for this specific concentration, the effect of the partial structure factors SNN and SNC is cancelled by a weighted term, which value is zero. Then the measured total structure factor S(q) gives directly the concentration-concentration structure factor SCC(q). We present here the first experimental results of neutron diffraction on the Mn66Ga34 "null matrix alloy" at 1050 °C. The main peak of the experimental SCC(q) gives a strong evidence of a hetero-atomic chemical order in this coordinated alloy. This order also appears in real space radial distribution function which is calculated by the Fourier transform of the structure factor. The degree of hetero-coordination is discussed together with other manganese-polyvalent alloys. However manganese also shows abnormal magnetic scattering in the alloy structure factor which must be corrected. This correction gives an experimental information on the mean effective spin of manganese in this liquid alloy. We present the first critical theoretical calculations of the magnetic correction factor in Mn-Ga zero-alloy based on our accurate experimental measurements of SCC(q).

  2. Moessbauer and SANS Studies of Anti-Invar Fe-Ni-C Alloy under Magnetic Field

    SciTech Connect

    Nadutov, V. M.; Kosintsev, S. G.; Svystunov, Ye. O.; Garamus, V. M.; Willumeit, R.; Eckerlebe, H.; Ericsson, T.; Annersten, H.

    2010-07-13

    Anti-Invar effect in the f.c.c.-Fe-25.3%Ni-C alloy was revealed, i.e., enhanced thermal expansion coefficient (TEC)({approx}20x10{sup -6} K{sup -1}) which was accompanied by almost temperature-insensitive behavior in a temperature range of 122-525 K that was considerably expanded to the low temperature range due to alloying with carbon. The Moessbauer and small-angle neutron scattering (SANS) experiments with the varying temperature and in an external magnetic field of 1.5-5 T have revealed an existence of inhomogeneous magnetic order in anti-Invar alloy below and above the magnetic transition point. The anti-Invar behavior correlates with the thermally induced change in the magnetic order and interspin interaction.

  3. The Magnetic Properties of Metal-Alloy Glass Composites Prepared by Ion Implantation

    SciTech Connect

    Julian Fernandez, Cesar de; Mattei, Giovanni; Sada, Cinzia; Maurizio, Chiara; Padovani, Sara; Mazzoldi, Paolo; Sangregorio, Claudio; Gatteschi, Dante

    2003-08-26

    The structural and magnetic properties of Co-Ni, Co-Fe and Ni-Cu alloy nanoparticles formed in silica matrix by sequential ion implantation are presented. These nanoparticles show crystal structure similar to the corresponding bulk alloys. In the Co-Ni and Co-Fe, magnetization saturation and coercive field depend on the the alloy composition, crystal structure and size effects. Ferromagnetic resonance studies show that collective magnetic processes are present and these are determined by the film-like morphology of the implanted region. The temperature dependence of the magnetization of the NixCu100-x samples indicates that their Curie Temperatures are larger than the corresponding bulk ones. This feature is discussed considering the composition of the nanoparticles and the size effects.

  4. Influence of Weak External Magnetic Field on Amorphous and Nanocrystalline Fe-based Alloys

    SciTech Connect

    Degmova, J.; Sitek, J.

    2010-07-13

    Nanoperm, Hitperm and Finamet amorphous and nanocrystalline alloys were measured by Moessbauer spectrometry in a weak external magnetic field of 0.5 T. It was shown that the most sensitive parameters of Moessbauer spectra are the intensities of the 2nd and the 5th lines. Rather small changes were observed also in the case of internal magnetic field values. The spectrum of nanocrystalline Nanoperm showed the increase in A{sub 23} parameter (ratio of line intensities) from 2.4 to 3.7 and decrease of internal magnetic field from 20 to 19 T for amorphous subspectrum under the influence of magnetic field. Spectrum of nanocrystalline Finemet shown decrease in A{sub 23} parameter from 3.5 to 2.6 almost without a change in the internal magnetic field value. In the case of amorphous Nanoperm and Finemet samples, the changes are almost negligible. Hitperm alloy showed the highest sensitivity to the weak magnetic field, when the A{sub 23} parameter increased from 0.4 to 2.5 in the external magnetic fields. The A{sub 23} parameter of crystalline subspectrum increased from 2.7 to 3.8 and the value of internal magnetic field corresponding to amorphous subspectrum increased from 22 to 24 T. The behavior of nanocrystalline alloys under weak external magnetic field was analyzed within the three-level relaxation model of magnetic dynamics in an assembly of single-domain particles.

  5. High Magnetic Field-Induced Formation of Banded Microstructures in Lamellar Eutectic Alloys During Directional Solidification

    NASA Astrophysics Data System (ADS)

    Li, Xi; Fautrelle, Yves; Gagnoud, Annie; Ren, Zhongming; Moreau, Rene

    2016-06-01

    The influences of high magnetic field (up to 12 T) on the morphology of Pb-Sn and Al-Al2Cu lamellar eutectics during directional solidification were investigated. The experimental results indicate that, along with a decrease in eutectic spacing, the banded structure forms at lower growth speeds under high magnetic field and the band spacing decreases as the magnetic field increases. Moreover, the application of a magnetic field enriches the Cu solute in the liquid ahead of the liquid/solid interface during directional solidification of an Al-Al2Cu eutectic alloy. The effects of high magnetic field on the eutectic points of non-ferromagnetic alloys and the stress acting on the eutectic lamellae during directional solidification have been studied. Both thermodynamic evaluation and DTA measurements reveal that the high magnetic field has a negligible effect on the eutectic points of non-ferromagnetic alloys. However, the high magnetic field caused an increase of the nucleation temperature and undercooling. The numerical results indicate that a considerable stress is produced on the eutectic lamellae during directional solidification under high magnetic field. The formation of a banded structure in a lamellar eutectic during directional solidification under high magnetic field may be attributed to both the buildup of the solute in the liquid ahead of the liquid/solid interface and the stress acting on the eutectic lamellae.

  6. High Magnetic Field-Induced Formation of Banded Microstructures in Lamellar Eutectic Alloys During Directional Solidification

    NASA Astrophysics Data System (ADS)

    Li, Xi; Fautrelle, Yves; Gagnoud, Annie; Ren, Zhongming; Moreau, Rene

    2016-08-01

    The influences of high magnetic field (up to 12 T) on the morphology of Pb-Sn and Al-Al2Cu lamellar eutectics during directional solidification were investigated. The experimental results indicate that, along with a decrease in eutectic spacing, the banded structure forms at lower growth speeds under high magnetic field and the band spacing decreases as the magnetic field increases. Moreover, the application of a magnetic field enriches the Cu solute in the liquid ahead of the liquid/solid interface during directional solidification of an Al-Al2Cu eutectic alloy. The effects of high magnetic field on the eutectic points of non-ferromagnetic alloys and the stress acting on the eutectic lamellae during directional solidification have been studied. Both thermodynamic evaluation and DTA measurements reveal that the high magnetic field has a negligible effect on the eutectic points of non-ferromagnetic alloys. However, the high magnetic field caused an increase of the nucleation temperature and undercooling. The numerical results indicate that a considerable stress is produced on the eutectic lamellae during directional solidification under high magnetic field. The formation of a banded structure in a lamellar eutectic during directional solidification under high magnetic field may be attributed to both the buildup of the solute in the liquid ahead of the liquid/solid interface and the stress acting on the eutectic lamellae.

  7. The formation of hysteretic magnetic properties in amorphous alloys of various classes upon thermomagmetic treatment in a transverse magnetic field

    NASA Astrophysics Data System (ADS)

    Kekalo, I. B.; Mogil'nikov, P. S.

    2016-06-01

    In this paper, we have studied the effects of the thermomagnetic treatment in a transverse magnetic field (TMaT⊥) on the permeability of the amorphous alloy Co69Fe3.7Cr3.8Si12.5B11 with such a low saturation magnetostriction ( λ s 10-7) that, in the ribbons of this alloy rolled into a toroid, a sharp longitudinal magnetic texture is observed ( K sq > 0.90). It has been revealed that the permeability μ4 ( H = 4 mOe, f = 1 kHz) as a function of the annealing temperature or time of holding at a temperature is described by a curve with a maximum. This maximum is observed at a coefficient of the squareness of the hysteresis loop K sq,m in the range of 0.2 ≤ K sq,m ≤ 0.4. The regimes of the TMaT have been determined that provide optimum values of the permeability μ4 (15000) without a loss of the ductile state of the ribbons of this alloy. Based on the example of an iron-based alloy of composition Fe57Co31Si2.9B9.1 with λs = 35 × 10-6, it has been shown that the formation of the hysteretic magnetic properties upon the TMaT⊥ depends substantially on the magnitude of the magnetostriction and the Curie temperature of the amorphous alloys.

  8. Change of Auger-electron emission from Ni-Pd alloys under magnetic phase transition

    NASA Astrophysics Data System (ADS)

    Elovikov, S. S.; Zykova, E. Y.; Gvozdover, R. S.; Colligon, J. S.; Yurasova, V. E.

    2006-04-01

    The change of Auger-electron emission from polycrystals of disordered ferromagnetic NiPd 3 and Ni 3 Pd alloys, under ferro- to paramagnetic transition, has been studied experimentally. It has been shown that the intensity of the Auger-lines, which are formed because of transition of valent zone 3d 3/2 and 3d 5/2 electrons, has local maxima near the Curie point T C for the alloys. Thus, the sensitivity of Auger-electron emission to a magnetic state of the alloy has been established.

  9. Mechanical activation of a hard magnetic Fe-Cr-Co alloy powder charge

    NASA Astrophysics Data System (ADS)

    Alymov, M. I.; Milyaev, I. M.; Sychev, A. E.; Kovalev, D. Yu.; Korneev, V. P.; Morozov, Yu. G.; Yusupov, V. S.; Bompe, T. A.

    2014-07-01

    The mechanical activation (MA) of a charge of a hard magnetic 22Kh15KT alloy is studied by wet and dry milling in a planetary mill in a medium of argon and ethyl alcohol with addition of surface-active materials and without them. It is shown that, upon dry MA, powder alloy components are alloyed with formation of two bcc solid solutions and, upon wet MA, charge particles are only intensely dispersed. Dispersion is developed at the highest degree in the first five minutes of MA.

  10. Martensite Transformation and Magnetic Properties of Ni-Fe-Ga Heusler Alloys

    NASA Astrophysics Data System (ADS)

    Nath, Hrusikesh; Phanikumar, Gandham

    2015-11-01

    Compositional instability and phase formation in Ni-Fe-Ga Heusler alloys are investigated. The alloys are synthesized into two-phase microstructure. Their structures are identified as fcc and L 21, respectively. The γ-phase formation could be suppressed with higher Ga-content in the alloy as Ga stabilizes austenite phase, but Ga lowers the martensite transformation temperature. The increase of Fe content improves the magnetization value and the increase of Ni from 52 to 55 at. pct raises the martensite transformation temperature from 216 K to 357 K (-57 °C to 84 °C). Magnetic properties and martensitic transformation behavior in Ni-Fe-Ga Heusler alloys follow opposite trends, while Ni replaces either Fe or Ga, whereas they follow similar trends, while Fe replaces Ga. Modulated martensite structure has low twinning stress and high magneto crystalline anisotropic properties. Thus, the observation of 10- and 14 M-modulated martensite structures in the studied Ni-Fe-Ga Heusler alloys is beneficial for shape memory applications. The interdependency of alloy composition, phase formation, magnetic properties, and martensite transformation are discussed.

  11. Effects of twin boundary mobility on domain microstructure evolution in magnetic shape memory alloys: Phase field simulation

    SciTech Connect

    Jin, Yongmei M.

    2009-02-09

    Effects of twin boundary mobility on domain microstructure evolution during magnetic field-induced deformation in magnetic shape memory alloys are studied by phase field micromagnetic microelastic modeling. The simulations show that different twin boundary mobilities lead to drastically different domain microstructures and evolution pathways, yielding very different magnetization and strain responses, even with opposite signs. The study also reveals complex domain phenomena in magnetic shape memory alloys.

  12. Microstructural Evolution and Magnetic Properties of Aged CoNiGaAl Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    El-Bagoury, N.; Rashad, M. M.

    2016-05-01

    A study on the influence of aging heat treatment conditions at 823 K for 3 h, 24 h, and 120 h, on microstructure, martensitic transformation, and magnetic and mechanical properties of Co50Ni23Ga27- X Al X alloys ( X = 0 and 1 at.%) was performed by using x-ray diffraction (XRD) analysis, optical microscopy (OM), energy-dispersive spectrometer (EDS), differential scanning calorimeter (DSC), and vibrating sample magnetometer (VSM). The results show that the microstructure of both aged alloys consists of martensite and fcc second γ phase in addition to ordered cubic gamma prime ( γ') phase precipitates in martensite. The martensitic transformation temperature peak ( M p) elevates with prolonging aging time and decreasing valence electron concentration ( e v/ a). Saturation magnetization ( M s) decreases, whereas both remanence magnetization ( M r) and coercivity ( H c) increase with aging time. Meanwhile, the aging time enhances the hardness property ( H v) of the investigated alloys.

  13. Phase structure and magnetic properties of Mn{sub 3}Ga{sub 2} alloy

    SciTech Connect

    Lu, Q. M. Yu, F.; Yue, M.; Zhang, H. G.; Li, Y. Q.; Liu, Y. Q.; Zhang, J. X.; Yan, X. L.

    2014-05-07

    In this paper, Mn{sub 3}Ga{sub 2} alloys with high saturation magnetization and high Curie temperatures were prepared by levitation melting high pure Mn and Ga elements followed by annealing. The effect of annealing temperature on phase structure and magnetic properties was investigated by means of x-ray diffraction and a vibrating sample magnetometer. A single phase alloy Mn{sub 3}Ga{sub 2}, which has tetragonal P4/mmm structure, was obtained with an annealing temperature of 773 K and annealing time of 24 h. The hysteresis curve of its easy axis for this single phase alloy shows that the room temperature coercivity and saturation magnetization are 4.18 kOe and 50.81 emu/g, respectively. The thermomagnetic curves indicate that the Curie temperature is about 650 K and a phase transformation occurs above 823 K.

  14. NiPt/Rh(111): A stable surface alloy with enhanced magnetic moments

    NASA Astrophysics Data System (ADS)

    Imam, Mighfar; Marathe, Madhura; Narasimhan, Shobhana

    2009-04-01

    We have performed ab initio density functional theory calculations to investigate the miscibility and magnetic properties of pseudomorphically grown monolayers of Ni xPt 1- x surface alloys on a Rh(111) substrate. We find that the formation of this alloy is energetically favored over phase-segregated forms, and its magnetic moment is also enhanced. A significant contribution to this enhanced magnetic moment is found to come from the induced moments on the otherwise non-magnetic elements Pt and Rh. A low concentration of Ni gives rise to a high magnetic moment per Ni atom. We find that a low effective coordination and a high non-spin-polarized density of states at the Fermi level are responsible for these enhanced moments.

  15. Magnetic states of Co-, Fe- and Mn-atoms in some Heusler alloys

    NASA Astrophysics Data System (ADS)

    Kido, M.; Ido, H.; Kido, G.

    1992-02-01

    Magnetic and thermal measurements have been made for the Heusler-type alloys Co 2TiSn and Co 2TiAl. The magnetic behaviour of Co 2TiSn was found to be of a typical localized character, and the Co moment has been estimated from the saturation magnetization to be 0.99μ B(=μ f), which agrees well with the Co moment of 1.0μ B(=μ p) estimated by applying the Curie-Weiss law to the observed susceptibility (χ) vs temperature ( T) curve above TC. The magnetic behaviour of Co 2TiAl is similar to that of Co 2TiSn, however, μ p = 0.44μ B is a little larger than μ f = 0.37μ B. The difference between the magnetic properties of the above two alloys is discussed.

  16. Magnetic properties of martensite in metamagnetic Ni-Co-Mn-Ga alloys

    NASA Astrophysics Data System (ADS)

    Seguí, C.; Cesari, E.; Lázpita, P.

    2016-04-01

    Ni50-x Co x Mn30Ga20 (x  =  6-9) alloys show metamagnetic behaviour, undergoing martensitic transformation (MT) between ferromagnetic austenite and weak magnetic martensite. The temperatures of the structural and magnetic transitions depend on composition and L21 order degree, in such a way that combined composition and thermal treatment allows for MT between any magnetic state of austenite and martensite. For these alloys, mutual influence between atomic and magnetic order has been widely studied. However, the type of magnetism of martensite remains unclear. In this work, the magnetic state of martensite in a Ni43Co7Mn30Ga20 alloy has been studied in detail. Its evolution as a function of post-quench ageing time indicates that improved atomic order enhances the ferromagnetic character of the weakly magnetic martensite. The most important changes occur when austenite switches from paramagnetic to ferromagnetic. The magnetic behavior of martensite is consistent with the presence of ferromagnetic clusters inside a paramagnetic matrix.

  17. Recent progress in high Bs Fe-based nanocrystalline soft magnetic alloys

    NASA Astrophysics Data System (ADS)

    Ohta, M.; Yoshizawa, Y.

    2011-02-01

    High saturation magnetic flux density (high-Bs) alloy has been developed in an Fe-based nanocrystalline alloy system. A nanocrystalline phase with an average grain size of about 20 nm is obtained by annealing Cu-substituted and/or Cu-and-Si-complex-substituted Fe-B amorphous alloys. The alloy exhibits low coercivity of less than 7 A m-1 and a high Bs of more than 1.8 T. The iron loss at 50 Hz and 1.6 T for a toroidal core made of Fe80.5Cu1.5Si4B14 nanocrystalline alloy is 0.46 W kg-1, which is about 2/3 of that of grain-oriented Si steel. Moreover, the iron loss at 10 kHz and 0.2 T for a wound core made of this alloy is 7.5 W kg-1, which is about 25% of that of non-grain-oriented Si steel and about 60% of that of an Fe-based amorphous alloy. In addition, the cut cores made of the alloy show good superimposed dc-current characteristics and appear promising in applications such as power choke coils (at the high-frequency region).

  18. Phase equilibria of Fe-C binary alloys in a magnetic field

    NASA Astrophysics Data System (ADS)

    England, Roger Dale

    The deployment of high flux magnetic processing in industry requires the ability to model the expected results of a proposed processing, and the current assumptions in the literature did not reflect the actual outcome in measurements of ductile iron. Simple binary iron-carbon alloys of less than one weight percent carbon were thermo-magnetically processed and then compared with Gibbs free energy phase transformation predictions. The data was used to quantify the change in the Gibbs free energy associated with the addition of a static high flux magnetic field, which is complicated by the change in magnetic response as the iron carbon alloys pass through the Curie point. A current common practice is to modify Gibbs free energy by -12J per mole per Tesla applied, as has been reported in the literature. This current prediction practice was employed in initial experiments for this work and the experimental data did not agree with these predicted values. This work suggests two specific influences that affect the model, chemistry and magnetic dipole changes. First, that the influence of alloying elements in the original chemistry, as the samples in the literature were a manganese alloy with 0.45 weight percent carbon, as well as not being precisely controlled for tramp elements that commonly occur in recycled material, created a change that was not predicted and therefore the temperatures were incorrect. Also, the phase transformation in a high flux magnetic field was measured to have a different response under warming versus cooling than the normal hysteresis under ambient magnetism. The change in Gibbs free energy for the binary alloys was calculated as -3J per mole per Tesla in warming, and -8J per mole per tesla in cooling. The change from these values to the -12J per mole per Tesla previously reported is attributed to the change in chemistry. This work attributes the published increase in physical properties to the Hall-Petch relation as a result of the finer product

  19. Giant induced magnetic anisotropy In strain annealed Co-based nanocomposite alloys

    NASA Astrophysics Data System (ADS)

    Kernion, Samuel J.; Ohodnicki, Paul. R.; Grossmann, Jane; Leary, Alex; Shen, Shen; Keylin, Vladimir; Huth, Joseph F.; Horwath, John; Lucas, Matthew S.; McHenry, Michael E.

    2012-09-01

    Low loss switching of soft magnetic materials at high frequencies benefits from tuning the induced anisotropy. We show induced anisotropies, Ku, as large as 1.89×104 J /m3, developed by strain annealing of Co-rich nanocomposite alloys. Crystalline phases in this alloy system have large negative magnetostrictive coefficients, leading to anisotropy fields per unit stress over twice those developed in FINEMET. Tunable permeability and reduced thicknesses achieved in this process can mitigate eddy-current losses. Giant induced magnetic anisotropies are discussed in light of models for the micromechanisms of amorphous metal deformation, stress-assisted transformations in the crystallites, and directional pair ordering.

  20. Testing spin-flip scattering as a possible mechanism of ultrafast demagnetization in ordered magnetic alloys

    NASA Astrophysics Data System (ADS)

    Günther, Stefan; Spezzani, Carlo; Ciprian, Roberta; Grazioli, Cesare; Ressel, Barbara; Coreno, Marcello; Poletto, Luca; Miotti, Paolo; Sacchi, Maurizio; Panaccione, Giancarlo; Uhlíř, Vojtěch; Fullerton, Eric E.; De Ninno, Giovanni; Back, Christian H.

    2014-11-01

    We use element-resolved IR-pump/extreme ultraviolet-probe experiments to disentangle the ultrafast interplay of the magnetic sublattices of an ordered crystalline magnetic alloy. As a paradigmatic example, we investigate the case of the FeRh alloy, which shows a delayed response for the different components. Furthermore, a detailed time-resolved magneto-optic study shows that the data can be analyzed by only assuming Elliot-Yafet-like scattering, as the underlying mechanism for ultrafast demagnetization, resulting in an unexpected nonmonotonic dependence of the spin-flip rate, as a function of quenching.

  1. First-principles study of magnetic properties of Fe-Ni based alloys

    NASA Astrophysics Data System (ADS)

    Onoue, M.; Trimarchi, G.; Freeman, A. J.

    2013-03-01

    Investigations of the magnetic properties of Fe-Ni based alloys are important from the fundamental as well as technological points of view. Furthermore, the magnetization at saturation and Curie temperature (TC) of FeNi can be tuned for specific applications by alloying with other metallic species. We have performed electronic structure calculations on Fe-Ni- M alloys, where M are 3d transition metals, to determine how the magnetization depends on the species M and alloy composition. Electronic band structure and total energies are calculated by the Korringa-Kohn-Rostoker method within the coherent-potential-approximation (KKR-CPA). For the KKR-CPA calculations, we use the generalized gradient approximation of the exchange and correlation functional. In the case of Fe0.50Ni0.45M0 . 05 (M=Sc, Ti, V, Cr, Mn, and Co), the early 3 d atoms have antiparallel magnetic moments to the Fe or Ni, whereas the late ones, Mn and Co, have a parallel magnetic moment. Supported by the NU-Boeing Alliance

  2. Magnetic properties and structure of nanocrystalline FINEMET alloys with various iron contents

    NASA Astrophysics Data System (ADS)

    Mushnikov, N. V.; Potapov, A. P.; Shishkin, D. A.; Protasov, A. V.; Golovnya, O. A.; Shchegoleva, N. N.; Gaviko, V. S.; Shunyaev, K. Yu.; Bykov, V. A.; Starodubtsev, Yu. N.; Belozerov, V. Ya.

    2015-07-01

    The effect of the composition and annealing temperature on the structure and magnetic properties of soft magnetic nanocrystalline Fe-Cu-Nb-Mo-Si-B alloys has been studied. An increase in the iron content compared to that in the traditional FINEMET alloy is shown to allow one to increase the magnetic induction by 18% at a coercive force of no less than 6 A/m. It has been found that, along with the amorphous phase, rapidly quenched ribbons of alloys enriched in Fe contain crystalline α-Fe-based phase precipitates, the (100) crystallographic directions of which are perpendicular to the ribbon plane. Thermomagnetic analysis and differential scanning calorimetry were used to determine the temperatures of structural and magnetic phase transformations of the alloys with different iron contents. It was found that the separation of amorphous phase into areas of different compositions precedes the precipitation of nano-sized soft magnetic Fe-Si phase grains in the rapidly quenched iron-enriched ribbons.

  3. Magnetic-Field Dependence of Thermoelectric Properties of Sintered Bi90Sb10 Alloy

    NASA Astrophysics Data System (ADS)

    Murata, Masayuki; Yamamoto, Atsushi; Hasegawa, Yasuhiro; Komine, Takashi

    2016-03-01

    The magnetic-field dependence of the thermoelectric properties and dimensionless figure of merit ( ZT) of a sintered Bi90Sb10 alloy were experimentally and theoretically evaluated. The Bi-Sb alloy was synthesized in a quartz ampule using the melting method, and the resultant ingot was then ground via ball milling. A sintered Bi90Sb10 alloy with a particle size in the range of several to several tens of micrometers was prepared using the spark plasma sintering (SPS) method. The magnetic-field dependence of the electrical resistivity, Seebeck coefficient, and thermal conductivity were experimentally evaluated at temperatures of 77-300 K for magnetic fields of up to 2.9 T. The results showed that ZT increased by 37% at 300 K under a 2.5-T magnetic field. A theoretical calculation of the magneto-Seebeck coefficient based on the Boltzmann equation with a relaxation time approximation was also performed. Hence, the experimental result for the magneto-Seebeck coefficient of the Bi90Sb10 alloy at 300 K was qualitatively and quantitatively explained. Specifically, the carrier scattering mechanism was shown to be acoustic phonon potential scattering and the carrier mobility ratio between the L- and T-points was found to be 3.3, which corresponds to the characteristics of a single crystal. It was concluded that the effect of the magnetic field on the Seebeck coefficient was demonstrated accurately using the theoretical calculation model.

  4. Large magnetic entropy change and magnetoresistance in a Ni41Co9Mn40Sn10 magnetic shape memory alloy

    DOE PAGESBeta

    Huang, L.; Cong, D. Y.; Ma, L.; Nie, Z. H.; Wang, M. G.; Wang, Z. L.; Suo, H. L.; Ren, Y.; Wang, Y. D.

    2015-07-02

    A polycrystalline Ni41Co9Mn40Sn10 (at. %) magnetic shape memory alloy was prepared by arc melting and characterized mainly by magnetic measurements, in-situ high-energy X-ray diffraction (HEXRD), and mechanical testing. A large magnetoresistance of 53.8% (under 5 T) and a large magnetic entropy change of 31.9 J/(kg K) (under 5 T) were simultaneously achieved. Both of these values are among the highest values reported so far in Ni-Mn-Sn-based Heusler alloys. The large magnetic entropy change, closely related to the structural entropy change, is attributed to the large unit cell volume change across martensitic transformation as revealed by our in-situ HEXRD experiment. Furthermore,more » good compressive properties were also obtained. Lastly, the combination of large magnetoresistance, large magnetic entropy change, and good compressive properties, as well as low cost makes this alloy a promising candidate for multifunctional applications.« less

  5. Pressure dependence on the remanent magnetization of Fe-Ni alloys and Ni metal

    NASA Astrophysics Data System (ADS)

    Wei, Qingguo; Gilder, Stuart Alan; Maier, Bernd

    2014-10-01

    We measured the acquisition of magnetic remanence of iron-nickel alloys (Fe64Ni36, Fe58Ni42, and Fe50Ni50) and pure Ni under pressures up to 23 GPa at room temperature. Magnetization decreases markedly for Fe64Ni36 between 5 and 7 GPa yet remains ferromagnetic until at least 16 GPa. Magnetization rises by a factor of 2-3 for the other compositions during compression to the highest applied pressures. Immediately upon decompression, magnetic remanence increases for all Fe-Ni alloys while magnetic coercivity remains fairly constant at relatively low values (5-20 mT). The amount of magnetization gained upon complete decompression correlates with the maximum pressure experienced by the sample. Martensitic effects best explain the increase in remanence rather than grain-size reduction, as the creation of single domain sized grains would raise the coercivity. The magnetic remanence of low Ni Invar alloys increases faster with pressure than for other body-centered-cubic compositions due to the higher magnetostriction of the low Ni Invar metals. Thermal demagnetization spectra of Fe64Ni36 measured after pressure release broaden as a function of peak pressure, with a systematic decrease in Curie temperature. Irreversible strain accumulation from the martensitic transition likely explains the broadening of the Curie temperature spectra, consistent with our x-ray diffraction analyses.

  6. Finemet nanocrystalline soft magnetic alloy: Investigation of glass forming ability, crystallization mechanism, production techniques, magnetic softness and the effect of replacing the main constituents by other elements

    NASA Astrophysics Data System (ADS)

    Gheiratmand, T.; Hosseini, H. R. Madaah

    2016-06-01

    Finemet soft magnetic alloy has been in the focus of interest in the last years due to its high saturation magnetization, high permeability and low core loss. The great quantity of papers has been devoted to the study of its structural and magnetic properties, confirms this claim. This paper reviews the different researches performed on Finemet up to now. The criteria that should be satisfied in order to have the high glass forming ability in an alloy and also the techniques applied for production of Finemet ribbons, powders and bulk samples have been explained. In addition, the mechanism of devitrification, nanocrystallization and magnetic softness in this applicable magnetic alloy has been discussed in detail. Finally, the effect of different elements substituted with the main constituents in Finemet has been summarized through the studies on the characterization and magnetic properties of different Finemet-type alloys.

  7. Study of magnetism in Ni-Cr hardface alloy deposit on 316LN stainless steel using magnetic force microscopy

    NASA Astrophysics Data System (ADS)

    Kishore, G. V. K.; Kumar, Anish; Chakraborty, Gopa; Albert, S. K.; Rao, B. Purna Chandra; Bhaduri, A. K.; Jayakumar, T.

    2015-07-01

    Nickel base Ni-Cr alloy variants are extensively used for hardfacing of austenitic stainless steel components in sodium cooled fast reactors (SFRs) to avoid self-welding and galling. Considerable difference in the compositions and melting points of the substrate and the Ni-Cr alloy results in significant dilution of the hardface deposit from the substrate. Even though, both the deposit and the substrate are non-magnetic, the diluted region exhibits ferromagnetic behavior. The present paper reports a systematic study carried out on the variations in microstructures and magnetic behavior of American Welding Society (AWS) Ni Cr-C deposited layers on 316 LN austenitic stainless steels, using atomic force microscopy (AFM) and magnetic force microscopy (MFM). The phase variations of the oscillations of a Co-Cr alloy coated magnetic field sensitive cantilever is used to quantitatively study the magnetic strength of the evolved microstructure in the diluted region as a function of the distance from the deposit/substrate interface, with the spatial resolution of about 100 nm. The acquired AFM/MFM images and the magnetic property profiles have been correlated with the variations in the chemical compositions in the diluted layers obtained by the energy dispersive spectroscopy (EDS). The study indicates that both the volume fraction of the ferromagnetic phase and its ferromagnetic strength decrease with increasing distance from the deposit/substrate interface. A distinct difference is observed in the ferromagnetic strength in the first few layers and the ferromagnetism is observed only near to the precipitates in the fifth layer. The study provides a better insight of the evolution of ferromagnetism in the diluted layers of Ni-Cr alloy deposits on stainless steel.

  8. Superior magnetic softness at elevated temperature of Si-rich Fe-based nanocrystalline alloy

    NASA Astrophysics Data System (ADS)

    Shi, Rui-min; Wang, Zhi; Jia, Yun-yun; Wen, Zhuan-ping; Wang, Bo-wen; Zhang, Tao

    2012-10-01

    An excellent high-temperature magnetic softness was observed in a Si-rich nanocrystalline Fe74.5Cu1Nb2Si17.5B5 alloy. The Curie temperatures of amorphous and crystal phases, TCA* and TCcry, for this alloy were detected to be 365 °C and 580 °C, respectively. For the 480 °C-annealed alloy, the initial permeability μi drops to nearly zero just above TCA*; however, for the 540 °C-annealed alloy, the μi of about 10 000 at f = 10 kHz has no perceivable decline in this temperature range and can hold up to more than 400 °C. Such a magnetic softness at elevated temperature is superior to that of Finemet-type Fe-based nanocrystalline alloys ever reported. The origin of the high temperature magnetic softness was interpreted by the enhancement effect of Curie temperature in residual amorphous matrix.

  9. Magnetic States in Ensemble of Ferromagnetic Nanoparticles in Cu-Mn-Al Alloy.

    PubMed

    Konoplyuk, S M; Kozlova, L E; Kokorin, V V; Perekos, A O; Kolomiets, O V

    2016-12-01

    Two Cu-Mn-Al samples of different compositions were studied: one exhibiting martensitic transformation, another without structural transition. X-ray diffraction and magnetic measurements demonstrate that different magnetic behaviors of alloys originate from different concentrations and sizes of ferromagnetic nanoparticles, which appear after solid solution decomposition.Estimation of magnetic moments of ferromagnetic nanoparticles from magnetization curves was performed using Langevin function and compared to those obtained from X-ray examination. Granular systems are known to show giant magnetoresistance. Therefore, magnetoresistance of Cu-Mn-Al melt-spun ribbons after different aging times was measured. The study has shown that increase in the concentration of Mn atoms and time of aging in Cu-Mn-Al alloy leads to an increase in the amount of precipitated phase appearing as ferromagnetic nanoparticles. PMID:26762264

  10. Wireless and passive temperature indicator utilizing the large hysteresis of magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Bergmair, Bernhard; Liu, Jian; Huber, Thomas; Gutfleisch, Oliver; Suess, Dieter

    2012-07-01

    An ultra-low cost, wireless magnetoelastic temperature indicator is presented. It comprises a magnetostrictive amorphous ribbon, a Ni-Mn-Sn-Co magnetic shape memory alloy with a highly tunable transformation temperature, and a bias magnet. It allows to remotely detect irreversible changes due to transgressions of upper or lower temperature thresholds. Therefore, the proposed temperature indicator is particularly suitable for monitoring the temperature-controlled supply chain of, e.g., deep frozen and chilled food or pharmaceuticals.

  11. Multiscale modeling of ultrafast element-specific magnetization dynamics of ferromagnetic alloys

    NASA Astrophysics Data System (ADS)

    Hinzke, D.; Atxitia, U.; Carva, K.; Nieves, P.; Chubykalo-Fesenko, O.; Oppeneer, P. M.; Nowak, U.

    2015-08-01

    A hierarchical multiscale approach to model the magnetization dynamics of ferromagnetic random alloys is presented. First-principles calculations of the Heisenberg exchange integrals are linked to atomistic spin models based upon the stochastic Landau-Lifshitz-Gilbert (LLG) equation to calculate temperature-dependent parameters (e.g., effective exchange interactions, damping parameters). These parameters are subsequently used in the Landau-Lifshitz-Bloch (LLB) model for multisublattice magnets to calculate numerically and analytically the ultrafast demagnetization times. The developed multiscale method is applied here to FeNi (permalloy) as well as to copper-doped FeNi alloys. We find that after an ultrafast heat pulse the Ni sublattice demagnetizes faster than the Fe sublattice for the here-studied FeNi-based alloys.

  12. Development of nanostructured CoFe-based alloys for high temperature magnetic applications.

    PubMed

    Panda, A K; Mohanta, O; Ghosh, M; Mitra, A

    2009-09-01

    The effect of substituting Fe by Co on the crystallization, structural and magnetic behaviour of Fe(72-x)Co(x)Si4B20Nb4 (X = 10, 20, 36, 50 at%) and Co36Fe36Si(4-Y)Al(y)B20Nb4 (Y = 0, 1 at%) alloys prepared in the form of melt spun ribbons has been discussed. Alloys containing optimum content of cobalt = 36 at% showed consistent coercivity at elevated temperatures. This soft magnetic property was further improved with aluminium incorporation. Transmission electron microscopy (TEM) indicated that such enhancement in the properties was due to finer dispersions of (CoFe)SiAl nanoparticles in amorphous matrix. Nanocrystallisation also raised the Curie temperature of the aluminium contained alloy. PMID:19928272

  13. Ti2FeZ (Z=Al, Ga, Ge) alloys: Structural, electronic, and magnetic properties

    NASA Astrophysics Data System (ADS)

    Liping, Mao; Yongfan, Shi; yu, Han

    2014-11-01

    Using the first-principle projector augmented wave potential within the generalized gradient approximation taking into account the on-site Coulomb repulsive, we investigate the structural, electronic and magnetic properties of Ti2FeZ (Z=Al, Ga, Ge) alloys with Hg2CuTi-type structure. These alloys are found to be half-metallic ferrimagnets. The total magnetic moments of the Heusler alloys Ti2FeZ follow the μt=Zt-18 rule and agree with the Slater-Pauling curve quite well. The band gaps are mainly determined by the bonding and antibonding states created from the hybridizations of the d states between the Ti(A)-Ti(B) coupling and Fe atom.

  14. Models of Mass Transport During Microgravity Crystal Growth of Alloyed Semiconductors in a Magnetic Field

    NASA Technical Reports Server (NTRS)

    Ma, Nancy

    2003-01-01

    Alloyed semiconductor crystals, such as germanium-silicon (GeSi) and various II-VI alloyed crystals, are extremely important for optoelectronic devices. Currently, high-quality crystals of GeSi and of II-VI alloys can be grown by epitaxial processes, but the time required to grow a certain amount of single crystal is roughly 1,000 times longer than the time required for Bridgman growth from a melt. Recent rapid advances in optoelectronics have led to a great demand for more and larger crystals with fewer dislocations and other microdefects and with more uniform and controllable compositions. Currently, alloyed crystals grown by bulk methods have unacceptable levels of segregation in the composition of the crystal. Alloyed crystals are being grown by the Bridgman process in space in order to develop successful bulk-growth methods, with the hope that the technology will be equally successful on earth. Unfortunately some crystals grown in space still have unacceptable segregation, for example, due to residual accelerations. The application of a weak magnetic field during crystal growth in space may eliminate the undesirable segregation. Understanding and improving the bulk growth of alloyed semiconductors in microgravity is critically important. The purpose of this grant to to develop models of the unsteady species transport during the bulk growth of alloyed semiconductor crystals in the presence of a magnetic field in microgravity. The research supports experiments being conducted in the High Magnetic Field Solidification Facility at Marshall Space Flight Center (MSFC) and future experiments on the International Space Station.

  15. Strong, non-magnetic, cube textured alloy substrates

    DOEpatents

    Goyal, Amit

    2011-02-01

    A warm-rolled, annealed, polycrystalline, cube-textured, {100}<100>, FCC-based alloy substrate is characterized by a yield strength greater than 200 MPa and a biaxial texture characterized by a FWHM of less than 15.degree. in all directions.

  16. Magnetic Properties of Al-Gd-TM Glass-Forming Alloys

    NASA Astrophysics Data System (ADS)

    Uporov, Sergey; Estemirova, Svetlana; Bykov, Viktor; Mitrofanov, Valentin

    2016-01-01

    We report results of magnetic studies of glass-forming alloys with nominal composition of Al86Gd6TM8 (where TM = Cu, Ni, Co, Fe, Mn, Cr, Ti, Zr, Mo, Ta) synthesized by arc-melting. X-ray diffraction analysis and vibrating sample magnetometry were applied to characterize the prepared samples. All the alloys exhibit antiferromagnetic ordering at low temperatures. In some compositions, we observed metamagnetic transitions in external magnetic fields up to 3 T. Analysis of the paramagnetic susceptibility of the considered Al-Gd-TM systems has revealed non-magnetic behavior of the transition metals. We found that the magnetic properties of the studied samples can be described satisfactorily using only the Gd trivalent ions. But in some cases the magnetic moments of gadolinium are slightly larger than the theoretical values, probably, because of an additional contribution of the 5 d electrons. The obtained results are discussed in framework of the assumptions of the strong s- p- d hybridization and frustrated magnetic states of gadolinium. We argue that the hybridization might be one of the main factors improving the glass-forming ability in these ternary alloys.

  17. Further investigations on high temperature magnetic after-effect in iron alloys containing oxygen

    NASA Astrophysics Data System (ADS)

    Földeáki, M.; Stefán, M.; Köszegi, L.; Kisdi-Koszó, É.

    1980-04-01

    Magnetic after-effect and disaccommodation measurements were performed on iron alloys containing oxygen. A new effect was found. Time dependence, activation energy and ageing properties were determined and interpreted as the relaxation of dislocations with mobile oxygen Cottrell clouds and as the relaxation of interstitial clusters around the precipitates.

  18. Magnetic irreversibility and pinning force density in the Mo100-xRex alloy superconductors

    NASA Astrophysics Data System (ADS)

    Sundar, Shyam; Chattopadhyay, M. K.; Sharath Chandra, L. S.; Roy, S. B.

    2015-12-01

    We have measured the isothermal field dependence of magnetization of the Mo100-xRex (15 ⩽ x ⩽ 48) alloys, and have estimated the critical current and pinning force density from these measurements. We have performed structural characterization of the above alloys using standard techniques, and analyzed the field dependence of critical current and pinning force density using existing theories. Our results indicate that dislocation networks and point defects like voids and interstitial imperfections are the main flux line pinning centers in the Mo100-xRex alloys in the intermediate fields, i.e., in the "small bundle" flux line pinning regime. In this regime, the critical current density is also quite robust against increasing magnetic field. In still higher fields, the critical current density is affected by flux creep. In the low field regime, on the other hand, the pinning of the flux lines seems to be influenced by the presence of two superconducting energy gaps in the Mo100-xRex alloys. This modifies the field dependence of critical current density, and also seems to contribute to the asymmetry in the magnetic irreversibility exhibited by the isothermal field dependence of magnetization.

  19. Study of the effect of short ranged ordering on the magnetism in FeCr alloys

    NASA Astrophysics Data System (ADS)

    Jena, Ambika Prasad; Sanyal, Biplab; Mookerjee, Abhijit

    2014-01-01

    For the study of magnetism in systems where the local environment plays an important role, we propose a marriage between the Monte Carlo simulation and Zunger's special quasi-random structures. We apply this technique on disordered FeCr alloys and show that our estimates of the transition temperature is in good agreement with earlier experiments.

  20. Magnetoelectric coupling characteristics in multiferroic heterostructures with different thickness of nanocrystalline soft magnetic alloy

    NASA Astrophysics Data System (ADS)

    Chen, Lei; Wang, Yao

    2016-05-01

    Magnetoelectric(ME) coupling characteristics in multiferroic heterostructures with different thickness of nanocrystalline soft magnetic alloy has been investigated at low frequency. The ME response with obvious hysteresis, self-biased and dual-peak phenomenon is observed for multiferroic heterostructures, which results from strong magnetic interactions between two ferromagnetic materials with different magnetic properties, magnetostrictions and optimum bias magnetic fields Hdc,opti. The proposed multiferroic heterostructures not only enhance ME coupling significantly, but also broaden dc magnetic bias operating range and overcomes the limitations of narrow bias range. By optimizing the thickness of nanocrystalline soft magnetic alloy Tf, a significantly zero-biased ME voltage coefficient(MEVC) of 14.8mV/Oe (185 mV/cmṡ Oe) at Tf = 0.09 mm can be obtained, which is about 10.8 times as large as that of traditional PZT/Terfenol-D composite with a weak ME coupling at zero bias Hdc,zero. Furthermore, when Tf increases from 0.03 mm to 0.18 mm, the maximum MEVC increases nearly linearly with the increased Tf at Hdc,opti. Additionally, the experimental results demonstrate the ME response for multiferroic heterostructures spreads over a wide magnetic dc bias operating range. The excellent ME performance provides a promising and practicable application for both highly sensitive magnetic field sensors without bias and ME energy harvesters.

  1. Effect of Processing of HIPERCO® 50 Alloy Laminates on Their Magnetic Properties

    NASA Astrophysics Data System (ADS)

    Jayaraman, Tanjore V.

    2015-11-01

    Fe-Co-based soft-magnetic materials form an important class of high-induction alloys that are widely used in energy conversion applications in the aerospace industry. In this work, the effect of processing—cut method [stamping and wire-electrical discharge machining (EDM)] and annealing (cut unannealed, cut followed by annealing, and annealing followed by cut)—on the magnetic properties of the HIPERCO® 50 Alloy laminates was investigated. A cold-rolled ˜0.006-in (˜150-μm)-thick strip of HIPERCO® 50 Alloy was cut into ring laminations and final-annealed in dry hydrogen. Scanning electron microscopy (SEM) and x-ray diffraction analysis indicated the presence of extraneous Cu on the cut edge of the wire-EDM cut ring laminates, along with the expected Fe-Co phase for HIPERCO® 50 alloy. SEM micrographs of the cut edge showed the typical sheared surface and irregular surface for stamped and wire-EDM cut ring laminates respectively. The rings that were stamped followed by annealing (STfA) showed superior direct current (DC) and alternating current (AC) magnetic properties. The presence of Cu (diamagnetic) in wire-EDM cut rings adversely affects induction ( B) and core loss ( P T), compared to the stamped rings for corresponding annealing conditions. The difference in the DC magnetic properties between the ring laminates STfA and annealed followed by stamping (AfST) was significantly large compared to that between the ring laminates that were wire-EDM cut followed by annealing (EDfA) and annealing followed by wire-EDM (AfED). This suggests that, for certain applications where the differences in DC magnetic properties between EDfA and AfED are acceptable, the AfED rings may be put to application/service after the wire-EDM cut operation, i.e. wire-EDM may be performed after `final-annealing'. However, the AC properties between EDfA and AfED rings were significantly different, hence for AC applications, the `final annealing', post-cutting, is critical irrespective

  2. Magnetic core loss of ultrahigh strength FeCo alloys

    NASA Astrophysics Data System (ADS)

    Cheng, X. M.; Zhang, X. K.; Zhang, D. Z.; Lee, S. H.; Duckham, A.; Weihs, T. P.; Cammarata, R. C.; Xiao, John Q.; Chien, C. L.

    2003-05-01

    Hiperco® 50 alloy heat treated between 450 and 650 °C exhibits superior mechanical properties. We report the measurements of the ac core loss at various frequencies up to 4500 Hz of the Hiperco® 50 alloy samples annealed at 450 and 650 °C. The 650 °C annealed specimens have lower ac core loss than that of the 450 °C annealed ones. The total core loss, consisting of contributions from hysteresis core loss and eddy-current core loss, depends on frequency f as af+bf2. The eddy-current loss of a single laminate is minor compared to the hysteresis loss.

  3. Crystallization behavior and magnetic properties in High Fe content FeBCSiCu alloy system

    NASA Astrophysics Data System (ADS)

    Fan, X. D.; Shen, B. L.

    2015-07-01

    High Fe content FeBCSiCu nanocrystalline alloys are prepared by annealing melt-spun amorphous ribbons with aim at increasing saturation magnetic flux density. Microstructures identified by XRD and TEM reveal that Cu addition inhibits the surface crystallization of Fe86B7C7 alloy and improve its glass-forming ability. Activation energy of crystallization calculated by Kissinger's equation indicates that both Cu and Si addition promotes the precipitation of α-Fe phase and improves the thermal stability. VSM and DC B-H loop tracer measurements show that the Fe85.5B7C6Si1Cu0.5 nanocrystalline alloy exhibits high saturation magnetic flux density of 1.8 T and low coercivity of 10 A/m, respectively. AC properties measured by AC B-H analyzer show this alloy exhibits low core loss of 0.35 W/kg at 1 T at 50 Hz. Low material cost and convenient productivity make the Fe85.5B7C6Si1Cu0.5 nanocrystalline alloy an economical application in industry.

  4. Magnetic susceptibilities of liquid Cr-Au, Mn-Au and Fe-Au alloys

    SciTech Connect

    Ohno, S.; Shimakura, H.; Tahara, S.; Okada, T.

    2015-08-17

    The magnetic susceptibility of liquid Cr-Au, Mn-Au, Fe-Au and Cu-Au alloys was investigated as a function of temperature and composition. Liquid Cr{sub 1-c}Au{sub c} with 0.5 ≤ c and Mn{sub 1-c}Au{sub c} with 0.3≤c obeyed the Curie-Weiss law with regard to their dependence of χ on temperature. The magnetic susceptibilities of liquid Fe-Au alloys also exhibited Curie-Weiss behavior with a reasonable value for the effective number of Bohr magneton. On the Au-rich side, the composition dependence of χ for liquid TM-Au (TM=Cr, Mn, Fe) alloys increased rapidly with increasing TM content, respectively. Additionally, the composition dependences of χ for liquid Cr-Au, Mn-Au, and Fe-Au alloys had maxima at compositions of 50 at% Cr, 70 at% Mn, and 85 at% Fe, respectively. We compared the composition dependences of χ{sub 3d} due to 3d electrons for liquid binary TM-M (M=Au, Al, Si, Sb), and investigated the relationship between χ{sub 3d} and E{sub F} in liquid binary TM-M alloys at a composition of 50 at% TM.

  5. Electronic structure and magnetism on FeSiAl alloy: A DFT study

    NASA Astrophysics Data System (ADS)

    Cardoso Schwindt, V.; Sandoval, M.; Ardenghi, J. S.; Bechthold, P.; González, E. A.; Jasen, P. V.

    2015-09-01

    Density functional theory (DFT) calculation has been performed to study the electronic structure and chemical bonding in FeSiAl alloy. These calculations are useful to understand the magnetic properties of this alloy. Our results show that the mean magnetic moment of Fe atoms decreases due to the crystal structure and the effect of Si and Al. Depending on the environment, the magnetic moment of one Fe site (Fe1) increases to about 14.3% while of the other site (Fe2) decreases to about 25.9% (compared with pure bcc Fe). All metal-metal overlap interactions are bonding and slightly weaker than those found in the bcc Fe structure. The electronic structure (DOS) shows an important hybridization among Fe, Si and Al atoms, thus making asymmetric the PDOS with a very slight polarization of Al and Si atoms. Our study explains the importance of crystal structure in determining the magnetic properties of the alloys. FeSiAl is a good candidate for electromagnetic interference shielding combining low price and good mechanical and magnetic properties.

  6. Electronic structure and magnetic properties of disordered Co{sub 2}FeAl Heusler alloy

    SciTech Connect

    Jain, Vishal Jain, Vivek Sudheesh, V. D. Lakshmi, N. Venugopalan, K.

    2014-04-24

    The effects of disorder on the magnetic properties of Co{sub 2}FeAl alloy are reported. X-ray diffraction exhibit A2-type disordered structure. Room temperature Mössbauer studies show the presence of two sextets with hyperfine field values of 31T and 30T along with a nonmagnetic singlet. The electronic structure of ordered and disordered Co{sub 2}FeAl alloys, investigated by means of the KKR Green's-function method shows that the magnetic moment of the ordered structure is 5.08μ{sub B} and is 5.10μ{sub B} when disordered. However, a much higher magnetic moment of 5.74μ{sub B} is observed experimentally.

  7. Electronic structure and magnetic properties of disordered Co2FeAl Heusler alloy

    NASA Astrophysics Data System (ADS)

    Jain, Vishal; Jain, Vivek; Sudheesh, V. D.; Lakshmi, N.; Venugopalan, K.

    2014-04-01

    The effects of disorder on the magnetic properties of Co2FeAl alloy are reported. X-ray diffraction exhibit A2-type disordered structure. Room temperature Mössbauer studies show the presence of two sextets with hyperfine field values of 31T and 30T along with a nonmagnetic singlet. The electronic structure of ordered and disordered Co2FeAl alloys, investigated by means of the KKR Green's-function method shows that the magnetic moment of the ordered structure is 5.08μB and is 5.10μB when disordered. However, a much higher magnetic moment of 5.74μB is observed experimentally.

  8. High tunneling magnetoresistance ratio in perpendicular magnetic tunnel junctions using Fe-based Heusler alloys

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Pu; Lim, Sze-Ter; Han, Gu-Chang; Teo, Kie-Leong

    2015-12-01

    Heulser alloys Fe2Cr1-xCoxSi (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 106 erg/cm3. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe2CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

  9. Anisotropy in magnetic and mechanical properties in textured HipercoxAE FeCoV alloys

    NASA Astrophysics Data System (ADS)

    Shang, Chang He; Weihs, T. P.; Cammarata, R. C.; Ji, Yi; Chien, C. L.

    2000-05-01

    Hiperco® FeCoV alloys are soft magnetic materials suitable for applications at high temperatures and under high stresses. We have studied the evolution of the rolling texture and its effects on the mechanical and magnetic properties after annealing the Hiperco® sheets at high temperatures. X-ray pole-figure measurements reveal that the main texture of the as-rolled HA50HS and HA50 sheets is {001}<11¯0>. This rolling texture causes the mechanical and magnetic properties to exhibit a uniaxial anisotropy, which is reduced by annealing.

  10. Magnetic vortex in epitaxially-grown Co2(Fe,Mn)Si alloy

    NASA Astrophysics Data System (ADS)

    Yamamoto, T.; Seki, T.; Kotsugi, M.; Takanashi, K.

    2016-04-01

    We report magnetic vortex formation in epitaxially grown Co2Fe0.4Mn0.6Si (CFMS) Heusler alloy discs that was confirmed using photoemission electron microscopy and the magneto-optical Kerr effect. The phase diagram of magnetic domain structures as functions of the disc thickness (t) and diameter (D) indicates that the magnetic vortex is stable in wide ranges of t and D even for the epitaxial CFMS. The annihilation field of vortex core depended not only on the disc aspect ratio but also on t. Numerical simulation suggests that this t dependence results from extrinsic pinning of a vortex core due to the epitaxial growth.

  11. Relative stability, electronic structure, and magnetism of MnN and (Ga,Mn)N alloys

    NASA Astrophysics Data System (ADS)

    Chan, J. A.; Liu, Jefferson Z.; Raebiger, Hannes; Lany, Stephan; Zunger, Alex

    2008-11-01

    Pure MnN and (Ga,Mn)N alloys are investigated using the ab initio generalized gradient approximation +U (GGA+U) or the hybrid-exchange density-functional (B3LYP) methods. These methods are found to predict dramatically different electronic structure, magnetic behavior, and relative stabilities compared to previous density-functional theory (DFT) calculations. A unique structural anomaly of MnN, in which local-density calculations fail to predict the experimentally observed distorted rocksalt as the ground-state structure, is resolved under the GGA+U and B3LYP formalisms. The magnetic configurations of MnN are studied and the results suggest the magnetic state of zinc-blende MnN might be complex. Epitaxial calculations are used to show that the epitaxial zinc-blende MnN can be stabilized on an InGaN substrate. The structural stability of (Ga,Mn)N alloys was examined and a crossover from the zinc-blende-stable alloy to the rocksalt-stable alloy at an Mn concentration of ˜65% was found. The tendency for zinc-blende (Ga,Mn)N alloys to phase separate is described by an asymmetric spinodal phase diagram calculated from a mixed-basis cluster expansion. This predicts that precipitates will consist of Mn concentrations of ˜5 and ˜50% at typical experimental growth temperatures. Thus, pure antiferromagnetic MnN, previously thought to suppress the Curie temperature, will not be formed. The Curie temperature for the 50% phase is calculated to be TC=354K , indicating the possibility of high-temperature ferromagnetism in zinc-blende (Ga,Mn)N alloys due to precipitates.

  12. Crystallization kinetics and magnetic properties of FeSiCr amorphous alloy powder cores

    NASA Astrophysics Data System (ADS)

    Xu, Hu-ping; Wang, Ru-wu; Wei, Ding; Zeng, Chun

    2015-07-01

    The crystallization kinetics of FeSiCr amorphous alloy, characterized by the crystallization activation energy, Avrami exponent and frequency factor, was studied by non-isothermal differential scanning calorimetric (DSC) measurements. The crystallization activation energy and frequency factor of amorphous alloy calculated from Augis-Bennett model were 476 kJ/mol and 5.5×1018 s-1, respectively. The Avrami exponent n was calculated to be 2.2 from the Johnson-Mehl-Avrami (JMA) equation. Toroid-shaped Fe-base amorphous powder cores were prepared from the commercial FeSiCr amorphous alloy powder and subsequent cold pressing using binder and insulation. The characteristics of FeSiCr amorphous alloy powder and the effects of compaction pressure and insulation content on the magnetic properties, i.e., effective permeability μe, quality factor Q and DC-bias properties of FeSiCr amorphous alloy powder cores, were investigated. The FeSiCr amorphous alloy powder cores exhibit a high value of quality factor and a stable permeability in the frequency range up to 1 MHz, showing superior DC-bias properties with a "percent permeability" of more than 82% at H=100 Oe.

  13. Electrodeposition of iron and iron-aluminium alloys in an ionic liquid and their magnetic properties.

    PubMed

    Giridhar, P; Weidenfeller, B; El Abedin, S Zein; Endres, F

    2014-05-28

    In this work we show that nanocrystalline iron and iron-aluminium alloys can be electrodeposited from the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate, [Py1,4]TfO, at 100 °C. The study comprises CV, SEM, XRD, and magnetic measurements. Two different sources of iron(ii) species, Fe(TfO)2 and FeCl2, were used for the electrodeposition of iron in [Py1,4]TfO. Cyclic voltammetry was employed to evaluate the electrochemical behavior of FeCl2, Fe(TfO)2, and (FeCl2 + AlCl3) in the employed ionic liquid. Thick iron deposits were obtained from FeCl2/[Py1,4]TfO at 100 °C. Electrodeposition of iron-aluminium alloys was successful in the same ionic liquid at 100 °C. The morphology and crystallinity of the obtained deposits were investigated using SEM and XRD, respectively. XRD measurements reveal the formation of iron-aluminium alloys. First magnetic measurements of some deposits gave relatively high coercive forces and power losses in comparison to commercial iron-silicon samples due to the small grain size in the nanometer regime. The present study shows the feasibility of preparing magnetic alloys from ionic liquids. PMID:24715034

  14. Separating Effect of a Novel Combined Magnetic Field on Inclusions in Molten Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    He, Yanjie; Li, Qiulin; Liu, Wei

    2012-10-01

    The feasibility and effectiveness of a novel combined magnetic field (CMF) on the removal of inclusions with a density smaller than the surrounding melt were investigated. The experiment of the separating effect of CMF was conducted on a laboratory-scale apparatus by the simultaneous application of a rotating magnetic field (RMF) and a downward traveling magnetic field (TMF). Primary silicon particles precipitating from the solidification process of Al-Si-Cu alloy were regarded as the inclusions in a molten aluminum alloy. It was found that a CMF consisting of both a RMF and a downward TMF was able to separate silicon particles from the molten Al-Si-Cu alloy by making these particles migrate vertically toward the upper part of the samples. Compared with downward TMF or RMF, CMF improved the separating effectiveness substantially. It was proposed that this type of CMF was approved to be highly effective at eliminating the inclusions with a density smaller than the surrounding molten alloy. A tentative mechanism for the high separating effect of CMF was discussed.

  15. Structural and magnetic characterization of FeNbBCu alloys as a function of Nb content

    NASA Astrophysics Data System (ADS)

    Torrens-Serra, J.; Bruna, P.; Roth, S.; Rodriguez-Viejo, J.; Clavaguera-Mora, M. T.

    2009-05-01

    In this work we describe the changes in the crystallization behaviour and the magnetic properties with variation of the Nb content in Fe79-xNb5+xB15Cu1 (x = 0,2,4) alloys. The microstructure of the samples, as-quenched and after several heat treatments, is analysed by transmission Mössbauer spectroscopy (TMS), x-ray diffraction, differential scanning calorimetry and vibrating sample magnetometry. The saturation polarization, Curie temperature, magnetic entropy change and the maximum value of the hyperfine field distribution of the amorphous phase are composition dependent and are enhanced with a reduction in Nb content. Devitrification is produced by the nanocrystallization of bcc-Fe followed by the precipitation of iron borides. The calorimetric analysis indicates that Nb stabilizes the alloy against nanocrystallization. Both the amount of bcc-Fe precipitates and their mean grain size decrease significantly with increasing Nb content, suggesting a higher level of disorder at the interface between the amorphous matrix and the nanocrystal that reduces grain growth. The variation in the Fe environments after crystallization events deduced from TMS measurements are analysed in terms of the amount of Nb in the alloy. Both amorphous and nanocrystallized alloys show a soft magnetic behaviour with coercivity values in the range 4-10 A m-1.

  16. Effects of hydrostatic pressure on the magnetism and martensitic transition of Ni-Mn-In magnetic superelastic alloys

    NASA Astrophysics Data System (ADS)

    Mañosa, Lluís; Moya, Xavier; Planes, Antoni; Gutfleisch, Oliver; Lyubina, Julia; Barrio, Maria; Tamarit, Josep-Lluís; Aksoy, Seda; Krenke, Thorsten; Acet, Mehmet

    2008-01-01

    We report magnetization and differential thermal analysis measurements as a function of pressure across the martensitic transition in magnetically superelastic Ni-Mn-In alloys. It is found that the properties of the martensitic transformation are significantly affected by the application of pressure. All transition temperatures shift to higher values with increasing pressure. The largest rate of temperature shift with pressure has been found for Ni50Mn34In16 as a consequence of its small entropy change at the transition. Such a strong pressure dependence of the transition temperature opens up the possibility of inducing the martensitic transition by applying relatively low hydrostatic pressures.

  17. Charge-density wave and magnetic phase diagram of chromium alloys

    SciTech Connect

    Fishman, R.S.; Jiang, X.W.

    1996-08-08

    The magnetic phase diagrams of all dilute Cr alloys can be explained by a simple theoretical model with coupled spin- and charge-density waves and a finite electron reservoir. If the charge-density wave and electron reservoir are sufficiently large, the paramagnetic to commensurate spin-density wave transition becomes strongly first order, as found in Cr{sub 1- x}Fe{sub x} and Cr{sub 1-x}Si{sub x} alloys. The observed discontinuity of the slope dT{sub N}/dx at the triple point and the bending of the CI phase boundary are also natural consequences of this model.

  18. Large reversible magnetocaloric effect in a Ni-Co-Mn-In magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Huang, L.; Cong, D. Y.; Ma, L.; Nie, Z. H.; Wang, Z. L.; Suo, H. L.; Ren, Y.; Wang, Y. D.

    2016-01-01

    Reversibility of the magnetocaloric effect in materials with first-order magnetostructural transformation is of vital significance for practical magnetic refrigeration applications. Here, we report a large reversible magnetocaloric effect in a Ni49.8Co1.2Mn33.5In15.5 magnetic shape memory alloy. A large reversible magnetic entropy change of 14.6 J/(kg K) and a broad operating temperature window of 18 K under 5 T were simultaneously achieved, correlated with the low thermal hysteresis (˜8 K) and large magnetic-field-induced shift of transformation temperatures (4.9 K/T) that lead to a narrow magnetic hysteresis (1.1 T) and small average magnetic hysteresis loss (48.4 J/kg under 5 T) as well. Furthermore, a large reversible effective refrigeration capacity (76.6 J/kg under 5 T) was obtained, as a result of the large reversible magnetic entropy change, broad operating temperature window, and small magnetic hysteresis loss. The large reversible magnetic entropy change and large reversible effective refrigeration capacity are important for improving the magnetocaloric performance, and the small magnetic hysteresis loss is beneficial to reducing energy dissipation during magnetic field cycle in potential applications.

  19. Study of magnetic properties and structural and phase transformations in the Co-19 at % Al-6 at % W alloy

    NASA Astrophysics Data System (ADS)

    Kazantseva, N. V.; Stepanova, N. N.; Rigmant, M. B.; Davydov, D. I.; Shishkin, D. A.; Demakov, S. L.; Ryzhkov, M. A.; Romanov, E. P.

    2015-06-01

    The Co-19 at % Al-6 at % W alloy prepared by two methods of melting in an inert atmosphere, namely, by arc melting followed by casting into a water cold copper mold and induction melting followed by casting in a ceramic (Al2O3) mold, has been studied. It was found that the phase composition of the alloy and its magnetic properties depend on the cooling rate of ingot after melting. Samples are ferromagnetic up to 800°C; the specific magnetization equal to σ= 10 emu/g is retained up to ˜700°C. The Curie temperatures of all phases found in the alloy have been determined. It was found that the formation of the Co7W6 phase in the alloy increases the coercive force of the alloy, whereas the saturation magnetization demonstrates a 1.5-fold decrease.

  20. Magnetic study and thermal analysis of a metastable Fe-Zr-based alloy: Influence of process control agents

    NASA Astrophysics Data System (ADS)

    Pilar, M.; Escoda, L.; Suñol, J. J.; Greneche, J. M.

    In this work a Fe 60Co 10(Ni 70Zr 30) 15B 15 nanocrystalline alloy was produced by mechanical alloying. Powders were milled using hexane or cyclohexane as process control agents (PCAs) and their properties compared with those of alloy developed without PCA. Structural and magnetic analysis was performed using X-ray diffraction (XRD), transmission 57Fe Mössbauer spectrometry (TMS) and vibrating sample magnetometry (VSM). High magnetization of saturation and low coercitive field values correspond to an alloy milled with hexane. Thermal analysis was performed by differential scanning calorimetry (DSC). High thermal stability characterizes alloys milled with PCA. Annealing treatments at 400 °C improve magnetic behavior of all samples. Compositional analysis shows low-milling media (<1.1 at.%) and C contamination (<0.2 at.%).

  1. Magnetic properties and remanent magnetization of a mixture of Fe-Ni alloys simulated to the Yamato 74646 (LL6) chondrite

    NASA Astrophysics Data System (ADS)

    Nagai, H.; Momose, K.-I.; Funaki, M.

    Magnetic properties of mixtures of two alloys, 5 at pct Ni-Fe and 29 at pct Ni-Fe, containing varying (from 0.0 to 100 at pct) concentrations of the former, were investigated and compared to those of a Ni-Fe alloy mixture simulating the Yamato 74646 (LL6) chondrite; this mixture was prepared in accordance with the analysis data of Nagahara (1979). The original thermoremanent magnetization of alloy mixtures was acquired by heating for 2 h at 850 C and cooling to room temperature in a geomagnetic field. Remanent magnetization (RM) was measured during cooling at 77 K. It was found that the RM of the alloys simulating the Yamato chondrite was thermally stable. The intensity of RM obtained by cooling at 77 K in geomagnetic field increased by about 10 percent compared to the original one, whereas that acquired by cooling at 77 K in zero magnetic field decreased by about 25 percent.

  2. Electronic structure and magnetic properties of CoTi 1- xAl x alloys

    NASA Astrophysics Data System (ADS)

    Jezierski, A.; Borstel, G.

    1995-02-01

    The band structure of ordered CoTi, CoAl and Co 2TiAl alloys is calculated by the spin-polarized TB LMTO method. We do not observe a magnetic moment on the Co atom in CoTi and CoAl compounds with the CsCl type structure. The Co 2TiAl alloy with the L2 1 type structure is ferromagnetic with a magnetic moment on the Co atom mCo = 0.27 μB and a small opposite induced magnetic moment on the Ti atom mTi = - 0.05 μB. The electronic densities of states of the disorder CoTi 1- xAl x alloys are computed by the TB LMTO CPA method. We find that the magnetic moment has the maximum for x = 0.5 and it decreases to zero for x = 0 and x = 1.0. From the values of the density of states at the Fermi level we calculate the electronic specific heat coefficient γ. The general trend of γ is close to the experimental data.

  3. Development of FeSiBNbCu Nanocrystalline Soft Magnetic Alloys with High B s and Good Manufacturability

    NASA Astrophysics Data System (ADS)

    Wan, Fangpei; He, Aina; Zhang, Jianhua; Song, Jiancheng; Wang, Anding; Chang, Chuntao; Wang, Xinmin

    2016-06-01

    In order to develop Fe-based nanocrystalline soft magnetic alloys with high saturation magnetic flux density (B s) and good manufacturability, the effect of the Nb content on the thermal stability, microstructural evolution and soft magnetic properties of Fe78-x Si13B8Nb x Cu1 (x = 0, 1, 2 and 3) alloys were investigated. It is found that proper Nb addition is effective in widening the optimum annealing temperature range and refining the α-Fe grain in addition to enhancing the soft magnetic properties. For the representative Fe76 Si13B8Nb2Cu1 alloy, the effective annealing time can be over 60 min in the optimal temperature range of 500-600°C. FeSiBNbCu nanocrystalline soft magnetic alloys with desirable soft magnetic properties including high B s of 1.39 T, low coercivity (H c) of 1.5 A/m and high effective permeability (μ e) of 21,500 at 1 kHz have been developed. The enhanced soft magnetic performance and manufacturability of the FeSiBNbCu nanocrystalline alloys are attributed to the high activated energy for the precipitation of α-Fe(Si) and the second phase. These alloys with excellent performance have promising applications in electromagnetic fields like inductors.

  4. Deterministic character of all-optical magnetization switching in GdFe-based ferrimagnetic alloys

    NASA Astrophysics Data System (ADS)

    Le Guyader, L.; El Moussaoui, S.; Buzzi, M.; Savoini, M.; Tsukamoto, A.; Itoh, A.; Kirilyuk, A.; Rasing, Th.; Nolting, F.; Kimel, A. V.

    2016-04-01

    Using photoemission electron microscopy with x-ray magnetic circular dichroism as a contrast mechanism, new insights into the all-optical magnetization switching (AOS) phenomenon in GdFe-based rare-earth transition-metal ferrimagnetic alloys are provided. From a sequence of static images taken after single linearly polarized laser pulse excitation, the repeatability of AOS can be quantified with a correlation coefficient. It is found that low coercivity enables thermally activated domain-wall motion, limiting in turn the repeatability of the switching. Time-resolved measurements of the magnetization dynamics reveal that while AOS occurs below and above the magnetization compensation temperature TM, it is not observed in GdFe samples where TM is absent. Finally, AOS is experimentally demonstrated against an applied magnetic field of up to 180 mT.

  5. Cytocompatibility evaluation of NiMnSn meta-magnetic shape memory alloys for biomedical applications.

    PubMed

    Guiza-Arguello, Viviana R; Monroe, James A; Karaman, Ibrahim; Hahn, Mariah S

    2016-07-01

    Recently, magnetic shape memory alloys (MSMAs) have emerged as an interesting extension to conventional shape memory alloys (SMAs) due to their capacity to undergo reversible deformation in response to an externally applied magnetic field. Meta-magnetic SMAs (M-MSMAs) are a class of MSMAs that are able to transform magnetic energy to mechanical work by harnessing a magnetic-field induced phase transformation, and thus have the capacity to impose up to 10 times greater stress than conventional MSMAs. As such, M-MSMAs may hold substantial promise in biomedical applications requiring extracorporeal device activation. In the present study, the cytotoxicity and ion release from an Ni50 Mn36 Sn14 atomic percent composition M-MSMA were evaluated using NIH/3T3 fibroblasts. Initial studies showed that the viability of cells exposed to NiMnSn ion leachants was 60 to 67% of tissue culture polystyrene (TCP) controls over 10 to 14 days of culture. This represents a significant improvement in cytocompatibility relative to NiMnGa alloys, one of the most extensively studied MSMA systems, which have been reported to induce 80% cell death in only 48 h. Furthermore, NiMnSn M-MSMA associated cell viability was increased to 80% of TCP controls following layer-by-layer alloy coating with poly(allylamine hydrochloride)/poly(acrylic acid) [PAH/PAA]. Ion release measures revealed that the PAH/PAA coatings decreased total Sn and Mn ion release by 50% and 25%, respectively, and optical microscopy evaluation indicated that the coatings reduced NiMnSn surface oxidation. To our knowledge, this study presents the first cytotoxicity evaluation of NiMnSn M-MSMAs and lays the groundwork for their further biological evaluation. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 853-863, 2016. PMID:25953682

  6. Magnetic x-ray linear dichroism of ultrathin Fe-Ni alloy films

    SciTech Connect

    Schumann, F.O.; Willis, R.F.; Goodman, K.W.

    1997-04-01

    The authors have studied the magnetic structure of ultrathin Fe-Ni alloy films as a function of Fe concentration by measuring the linear dichroism of the 3p-core levels in angle-resolved photoemission spectroscopy. The alloy films, grown by molecular-beam epitaxy on Cu(001) surfaces, were fcc and approximately four monolayers thick. The intensity of the Fe dichroism varied with Fe concentration, with larger dichroisms at lower Fe concentrations. The implication of these results to an ultrathin film analogue of the bulk Invar effect in Fe-Ni alloys will be discussed. These measurements were performed at the Spectromicroscopy Facility (Beamline 7.0.1) of the Advanced Light Source.

  7. Magnetic, structural and optical properties of Mn-based and Cr-based diluted magnetic semiconductors and alloys

    NASA Astrophysics Data System (ADS)

    Alsaad, A.

    2009-03-01

    We have implemented supercell approach by using local spin density functional theory for Mn-doped GaN, Mn-doped ScN and the linear muffin-tin orbital method to predict the structural and magnetic properties of these novel diluted magnetic semiconductors and their GaxMn1-xN and ScxMn1-xN alloys. The global energy minimum of MnN is obtained for zinc-blende structure. If the compound is compressed by 6 % the energy minimum corresponds to the NaCl structure in disagreement with the experimentally observed a slightly tetragonally distorted rocksalt structure, known as ? phase. The rocksalt structure of CrN at about 8 % lattice expansion becomes stable in the ferromagnetic (FM) state and has a global minimum energy at a lattice constant of 3.9 å. We have observed an isostructural phase transition for ScxMn1-xN alloys from zince-blende phase to hexagonal phase that occurs at a hydrostatic pressure of 17.5 GPa. Moreover, the structural and optical properties of single crystal CrN/ScN superlattices and Cr1-xScxN alloys are studied in details. We report an isostructural phase transition from wurtzite (w-CrN) to hexagonal (h-ScN) at a hydrostatic pressure of 21 GPa. We have also used first-principles methods to study the electronic, optical and magnetic properties of MnN and MnAs compounds in the hypothetical cubic zinc-blende phase, a phase in which the two MnN and MnAs binaries have the same local environment as that they have in GaMnN and GaMnAs alloys. We show that MnN exhibits antiferromagnetic (AFM) ground state and MnAs adopts ferromagnetic (FM) ground state.

  8. Magnetic properties of Nd-Fe-Co(Cu)-Al-B amorphous alloys prepared by nonequilibrium techniques

    NASA Astrophysics Data System (ADS)

    Kumar, G.; Eckert, J.; Roth, S.; Löser, W.; Ram, S.; Schultz, L.

    2002-03-01

    The amorphous alloys Nd40Fe40Co5Al8B7, Nd57Fe20Co5Al10B8, and Nd57Fe20Cu5Al10B8 were prepared by copper mold casting, melt spinning, and mechanical alloying. Despite their similar x-ray diffraction patterns, samples display different magnetic and thermal behavior correlated with the method of preparation. The fully amorphous melt-spun ribbons exhibit relatively soft magnetic properties with coercivities ≈40 kA/m at room temperature and a Curie temperature (TC)≈474 K. Apparently only the mold-cast cylinders of 3 mm diameter show hard magnetic behavior with a coercivity in the range of 258-270 kA/m (depending on composition) and have approximately the same TC as that of the melt-spun ribbons. An additional magnetic transition at 585 K due to the presence of Nd2Fe14B phase in the case of Nd40Fe40Co5Al8B7 cast rod has been observed. Heat treatment above crystallization temperature in as-cast Nd57Fe20Co5Al10B8 and Nd57Fe20Cu5Al10B8 samples destroys the hard magnetic properties. In contrast, mechanically alloyed amorphous samples are soft magnetic with maximum coercivity up to 11 kA/m but show an entirely different TC≈680-740 K, which is rather characteristic of an Fe solid solution. The magnetic properties are discussed in terms of different local atomic environment and cluster sizes in amorphous samples prepared by different methods.

  9. Magnetic, Caloric and Crystallographic Properties of Dy5(SixGe1-x)4 Alloys

    SciTech Connect

    Vitaliy Vladislavovich Ivchenko

    2002-07-19

    Polycrystals of the intermetallic compound of the Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} system, where x = 0, 0.25, 0.5, 0.625, 0.675, 0.725, 0.75, 0.775, 0.825, 0.875, and 1, have been prepared by electric-arc-melting on water-cooled copper hearth in an argon atmosphere. A study of phase relationships and crystallography in the pseudobinary system Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} using X-ray powder diffraction data and optical metallography was completed. It revealed that silicides in the composition range from 0.825 to 1 crystallize in the Gd{sub 5}Si{sub 4}-type crystal structure: germanides in the composition range from 0 to 0.625 crystallize in the Sm{sub 5}Ge{sub 4}-type structure, and alloys with intermediate composition range from 0.675 to 0.775 crystallize in the monoclinic Gd{sub 5}Si{sub 2}Ge{sub 2}-type structure. The -{Delta}S{sub m} values were determined from magnetization measurements for 7 alloys. The alloys with a monoclinic crystal structure which belong to an intermediate phase region have large MCE value, which exceeds those observed in the other two phase regions by 300 to 500%. The nature of the observed magnetic and structural transformations in the Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} system seems to be similar with those reported for the Gd{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} system. However, the interval and concentration range of three different phase regions in the Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} system are different from that observed in Gd-based alloys. A non-collinear ordering of magnetic moments at low temperature was observed for the alloys with monoclinic crystal structure. The Dy{sub 5}Si{sub 3}Ge alloy exhibited FM phase transition below Curie temperature. A series of magnetic transitions were observed at low temperature in the Dy{sub 5}(Si{sub x}Ge{sub 1-x}){sub 4} alloys. The number of transitions increased and the magnetization decreased with increasing germanium content in the alloys. The -{Delta}S{sub m} and

  10. Synthesis of soft/hard magnetic FePt-based glassy alloys with supercooled liquid region

    NASA Astrophysics Data System (ADS)

    Makino, Akihiro; Kazahari, Akihiro; Zhang, Wei; Yubuta, Kunio; Kubota, Takeshi; Inoue, Akihisa

    2008-11-01

    Since the glassy alloys have structural homogeneity on a nanoscopic scale and wide supercooled liquid region, ΔTx (temperature interval between glass transition and crystallization), these materials are recognized as promising micro/nano-materials for nanomachines or micro electro-mechanical systems (MEMS). As one of the micro/nano components, the hard magnetic one is immensely desired. We systematically investigated the effect of metalloids composition in Fe-Pt-metalloids alloys on the glass-forming ability, and developed Fe55Pt25Si16B2P2, Fe55Pt25Si15B3P2 and (Fe0.55Pt0.25Si0.16B0.02P0.02)96Zr4 (at%) glassy alloys with ΔTx of 37 K and 48 K, respectively. With structural change from the glassy phase to a nano-composite structure consisting of L10 FePt phase, the coercivity significantly increases from 15 A/m to 170 kA/m for the former one. There is possibility for making the hard magnetic components by the fabrication in ΔTx followed by annealing for the crystallization of the FePt-based glassy alloys. Considering the high magnetocrystalline anisotropy of the L10 phase, which should lead to room-temperature ferromagnetic stability for component sizes as small as nm-order, these Fe-Pt-based glassy alloys have great potential for fabrication of hard magnetic micro/nano structures.

  11. Geometry Dependence of Magnetization Reversal in Nanocomposite Alloys

    NASA Astrophysics Data System (ADS)

    Skomski, Ralph; Manchanda, Priyanka; Takeuchi, Ichiro; Cui, Jun

    2014-07-01

    The geometrical optimization of aligned hard-soft permanent-magnet nanocomposites is investigated by model calculations. Considered criteria are the shapes of the soft and c-axis-aligned hard phases, the packing fraction of the soft phase, and magnetostatic interactions. Taking into account that the energy product is enhanced via the volume fraction of the soft phase, subject to maintaining coercivity, we find that the best structures are soft-magnetic cubes as well as long rods with a square cross section. Comparing embedded soft cubes with embedded soft spheres of the same size, our nucleation-field analysis shows that the volume fraction of the soft phase is enhanced by 91%, with a coercivity reduction of only 25%. Magnetostatic interactions often but not always deteriorate the permanent-magnet performance, as exemplified by the example of MnBi:FeCo bilayers and multilayers.

  12. Geometry Dependence of Magnetization Reversal in Nanocomposite Alloys

    SciTech Connect

    Skomski, R; Manchanda, P; Takeuchi, I; Cui, J

    2014-05-31

    The geometrical optimization of aligned hard-soft permanent-magnet nanocomposites is investigated by model calculations. Considered criteria are the shapes of the soft and c-axis-aligned hard phases, the packing fraction of the soft phase, and magnetostatic interactions. Taking into account that the energy product is enhanced via the volume fraction of the soft phase, subject to maintaining coercivity, we find that the best structures are soft-magnetic cubes as well as long rods with a square cross section. Comparing embedded soft cubes with embedded soft spheres of the same size, our nucleation-field analysis shows that the volume fraction of the soft phase is enhanced by 91%, with a coercivity reduction of only 25%. Magnetostatic interactions often but not always deteriorate the permanent-magnet performance, as exemplified by the example of MnBi:FeCo bilayers and multilayers.

  13. Geometry Dependence of Magnetization Reversal in Nanocomposite Alloys

    SciTech Connect

    Skomski, Ralph; Manchanda, Priyanka; Takeuchi, Ichiro; Cui, Jun

    2014-06-11

    The geometrical optimization of aligned hard-soft permanent-magnet nanocomposites is investigated by model calculations. Considered criteria are the shapes of the soft and c-axis-aligned hard phases, the packing fraction of the soft phase, and magnetostatic interactions. Taking into account that the energy product is enhanced via the volume fraction of the soft phase, subject to maintaining coercivity, we find that the best structures are soft-magnetic cubes as well as long rods with a square cross section. Comparing embedded soft cubes with embedded soft spheres of the same size, our nucleation-field analysis shows that the volume fraction of the soft phase is enhanced by 91%, with a coercivity reduction of only 25%. Magnetostatic interactions often but not always deteriorate the permanent-magnet performance, as exemplified by the example of MnBi:FeCo bilayers and multilayers.

  14. Effect of residual strain in Fe-based amorphous alloys on field induced magnetic anisotropy and domain structure

    NASA Astrophysics Data System (ADS)

    Azuma, Daichi; Hasegawa, Ryusuke; Saito, Shin; Takahashi, Migaku

    2013-05-01

    Field induced magnetic anisotropy in two Fe-based amorphous alloys with different saturation induction levels (1.56 T and 1.64 T) was investigated by varying magnetic field strength and annealing temperature and domain images were taken on these samples. Residual strain was evaluated by measuring coercivities of the materials after stress-relief annealing. These results are discussed, clarifying the difference between the two Fe-based amorphous alloys.

  15. Phase stability, ordering, and magnetism of single-phase fcc Fe-Au alloys

    NASA Astrophysics Data System (ADS)

    An, Joonhee M.; Barabash, Sergey V.; Belashchenko, Kirill D.

    2013-03-01

    Motivated by experimental evidence of L10 ordering in single-phase fcc Fe-Au nanoparticles, we study the structural thermodynamics of Fe-Au alloys. First, separate cluster expansions for fcc and bcc lattices are constructed for fully optimized ferromagnetic structures using density functional theory calculations. The optimized structures were assigned to fcc or bcc lattice by a structural filter. Although the lowest formation enthalpy at 50% Au is reached in the bcc lattice, the fcc lattice is preferred for the random alloy. Dynamical stability of specific orderings strongly depends on the magnetic configuration. To analyze the ordering tendencies of the fcc alloy, we restrict uniform lattice relaxations and separate the contributions of chemical interaction and local relaxations. By using the effective tetrahedron model (Ruban et al., Phys. Rev. B 67, 214302 (2003)) and explicit calculations for ordered and special quasi-random structures, we find that the local relaxation energies depend weakly on the magnetization. Although the L10 ordering is the ground state at 50% Au on the ideal lattice, local relaxations make it unfavorable compared to the random alloy. Moderate compression due to the size effect tends to slightly stabilize the L10 ordering.

  16. Structural and magnetic properties CuAl1-xCrxS2 alloys

    NASA Astrophysics Data System (ADS)

    Ortega López, C.; Casiano Jiménez, G.; Espitia, M. J.

    2016-02-01

    In this paper computational calculations were performed based on the density functional theory DFT, to investigate the structural, electronic and magnetic properties of CuAl1-xCrxS2 (x=0.0, 0.50 and 1.00) alloys. Pseudopotential method was used, as is implemented in the Quantum-Espresso code. We found that the alloys crystallize in a tetragonal structure belonging to space group 122 (I-42d) with lattice constants a=5.290Å, c=10.378Å for x=0.5 and a=5.283Å, c=10.366Å for x=1.00. These values are in good agreement with experimental results. Additionally, we found that the alloys possess an antiferromagnetic behaviour with magnetic moments 4,20μβ/cell and 4,05μβ/cell, respectively. From the analysis of the density of states, it is clear that the alloys have a half-metallic behaviour due to the Cr-d and Cu-d states crossing the Fermi level. This compounds can be used in spintronic.

  17. Laser surface modification of medical grade alloys for reduced heating in a magnetic resonance imaging environment

    SciTech Connect

    Benafan, O. E-mail: raj@ucf.edu; Vaidyanathan, R. E-mail: raj@ucf.edu; Chen, S.-Y.; Kar, A.

    2015-12-15

    Nanoscale surface modification of medical grade metallic alloys was conducted using a neodymium-doped yttrium aluminum garnet laser-based dopant diffusion technique. The objective of this approach was to minimize the induction heating by reducing the absorbed radio frequency field. Such an approach is advantageous in that the dopant is diffused into the alloy and is not susceptible to detachment or spallation as would an externally applied coating, and is expected to not deteriorate the mechanical and electrical properties of the base alloy or device. Experiments were conducted using a controlled environment laser system with the ability to control laser properties (i.e., laser power, spot size, and irradiation time) and dopant characteristics (i.e., temperature, concentration, and pressure). The reflective and transmissive properties of both the doped and untreated samples were measured in a radio frequency (63.86 MHz) magnetic field using a system comprising a high power signal generator, a localized magnetic field source and sensor, and a signal analyzer. The results indicate an increase in the reflectivity of the laser-treated samples compared to untreated samples. The effect of reflectivity on the heating of the alloys is investigated through a mathematical model incorporating Maxwell’s equations and heat conduction.

  18. Laser surface modification of medical grade alloys for reduced heating in a magnetic resonance imaging environment.

    PubMed

    Benafan, O; Chen, S-Y; Kar, A; Vaidyanathan, R

    2015-12-01

    Nanoscale surface modification of medical grade metallic alloys was conducted using a neodymium-doped yttrium aluminum garnet laser-based dopant diffusion technique. The objective of this approach was to minimize the induction heating by reducing the absorbed radio frequency field. Such an approach is advantageous in that the dopant is diffused into the alloy and is not susceptible to detachment or spallation as would an externally applied coating, and is expected to not deteriorate the mechanical and electrical properties of the base alloy or device. Experiments were conducted using a controlled environment laser system with the ability to control laser properties (i.e., laser power, spot size, and irradiation time) and dopant characteristics (i.e., temperature, concentration, and pressure). The reflective and transmissive properties of both the doped and untreated samples were measured in a radio frequency (63.86 MHz) magnetic field using a system comprising a high power signal generator, a localized magnetic field source and sensor, and a signal analyzer. The results indicate an increase in the reflectivity of the laser-treated samples compared to untreated samples. The effect of reflectivity on the heating of the alloys is investigated through a mathematical model incorporating Maxwell's equations and heat conduction. PMID:26724043

  19. Laser surface modification of medical grade alloys for reduced heating in a magnetic resonance imaging environment

    NASA Astrophysics Data System (ADS)

    Benafan, O.; Chen, S.-Y.; Kar, A.; Vaidyanathan, R.

    2015-12-01

    Nanoscale surface modification of medical grade metallic alloys was conducted using a neodymium-doped yttrium aluminum garnet laser-based dopant diffusion technique. The objective of this approach was to minimize the induction heating by reducing the absorbed radio frequency field. Such an approach is advantageous in that the dopant is diffused into the alloy and is not susceptible to detachment or spallation as would an externally applied coating, and is expected to not deteriorate the mechanical and electrical properties of the base alloy or device. Experiments were conducted using a controlled environment laser system with the ability to control laser properties (i.e., laser power, spot size, and irradiation time) and dopant characteristics (i.e., temperature, concentration, and pressure). The reflective and transmissive properties of both the doped and untreated samples were measured in a radio frequency (63.86 MHz) magnetic field using a system comprising a high power signal generator, a localized magnetic field source and sensor, and a signal analyzer. The results indicate an increase in the reflectivity of the laser-treated samples compared to untreated samples. The effect of reflectivity on the heating of the alloys is investigated through a mathematical model incorporating Maxwell's equations and heat conduction.

  20. Magnetic behavior of Cr74Fe26 alloy investigated by Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Bansal, C.; Kumaran, T.; Campbell, S. J.; Whittle, G. L.

    1991-10-01

    Two recently published comments [P. A. Beck, Phys. Rev. B 39, 752 (1989) and D. Boumazouza et al., Phys. Rev. B 39, 749 (1989)] have drawn attention to the interesting magnetic behavior of reentrant spin-glass systems. We present a temperature-dependent Mössbauer-effect study on Cr74Fe26 alloy whose composition is close to and slightly above the percolation threshold (xFe=19.9 at. %), to resolve the controversy that has arisen out of these discussions. Our results suggest that the nature of magnetic ordering at the paramagnetic-to-ferromagnetic transition in this system also does not correspond to a true cooperative transition, as pointed out by Beck for Au82.5Fe17.5 alloy.

  1. Fabrication and Spark Plasma Sintering of Magnetic alpha-Fe/MgO Nanocomposite by Mechanical Alloying.

    PubMed

    Lee, Chung-Hyo

    2016-02-01

    Solid-state reduction has occurred during mechanical alloying of a mixture of Fe2O3 and Mg powders at room temperature. It is found that magnetic nanocomposite in which MgO is dispersed in alpha-Fe matrix with nano-sized grains is obtained by mechanical alloying of Fe2O3 with Mg for 30 min. Consolidation of the ball-milled powders was performed in a spark plasma sintering (SPS) machine up to 800-1000 degrees C. X-ray diffraction result shows that the average grain size of alpha-Fe in a-Fe/MgO nanocomposite sintered at 800 degrees C is in the range of 110 nm. It can be also seen that the coercivity of SPS sample sintered at 800 degrees C is still high value of 88 Oe, suggesting that the grain growth of magnetic alpha-Fe phase during SPS process tends to be suppressed. PMID:27433621

  2. Effect of steady and time-harmonic magnetic fields on macrosegragation in alloy solidification

    SciTech Connect

    Incropera, F.P.; Prescott, P.J.

    1995-12-31

    Buoyancy-induced convection during the solidification of alloys can contribute significantly to the redistribution of alloy constituents, thereby creating large composition gradients in the final ingot. Termed macrosegregation, the condition diminishes the quality of the casting and, in the extreme, may require that the casting be remelted. The deleterious effects of buoyancy-driven flows may be suppressed through application of an external magnetic field, and in this study the effects of both steady and time-harmonic fields have been considered. For a steady magnetic field, extremely large field strengths would be required to effectively dampen convection patterns that contribute to macrosegregation. However, by reducing spatial variations in temperature and composition, turbulent mixing induced by a time-harmonic field reduces the number and severity of segregates in the final casting.

  3. Optimization of the magnetic properties of nanostructured Y-Co-Fe alloys for permanent magnets

    NASA Astrophysics Data System (ADS)

    Tozman, P.; Venkatesan, M.; Coey, J. M. D.

    2016-05-01

    The structural and magnetic properties of ball-milled Fe-doped Y Co5-xFex(0 ≤ x ≤ 0.5) were investigated. The magnetization increases with Fe-doping up to the solid solubility limit, x = 0.3 without destroying the crystal structure or degrading the coercivity. A special magnet array is designed using ring magnets for pressing the powders under magnetic field in order to achieve magnetic alignment. A dramatic increase in magnetization is observed for magnetically aligned Y Co4.8Fe0.2 pressed ingots.

  4. Laser-Induced Fast Magnetization Precession and Gilbert Damping for CoCrPt Alloy Thin Films with Perpendicular Magnetic Anisotropy

    NASA Astrophysics Data System (ADS)

    Mizukami, Shigemi; Watanabe, Daisuke; Kubota, Takahide; Zhang, Xianmin; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Miyazaki, Terunobu

    2010-12-01

    We have investigated magnetic field strength (up to 10 kOe) and angle dependences of spin dynamics in 4-nm-thick films of CoCrPt alloys with perpendicular magnetic anisotropy using the all-optical time-resolved magneto-optical Kerr effect (TRMOKE). The comprehensive TRMOKE measurements have indicated the Gilbert damping constant α of 0.05 for the alloy film with low coercivity. The experiments also indicated that α values for the alloy films deposited at higher temperatures with higher coercivities were also no greater than 0.06.

  5. Feedforward-Feedback Hybrid Control for Magnetic Shape Memory Alloy Actuators Based on the Krasnosel'skii-Pokrovskii Model

    PubMed Central

    Zhou, Miaolei; Zhang, Qi; Wang, Jingyuan

    2014-01-01

    As a new type of smart material, magnetic shape memory alloy has the advantages of a fast response frequency and outstanding strain capability in the field of microdrive and microposition actuators. The hysteresis nonlinearity in magnetic shape memory alloy actuators, however, limits system performance and further application. Here we propose a feedforward-feedback hybrid control method to improve control precision and mitigate the effects of the hysteresis nonlinearity of magnetic shape memory alloy actuators. First, hysteresis nonlinearity compensation for the magnetic shape memory alloy actuator is implemented by establishing a feedforward controller which is an inverse hysteresis model based on Krasnosel'skii-Pokrovskii operator. Secondly, the paper employs the classical Proportion Integration Differentiation feedback control with feedforward control to comprise the hybrid control system, and for further enhancing the adaptive performance of the system and improving the control accuracy, the Radial Basis Function neural network self-tuning Proportion Integration Differentiation feedback control replaces the classical Proportion Integration Differentiation feedback control. Utilizing self-learning ability of the Radial Basis Function neural network obtains Jacobian information of magnetic shape memory alloy actuator for the on-line adjustment of parameters in Proportion Integration Differentiation controller. Finally, simulation results show that the hybrid control method proposed in this paper can greatly improve the control precision of magnetic shape memory alloy actuator and the maximum tracking error is reduced from 1.1% in the open-loop system to 0.43% in the hybrid control system. PMID:24828010

  6. Constitutive modelling of magnetic shape memory alloys with discrete and continuous symmetries

    PubMed Central

    Haldar, K.; Lagoudas, D. C.

    2014-01-01

    A free energy-based constitutive formulation is considered for magnetic shape memory alloys. Internal state variables are introduced whose evolution describes the transition from reference state to the deformed and transformed one. We impose material symmetry restrictions on the Gibbs free energy and on the evolution equations of the internal state variables. Discrete symmetry is considered for single crystals, whereas continuous symmetry is considered for polycrystalline materials. PMID:25197247

  7. Constitutive modelling of magnetic shape memory alloys with discrete and continuous symmetries.

    PubMed

    Haldar, K; Lagoudas, D C

    2014-09-01

    A free energy-based constitutive formulation is considered for magnetic shape memory alloys. Internal state variables are introduced whose evolution describes the transition from reference state to the deformed and transformed one. We impose material symmetry restrictions on the Gibbs free energy and on the evolution equations of the internal state variables. Discrete symmetry is considered for single crystals, whereas continuous symmetry is considered for polycrystalline materials. PMID:25197247

  8. Magnetic circular x-ray dichroisms of Fe-Ni alloys at K edge.

    SciTech Connect

    Freeman, A. J.; Gofron, K. J.; Kimball, C. W.; Lee, P. L.; Montano, P. A.; Rao, F.; Wang, X.

    1997-04-03

    Magnetic Circular X-ray Dichroism (MCXD) studies at K edges of Fe-Ni alloys reveal changes of the MCXD signal with composition and crystal structure. We observe that the signal at the invar composition is of comparable strength as other compositions. Moreover, the edge position is strongly dependent on lattice constant. First principles calculations demonstrate that the shape and strength of the signal strongly depends on the crystal orientation, composition, and lattice constant. We find direct relation between the MCXD signal and the p DOS. We find that the MCXD at K edge probes the magnetism due to itinerant electrons.

  9. Investigation of Magnetic Signatures and Microstructures for Heat-Treated Ferritic/Martensitic HT-9 Alloy

    SciTech Connect

    Henager, Charles H.; McCloy, John S.; Ramuhalli, Pradeep; Edwards, Danny J.; Hu, Shenyang Y.; Li, Yulan

    2013-05-01

    There is increased interest in improved methods for in-situ nondestructive interrogation of materials for nuclear reactors in order to ensure reactor safety and quantify material degradation (particularly embrittlement) prior to failure. Therefore, a prototypical ferritic/martensitic alloy, HT-9, of interest to the nuclear materials community was investigated to assess microstructure effects on micromagnetics measurements – Barkhausen noise emission, magnetic hysteresis measurements, and first-order reversal curve analysis – for samples with three different heat-treatments. Microstructural and physical measurements consisted of high-precision density, resonant ultrasound elastic constant determination, Vickers microhardness, grain size, and texture. These were varied in the HT-9 alloy samples and related to various magnetic signatures. In parallel, a meso-scale microstructure model was created for alpha iron and effects of polycrystallinity and demagnetization factor were explored. It was observed that Barkhausen noise emission decreased with increasing hardness and decreasing grain size (lath spacing) while coercivity increased. The results are discussed in terms of the use of magnetic signatures for nondestructive interrogation of radiation damage and other microstructural changes in ferritic/martensitic alloys.

  10. Industrialization of nanocrystalline Fe-Si-B-P-Cu alloys for high magnetic flux density cores

    NASA Astrophysics Data System (ADS)

    Takenaka, Kana; Setyawan, Albertus D.; Sharma, Parmanand; Nishiyama, Nobuyuki; Makino, Akihiro

    2016-03-01

    Nanocrystalline Fe-Si-B-P-Cu alloys exhibit high saturation magnetic flux density (Bs) and extremely low magnetic core loss (W), simultaneously. Low amorphous-forming ability of these alloys hinders their application potential in power transformers and motors. Here we report a solution to this problem. Minor addition of C is found to be effective in increasing the amorphous-forming ability of Fe-Si-B-P-Cu alloys. It allows fabrication of 120 mm wide ribbons (which was limited to less than 40 mm) without noticeable degradation in magnetic properties. The nanocrystalline (Fe85.7Si0.5B9.5P3.5Cu0.8)99C1 ribbons exhibit low coercivity (Hc)~4.5 A/m, high Bs~1.83 T and low W~0.27 W/kg (@ 1.5 T and 50 Hz). Success in fabrication of long (60-100 m) and wide (~120 mm) ribbons, which are made up of low cost elements is promising for mass production of energy efficient high power transformers and motors

  11. Static and dynamic magnetic properties of epitaxial Co2FeAl Heusler alloy thin films

    NASA Astrophysics Data System (ADS)

    Ortiz, G.; Gabor, M. S.; Petrisor, T., Jr.; Boust, F.; Issac, F.; Tiusan, C.; Hehn, M.; Bobo, J. F.

    2011-04-01

    Structural and magnetic properties of epitaxial Co2FeAl Heusler alloy thin films were investigated. Films were deposited on single crystal MgO (001XS) substrates at room temperature, followed by an annealing process at 600 °C. MgO and Cr buffer layers were introduced in order to enhance crystalline quality, and improve magnetic properties. Structural analyses indicate that samples have grown in the B2 ordered epitaxial structure. VSM measures show that the MgO buffered sample displays a magnetization saturation of 1010 ± 30 emu/cm3, and Cr buffered sample displays a magnetization saturation of 1032 ± 40 emu/cm3. Damping factor was studied by strip-line ferromagnetic resonance measures. We observed a maximum value for the MgO buffered sample of about 8.5 × 10-3, and a minimum value of 3.8 × 10-3 for the Cr buffered one.

  12. High-field magnetization measurements on a ferromagnetic amorphous alloy from 295 to 5K

    SciTech Connect

    Szymczak, P. ); Graham, C.D. Jr. ); Gibbs, M.R.J. )

    1994-11-01

    Magnetization measurements on an amorphous ferromagnetic alloy Fe[sub 78](SiB)[sub 22] have been made over the temperature range from 5 to 295K and in fields to 5T, using a SQUID magnetometer and a superconducting magnet. As-received and field-annealed samples were measured. Having data over a range of temperatures allows the spin-wave contribution to the magnetization to be determined, and then subtracted. When the spin-wave contribution is removed, a substantial high-field susceptibility remains, which is independent of temperature. Attempts to fit the corrected curves to one of two theoretical equations were not conclusive, but the best fit seems to be to M = M[sub 0] + aH[sup [minus]0.5] + bH. The annealing treatment has no significant effect on the high-field magnetization.

  13. Structural and magnetic properties of Pr-alloyed MnBi nanostructures

    SciTech Connect

    Kharel, P; Shah, VR; Li, XZ; Zhang, WY; Skomski, R; Shield, JE; Sellmyer, DJ

    2013-02-05

    The structural and magnetic properties of Pr-alloyed MnBi (short MnBi-Pr) nanostructures with a range of Pr concentrations are investigated. The nanostructures include thin films having Pr concentrations 0, 2, 3, 5 and 9 at.% and melt-spun ribbons having Pr concentrations 0%, 2%, 4% and 6%, respectively. Addition of Pr into the MnBi lattice has produced a significant change in the magnetic properties of these nanostructures including an increase in coercivity and structural phase transition temperature, and a decrease in saturation magnetization and anisotropy energy. The highest value of coercivity measured in the films is 23 kOe and in the ribbons is 5.6 kOe. The observed magnetic properties are explained as the consequences of competing ferromagnetic and antiferromagnetic interactions.

  14. Tunable exchange bias in dilute magnetic alloys – chiral spin glasses

    PubMed Central

    Hudl, Matthias; Mathieu, Roland; Nordblad, Per

    2016-01-01

    A unidirectional anisotropy appears in field cooled samples of dilute magnetic alloys at temperatures well below the cusp temperature of the zero field cooled magnetization curve. Magnetization measurements on a Cu(13.5 at% Mn) sample show that this anisotropy is essentially temperature independent and acts on a temperature dependent excess magnetization, ΔM. The anisotropy can be partially or fully transferred from being locked to the direction of the cooling field at lower fields to becoming locked to the direction of ΔM at larger fields, thus instead appearing as a uniaxial anisotropy. This introduces a deceiving division of the anisotropy into a superposition of a unidirectional and a uniaxial part. This two faced nature of the anisotropy has been empirically scrutinized and concluded to originate from one and the same exchange mechanism: the Dzyaloshinsky-Moriya interaction. PMID:26817418

  15. Perpendicular magnetization of Co2FeAl full-Heusler alloy films induced by MgO interface

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Sukegawa, Hiroaki; Mitani, Seiji; Inomata, Koichiro

    2011-06-01

    The perpendicular magnetization of Co2FeAl (CFA) full-Heusler alloy films was achieved in the structures of CFA/MgO and MgO/CFA with the perpendicular magnetic anisotropy energy density (KU) of 2-3×106 erg/cm3, which can be used as the perpendicular ferromagnetic electrodes of MgO-based magnetic tunnel junctions (MTJs) with high thermal stability at sub-50-nm dimension. The CFA thickness dependence of KU was investigated at different annealing temperatures, indicating that the perpendicular anisotropy of CFA is contributed by the interfacial anisotropy between CFA and MgO. This letter will open up a way for obtaining perpendicular magnetization of Co-based full-Heusler alloys, which is promising for further reduction in the critical current of current induced magnetization switching in MgO-based MTJ nanopillars with perpendicular full-Heusler alloy electrodes.

  16. Pressure Dependence on the Remanent Magnetization of Fe-Ni Alloys

    NASA Astrophysics Data System (ADS)

    Gilder, S. A.; Wei, Q.; Maier, B.

    2014-12-01

    We measured the acquisition of magnetic remanence of iron-nickel alloys under pressures up to 23 GPa at room temperature. Experiments on pure iron using different pressure transmission media reveal a higher remanent magnetization at 21.5 GPa than at initial conditions, which could be attributed to a distorted hexagonal closed packed phase grown during the martensitic transition. Upon both compression and decompression, the remanent magnetization of the body centered cubic phases increase several times over initial conditions while the coercivity of remanence remains mostly invariant with pressure. Similar behavior is observed for the face centered cubic phases, where magnetization rises by a factor of 2-3 during compression to the highest applied pressures. Immediately upon decompression, magnetic remanence increases while magnetic coercivity remains fairly constant at relatively low values (5-20 mT). One exception is for the invar composition Fe64Ni36, where magnetization decreases markedly between 5 and 7 GPa. Martensitic effects best explain the increase in remanence rather than grain-size reduction, as the creation of single domain sized grains would raise the coercivity. The magnetic remanence of low Ni invar alloys increases faster with pressure than for other body centered cubic compositions due to the higher magnetostriction of the low Ni invar metals. Thermal demagnetization spectra of Fe64Ni36 measured after pressure cycling broaden as a function of peak pressure, with a systematic decrease in Curie temperature. Irreversible strain accumulation from the martensitic transition likely explains the broadening of the Curie temperature spectra, consistent with our X-ray diffraction analyses.

  17. Influence of radiation damage and isochronal annealing on the magnetic susceptibility of Pu(1-x)Am(x) alloys

    SciTech Connect

    McCall, S; Fluss, M; Chung, B; Haire, R

    2008-05-02

    Results of radiation damage in Pu and Pu{sub 1-x}Am{sub x} alloys studied with magnetic susceptibility, {chi}(T), and resistivity are presented. Damage accumulated at low temperatures increases {chi}(T) for all measured alloys, with the trend generally enhanced as the lattice expands. There is a trend towards saturation observable in the damage induced magnetic susceptibility data, that is not evident in similar damage induced resistivity data taken on the same specimen. A comparison of isochronal annealing curves measured by both resistivity and magnetic susceptibility on a 4.3at% Ga stabilized {delta}-Pu specimen show that Stage I annealing, where interstitials begin to move, is largely transparent to the magnetic measurement. This indicates that interstitials have little impact on the damage induced increase in the magnetic susceptibility. The isochronal annealing curves of the Pu{sub 1-x}Am{sub x} alloys do not show distinct annealing stages as expected for alloys. However, samples near 20% Am concentration show an unexpected increase in magnetization beginning when specimens are annealed to 35K. This behavior is also reflected in a time dependent increase in the magnetic susceptibility of damaged specimens indicative of first order kinetics. These results suggest there may be a metastable phase induced by radiation damage and annealing in Pu{sub 1-x}Am{sub x} alloys.

  18. Influences of intergranular structure on the magnetic properties of directly cast nanocrystalline NdFeCoTiNbBC alloys

    NASA Astrophysics Data System (ADS)

    Zhao, L. Z.; Hong, Y.; Jiao, D. L.; Qiu, Z. G.; Zhou, Q.; Hussain, M.; Liu, Z. W.; Greneche, J. M.; Zhang, G. Q.

    2016-05-01

    The millimeter-sized Nd9.5Fe61.5Co10Ti2.5Nb0.5B16‑x C x (x  =  0–1.25) alloy rods with various compositions were fabricated by direct casting. Nano-sized hard phase Nd2(FeCo)14B, soft phase ɑ-FeCo, and amorphous phase were observed in all alloys. An optimized amount of carbon additions improved the magnetic properties by enhancing the glass forming ability and forming near single domain-sized Nd2(FeCo)14B grains around the rod surface. Various intergranular structures were observed in the alloys with x  =  0.25–1. Micromagnetic simulation using the images obtained from the magnetic force microscope and transition electron microscope indicates that the distribution and magnetism of the intergranular phase have an important influence on the magnetic properties and demagnetization process of the alloys. A uniformly distributed nonmagnetic intergranular amorphous phase may enhance the magnetic properties, but the coercivity decreases when the amorphous phase is magnetic. It is important to modify the structure and distribution of the inter-grain amorphous phase in order to achieve high hard magnetic properties in these alloys.

  19. Effect of aging on magnetic properties of Hiperco® 27, Hiperco® 50, and Hiperco 50 HS® alloys

    NASA Astrophysics Data System (ADS)

    Fingers, Richard T.; Carr, Roger P.; Turgut, Zafer

    2002-05-01

    We started a long-term aging study that will identify the aging related changes in magnetic, mechanical, and electrical properties of three Fe-Co soft magnetic alloys. We performed the aging at a temperature of 773 K and in two different environmental chambers, argon gas and air, in order to determine the oxidation resistance of these alloy laminates as well. Each aging batch includes creep and yield stress test specimens, rings for ac magnetic measurements and specimens for electrical resistivity and microstructural analysis. Here we report the change in total power losses after 2000 h annealing up to frequencies of 2 kHz for the Hiperco® 27, Hiperco® 50, and Hiperco® 50 HS alloys. We also report the temperature dependence of total power losses between 298 and 773 K for these alloys.

  20. Spin Transfer Torque Switching and Perpendicular Magnetic Anisotropy in Full Heusler Alloy Co2FeAl-BASED Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Sukegawa, H.; Wen, Z. C.; Kasai, S.; Inomata, K.; Mitani, S.

    2014-12-01

    Some of Co-based full Heusler alloys have remarkable properties in spintronics, that is, high spin polarization of conduction electrons and low magnetic damping. Owing to these properties, magnetic tunnel junctions (MTJs) using Co-based full Heusler alloys are potentially of particular importance for spintronic application such as magnetoresistive random access memories (MRAMs). Recently, we have first demonstrated spin transfer torque (STT) switching and perpendicular magnetic anisotropy (PMA), which are required for developing high-density MRAMs, in full-Heusler Co2FeAl alloy-based MTJs. In this review, the main results of the experimental demonstrations are shown with referring to related issues, and the prospect of MTJs using Heusler alloys is also discussed.

  1. In-situ neutron scattering studies of magnetic shape memory alloys under stress, temperature, and magnetic fields

    SciTech Connect

    Brown, Donald W; Sisneros, Thomas A; Kabra, Saurabh; Schlagel, Deborah

    2010-01-01

    We have utilized the SMARTS engineering neutron diffractometer to study the crystallographic orientation and phase transformations in the ferromagnetic shape memory alloy Ni 2MnGa under conditions of temperature (200-600K), stress (500MPa), and magnetic field (2T). Neutrons are uniquely suited to probe the crystallographic response of materials to external stimuli because of their high penetration, which allows them to sample the bulk of the material (as opposed to the surface) as well as pass through environmental chambers. A single crystal of Ni{sub 5}MnGa was repeatedly thermally cycled through the Austenitic-Martensitic phase transformation under varying conditions of applied stress, magnetic field or both. In-situ neutron diffraction was used to quantitatively monitor the population of the crystallographic variants in the martensitic phase as a function of the external stimuli during cooling. Neutron diffraction was used to monitor variant selection in the Ferromagnetic Shape Memory Alloy Ni{sub 2}Mn Ga during austenitic to martensitic transformation under varying conditions of externally applied stress and magnetic field. Qualitatively, the results were to be expected in this simple example. The shorter and magnetically soft c-axis of the tetragonal martensitic phase aligned with the compressive stress or magnetic field. However, neutron diffraction proved useful in directly quantifying the selection of the preferred variant by external influence. For instance, by quantifying the variant selection, the neutron diffraction results made apparent that the sample 'remembered' a loading cycle following a 'reset' cycle with no external applied stress. Moreover, the power of in-situ neutron diffraction will become more apparent when applied to more complex, less understood, samples such as polycrystalline samples or composite samples.

  2. Perpendicular magnetic anisotropy in granular multilayers of CoPd alloyed nanoparticles

    NASA Astrophysics Data System (ADS)

    Vivas, L. G.; Rubín, J.; Figueroa, A. I.; Bartolomé, F.; García, L. M.; Deranlot, C.; Petroff, F.; Ruiz, L.; González-Calbet, J. M.; Pascarelli, S.; Brookes, N. B.; Wilhelm, F.; Chorro, M.; Rogalev, A.; Bartolomé, J.

    2016-05-01

    Co-Pd multilayers obtained by Pd capping of pre-deposited Co nanoparticles on amorphous alumina are systematically studied by means of high-resolution transmission electron microscopy, x-ray diffraction, extended x-ray absorption fine structure, SQUID-based magnetometry, and x-ray magnetic circular dichroism. The films are formed by CoPd alloyed nanoparticles self-organized across the layers, with the interspace between the nanoparticles filled by the non-alloyed Pd metal. The nanoparticles show atomic arrangements compatible with short-range chemical order of L 10 strucure type. The collective magnetic behavior is that of ferromagnetically coupled particles with perpendicular magnetic anisotropy, irrespective of the amount of deposited Pd. For increasing temperature three magnetic phases are identified: hard ferromagnetic with strong coercive field, soft-ferromagnetic as in an amorphous asperomagnet, and superparamagnetic. Increasing the amount of Pd in the system leads to both magnetic hardness increment and higher transition temperatures. Magnetic total moments of 1.77(4) μB and 0.45(4) μB are found at Co and Pd sites, respectively, where the orbital moment of Co, 0.40(2) μB, is high, while that of Pd is negligible. The effective magnetic anisotropy is the largest in the capping metal series (Pd, Pt, W, Cu, Ag, Au), which is attributed to the interparticle interaction between de nanoparticles, in addition to the intraparticle anisotropy arising from hybridization between the 3 d -4 d bands associated to the Co and Pd chemical arrangement in a L 10 structure type.

  3. Development of magnetic shape memory alloy actuators for a swashplateless helicopter rotor

    NASA Astrophysics Data System (ADS)

    Couch, Ronald Newton

    Actuator concepts utilizing NiMnGa, ferromagnetic shape memory alloy are investigated for potential use on a smart rotor for trailing edge flap actuation. With their high energy density, large dynamic stroke, and wide operating bandwidth, ferromagnetic shape memory alloys (FSMA) like NiMnGa, seem like attractive candidates for smart rotor actuators, potentially able to fulfill the requirements for both primary rotor control and vibration suppression. However, because of the recent discovery of the material, current experimental data and analytical tools are limited. To rectify these shortcomings, an extensive set of detailed experiments were conducted on samples of NiMnGa to characterize the response of the alloy for a wide variety of mechanical and magnetic loading conditions. Measurements of the material performance parameters such as power density, damping properties, magneto-mechanical coupling, and transduction efficiency were included. Once characterized, the experimental data were used to develop a series of analytical tools to predict the behavior of the material. A model, developed in parallel to thermal shape memory alloy models is proposed to predict the quasi-static stress-strain behavior. A simple, low frequency, parameter based model was also developed to predict the alloy's dynamic strain response. A method for developing conceptual actuators utilizing NiMnGa as the actuation element was proposed. This approach incorporates experimental data into a process that down-selects a series of possible actuator configurations to obtain a single configuration optimized for volumetric and weight considerations. The proposed actuator was designed to deliver 2 mm of stroke and 60 N of force at an actuation frequency of 50 Hz. However, to generate the 1.0 T magnetic field, the actuator mass was determined to be 2.8 kg and required a minimum of 320 Watts of power for operation. The mass of the NiMnGa element was only 18.3 g. It was concluded that although the Ni

  4. HfCo7-Based Rare-Earth-Free Permanent-Magnet Alloys

    SciTech Connect

    Das, B; Balamurugan, B; Kumar, P; Skomski, R; Shah, VR; Shield, JE; Kashyap, A; Sellmyer, DJ

    2013-07-01

    This study presents the structural and magnetic properties of melt-spun HfCo7, HfCo7-xFex (0.25 <= x <=), and HfCo7Six (0.2 <= x <= 1.2) alloys. Appreciable permanent-magnet properties with a magnetocrystalline anisotropy of about 9.6-16.5, Mergs/cm(3), a magnetic polarization J(s) approximate to 7.2-10.6 kG, and coercivities H-c = 0.5-3.0 kOe were obtained by varying the composition of these alloys. Structural analysis reveals that the positions of x-ray diffraction peaks of HfCo7 show good agreement with those corresponding to an orthorhombic structure having lattice parameters of about a = 4.719 angstrom, b = 4.278 angstrom, and c = 8.070 angstrom. Based on these results, a model crystal structure for HfCo7 is developed and used to estimate the magnetic properties of HfCo7 using density-functional calculations, which agree with the experimental results.

  5. Structural and magnetic properties of Cu-alloyed FePd films

    NASA Astrophysics Data System (ADS)

    Polit, A.; Makarov, D.; Brombacher, C.; Krupinski, M.; Perzanowski, M.; Zabila, Y.; Albrecht, M.; Marszałek, M.

    2015-05-01

    Multilayer films [Cu(d Å)/Fe(9 Å)/Pd(11 Å)]5 were deposited at room temperature on Si(001)/SiO2(400 nm) substrates. In order to induce chemical L10 ordering, the as-deposited samples were post-annealed by rapid thermal annealing (RTA) at 600 °C for 90 s followed additionally by heating in ultra-high vacuum (UHV) at 700 °C up to several hours. In this study the impact of post-annealing on the structural and magnetic properties of FePdCu alloy films in dependence on the Cu content was investigated. It was found that the addition of Cu to the FePd alloy has a strong influence on the chemical ordering process and the (001) texture formation. After the RTA treatment only an isotropic distribution of the easy axis of magnetization with coercive fields in the range of a few hundred mT was observed. In contrast, samples which were additionally heated for 1 h at 700 °C revealed an out-of-plane easy axis of magnetization with an effective magnetic anisotropy of about 2×105 J/m3 for the sample containing 10 at% of Cu.

  6. Effect of disorder on electronic and magnetic properties of Co{sub 2}VGa Heusler alloy

    SciTech Connect

    Seema, K.; Kumar, Ranjan

    2015-08-28

    This paper presents the effect of disorder on electronic, magnetic and half-metallic properties of Co{sub 2}VGa Heusler alloy using density functional theory. Binary mixing is the most common form of atomic disorder in these compounds. We have considered three types of disorders: DO{sub 3}, A2 and B2 disorder which corresponds to X-Y, X-Z and Y-Z mixing respectively. After structural optimization, we found that A2 disorder has high formation energy and is most unlikely to occur. The half-metallic nature of the alloy is destroyed in presence of DO{sub 3} and A2 disorder. The destruction of half-metallicity is due to reconstruction of energy states. Also the loss of half-metallicity is accompanied by reversal of spin-polarization at the Fermi level. B2 disorder retains the half-metallic nature of the alloy but spin-polarization value is reduced as compared to the ordered alloy.

  7. Low-cost Ce1-xSmx(Fe, Co, Ti)12 alloys for permanent magnets

    NASA Astrophysics Data System (ADS)

    Gabay, A. M.; Martín-Cid, A.; Barandiaran, J. M.; Salazar, D.; Hadjipanayis, G. C.

    2016-05-01

    Ce1-xSmxFe9Co2Ti alloys based on the ThMn12-type crystal structure have been synthesized via melt-spinning of prefabricated alloys and via mechanochemical processing of CeO2- Sm2O3- Fe2O3-TiO2- Co - Ca - CaO powder mixtures. Coercive fields up to 0.8 kOe and 2.1 kOe were obtained in annealed melt-spun alloys with x = 0 and x = 0.5, respectively. Submicron, partially anisotropic particles collected after the mechanochemical synthesis for x = 0.5 and x = 1 exhibited coercivity (energy product) of 1.8 kOe (5.4 MGOe) and 5.8 kOe (9.9 MGOe), respectively. The low magnetic anisotropy field of CeFe9Co2Ti alloy requires at least a partial Sm-substitution for Ce in order to develop a reasonably high coercivity.

  8. Hyperfine magnetic field on Cd-111 in Heusler alloys Co2MnZ (Z = Si, Ga, Ge, Sn)

    NASA Technical Reports Server (NTRS)

    Jha, S.; Mitros, C.; Lahamer, Amer; Yehia, Sherif; Julian, Glenn M.

    1989-01-01

    The time differential perturbed angular correlation method has been used to measure, as a function of temperature, the hyperfine magnetic field at Cd sites in the Heusler alloys Co2MnZ (Z = Si, Ga, Ge, Sn). The hyperfine fields, normalized to the total magnetic moment per formula unit, show an approximately linear trend toward more positive values with increasing lattice parameter.

  9. Effects of copper precipitation on the magnetic properties of aged copper-containing ferrous alloys

    NASA Astrophysics Data System (ADS)

    Lo, C. C. H.

    2012-05-01

    Formation of nano-sized copper precipitates induced by neutron irradiation has been identified as one of the primary causes of radiation embrittlement of reactor pressure vessel steels. Although it has been shown that magnetic properties are sensitive to these microstructural changes, fundamental understanding is yet to be developed before magnetic NDE techniques can be reliably employed to detect radiation damages. This paper reports on a systematic study of the effects of copper precipitation on magnetic properties using an Fe-1wt%Cu alloy as a model system. Magnetic hysteresis and Barkhausen effect measurements were performed on a series of FeCu samples aged for different periods of time to produce different extents of copper precipitation in an iron matrix. The magnetic properties, including coercivity, initial permeability, the Rayleigh constant and Barkhausen effect signal, were found to correlate with the sample hardness as a result of precipitation hardening. The empirical relationships between magnetic and mechanical properties are interpreted in terms of pinning of magnetic domain walls and dislocations by a network of randomly distributed copper precipitates.

  10. The structural, electronic and magnetic properties of quaternary Heusler alloy TiZrCoIn

    NASA Astrophysics Data System (ADS)

    Yan, Peng-Li; Zhang, Jian-Min; Xu, Ke-Wei

    2016-04-01

    Employing the first-principles calculations, we have investigated the structural, electronic and magnetic properties of quaternary Heusler alloy TiZrCoIn. The TiZrCoIn alloy with type (I) configuration is predicted to be half-metallic ferromagnet at its equilibrium lattice constant 6.525 Å with an indirect band gap of 0.930 eV in minority spin channel. The total magnetic moment is 2 μB/f.u., following the Slater-Pauling rule μt=Zt-18. Moreover, the negative formation energy indicates the thermodynamical stability of this alloy. The band gap of minority spin channel is determined by the bonding (t2g) and antibonding (t1u) states created from the hybridizations of the d states of transition metal atoms Ti, Zr and Co. In addition, the HM, character is kept as hydrostatic strain ranged from -10% to 7.6% and tetragonal strain ranged from -19% to 27%.

  11. Influence of Sn on the magnetic ordering of Ni-Sn alloy synthesized using chemical reduction method

    NASA Astrophysics Data System (ADS)

    Dhanapal, K.; Narayanan, V.; Stephen, A.

    2016-05-01

    The Ni-Sn alloy was synthesized using borohydride assisted chemical reduction method. The composition of the synthesized alloy was determined using atomic absorption spectroscopy which revealed that the observed composition of Sn is high when compared to the initial composition. The ultrafine particles are clearly observed from field emission scanning electron microscope for all the sample. The X-ray diffraction measurement confirmed that the as-synthesized samples are of amorphous like nature while the samples annealed at 773 K showed crystalline nature. The Fourier transform infrared spectroscopy confirmed metallic bond stretching in the alloy samples. The crystallization and phase transition temperature was observed from differential scanning calorimetry. The shift in the crystallization temperature of Ni with increasing percentage of Sn was observed. The vibrating sample magnetometer was employed to understand the magnetic behavior of the Ni-Sn alloy. As-synthesized alloy samples showed paramagnetic nature while the annealed ones exhibit the soft ferromagnetic, antiferromagnetic and paramagnetic nature. The saturation magnetization value and magnetic ordering in the Ni-Sn alloys depend on the percentage of Sn present in the alloy.

  12. Effect of C and Ce addition on the microstructure and magnetic property of the mechanically alloyed FeSiBAlNi high entropy alloys

    NASA Astrophysics Data System (ADS)

    Xu, Jing; Axinte, Eugen; Zhao, Zhengfeng; Wang, Yan

    2016-09-01

    The effects of elemental addition, C and Ce, on the microstructure, thermal property and magnetic property of mechanically alloyed FeSiBAlNi (based-W5) high entropy alloys (HEAs) have been investigated in depth in the present work. The amorphous HEAs have been successfully fabricated by mechanical alloying. The results reveal that Ce addition obviously shortens the formation time of fully amorphous phase, therefore leading to the enhanced glass forming ability (GFA) of the based-W5. The final products of as-milled FeSiBAlNiC alloy consist of the main amorphous phase and a small amount of Si nanocrystals. In addition, C and Ce addition are both beneficial to enhance the thermal stability. The coercivity force (Hc) of the tested samples lies in the range of 50-378 Oe, suggesting the semi-hard magnetic property. The saturation magnetization (Ms) becomes decreased with increasing the milling time. C addition effectively increases Ms exhibiting the good magnetic property, however, Ce addition presents the negative effect. It should be noted that the amorphous phase tends to be formed when the radius ratio (Rr) is larger than 1, and the GFA is enhanced with increasing Rr and valence electron concentration.

  13. One-Step Synthesis and Magnetic Phase Transformation of Ln-TM-B Alloy by Chemical Reduction.

    PubMed

    Kim, Chang Woo; Kim, Young Hwan; Cha, Hyun Gil; Lee, Don Keun; Kang, Young Soo

    2007-04-11

    Binary and ternary intermetallic alloy systems are of interest for a variety of academic and technological applications. Despite recent advances in synthesizing binary alloy, there are very few reports of ternary alloy related to lanthanide series. The purpose of this work is to contribute to ternary alloy systems such as lanthanide-transition metal-boron with a simple chemical method and analysis of its magnetic behavior. Ternary Nd-Fe-B amorphous alloy was successfully synthesized with borohydride. The magnetic behavior in the process of formation of ternary Nd-Fe-B alloy and Nd2Fe14B from amorphous phase alloy is reported. Compared with the synthesis of a transition metal, the existence of a lanthanide ion makes aggregates-like particles with a diameter of 2 nm possible in the formation of a nanosphere, which is a significantly important result in terms of acceleration of the reduction-diffusion reaction for the formation of ternary alloy. In the process of reduction and diffusion, the Nd phase is diffused into the Fe-based phase, and then the ternary Nd2Fe14B intermetallic compound is fabricated. PMID:17425319

  14. High strength and high induction Co27-Fe-Co0.23 soft magnetic alloy for forge application

    NASA Astrophysics Data System (ADS)

    Li, Lin

    2000-05-01

    In magnetic bearing or flywheel technologies, there is a demand for high induction soft magnetic alloys for forged components rotating at high speed (50 000-80 000 rpm). Hiperco® Alloy 27 (Co27-Fe) is ductile and has high magnetic saturation (24 kG) but with low yield stress (35-55 ksi). This work reports a carbon strengthened Co27Fe-C0.23 alloy with high yield stress (75-85 ksi), high induction (B=20 and 21 kG at H=100 and 150 Oe, respectively), and good ductility (1 in. elongation=21%). Postforge annealing is critical to achieve desired combination of high magnetic induction, high yield stress, and good ductility.

  15. Intrinsic magnetic properties of single-phase Mn1+xGa (0 < x < 1) alloys

    PubMed Central

    Lu, Q. M.; Yue, M.; Zhang, H. G.; Wang, M. L.; Yu, F.; Huang, Q. Z.; Ryan, D. H.; Altounian, Z.

    2015-01-01

    Magnetization measurements have been carried out on a series of carefully prepared single-phase Mn1 + xGa (0 < x < 1) alloys. The saturation magnetization Ms, measured at 5 K, has a value of 92.0 emu/g for x = 0.15. This is the highest value reported in these alloys and is close to the calculated value of 116 emu/g for the stoichiometric compound (x = 0). Ms decreases gradually with x and has a value of 60.7 emu/g for x = 0.86. This behavior is consistent with the extra Mn atoms occupying Ga sites and coupling antiferromagnetically with the rest of the Mn atoms. The intrinsic magnetic properties of the Mn-Ga alloys indicate their great potential as novel, rare-earth free permanent magnetic materials. PMID:26597458

  16. Nucleation controlled magnetization reversal mechanism in oriented L10 FeCoPt ternary alloys

    NASA Astrophysics Data System (ADS)

    Goyal, Rajan; Sehdev, Neeru; Lamba, S.; Annapoorni, S.

    2016-01-01

    The angular dependence of scaled coercivity is investigated within the framework of various theoretical models to gather an insight into the magnetization reversal mechanism in hard magnetic materials. FeCoPt ternary alloy thin films with low concentration of Co were successfully fabricated on an <100> Si substrate with different working pressures in order to attain an optimum energy product. The structural and hysteresis curve analysis show an improvement in atomic ordering and orientation of easy axis with annealing temperature. The experimental data for angular dependence of coercivity along with the theoretical predications based on the nucleation model indicates that the dominant reversal mechanism is nucleation along with a slight contribution from pinning. The magnetic force microscopy (MFM) imaging also supports the above model. The evolution of morphology and microstructure characterized by atomic force microscopy (AFM) was directly linked to an increase in surface roughness.

  17. Kinetics of crystallization in FeB based nanocrystalline soft magnetic alloys

    NASA Astrophysics Data System (ADS)

    Hosseini-Nasab, Farzad; Tavakoli, Mohammad Mahdi; Beitollahi, Ali; Moravvej-Farshi, Mohammad Kazem

    2016-06-01

    An attempt is made to study the effect of substituting Si and Cu atoms for B in Fe84B16 alloys on the microstructure and magnetic properties of the resulting melt spun compositions (i.e., Fe84B14Si2 and Fe84B12Si3.3Cu0.7). As-spun and annealed samples were characterized by various techniques to investigate their crystallization kinetics and the magnetic properties of the resulting microstructures. Experiments have revealed that Fe84B12Si3.3Cu0.7 composition exhibits the optimum magnetic properties of MS=1.92 T and HC=11 A/m among the three samples under study.

  18. Epitaxial growth, alloying and magnetic structure of interfaces in Fe/Cr (0 0 1) superlattices

    NASA Astrophysics Data System (ADS)

    Uzdin, V.; Keune, W.; Walterfang, M.

    2002-02-01

    Fe/Cr(0 0 1) superlattices containing two-monolayers thick 57Fe probe layers at the Fe/Cr (Fe-on-Cr) or Cr/Fe (Cr-on-Fe) interfaces were studied using conversion electron Mössbauer spectroscopy (CEMS). For the interpretation of the CEMS data of superlattices annealed at different temperatures, we performed theoretical modeling of their chemical and magnetic structure. Roughness and interface alloying were introduced to the model by algorithms of epitaxial growth, which included ballistic deposition with subsequent floating of some atoms on the surface. Self-consistent calculations of magnetic moments within the periodic Anderson model confirmed the proportionality between hyperfine fields and magnetic moments. For the explanation of the evolution of CEM spectra versus annealing temperature, the difference in the melting points of bulk Fe and Cr has to be taken into account.

  19. Investigation of thermal, mechanical and magnetic behaviors of the Cu-11%Al alloy with Ag and Mn additions

    SciTech Connect

    Silva, R.A.G.; Paganotti, A.; Gama, S.; Adorno, A.T.; Carvalho, T.M.; Santos, C.M.A.

    2013-01-15

    The investigation of thermal, mechanical and magnetic behaviors of the Cu-11%Al, Cu-11%Al-3%Ag, Cu-11%Al-10%Mn and Cu-11%Al-10%Mn-3%Ag alloys was made using microhardness measurements, differential scanning calorimetry, X-ray diffractometry, scanning electron microscopy, energy dispersion X-ray spectroscopy and magnetic moment change with applied field measurement. The results indicated that the Mn addition changes the phase stability range, the microhardness values and makes undetectable the eutectoid reaction in annealed Cu-11%Al and Cu-11%Al-3%Ag alloys while the presence of Ag does not modify the phase transformation sequence neither microhardness values of the annealed Cu-11%Al and Cu-11%Al-10%Mn alloys, but it increases the magnetic moment of this latter at about 2.7 times and decreases the rates of eutectoid and peritectoid reactions of the former. - Highlights: Black-Right-Pointing-Pointer The microstructure of Cu-Al alloy is modified in the Ag presence. Black-Right-Pointing-Pointer ({alpha} + {gamma}) phase is stabilized down to room temperature when Ag is added to Cu-Al alloy. Black-Right-Pointing-Pointer Ag-rich phase modifies the magnetic characteristics of Cu-Al-Mn alloy.

  20. New developments in actuator materials as reflected in magnetically controlled shape memory alloys and high-strength shape memory steels

    NASA Astrophysics Data System (ADS)

    Ullakko, Kari; Yakovenko, Peter G.; Gavriljuk, Valentin G.

    1996-05-01

    Shape memory alloys (SMA) are applied as actuator materials in smart structures and in fastening and pre-stressing devices. Shape memory alloys can be divided into three groups: one-way alloys, two-way alloys and magnetically controlled SMAs. The magnetically controlled SMAs recently suggested by one of the present authors are potential actuator materials for smart structures because they may provide rapid strokes with large amplitudes under precise control. The most extensively applied conventional SMAs are Ni-Ti and Cu- based alloys. Iron-based shape memory alloys, especially Fe-Mn-Si steels, are becoming more and more important in engineering applications due to their low price. The properties of Fe- Mn-Si steels have been improved by alloying, for example, with Cr, Ni and Co. Nitrogen alloying was shown to significantly improve shape memory, mechanical and corrosion properties of Fe-Mn-Si-based steels. Tensile strengths over 1500 MPa, recovery stresses of 300 MPa and recoverable strains of 4% have been attained. In fasteners made from these steels, stresses of 700 MPa were reached. The beneficial effect of nitrogen alloying on shape memory and mechanical properties is based on the decrease of stacking fault energy and increase of the strength of austenite caused by nitrogen atoms. Nitrogen alloyed Fe-Mn-Si- based steels are expected to be employed as actuator materials in pre-stressing and fastening applications in many fields of engineering. Nitrogen alloyed shape memory steels possess good manufacturing properties and weldability, and they are economical to process using conventional industrial methods.

  1. Magnetic properties of ultrasoft-nanocomposite FeAlSiBNbCu alloys

    NASA Astrophysics Data System (ADS)

    Todd, I.; Tate, B. J.; Davies, H. A.; Gibbs, M. R. J.; Kendall, D.; Major, R. V.

    2000-06-01

    The effects of up to 10 at% substitution of Fe by Al on the microstructure and DC and AC magnetic properties of nanocrystalline FeSiBCuNb alloy ribbon are summarised and analysed. The minimum DC H c developed during annealing decreases by 40% for 2 at% Al (to 0.3 A/m) and remains roughly constant for larger Al contents. The largest peak value of μ 0.4 at 50 Hz also corresponds to 2 at% Al. The best frequency response for μ 0.4 occurs for 6 at% Al while there was no improvement in AC power loss behaviour over the 0% Al alloy. The improvements in DC H c and AC μ 0.4 are ascribed to a reduction in K 1 of the Fe-Si-based nanocrystallites by the introduction of Al.

  2. Two magnetic states of iron atoms in Invar Fe-Ni alloys and positron annihilation

    NASA Astrophysics Data System (ADS)

    Sedov, V. L.; Tsigel'nik, O. A.

    1999-11-01

    The temperature dependence of angular correlation annihilation radiation (ACAR) in Invar Fe-Ni alloys is investigated. It is found that the ACAR distribution in the Curie temperature region TC depends on temperature. This effect is created only by those positrons that are trapped by vacancies. The effect is enhanced if the positrons trapped by vacancy-hydrogen complexes. The ACAR distribution is changed due to enhanced interaction of these positrons with 3d electrons. A simple interpretation of this phenomenon can be given on the basis of the model of two magnetic states of Fe atoms in Invar alloys. According to this model the enhancement of the electron-positron correlation interaction in the TC region occurs as a result of the convergence of the energy levels εHS and εLS corresponding to the high-spin (HS) and low-spin (LS) states of Fe atoms.

  3. Magnetic ordering in digital alloys of group-IV semiconductors with 3d-transition metals

    SciTech Connect

    Otrokov, M. M.; Tugushev, V. V.; Ernst, A.; Ostanin, S. A.; Kuznetsov, V. M.; Chulkov, E. V.

    2011-04-15

    The ab initio investigation of the magnetic ordering in digital alloys consisting of monolayers of 3d-transition metals Ti, V, Cr, Mn, Fe, Co, and Ni introduced into the Si, Ge, and Si{sub 0.5}Ge{sub 0.5} semiconductor hosts is reported. The calculations of the parameters of the exchange interactions and total-energy calculations indicate that the ferromagnetic order appears only in the manganese monolayers, whereas the antiferromagnetic order is more probable in V, Cr, and Fe monolayers, and Ti, Co, and Ni monolayers are nonmagnetic. The stability of the ferromagnetic phase in digital alloys containing manganese monolayers has been analyzed using the calculations of magnon spectra.

  4. Anomalous Hall effect in magnetic disordered alloys: Effects of spin orbital coupling

    SciTech Connect

    Ma, L.; Gao, W. B.; Zhou, S. M.; Shi, Z.; He, P.; Miao, J.; Jiang, Y.

    2013-12-28

    For disordered ternary Fe{sub 0.5}(Pd{sub 1−x}Pt{sub x}){sub 0.5} alloy films, the anomalous Hall effect obeys the conventional scaling law ρ{sub AH}=aρ{sub xx}+bρ{sub xx}{sup 2} with the longitudinal resistivity ρ{sub xx} and anomalous Hall resistivity ρ{sub AH}. Contributed by the intrinsic term and the extrinsic side-jump one, the scattering-independent anomalous Hall conductivity b increases with increasing Pt/Pd concentration. In contrast, the skew scattering parameter a is mainly influenced by the residual resistivity. The present results will facilitate the theoretical studies of the anomalous Hall effect in magnetic disordered alloys.

  5. Structural and magnetic properties of He+ irradiated Co2MnSi Heusler alloys

    NASA Astrophysics Data System (ADS)

    Abdallah, I.; Ratel-Ramond, N.; Magen, C.; Pecassou, B.; Cours, R.; Arnoult, A.; Respaud, M.; Bobo, J. F.; BenAssayag, G.; Snoeck, E.; Biziere, N.

    2016-04-01

    We have investigated the atomic disorder induced by a 150 keV He+ ion irradiation in a 40 nm thick Co2MnSi Heusler alloy. Disorder parameters on each atomic site are deduced from normal and anomalous x-ray diffraction measurements with Co and Cu Kα sources. While the film grows mainly in the L21 phase with inclusion of B2 grains, we observe an increase of both the Mn–Si and Co–Mn exchanges with the ion fluence. HAADF-STEM analysis demonstrates that the increase in Mn–Si disorder corresponds to a growing size of the B2 grains while the Co–Mn exchange is accounted for a D03 disorder type in the L21 matrix. These structural modifications are shown to decrease the average magnetization of the alloy, which is due to D03 disorder and local defects induced by irradiation.

  6. Effect of Si addition on AC and DC magnetic properties of (Fe-P)-Si alloy

    NASA Astrophysics Data System (ADS)

    Gautam, Ravi; Prabhu, D.; Chandrasekaran, V.; Gopalan, R.; Sundararajan, G.

    2016-05-01

    We report a new (Fe-P)-Si based alloy with relatively high induction (1.8-1.9 T), low coercivity (< 80 A/m), high resistivity (˜38 μΩ cm) and low core loss (217 W/kg @ 1 T/1 kHz) comparable to the commercially available M530-50 A5 Si-steel. The attractive magnetic and electrical properties are attributed to i) the two phase microstructure of fine nano precipitates of Fe3P dispersed in α-Fe matrix achieved by a two-step heat-treatment process and ii) Si addition enhancing the resistivity of the α-Fe matrix phase. As the alloy processing is by conventional wrought metallurgy method, it has the potential for large scale production.

  7. Tunable assembly of colloidal crystal alloys using magnetic nanoparticle fluids.

    PubMed

    Yang, Ye; Gao, Lu; Lopez, Gabriel P; Yellen, Benjamin B

    2013-03-26

    We demonstrate a magnetic technique for assembling bidisperse and tridisperse colloidal particle fluids into a variety of complex structures with dimensionality ranging from 0-D (rings) to 1-D (chains) to 2-D (tiles). Compared with prior work on bidisperse particles that are commensurate in size, here we explore the assembly of different sized particles, and we show that due to packing constraints, new particle structures can be realized experimentally. Extending these experiments to a tridisperse system, we demonstrate that at low concentrations the smallest particle does not change the underlying crystal structures of the bidisperse system; however, it can assist in the formation of crystallite structures that were not stable in a bidisperse system. Additionally, we discovered that the smallest particle mimics the role of the ferrofluid, by shifting the locations in phase space where the bidisperse crystal structures can be experimentally obtained. Finally, we demonstrate that 3-particle crystal structures can be tuned by varying the strength of the external field, which is not possible in a 2-particle system. PMID:23373586

  8. First-principle simulation on the crystallization tendency and enhanced magnetization of Fe76B19P5 amorphous alloy

    NASA Astrophysics Data System (ADS)

    Wang, Yaocen; Zhang, Yan; Takeuchi, Akira; Makino, Akihiro; Liang, Yunye; Kawazoe, Yoshiyuki

    2015-01-01

    Iron-based amorphous alloys have attracted a growing interest due to their potential in the application of magnetic coil production. However, the magnetization of this kind of material is usually low due to the lack of long range ordering and high alloying element content. In this paper, an Fe76B19P5 amorphous alloy was simulated with ab initio molecular dynamics based on a previous simulation work on an Fe76Si9B10P5 amorphous alloy exhibiting that electron absorbers such as B and P can help enhance the magnetization of nearby Fe atoms. The present simulation results show that replacing Si with B can destabilize the amorphous structure, making it easier to crystallize, but no separate α-Fe participation can be observed in experiments during annealing due to its high B/P content. The results also show an increase in saturation magnetization by 8% can be expected due to the intensified electron transfer from Fe to B/P, and the glass forming ability decreases correspondingly. The idea of enhancing electron transfer can be applied to the development of other Fe-based amorphous alloys for the purpose of larger saturation magnetization.

  9. Magnetic and anomalous electronic transport properties of the quaternary Heusler alloys Co2Ti1-xFexGe

    NASA Astrophysics Data System (ADS)

    Venkateswarlu, B.; Midhunlal, P. V.; Babu, P. D.; Kumar, N. Harish

    2016-06-01

    The half-metallic Heusler alloy Co2TiGe has a ferromagnetic ground state with a low magnetic moment (2 μB). It is free of atomic antisite disorder but has low Curie temperature (~390 K). In contrast the other cobalt based Heusler alloy Co2FeGe has high Curie temperature (~980 K) and high magnetic moment (5.6 μB) while exhibiting antisite disorder and lack of half-metallicity. Hence it is of interest to investigate the magnetic and transport properties of solid solutions of these two materials with contrasting characteristics. We report the structural, magnetic and electronic transport properties of quaternary Co2Ti1-x FexGe (x=0.2, 0.4, 0.6, 0.8) Heusler alloys. The alloys crystallize in L21 structure but with antisite disorder. The magnetization measurements revealed that the alloys were of soft ferromagnetic type with high Curie temperatures. Deviation from Slater-Pauling behavior and drastic change in electronic transport properties with some anomalous features were observed.The complex electronic transport properties have been explained using different scattering mechanisms.

  10. An increase of structural order parameter in Fe-Co-V soft magnetic alloy after thermal aging

    NASA Astrophysics Data System (ADS)

    Zhu, Q.; Li, L.; Masteller, M. S.; Del Corso, G. J.

    1996-12-01

    Alloys of Fe49Co49V2 (Hiperco Alloy 50) (Hiperco is a registered trademark of CRS Holdings, Inc.), both annealed and thermally aged, were studied using anomalous synchrotron x-ray and neutron powder diffraction. Rietveld and diffraction profile analysis indicated both an increase in the structural order parameter and a small lattice expansion (˜0.0004 Å) after aging at 450 °C for 200 h. In addition, a cubic minority phase (<0.3%) was identified in the ``annealed'' sample, which increased noticeably (0.3%→0.8%) as a result of aging. The presence of antiphase domain boundaries in the alloys was also revealed. These results directly correlate with the observed changes in the magnetization behavior and challenge the notion that a ``fully'' ordered Fe-Co alloy demonstrates optimum soft magnetic properties.

  11. Magnetic, transport, and magnetocaloric properties of boron doped Ni-Mn-In alloys

    SciTech Connect

    Pandey, S.; Quetz, A.; Aryal, A.; Dubenko, I.; Ali, N.; Rodionov, I. D.; Blinov, M. I.; Titov, I. S.; Prudnikov, V. N.; Granovsky, A. B.; Stadler, S.

    2015-05-14

    The impact of B substitution in Ni{sub 50}Mn{sub 35}In{sub 15−x}B{sub x} Heusler alloys on the structural, magnetic, transport, and parameters of the magnetocaloric effect (MCE) has been studied by means of room-temperature X-ray diffraction and thermomagnetic measurements (in magnetic fields (H) up to 5 T, and in the temperature interval 5–400 K). Direct adiabatic temperature change (ΔT{sub AD}) measurements have been carried out for an applied magnetic field change of 1.8 T. The transition temperatures (T-x) phase diagram has been constructed for H = 0.005 T. The MCE parameters were found to be comparable to those observed in other MCE materials such as Ni{sub 50}Mn{sub 34.8}In{sub 14.2}B and Ni{sub 50}Mn{sub 35}In{sub 14}X (X=In, Al, and Ge) Heusler alloys. The maximum absolute value of ΔT{sub AD} = 2.5 K was observed at the magnetostructural transition for Ni{sub 50}Mn{sub 35}In{sub 14.5}B{sub 0.5}.

  12. Magnetic, transport, and magnetocaloric properties of boron doped Ni-Mn-In alloys

    NASA Astrophysics Data System (ADS)

    Pandey, S.; Quetz, A.; Rodionov, I. D.; Aryal, A.; Blinov, M. I.; Titov, I. S.; Prudnikov, V. N.; Granovsky, A. B.; Dubenko, I.; Stadler, S.; Ali, N.

    2015-05-01

    The impact of B substitution in Ni50Mn35In15-xBx Heusler alloys on the structural, magnetic, transport, and parameters of the magnetocaloric effect (MCE) has been studied by means of room-temperature X-ray diffraction and thermomagnetic measurements (in magnetic fields (H) up to 5 T, and in the temperature interval 5-400 K). Direct adiabatic temperature change (ΔTAD) measurements have been carried out for an applied magnetic field change of 1.8 T. The transition temperatures (T-x) phase diagram has been constructed for H = 0.005 T. The MCE parameters were found to be comparable to those observed in other MCE materials such as Ni50Mn34.8In14.2B and Ni50Mn35In14X (X=In, Al, and Ge) Heusler alloys. The maximum absolute value of ΔTAD = 2.5 K was observed at the magnetostructural transition for Ni50Mn35In14.5B0.5.

  13. High tunneling magnetoresistance ratio in perpendicular magnetic tunnel junctions using Fe-based Heusler alloys

    SciTech Connect

    Wang, Yu-Pu; Lim, Sze-Ter; Han, Gu-Chang; Teo, Kie-Leong

    2015-12-21

    Heulser alloys Fe{sub 2}Cr{sub 1−x}Co{sub x}Si (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 10{sup 6 }erg/cm{sup 3}. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe{sub 2}CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

  14. Magnetic properties of Fe and Fe-Si alloys with {100}<0vw> texture

    NASA Astrophysics Data System (ADS)

    Kyung Sung, Jin; Mo Koo, Yang

    2013-05-01

    When iron and its alloy sheets with clean metal surfaces undergo the γ to α phase transformation, they develop strong {100}<0vw> texture with grain size being larger than the sheet thickness. For example, when Fe or Fe-1%Si sheets were subjected to the γ to α phase transformation in a reducing gas atmosphere (hydrogen gas having the dew point below -50 °C), strong {100}<0vw> texture developed. Magnetic properties of Fe and Fe-Si alloys show that, by developing the {100}<0vw> texture, the core loss can be reduced by more than 25% and the permeability can be increased by 2-5 times. With 0.35 mm-thick Fe-1%Si with the {100}<0vw> texture, the magnetic properties are W15/50 (core loss at 1.5 T, 50 Hz) = 2.7 W/kg and B50 (magnetic flux density at 5000 A/m) = 1.80 T. The improvement of permeability together with reducing iron loss by texture control will make a significant contribution to improving power density as well as reducing copper losses in induction motors.

  15. Method of making active magnetic refrigerant, colossal magnetostriction and giant magnetoresistive materials based on Gd-Si-Ge alloys

    DOEpatents

    Gschneidner, Jr., Karl A.; Pecharsky, Alexandra O.; Pecharsky, Vitalij K.

    2003-07-08

    Method of making an active magnetic refrigerant represented by Gd.sub.5 (Si.sub.x Ge.sub.1-x).sub.4 alloy for 0.ltoreq.x.ltoreq.1.0 comprising placing amounts of the commercially pure Gd, Si, and Ge charge components in a crucible, heating the charge contents under subambient pressure to a melting temperature of the alloy for a time sufficient to homogenize the alloy and oxidize carbon with oxygen present in the Gd charge component to reduce carbon, rapidly solidifying the alloy in the crucible, and heat treating the solidified alloy at a temperature below the melting temperature for a time effective to homogenize a microstructure of the solidified material, and then cooling sufficiently fast to prevent the eutectoid decomposition and improve magnetocaloric and/or the magnetostrictive and/or the magnetoresistive properties thereof.

  16. Structural and magnetization behavior of highly spin polarized Co{sub 2}CrAl full Heusler alloy

    SciTech Connect

    Saha, S. N. Panda, J. Nath, T. K.

    2014-04-24

    The half metallic ferromagnet Co{sub 2}CrAl full Huesler alloy was successfully prepared by arc melting process. The electrical and magnetic properties of Co{sub 2}CrAl alloy have been studied in the temperature range of 5 – 300 K. The ferromagnetic Curie temperature T{sub c} of the same alloy has been observed at 329.8 K. The alloy shows semiconducting like electronic transport behavior throughout the studied temperature range. The origin of the semiconducting behavior of Co{sub 2}CrAl alloy can be best explained by the localization of conduction electrons and the presence of an energy gap in the electronic spectrum near the Fermi level E{sub F}.

  17. Fingerprinting Morphology of Magnetic Shape Memory Alloys Using First Order Reversal Curves (FORC) and Neutron Scattering

    NASA Astrophysics Data System (ADS)

    Roshchin, Igor V.; Lapa, Pavel N.; Krycka, Kathryn L.; Maranville, Brian B.; Monroe, James A.; Franco, Brian E.; Karaman, Ibrahim

    In Ni-Mn-In- and Ni-Mn-Sn-based alloys, two magnetic phases with ferromagnetic and antiferromagnetic exchange couplings between two nearest Mn atoms can coexist. The interaction between these phases results in exchange bias (EB). The EB field depends on the cluster sizes. Using the first order reversal curve (FORC) analysis of magnetization for Ni-Co-Mn-Sn and Ni-Co-Mn-In samples with different heat treatment, we can obtain information about cluster sizes of the structural phases in these alloys. This is especially important for polycrystalline alloy samples where dark-field images showing different phases are hard to obtain. Such a Ni-Co-Mn-Sn polycrystalline sample was characterized with small angle neutron scattering (SANS). Analyses of the scattering as a function of wavevector transfer in 50 Oe and 15 kOe applied field yield the average magnetic domain size of 21.2 +/-6.6 nm and a polydispersity of 0.32 +/-0.02 at 300 K, in good agreement with our prediction. The temperature evolution of the domain size will be discussed. Using an off-specular reflectometer in transmission geometry, the same sample was measured at a field of 270 Oe and 5.15 kOe. The fit of the 270 Oe data yields grain sizes of approximately 0.11-0.12 μm with polydispersities between 0.98 and 1.27. Supported by Texas A&M University, US-DOE, and US NSF-DMR.

  18. Towards Rare-Earth-Free Permanent Magnets: Exchange Bias In Binary Manganese-based Alloys

    NASA Astrophysics Data System (ADS)

    Marion, Joshua Leland

    Quantum-mechanical exchange interactions between phases in ferromagnetic/antiferromagnetic (FM/AF) magnetic nanocomposite systems can result in useful effects such as exchange bias (Hex) and remanence enhancement. These effects are more pronounced in nanostructured systems than in their coarse-grained counterparts due to improved interphase contact and can be developed to create good permanent magnetic behavior, but are currently poorly understood in bulk three-dimensional systems. To achieve this goal, factors such as the magnetic and structural phase identity, chemistry, size, shape, and character are investigated. To this end, synthesis, characterization and analysis of the magnetic and structural properties of nanocomposites are carried out on MnX (X = Cu, Al) alloys comprised of nanostructured FM and AF phases. It is recommended for future work that Fe be added to augment the FM response of the nanostructured MnX alloys. Cu30Mn70 and Al45Mn55 ribbons are fabricated using the nonequilibrium technique of rapid solidification via melt-spinning to access and retain metastable nanostructured states, then subject to post-synthesis processing techniques — thermal annealing and cryogenic milling — to investigate the effects of structural modifications on the magnetic response. X-ray diffraction (XRD) analyses of the crystal structure show the as-quenched ribbons consist of two majority crystallographic phases with slightly different lattice dimensions. Superconducting quantum interference device (SQUID) magnetometry reveals prominent hysteresis shifts of ˜10-13 kOe at T = 10 K, attributed to the Hex effect. These data suggest that nanoscopic disproportionation of local Mn content causes a structural and corresponding magnetic phase separation into FM Mn-poor and AF Mn-rich regions; exchange interactions between these regions produce the large low-temperature Hex values observed. Interestingly, magnetic and calorimetric analyses of Al45Mn 55 melt-spun ribbons also

  19. Modelling current-induced magnetization switching in Heusler alloy Co2FeAl-based spin-valve nanopillar

    NASA Astrophysics Data System (ADS)

    Huang, H. B.; Ma, X. Q.; Liu, Z. H.; Zhao, C. P.; Chen, L. Q.

    2014-04-01

    We investigated the current-induced magnetization switching in a Heusler alloy Co2FeAl-based spin-valve nanopillar by using micromagnetic simulations. We demonstrated that the elimination of the intermediate state is originally resulted from the decease of effective magnetic anisotropy constant. The magnetization switching can be achieved at a small current density of 1.0 × 104 A/cm2 by increasing the demagnetization factors of x and y axes. Based on our simulation, we found magnetic anisotropy and demagnetization energies have different contributions to the magnetization switching.

  20. Effect of a transverse magnetic field on solidification structure in directionally solidified Al-Cu-Ag ternary alloys

    NASA Astrophysics Data System (ADS)

    Guan, Guang; Du, Dafan; Fautrelle, Yves; Moreau, Rene; Ren, Zhongming; Li, Xi

    2015-07-01

    The effect of a transverse magnetic field on solidification structure in directionally solidified Al-Cu-Ag ternary alloys was investigated experimentally. The results show that the application of the transverse magnetic field significantly modified the solidification structures. Indeed, the magnetic field caused the formation of macrosegregation and the transformation of the liquid/solid interface from cellular to planar. Moreover, it was found that the magnetic field refined the eutectic cell and decreased the mushy zone length. This may be attributed to the thermoelectric magnetic convection between eutectic cells.

  1. Atomic structure, alloying behavior, and magnetism in small Fe-Pt clusters

    NASA Astrophysics Data System (ADS)

    Chittari, Bheema Lingam; Kumar, Vijay

    2015-09-01

    We report results of the atomic structure, alloying behavior, and magnetism in F emP tn(m +n =2 -10 ) clusters using projector augmented wave (PAW) pseudopotential method and spin-polarized generalized gradient approximation (GGA) for the exchange-correlation energy. These results are compared with those obtained by using HCTH exchange-correlation functional and LANL2DZ basis set in the Gaussian program and the overall trends are found to be similar. As in bulk Fe-Pt alloys, clusters with equal composition of Fe and Pt have the largest binding energy and the largest heat of nanoalloy formation for a given number of atoms in the cluster. There are some deviations due to the different symmetries in clusters and in cases where the total number of atoms is odd. The lowest energy isomers tend to maximize bonds between unlike atoms with Fe (Pt) atoms occupying high (low) coordination sites in the core (surface) of the cluster. The binding energy, heat of formation, and the second order difference of the total energy show F e2P t2 , F e4P t4 , and F e4P t6 clusters to be the most stable ones among the different clusters we have studied. The magnetic moments on Fe atoms are high in Pt-rich clusters as well as in small Fe-rich clusters and decrease as the aggregation of Fe atoms and the cluster size increases. The maximum value of the magnetic moments on Fe atoms is ˜3.8 μB , whereas for Pt atoms it is 1 μB. These are quite high compared with the values for bulk Fe as well as bulk FePt and F e3Pt phases while bulk Pt is nonmagnetic. There is significant charge transfer from those Fe atoms that interact directly with Pt atoms. We discuss the hybridization between the electronic states of Pt and Fe atoms as well as the variation in the magnetic moments on Fe and Pt atoms. Our results provide insight into the understanding of the nanoalloy behavior of Fe-Pt and we hope that this would help to design Fe based nanoalloys and their assemblies with high magnetic moments for

  2. Method of making active magnetic refrigerant materials based on Gd-Si-Ge alloys

    DOEpatents

    Pecharsky, Alexandra O.; Gschneidner, Jr., Karl A.; Pecharsky, Vitalij K.

    2006-10-03

    An alloy made of heat treated material represented by Gd.sub.5(Si.sub.xGe.sub.1-x).sub.4 where 0.47.ltoreq.x.ltoreq.0.56 that exhibits a magnetic entropy change (-.DELTA.S.sub.m) of at least 16 J/kg K, a magnetostriction of at least 2000 parts per million, and a magnetoresistance of at least 5 percent at a temperature of about 300K and below, and method of heat treating the material between 800 to 1600 degrees C. for a time to this end.

  3. Magnetic properties of nanocrystalline FeCuNb(Sb/W)SiB alloys

    SciTech Connect

    Degro, J.; Vojtanik, P.; Konc, M.; Zentko, A.; Csach, K.; Ocelik, V.

    1994-03-01

    The magnetic relaxation {Delta}r/r, the perminvar critical field H{sub CR}, the initial susceptibility {chi}{sub 10}, the coercive field H{sub c} as a function of annealing temperature in Fe{sub 73.5}Cu{sub 1}Nb{sub 2.95}Sb{sub 0.05}Si{sub 13.5}B{sub 9} and Fe{sub 73.5}Cu{sub 1}W{sub 3}Si{sub 13.5}B{sub 9} alloys were investigated. DSC measurements and thermomagnetic analyses were also done. The results using random anisotropy model can be explained.

  4. Improvement of Thermal Stability with Alloy Impregnation in Gd-Ba-Cu-O Superconductors for Pulsed Field Magnetization

    NASA Astrophysics Data System (ADS)

    Kimura, Y.; Matsumoto, H.; Fukai, H.; Sakai, N.; Hirabayashi, I.; Izumi, M.; Murakami, M.

    2006-06-01

    We present a post-fabrication treatment that improves thermal conductivity of bulk Gd-Ba-Cu-O magnets. A small hole about 1 mm in diameter was artificially drilled into the centre of bulk Gd-Ba-Cu-O 25 mm in diameter and 18 mm in thickness. An aluminium wire was inserted into the hole, and then the sample was subjected to the impregnation by using Bi- Su-Cd alloy. A pulsed-field magnetization was performed for Gd-Ba-Cu-O bulk with and without the alloy impregnation treatment. The temperature of samples was monitored with thermocouples and local magnetic field density was measured with a Hall sensor at several positions. The maximum temperature rise was depressed by 4 K and the trapped field was increased by 25 % at 44 K. The result shows that the alloy impregnation is very effective in enhancing the thermal conductivity and thereby improving the field trapping ability.

  5. Synthesis, structures and magnetic properties of Pr-lean Pr2Fe14B/Fe3B nanocomposite alloys

    NASA Astrophysics Data System (ADS)

    Mingxiang, Pan; Pengyue, Zhang; Hongliang, Ge; Hangfu, Yang; Qiong, Wu

    2012-09-01

    The lean rare-earth Pr4.5Fe77-xTixB18.5 (x=0, 1, 4, 5) nanocomposite alloys were prepared by melt spinning method and subsequent thermal annealing. The effect of Ti content and annealing temperature on the magnetic properties and the microstructure of these magnets were investigated. The enhancing coercivity Hc from 211.4 to 338.2 kA/m has been observed at the optimal annealing temperature of 700 °C by the addition of 5 at% Ti in Pr2Fe14B/Fe3B alloys. It was also found that increasing Ti content leads to marked grain refinement in the annealed alloys, resulting in strong exchange-coupling interaction between the hard and the soft phases in these ribbons. In addition, the magnetization reversal behaviors of Pr2Fe14B/Fe3B nanocomposites were discussed in detail.

  6. Tunneling Spectroscopy of Amorphous Magnetic Rare Earth-Si Alloys near the Metal-Insulator Transition

    NASA Astrophysics Data System (ADS)

    Xiong, P.; Zink, B. L.; Tran, M. Q.; Gebala, A. E.; Wilcox, E. M.; Hellman, F.; Dynes, R. C.

    1997-03-01

    Amorphous dilute magnetic semiconductors exhibit striking differences in the electrical and magneto-transport behavior from their crystalline or nonmagnetic analogs.(F. Hellman et al., Phys. Rev. Lett. 77, 4652 (1996).) Magnetic impurities cause a large suppression of conductivity below 50 K in a-Si_xGd_1-x and a-Si_xTb_1-x relative to the nonmagnetic a-Si_xY_1-x (x ~ 0.85-0.9). Application of a magnetic field increases the conductivity by orders of magnitude. We have fabricated good quality tunnel junctions on a-Si:Gd and the nonmagnetic a-Si:Y to probe the electronic density of states in these two systems. We present the results of the tunneling spectroscopy and its magnetic field dependence for a series of the two alloys at different compositions. We will discuss the correlation between the tunneling spectra and the transport properties and its implications on the possible origin of the magnetic field tuned insulator-metal transition in a-Si:Gd. Research Supported by ONR Grant No. N000149151320 and NSF Grant No. DMR-9208599.

  7. Premartensitic transition and relevant magnetic effects in Ni50Mn34In15.5Al0.5 alloy

    PubMed Central

    Wu, Yuqin; Guo, Shaopu; Yu, Shuyun; Cheng, Hui; Wang, Ruilong; Xiao, Haibo; Xu, Lingfang; Xiong, Rui; Liu, Yong; Xia, Zhengcai; Yang, Changping

    2016-01-01

    Resistance measurement, in situ optical microscopic observation, thermal and magnetic measurements have been carried out on Ni50Mn34In15.5Al0.5 alloy. The existence of a pronounced premartensitic transition prior to martensitic transition can be characterized by microstructure evolution as well as exothermic peak and smooth decrease of resistance and magnetization with obvious hysteresis over a wide temperature range upon cooling. Consequently, the alloy undergoes two successive magneto-structural transitions consisting of premartensitic and martensitic transitions. Magnetoelastic coupling between magnetic and structural degrees of freedom would be responsible for the appearance of premartensitic transition, as evinced by the distinct shift of transitions temperatures to lower temperature with external applied field of 50 kOe. The inverse premartensitic transition induced by magnetic field results in large magnetoresistance, and contributes to the enhanced inverse magnetocaloric effect through enlarging the peak value and temperature interval of magnetic entropy change ΔSm. PMID:27183331

  8. Effect of Annealing in Magnetic Field on Ferromagnetic Nanoparticle Formation in Cu-Al-Mn Alloy with Induced Martensite Transformation.

    PubMed

    Titenko, Anatoliy; Demchenko, Lesya

    2016-12-01

    The paper considers the influence of aging of high-temperature phase on subsequent martensitic transformation in Cu-Al-Mn alloy. The morphology of behavior of martensitic transformation as a result of alloy aging under annealing in a constant magnetic field with different sample orientation relatively to the field direction and without field was studied for direct control of the processes of martensite induction at cooling. Temperature dependences of electrical resistance, magnetic susceptibility, and magnetization, as well as field dependences of magnetization, and phase composition were found. The tendency to the oriented growth of precipitated ferromagnetic phase nanoparticles in a direction of applied field and to an increase of their volume fraction under thermal magnetic treatment of material that favors a reversibility of induced martensitic transformation is observed. PMID:27142875

  9. Effect of Annealing in Magnetic Field on Ferromagnetic Nanoparticle Formation in Cu-Al-Mn Alloy with Induced Martensite Transformation

    NASA Astrophysics Data System (ADS)

    Titenko, Anatoliy; Demchenko, Lesya

    2016-05-01

    The paper considers the influence of aging of high-temperature phase on subsequent martensitic transformation in Cu-Al-Mn alloy. The morphology of behavior of martensitic transformation as a result of alloy aging under annealing in a constant magnetic field with different sample orientation relatively to the field direction and without field was studied for direct control of the processes of martensite induction at cooling. Temperature dependences of electrical resistance, magnetic susceptibility, and magnetization, as well as field dependences of magnetization, and phase composition were found. The tendency to the oriented growth of precipitated ferromagnetic phase nanoparticles in a direction of applied field and to an increase of their volume fraction under thermal magnetic treatment of material that favors a reversibility of induced martensitic transformation is observed.

  10. Premartensitic transition and relevant magnetic effects in Ni50Mn34In15.5Al0.5 alloy

    NASA Astrophysics Data System (ADS)

    Wu, Yuqin; Guo, Shaopu; Yu, Shuyun; Cheng, Hui; Wang, Ruilong; Xiao, Haibo; Xu, Lingfang; Xiong, Rui; Liu, Yong; Xia, Zhengcai; Yang, Changping

    2016-05-01

    Resistance measurement, in situ optical microscopic observation, thermal and magnetic measurements have been carried out on Ni50Mn34In15.5Al0.5 alloy. The existence of a pronounced premartensitic transition prior to martensitic transition can be characterized by microstructure evolution as well as exothermic peak and smooth decrease of resistance and magnetization with obvious hysteresis over a wide temperature range upon cooling. Consequently, the alloy undergoes two successive magneto-structural transitions consisting of premartensitic and martensitic transitions. Magnetoelastic coupling between magnetic and structural degrees of freedom would be responsible for the appearance of premartensitic transition, as evinced by the distinct shift of transitions temperatures to lower temperature with external applied field of 50 kOe. The inverse premartensitic transition induced by magnetic field results in large magnetoresistance, and contributes to the enhanced inverse magnetocaloric effect through enlarging the peak value and temperature interval of magnetic entropy change ΔSm.

  11. Premartensitic transition and relevant magnetic effects in Ni50Mn34In15.5Al0.5 alloy.

    PubMed

    Wu, Yuqin; Guo, Shaopu; Yu, Shuyun; Cheng, Hui; Wang, Ruilong; Xiao, Haibo; Xu, Lingfang; Xiong, Rui; Liu, Yong; Xia, Zhengcai; Yang, Changping

    2016-01-01

    Resistance measurement, in situ optical microscopic observation, thermal and magnetic measurements have been carried out on Ni50Mn34In15.5Al0.5 alloy. The existence of a pronounced premartensitic transition prior to martensitic transition can be characterized by microstructure evolution as well as exothermic peak and smooth decrease of resistance and magnetization with obvious hysteresis over a wide temperature range upon cooling. Consequently, the alloy undergoes two successive magneto-structural transitions consisting of premartensitic and martensitic transitions. Magnetoelastic coupling between magnetic and structural degrees of freedom would be responsible for the appearance of premartensitic transition, as evinced by the distinct shift of transitions temperatures to lower temperature with external applied field of 50 kOe. The inverse premartensitic transition induced by magnetic field results in large magnetoresistance, and contributes to the enhanced inverse magnetocaloric effect through enlarging the peak value and temperature interval of magnetic entropy change ΔSm. PMID:27183331

  12. Comparison of the Magnetic and Absorption Properties of Flaky Super Sendust and Sendust Alloys

    NASA Astrophysics Data System (ADS)

    Li, Qifan; Feng, Zekun; Yan, Shuoqing; Nie, Yan; Wang, Xian

    2015-10-01

    Super Sendust and Sendust alloy powders were ball-milled for the same time to produce flakes and their static and dynamic magnetic properties were determined. The average size of flaky Super Sendust alloy particles was approximately 45.25 μm; the average size of Sendust alloy flakes was 40 μm. Fe-Si-Al-Ni flaky particle composites have better electromagnetic properties than Fe-Si-Al flaky particles; they have lower complex permittivity and a permeability that is approximately 1.5 times the permeability of Fe-Si-Al composites. Fe-Si-Al-Ni particles also have higher resonance than Fe-Si-Al composites, which contributes to a wider applied frequency band. The calculated reflection loss shows that the microwave-absorption performance of Fe-Si-Al-Ni composites exceeds that of Fe-Si-Al. In addition, the Fe-Si-Al-Ni composite's absorbing band of the reflection loss below -5 dB can cover both the L-band and S-band for an absorber thickness of 2.3 mm; this is three times as wide as that of the Fe-Si-Al composite.

  13. Temperature Dependence of the Magnetization of the Ni52Mn24Ga24 Alloy in Various Structural States

    NASA Astrophysics Data System (ADS)

    Musabirov, I. I.; Sharipov, I. Z.; Mulyukov, R. R.

    2015-10-01

    are presented of a study of the temperature dependence of the magnetization σ(Т) of the polycrystalline Ni52Mn24Ga24 alloy in various structural states: in the initial coarse-grained state, after severe plastic deformation by high pressure torsion, and after stepped annealing of the deformed specimen at temperatures from 200 to 700°С for 30 min. As a study of the σ(Т) curve shows, in an alloy possessing a coarse-grained initial structure, a martensitic phase transition and a magnetic phase transition are observed in the room temperature interval. The martensitic transformation takes place in the ferromagnetic state of the alloy. This transformation is accompanied by an abrupt lowering of the magnetization of the material, associated with a lowering of the symmetry of the crystalline lattice and a high value of the magnetocrystalline anisotropy constant of the alloy in the martensitic phase. It is shown that as a result of plastic deformation there takes place a destruction of ferromagnetic order and a suppression of the martensitic transformation. Consecutive annealing after deformation leads to a gradual recovery of ferromagnetic order and growth of the magnetization of the material. Recovery of the martensitic transformation begins to be manifested only after annealing of the alloy at a temperature of 500°C, when the mean grain size in the recrystallized structure reaches a value around 1 μm.

  14. Magnetic properties and atomic ordering of BCC Heusler alloy Fe2MnGa ribbons

    NASA Astrophysics Data System (ADS)

    Xin, Yuepeng; Ma, Yuexing; Luo, Hongzhi; Meng, Fanbin; Liu, Heyan

    2016-05-01

    The electronic structure, atomic disorder and magnetic properties of the Heusler alloy Fe2MnGa have been investigated experimentally and theoretically. BCC Fe2MnGa ribbon samples were prepared. Experimentally, a saturation magnetic moment (3.68 μB at 5 K) much larger than the theoretical value (2.04 μB) has been reported. First-principles calculations indicate that the difference is related to the Fe-Mn disorder between A, B sites, as can also be deduced from the XRD pattern. L21 type Fe2MnGa is a ferrimagnet with antiparallel Fe and Mn spin moments. However, when Fe-Mn disorder occurs, part of Mn moments will be parallel to Fe moments, and the Fe moments also clearly increase simultaneously. All this results in a total moment of 3.74 μB, close to the experimental value.

  15. Relation between the magnetization and the electrical properties of alloy GaSb-MnSb films

    SciTech Connect

    Koplak, O. V.; Polyakov, A. A.; Davydov, A. B.; Morgunov, R. B.; Talantsev, A. D.; Kochura, A. V.; Fedorchenko, I. V.; Novodvorskii, O. A.; Parshina, L. S.; Khramova, O. D.; Shorokhova, A. V.; Aronzon, B. A.

    2015-06-15

    The influence of the charge carrier concentration on the magnetic properties of GaSb-MnSb alloys is studied. The ferromagnetism of GaSb-MnSb films is caused by the presence of MnSb granules and manifests itself in both magnetometric measurements and the presence of an anisotropic magnetoresistance and the anomalous Hall effect. Electric conduction is executed by charge carriers (holes) in a GaSb matrix. The magnetization of clusters depends on stoichiometry and the concentration of Mn{sup 2+} and Mn{sup 3+} ions, which is specified by the film growth conditions. At high film growth temperatures, ferromagnetic clusters containing Mn{sup 2+} ions mainly form. At low growth temperatures, an antiferromagnetic phase containing Mn{sup 3+} ions forms.

  16. Multiscale model for phase transformation in magnetic shape memory alloy single crystals

    NASA Astrophysics Data System (ADS)

    Stoilov, Vesselin

    2006-03-01

    This paper investigates the nano-macro transition in magnetic shape memory alloy(MSMA) thin films using a recently developed sharp phase front-based three-dimensional (3D) constitutive model outlined by Stoilov (JSMS 2005), and originally proposed in the 1D context by Stoilov and Bhattacharyya (Acta Mat 2002). The key ingredient in the model is the recognition of martensitic variants as separate phases in a MSMA domain. Evolution of the interface between these phases is taken as an indicator of the process of reorientation in progress. A formulation of the Helmholtz free energy potential based on Ising model has been derived. The implications of the external magnetic field on the initiation of phase transformation are studied for various mechanical loading modes.

  17. Growth-induced perpendicular magnetic anisotropy and clustering in Ni xPt 1- x alloys

    NASA Astrophysics Data System (ADS)

    Vasumathi, D.; Shapiro, A. L.; Maranville, B. B.; Hellman, F.

    2001-02-01

    Polycrystalline and epitaxial (1 0 0), (1 1 0), and (1 1 1)-oriented Ni 3Pt, NiPt, and NiPt 3 films were deposited over a range of growth temperatures from 80°C to 700°C. Films grown at moderate temperatures (200-400°C) exhibit growth-induced properties similar to Co-Pt alloys: enhanced and broadened Curie temperature, perpendicular magnetic anisotropy and large coercivity. As in Co-Pt, the magnetic properties suggest a clustering of Ni into platelets on the growth surface, as the films are being grown. Unlike Co-Pt, however, NiPt films exhibit a strong orientational dependence of anisotropy and enhanced Curie temperature, possibly resulting from different types of surface reconstructions which affect the growth surface.

  18. Laminated composite of magnetic alloy powder and ceramic powder and process for making same

    DOEpatents

    Moorhead, A.J.; Kim, H.

    1999-08-10

    A laminated composite structure of alternating metal powder layers, and layers formed of an inorganic bonding media powder, and a method for manufacturing same are disclosed. The method includes the steps of assembling in a cavity alternating layers of a metal powder and an inorganic bonding media of a ceramic, glass, and glass-ceramic. Heat, with or without pressure, is applied to the alternating layers until the particles of the metal powder are sintered together and bonded into the laminated composite structure by the layers of sintered inorganic bonding media to form a strong composite structure. The method finds particular application in the manufacture of high performance magnets wherein the metal powder is a magnetic alloy powder. 9 figs.

  19. Laminated composite of magnetic alloy powder and ceramic powder and process for making same

    DOEpatents

    Moorhead, Arthur J.; Kim, Hyoun-Ee

    1999-01-01

    A laminated composite structure of alternating metal powder layers, and layers formed of an inorganic bonding media powder, and a method for manufacturing same are discosed. The method includes the steps of assembling in a cavity alternating layers of a metal powder and an inorganic bonding media of a ceramic, glass, and glass-ceramic. Heat, with or without pressure, is applied to the alternating layers until the particles of the metal powder are sintered together and bonded into the laminated composite structure by the layers of sintered inorganic bonding media to form a strong composite structure. The method finds particular application in the manufacture of high performance magnets wherein the metal powder is a magnetic alloy powder.

  20. Change in magnetic properties of a cold rolled and thermally aged Fe-Cu alloy

    NASA Astrophysics Data System (ADS)

    Park, D. G.; Ryu, K. S.; Kobayashi, S.; Takahashi, S.; Cheong, Y. M.

    2010-05-01

    The variation in magnetic properties of a Fe-1%Cu model alloy due to a cold rolling and a thermal aging has been evaluated to simulate the radiation damage of reactor pressure vessel of nuclear power plant. The thermal aging was conducted at 500 °C with different aging times in series. The hysteresis loops, magnetic Barkhausen noise (BN) and Vickers microhardness were measured for prestrained, strained, and thermal aged samples. The coercivity increased by a plastic strain and decreased by thermal aging, The BN decreased in the prestrained and strained samples but large changes were observed in the strained sample. These results were interpreted in terms of the domain wall motion signified by a change in the mean free path associated with microinternal stress and copper rich precipitates.

  1. Soft Magnetic Alloy-Polymer Composite for High-Frequency Power Electronics Application

    NASA Astrophysics Data System (ADS)

    Calata, Jesus N.; Lu, Guo-Quan; Ngo, Khai

    2014-01-01

    Soft magnetic alloys are limited to lower frequencies because of increased eddy-current losses at higher frequencies. A simple low-temperature solvent-based process was developed to coat permalloy powder with a benzocyclobutene insulating layer to reduce interparticle eddy-current loss. Low-signal measurements show that the permeability of the cured composite exhibits a bandwidth beyond 10 MHz. In contrast, the permeability of the pure powder rolled off well below 1 MHz with a corresponding increase in the imaginary permeability. Measurements of the core loss density at 5 MHz on pressed composite cores show a core loss of 300 mW/cm3 at more than 90 gauss, while the pure powder core achieved the same core loss density at just over 10 gauss. The results demonstrate that the polymer coating process is an effective way of reducing the interparticle eddy-current loss in powdered magnetic cores at high frequencies.

  2. Atomic disorder and the magnetic, electrical, and optical properties of a Co{sub 2}CrAl Heusler alloy

    SciTech Connect

    Svyazhin, A. D. Shreder, E. I.; Voronin, V. I.; Berger, I. F.; Danilov, S. E.

    2013-03-15

    Two Co{sub 2}CrAl alloy samples subjected to different heat treatment regimes are studied. An exact distribution of atoms over the sublattices in the samples is determined by X-ray diffraction and neutron diffraction methods. These data are used to perform ab initio density of states calculations and to calculate the magnetic moments of the samples in a coherent potential approximation. The calculated magnetic moments are compared to the experimental values. The effect of atomic ordering on the electronic structure near the Fermi level is analyzed using optical methods. The possible causes of the detected temperature dependence of the electrical resistivity, unusual for metallic alloys, are discussed.

  3. The migration behavior of atomic clusters in early nanocrystalline process of soft magnetic Finemet alloy.

    PubMed

    Wang, Yuxin; Li, Xiang; Zhang, Yu; Zhao, Guannan; Yan, Biao; Lu, Wei

    2010-11-01

    The Finemet alloys are commonly used as cores in transformers and generators, stress and field sensors in technological application for their excellent soft magnetic characteristics. To clarify the nanocrystallization mechanism of Finemet especially about the atomic migration in early stage is very essential for developing their distinctive characteristics. In this study, we investigate the migration behavior of atoms in order to clarify the mechanism of the early-stage nanocrystallization in amorphous Finemet alloys. The Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous ribbons were prepared by single-roller melt-spinning process in argon atmosphere, and then annealed at 350 degrees C-400 degrees C for 10 minutes in vacuum. The atom force microscope (AFM) and the coincidence Doppler broadening spectra (CDB) were used to characterize the migration behavior of different atoms in Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous alloy during the early-stage nanocrystallization. The X-ray diffraction (XRD) patterns show that all annealed samples are in the amorphous state. But the AFM observation shows clearly that there are many small atomic clusters (nuclei) which distribute in the amorphous matrix of the annealed samples. With increasing annealing temperature, there is a significant increase in the amount of atomic clusters and a dramatic drop in the average size of clusters with very limited Cu contention in the samples, which reflect the structural evolution into more homogeneity. The CDB spectrum indicates that the peaks of positron annihilation spectrum are gradually reduced, which means the number of grain boundary and the defects in samples are gradually increased. It can be concluded that more defects are introduced by the formation of atomic clusters through atomic migration during the early-stage nanocrystallization in Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous alloys. PMID:21137965

  4. Investigation on macrosegregation and dendrite morphology during directional solidification of Al-Cu hypereutectic alloys under a strong magnetic field

    NASA Astrophysics Data System (ADS)

    Li, Xi; Du, DaFan; Fautrelle, Yves; Ren, ZhongMing; Moreau, Rene

    2015-08-01

    The effect of a strong magnetic field (up to 12 T) on the macrosegregation and dendrite morphology during directional solidification of the Al-22at.%Cu alloy has been investigated. Experimental results show that the application of the magnetic field caused the freckle macrosegregation and the fracture of the Al2Cu dendrites during directional solidification. With the increase of the magnetic field, the size of the freckle and dendrite decreases. Moreover, the electron back-scatter diffraction (EBSD) was applied to study the effect of the magnetic field on the morphology and orientation of the Al2Cu dendrite. The EBSD results revealed that although the dendrites were destroyed under the magnetic field, the magnetic field did not yet change the orientation of the Al2Cu crystal. The formation of the freckles and the fracture of the dendrites under the magnetic field may be attributed to the TE magnetic effects.

  5. Microstructure and Magnetic Properties of Sm2Fe17NNx-ALLOY- Powders and of Bonded Anisotropic Magnets

    NASA Astrophysics Data System (ADS)

    Wall, B.; Katter, M.; Rodewald, W.; Velicescu, M.

    In cast Sm2Fe17 ingots minor fractions of SmFe2 and SmFe3 may occur. Nitrogenation of such alloy-powders inidicates that only Sm2Fe17 forms an interstitial solid solution whereas SmFe2 and SmFe3 decompose directly into SmN and α-Fe. From Sm2Fe17Nx alloy powders with an average particle size of about 3 μm anisotropic magnets were prepared by adding 15 wt% Zn-powder. Annealing at 390 ºC results in intrinsic coercivities > 15 kOe promoted by the formation of an unknown binary Fe8Zn92-compound. Whereas annealing at temperatures > 420 ºC leads to the formation of binary Fe3Zn7 and ternary Sm2FeZn2. By the formation of Sm2FeZn2 from Sm2Fe17Nx+Zn some α-Fe occurs inducing a step in the demagnetization curve J(H).

  6. Annealing temperature effect on microstructure, magnetic and microwave properties of Fe-based amorphous alloy powders

    NASA Astrophysics Data System (ADS)

    He, Jinghua; Wang, Wei; Wang, Aimin; Guan, Jianguo

    2012-09-01

    Fe74Ni3Si13Cr6W4 amorphous alloy powders were annealed at different temperature (T) for 1.5 h to fabricate the corresponding amorphous and nanocrystalline powders. The influences of T on the crystalline structure, morphology, magnetic and microwave electromagnetic properties of the resultant samples were investigated via X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer and vector network analyzer. The results show that the powder samples obtained at T of 650 °C or more are composed of lots of ultra-fine α-Fe(Si) grains embedded in an amorphous matrix. When T increases from 350 to 750 °C, the saturated magnetization and coercivity of the as-annealed powder samples both increase monotonously whereas the relative real permittivity shows a minimal value and the relative real permeability shows a maximal value at T of 650 °C. Thus the powder samples annealed at 650 °C show optimal reflection loss under -10 dB in the whole C-band. These results here suggest that the annealing heat treatment of Fe-based amorphous alloy is an effective approach to fabricate high performance microwave absorber with reasonable permittivity and large permeability simultaneously via adjusting T.

  7. Structural, morphological, magnetic and hydrogen absorption properties of LaNi5 alloy: A comprehensive study

    NASA Astrophysics Data System (ADS)

    Sarhaddi, Reza; Arabi, Hadi; Pourarian, Faiz

    2014-04-01

    A comprehensive study of structural, morphological, magnetic and hydrogen absorption properties of LaNi5-H system was investigated. The X-ray diffraction patterns show that as-synthesized LaNi5 alloy is single phase with CaCu5-type structure while some weak peaks of elemental nickel also appeared after several hydrogenation/dehydrogenation (H/D) cycling. The presence of pure Ni was also followed using the room temperature magnetic measurements. After H/D cycling, the particle size decreases and particle size distribution was found nearly uniform compared to noncycled alloy. The pressure-composition isotherms (PCIs) of the hydrogen absorption reaction were determined in the temperature range 20-80°C using a homemade Sievert's type experimental apparatus, and then the enthalpy and entropy of hydride formation were calculated. The hydriding kinetic mechanism of LaNi5 was evaluated using the different fitting models: Jander diffusion model (JDM), Johnson-Mehl-Avrami (JMA) and Chou models. All employed models confirm an increase in the hydriding reaction rate with temperature. However, the calculated results using JMA model show a better agreement with the experimental data and hence we believe that diffusion along with nucleation and growth is the rate-controlling step for the hydriding reaction. The values of activation energy for hydriding reaction were also obtained by JD and JMA models.

  8. Low temperature magnetic transition and high temperature oxidation in INCONEL alloy 718

    SciTech Connect

    Seehra, M.S.; Babu, V.S.

    1996-05-01

    X-ray diffraction and temperature dependent (5 K{endash}380 K) magnetic measurements have been carried out in INCONEL 718 superalloy before and after high temperature aging treatments (INCONEL is a trademark of the INCO family of companies). The nominal composition of this alloy is Ni (52.5{percent}), Cr (19.0{percent}), Fe (18.5{percent}), Nb (5.1{percent}), Mo (3.0{percent}), Ti (0.9{percent}), Al (0.5{percent}), Cu (0.15{percent}) and C (0.08{percent}) and it yields an x-ray diffraction pattern consisting of a fcc phase with {ital a}=3.5987 (3) A and an orthorhombic phase associated with {delta}{minus}Ni{sub 3}Nb. It is concluded that the fcc pattern is due to both the {gamma} austenitic phase and {gamma}{prime} Ni{sub 3}(Al,Ti) phase of alloy 718. The standard annealing and aging treatment carried out in air at temperatures between 621 and 982{degree}C produces surface oxides (Cr,Fe){sub 2}O{sub 3} and FeNbO{sub 4} (which are easily removed by etching and polishing) and contracts the lattice. Magnetic measurements show a distinct phase transition at {ital T}{sub {ital c}}=14 K, which has been attributed to the {gamma}{prime}{minus}Ni{sub 3}(Al,Ti) phase by the process of elimination and by observing that it has most of the characteristics of the weak itinerant ferromagnet Ni{sub 74.5}Al{sub 25.5}. This transition may have some effects on the cryogenic applications of this alloy. {copyright} {ital 1996 Materials Research Society.}

  9. Magnetic properties of FeCu (3 d transition metals) SiB alloys with fine grain structure

    SciTech Connect

    Sawa, T. ); Takahashi, Y. )

    1990-05-01

    Soft magnetic properties were investigated together with crystallization process and grain size for FeCu (3{ital d} transition metals) SiB alloys with fine grains. They were rapidly quenched from the melt to achieve amorphous states and then annealed above their crystallization temperatures. In the group of 3{ital d} transition metals studied, low magnetic core loss at high frequency was obtained for V-substituted Fe-based alloys, because only a bcc Fe solid solution with diameter of about 20 nm precipitated. On the other hand, Cr- or Mn-substituted alloys could not be attained with good soft magnetic properties because of the existence of Fe-metalloid compounds besides the bcc phase by annealing above their crystallization temperatures. The effect of grain size on the soft magnetic properties is more prominent at lower frequency. Diffraction peaks which are characteristics of an ordered phase (DO{sub 3}) are observed, which is the origin of excellent soft magnetic properties in FeAlSi alloys.

  10. The magnetic phase transition in Mn1.1Fe0.9P1-xGex magnetocaloric alloys

    NASA Astrophysics Data System (ADS)

    Chen, X.; Ramanujan, R. V.

    2015-02-01

    Mn-Fe-P-Ge alloys are promising, low cost, high performance candidates for magnetic cooling applications based on the magnetocaloric effect. These alloys undergo a magnetic phase transition which induces a large entropy change (ΔS). Experimental and modeling studies were conducted to study this transition for varying Ge content. Landau theory and the Bean-Rodbell model were applied to Mn1.1Fe0.9P1-xGex (x = 0.26, 0.3, and 0.32) melt spun ribbons to model the phase transition and the associated entropy change. The critical behavior of these alloys was studied. The critical composition range at which the cross over from first order to second order magnetic transition occurs was determined. The calculated thermodynamic values and critical temperatures were in good agreement with our experimental results. A high maximum entropy change (ΔS) of ˜44.9 J kg-1 K-1 was observed in Mn1.1Fe0.9P0.74Ge0.26 in a 5 T applied magnetic field. The results suggest that Mn-Fe-P-Ge alloys are very attractive materials for near room temperature magnetic cooling.

  11. Microstructure and magnetic properties of nanostructured (Fe0.8Al0.2)100-xSix alloy produced by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Boukherroub, N.; Guittoum, A.; Laggoun, A.; Hemmous, M.; Martínez-Blanco, D.; Blanco, J. A.; Souami, N.; Gorria, P.; Bourzami, A.; Lenoble, O.

    2015-07-01

    We report on how the microstructure and the silicon content of nanocrystalline ternary (Fe0.8Al0.2)100-xSix powders (x=0, 5, 10, 15 and 20 at%) elaborated by high energy ball milling affect the magnetic properties of these alloys. The formation of a single-phase alloy with body centred cubic (bcc) crystal structure is completed after 72 h of milling time for all the compositions. This bcc phase is in fact a disordered Fe(Al,Si) solid solution with a lattice parameter that reduces its value almost linearly as the Si content is increased, from about 2.9 Å in the binary Fe80Al20 alloy to 2.85 Å in the powder with x=20. The average nanocrystalline grain size also decreases linearly down to 10 nm for x=20, being roughly half of the value for the binary alloy, while the microstrain is somewhat enlarged. Mössbauer spectra show a sextet thus suggesting that the disordered Fe(Al,Si) solid solution is ferromagnetic at room temperature. However, the average hyperfine field diminishes from 27 T (x=0) to 16 T (x=20), and a paramagnetic doublet is observed for the powders with higher Si content. These results together with the evolution of both the saturation magnetization and the coercive field are discussed in terms of intrinsic and extrinsic properties.

  12. Microstructure and Magnetic Properties of Iron-Cobalt-Based Soft Magnetic Alloys

    NASA Astrophysics Data System (ADS)

    Yu, R. H.; Basu, S.; Taylor, R.; Unruh, K. M.; Xiao, J. Q.

    1998-03-01

    The magnetic properties in a temperature range of 20-700^circ C of Fe_49Co_49V2 (Hiperco50), Fe_49Co_49V_1.7Nb_0.3 (Hiperco 50HS), and Fe_72Co_27Cr_0.5Mn_0.5 (Hiperco 27) have been studied. The samples were annealed at high temperature followed by cooling to room temperature with different rates to achieve different microstructures. The details of the microstructures have been analyzed in association with temperature dependence of the magnetic properties. The structural evolution has also been studied using differential scanning calorimetry (DSC) and TEM. The ordering parameter was determined by neutron diffraction. The coercivity H_c, saturation magnetization Ms and initial magnetic permeability μ were found to decrease with increasing temperature up to 750^circ C. Microstructural observation indicates that the second phase was formed during thermal cycling or aging at 600^circ C. For the ordered Hiperco 50 series, this second phase acts as a barrier for the domain wall movement resulting in the increase of Hc and decrease of Ms and μ. Hiperco 27 samples, which retains their disordered phase, exhibit relatively high H_c, and lower Ms and μ at room temperature. Mössbauer analysis indicates that the magnetic moments tends to align parallel to the surfaces of the sample and the average hyperfine fields decrease as the ordering parameter increases.

  13. Structural and magnetic characterization of plasma ion nitrided layer on 316L stainless steel alloy

    NASA Astrophysics Data System (ADS)

    Öztürk, O.; Okur, S.; Riviere, J. P.

    2009-05-01

    In this study, an FeCrNi alloy (316L stainless steel disc) was nitrided in a low-pressure R.F. plasma at 430 °C for 72 min under a gas mixture of 60% N2-40% H2. Structural, compositional and magnetic properties of the plasma nitrided layer was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and magnetic force microscopy (MFM). The magnetic behaviour of the nitrided layer was also investigated with a vibrating sample magnetometer (VSM). Combined X-ray diffraction, cross-sectional SEM, AFM and MFM, as well as VSM analyses provide strong evidence for the formation of the γN phase, [γN-(Fe, Cr, Ni)], with mainly ferromagnetic characteristics. The uniform nature of the γN layer is clearly demonstrated by the XRD, cross-sectional SEM and AFM analyses. Based on the AFM and SEM data, the thickness of the γN layer is found to be ∼6 μm. According to the MFM and VSM analyses, ferromagnetism in the γN layer is revealed by the observation of stripe domain structures and the hysteresis loops. The cross-sectional MFM results demonstrate the ferromagnetic γN phase distributed across the plasma nitrided layer. The MFM images show variation in the size and form of the magnetic domains from one grain to another.

  14. Relationship between Magnetocrystalline Anisotropy and Orbital Magnetic Moment in L10-Type Ordered and Disordered Alloys

    NASA Astrophysics Data System (ADS)

    Kota, Yohei; Sakuma, Akimasa

    2012-08-01

    The magnetocrystalline anisotropy energy and orbital magnetic moment in L10-type transition metal alloys such as FePt, FePd, FeNi, CoPt, CoPd, and MnAl are evaluated while continuously varying the degree of order. The electronic structure with spin--orbit interaction is calculated by employing the tight-binding linear muffin-tin orbital method based on the local spin-density approximation. To control the degree of order, we consider a substitutional disorder and then adopt the coherent potential approximation. The magnetocrystalline anisotropy energy Δ E is roughly proportional to the power of the long-range order parameter S, i.e., Δ E \\propto Sn (n ˜ 1.6{--}2.4). We also discuss the relationship between the magnetocrystalline anisotropy energy and the orbital magnetic moment. In the same compositional system with different degrees of order, the difference between the orbital magnetic moment in the magnetic easy axis and that in the hard one is proportional to Δ E. However, the coefficient corresponding to the effective spin--orbit coupling is inconsistent with the intrinsic one in some cases.

  15. Outstanding efficiency in energy conversion for electric motors constructed by nanocrystalline soft magnetic alloy "NANOMET®" cores

    NASA Astrophysics Data System (ADS)

    Nishiyama, N.; Tanimoto, K.; Makino, A.

    2016-05-01

    Recently updated nanocrystalline soft magnetic Fe-Co-Si-B-P-Cu alloys "NANOMET®" exhibit high saturation magnetic flux density (Bs > 1.8 T), low coercivity (Hc < 10 A/m) and low core loss (W1.7/50 ˜ 0.4 W/kg) even in a ribbon form with a thickness of up to 40 μm. By utilize excellent magnetic softness, several products such as motors or transformers for electrical appliances are now under developing by industry-academia collaboration. In particular, it is found that a brushless DC motor using NANOMET® core exhibited remarkable improvement in energy consumption. The prototype motor with an outer core diameter of 70 mm and a core thickness of 50 mm was constructed using laminated nano-crystallized NANOMET® ribbons. Core-loss for the constructed motor was improved from 1.4 W to 0.4 W only by replacing the non-oriented Si-steel core with NANOMET® one. The overall motor efficiency is evaluated to be 3% improvement. In this work, the relation between processing and resulting magnetic properties will be presented. In addition, feasibility for commercialization will also be discussed.

  16. Magnetic properties of Nd-Ga-Fe{sub bal}-Nb-B alloy

    SciTech Connect

    Kim, Hyunkyu; Sung Kim, Chul; Yong An, Sung; Ryong Choi, Kang; Choi, Moonhee

    2014-05-07

    Here, we have synthesized Nd-Ga-Fe{sub bal}-Nb-B alloy by strip casting method. The crystalline and magnetic properties of sample were investigated with x-ray diffractometer (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectrometer. The XRD pattern was analyzed with the Rietveld refinement method, indicating a tetragonal structure and the space group of P4{sub 2}/mnm. The temperature dependence of zero-field cooled (ZFC) magnetization curve was measured under applied field at temperature ranging from 4.2 to 740 K. From the ZFC curve, Curie temperature and spin reorientation temperature are determined to be 615 K and 130 K, respectively. Also, Mössbauer spectra were measured at various temperatures ranging from 4.2 to 620 K. Each spectrum was fitted with 6-sextets for Fe site (8j{sub 1}, 8j{sub 2}, 16k{sub 1}, 16k{sub 2}, 4c, and 4e), and magnetic hyperfine field, Isomer shift, electric quadrupole shift, and area ratio values were obtained from the fit. We observed the change in slope of magnetic hyperfine field and electric quadrupole shift at 130 K while the Curie temperature was determined to be 615 K from the measurement of zero velocity counter, agreeing with the values obtained from VSM measurements.

  17. Magnetism of σ-phase Fe-Mo alloys: Its characterization by magnetometry and Mo¨ssbauer spectrometry

    NASA Astrophysics Data System (ADS)

    Cieślak, J.; Dubiel, S. M.; Reissner, M.

    2016-03-01

    Sigma-phase Fe100-xMox alloys (x=45-53) were revealed to exhibit a low temperature magnetism. Its characterization has been done using vibrating sample magnetometry and Mössbauer spectroscopy techniques. The magnetic ordering temperature was determined to lie in the range of ∼46 K for x=45 and ∼22 K for x=53, and the irreversibility of the magnetization process carried out in zero-field cooled (ZFC) and in field cooled (FC) conditions is in line with the spin-glass being the ground magnetic state of the samples.

  18. Magnetic anisotropy of Fe1-yXyPt-L10 [X = Cr, Mn, Co, Ni, Cu] bulk alloys

    NASA Astrophysics Data System (ADS)

    Cuadrado, R.; Klemmer, Timothy J.; Chantrell, R. W.

    2014-10-01

    We demonstrate by means of fully relativistic first principles calculations that, by substitution of Fe by Cr, Mn, Co, Ni, or Cu in FePt-L10 bulk alloys, with fixed Pt content, it is possible to tune the magnetocrystalline anisotropy energy by adjusting the content of the non-magnetic species in the material. The changes in the geometry due to the inclusion of each element induces different values of the tetragonality and hence changes in the magnetic anisotropy and in the net magnetic moment. The site resolved magnetic moments of Fe increase with the X content while those of Pt and X are simultaneously reduced. The calculations are in good quantitative agreement with experimental data and demonstrate that models with fixed band structure but varying numbers of electrons per unit cell are insufficient to describe the experimental data for doped FePt-L10 alloys.

  19. Chemical synthesis, characterizations and magnetic properties of nanocrystalline Fe{sub 50}Co{sub 50} alloy

    SciTech Connect

    Dalavi, Shankar B.; Panda, Rabi Narayan; Raja, M. Manivel

    2014-04-24

    Nanocrystalline Fe{sub 50}Co{sub 50} alloy has been synthesized successfully by chemical reduction route using superhydride as reducing agent and oleic acid and oleylamine as capping agents. Phase purity, crystallite size and lattice parameters of the synthesized NPs are determined by X-ray powder diffraction method. FeCo alloy crystallizes in body centered cubic (bcc) structure having crystallite size equal to 29 nm and lattice parameters equal to 2.8546 Å. The size and shape morphologies of the material were studied by SEM analysis. SEM micrograph study shows the average particle size to be 60 nm and indicates the appearance of agglomerates of the nano-particles consisting of several crystallites. The room temperature magnetic hysteresis studies indicate ferromagnetic behavior of the materials. The values of saturation magnetization and coercivity were 65 emu/g and 460 Oe, respectively. Magnetic properties of the material were interpreted on the basis of fine particle magnetism.

  20. Evolution of magnetic properties and microstructure of Hf2Co11B alloys

    SciTech Connect

    McGuire, Michael A.; Rios, Orlando

    2015-02-05

    Amorphous Hf2Co11B alloys produced by melt-spinning have been crystallized by annealing at 500-800 °C, and the products have been investigated using magnetization measurements, x-ray diffraction, and scanning electron microscopy. The results reveal the evolution of the phase fractions, microstructure, and magnetic properties with both annealing temperature and time. Crystallization of the phase denoted HfCo7, which is associated with the development of coercivity, occurs slowly at 500 °C. Annealing at intermediate temperatures produces mixed phase samples containing some of the HfCo7 phase with the highest values of remanent magnetization and coercivity. The equilibrium structure at 800 °C contains HfCo3B2, Hf6Co23 and Co, and displays soft ferromagnetism. Maximum values for the remanent magnetization, intrinsic coercivity, and magnetic energy product among the samples are approximately 5.2 kG, 2.0 kOe, and 3.1 MGOe, respectively, which indicates that the significantly higher values observed in crystalline, melt-spun Hf2Co11B ribbons are a consequence of the non-equilibrium solidification during the melt-spinning process. Application of high magnetic fields during annealing is observed to strongly affect the microstructural evolution, which may provide access to higher performance materials in Zr/Hf-Co hard ferromagnets. The crystal structure of HfCo7 and the related Zr analogues is unknown, and without knowledge of atomic positions powder diffraction cannot distinguish among proposed unit cells and symmetries found in the literature.

  1. Evolution of magnetic properties and microstructure of Hf2Co11B alloys

    DOE PAGESBeta

    McGuire, Michael A.; Rios, Orlando

    2015-02-05

    Amorphous Hf2Co11B alloys produced by melt-spinning have been crystallized by annealing at 500-800 °C, and the products have been investigated using magnetization measurements, x-ray diffraction, and scanning electron microscopy. The results reveal the evolution of the phase fractions, microstructure, and magnetic properties with both annealing temperature and time. Crystallization of the phase denoted HfCo7, which is associated with the development of coercivity, occurs slowly at 500 °C. Annealing at intermediate temperatures produces mixed phase samples containing some of the HfCo7 phase with the highest values of remanent magnetization and coercivity. The equilibrium structure at 800 °C contains HfCo3B2, Hf6Co23 andmore » Co, and displays soft ferromagnetism. Maximum values for the remanent magnetization, intrinsic coercivity, and magnetic energy product among the samples are approximately 5.2 kG, 2.0 kOe, and 3.1 MGOe, respectively, which indicates that the significantly higher values observed in crystalline, melt-spun Hf2Co11B ribbons are a consequence of the non-equilibrium solidification during the melt-spinning process. Application of high magnetic fields during annealing is observed to strongly affect the microstructural evolution, which may provide access to higher performance materials in Zr/Hf-Co hard ferromagnets. The crystal structure of HfCo7 and the related Zr analogues is unknown, and without knowledge of atomic positions powder diffraction cannot distinguish among proposed unit cells and symmetries found in the literature.« less

  2. Magnetic properties of Ce-Nd-Fe-Mo alloys and their nitrides

    SciTech Connect

    Zhou, C; Pinkerton, FE

    2014-11-01

    New quaternary alloys of Ce-1 xNdxFe12 Mo-y(y) with x=0, 0.2, 0.4, 0.6, 0.8, 1 and y=0, 1.5, 2 have been prepared and magnetically hardened by melt spinning. X-ray diffraction indicates that the as-spun materials exhibit the tetragonal ThMn12-type structure. Prior to nitriding, the coercivity H-ci is less than 0.6 kOe in all alloys and is independent of Nd content, while the magnetization 4 pi M-19 (measured in an applied held of 19 kOe) and Curie temperature T-c increase with added Nd content x. The effects of nitriding pressure P, time t, and temperature TOR magnetic properties have been carefully evaluated on NdFe10Mo2 in order to identify the optimal nitriding parameters. The optimized nitriding profile was subsequently adopted to nitride the remaining samples. After nitrogenation, T-c and 4 pi M-19 have been substantially enhanced primarily due to the increased Fe-Fe exchange from nitrogen induced lattice dilation. Benefitting from the positive contribution from Nd, H-ci has been greatly improved in the Nd containing samples. As a result, Ce0.2Nd0.8Fe10Mo2 nitride features H-ci=2.9 kOe and (BH)(max) = 1.6 MGOe and Ce0.2Nd0.8Fe10.5Mo1.5 nitride demonstrates H-ci=2.5 kOe, (BH)(max) = 1.5 MGOe at room temperature, and T-c=337 degrees C. which are substantial advancements compared to the pure Ce based ThMn12-type materials previously reported. (C) 2014 Published by Elsevier B.V.

  3. Preparation of Soft Magnetic Fe-Ni-Pb-B Alloy Nanoparticles by Room Temperature Solid-Solid Reaction

    PubMed Central

    Zhong, Qin

    2013-01-01

    The Fe-Ni-Pb-B alloy nanoparticles was prepared by a solid-solid chemical reaction of ferric trichloride, nickel chloride, lead acetate, and potassium borohydride powders at room temperature. The research results of the ICP and thermal analysis indicate that the resultants are composed of iron, nickel, lead, boron, and PVP, and the component of the alloy is connected with the mole ratio of potassium borohydride and the metal salts. The TEM images show that the resultants are ultrafine and spherical particles, and the particle size is about a diameter of 25 nm. The largest saturation magnetization value of the 21.18 emu g−1 is obtained in the Fe-Ni-Pb-B alloy. The mechanism of the preparation reaction for the Fe-Ni-Pb-B multicomponent alloys is discussed. PMID:24348196

  4. Preparation of soft magnetic Fe-Ni-Pb-B alloy nanoparticles by room temperature solid-solid reaction.

    PubMed

    Zhong, Guo-Qing; Zhong, Qin

    2013-01-01

    The Fe-Ni-Pb-B alloy nanoparticles was prepared by a solid-solid chemical reaction of ferric trichloride, nickel chloride, lead acetate, and potassium borohydride powders at room temperature. The research results of the ICP and thermal analysis indicate that the resultants are composed of iron, nickel, lead, boron, and PVP, and the component of the alloy is connected with the mole ratio of potassium borohydride and the metal salts. The TEM images show that the resultants are ultrafine and spherical particles, and the particle size is about a diameter of 25 nm. The largest saturation magnetization value of the 21.18 emu g(-1) is obtained in the Fe-Ni-Pb-B alloy. The mechanism of the preparation reaction for the Fe-Ni-Pb-B multicomponent alloys is discussed. PMID:24348196

  5. Effect of cooling rate on magnetostriction gradients of Tb0.27Dy0.73Fe1.95 alloys solidified in high magnetic field gradients

    NASA Astrophysics Data System (ADS)

    Liu, Tie; Gao, Peng-Fei; Dong, Meng; Xiao, Yu-Bao; Wang, Qiang

    2016-05-01

    In this work, Tb0.27Dy0.73Fe1.95 alloys were solidified in a high magnetic field gradient (8.8 T, -565 T2/m) at various cooling rates. Changes in the magnetostriction, crystal orientation, and magnetization of the alloys were investigated. The application of the magnetic field gradient has a strong influence on the magnetostrictive performance. At lower cooling rates, the maximum magnetostriction increases gradually with depth from the top surface of the alloys. However, the effect of the magnetic field gradient is strongly dependent on the cooling rate. With increasing cooling rate, the magnetostriction gradient decreases. The magnetization measurement shows that the saturation magnetization at lower cooling rates increases gradually with depth from the top surface of the alloys. However, with increasing cooling rate, the increase in the saturation magnetization is reduced. The XRD measurement results show that the orientation behavior of the (Tb, Dy)Fe2 phase exhibits a continuous change throughout the alloys at lower cooling rates, but is almost unchanged at higher cooling rates. The change in the magnetostriction of the alloys can be attributed to the changes in crystal orientation and the amount of the (Tb, Dy)Fe2 phase in the alloys caused by both the magnetic field gradient and cooling rate.

  6. Domain structure and magnetization loss in a toroidal core based on an Fe-based amorphous alloy

    NASA Astrophysics Data System (ADS)

    Azuma, Daichi; Hasegawa, Ryusuke; Saito, Shin; Takahashi, Migaku

    2012-04-01

    By utilizing a wide-view Kerr-effect magnetic domain observation system designed for domain observation on curved surfaces, domain images were taken on the surface of a toroidal core based on an Fe-based amorphous alloy. The results of the observation are discussed in terms of Bertotti's eddy-current loss model, helping to clarify the concept of magnetic objects proposed by the model.

  7. Ab initio construction of magnetic phase diagrams in alloys: The case of Fe1-xMnxPt

    DOE PAGESBeta

    Pujari, B. S.; Larson, P.; Antropov, V. P.; Belashchenko, K. D.

    2015-07-28

    A first-principles approach to the construction of concentration-temperature magnetic phase diagrams of metallic alloys is presented. The method employs self-consistent total energy calculations based on the coherent potential approximation for partially ordered and noncollinear magnetic states and is able to account for competing interactions and multiple magnetic phases. The application to the Fe1–xMnxPt “magnetic chameleon” system yields the sequence of magnetic phases at T = 0 and the c-T magnetic phase diagram in good agreement with experiment, and a new low-temperature phase is predicted at the Mn-rich end. The importance of non-Heisenberg interactions for the description of the magnetic phasemore » diagram is demonstrated.« less

  8. Ab Initio Construction of Magnetic Phase Diagrams in Alloys: The Case of Fe(1-x)Mn(x)Pt.

    PubMed

    Pujari, B S; Larson, P; Antropov, V P; Belashchenko, K D

    2015-07-31

    A first-principles approach to the construction of concentration-temperature magnetic phase diagrams of metallic alloys is presented. The method employs self-consistent total energy calculations based on the coherent potential approximation for partially ordered and noncollinear magnetic states and is able to account for competing interactions and multiple magnetic phases. Application to the Fe(1-x)Mn(x)Pt "magnetic chameleon" system yields the sequence of magnetic phases at T=0 and the c-T magnetic phase diagram in good agreement with experiment, and a new low-temperature phase is predicted at the Mn-rich end. The importance of non-Heisenberg interactions for the description of the magnetic phase diagram is demonstrated. PMID:26274437

  9. Effect of sputtering pressure on stacking fault density and perpendicular magnetic anisotropy of CoPt alloys

    NASA Astrophysics Data System (ADS)

    Park, Kyung-Woong; Oh, Young-Wan; Kim, Dae-Hoon; Kim, Jai-Young; Park, Byong-Guk

    2016-09-01

    We report the effects of Ar sputtering pressure on perpendicular magnetic anisotropy in disordered CoPt alloys via the modulation of stacking fault density. The coercivity and anisotropy field of CoPt alloys are gradually enlarged with an increase in Ar sputtering pressure from 3 mTorr to 30 mTorr. Structural analyses using transmission electron microscopy, atomic force microscopy and x-ray reflectivity show that the structural properties of the samples, such as roughness or grain size, are not significantly changed by variations in Ar sputtering pressure. On the other hand, in-plane x-ray diffraction measurements reveal that the stacking fault density is reduced in films grown under higher pressure, and instead favors HCP stacking. Our results suggest that perpendicular magnetic anisotropy in CoPt alloys can be enhanced by the growth of the sample under a high Ar sputtering pressure, which decreases stacking fault density.

  10. Effect of current density and bath composition on crystalline structure and magnetic properties of electrodeposited FeCoW alloy

    NASA Astrophysics Data System (ADS)

    Ghaferi, Z.; Sharafi, S.; Bahrololoom, M. E.

    2015-11-01

    In this research, FeCoW alloy coatings were prepared by galvanostatic method. The influence of current density and bath composition on microstructure and magnetic properties of electrodeposited FeCoW alloys were also studied. All coatings showed (2 2 0) preferred orientation with a two phase structure at higher current densities. Grain size of the coatings deposited from 0.01 and 0.03 M tungsten content electrolytes was in the range of 29-126 and 10-42 nm, respectively. Microhardness of the coatings deposited from the former electrolyte changed by chemical composition of the alloys, while this parameter changed by grain-size reduction for the coatings deposited from the latter one. The coercivity was controlled by grain-size reduction and surface morphology. It could be stated that the high-tungsten content electrolyte produced coatings with superior magnetic behaviour and microhardness compared with the electrolyte with low -tungsten content.

  11. Effect of Co on the thermal stability and magnetic properties of AlNiCo 8 alloys

    SciTech Connect

    Liu, Tao Li, Wei; Zhu, Minggang; Guo, Zhaohui; Li, Yanfeng

    2014-05-07

    The magnetic properties, microstructure, and reversible temperature coefficient of magnetic flux of Alnico 8 alloys with the different Co and Ti have been investigated in this paper. The Alnico alloys containing 34, 36, 38, and 40 mass percent cobalt were fabricated by the conventional casting method including thermomagnetic treatment. The transmission electron microscopy (TEM) testing shows that there are more α1 phases particles with the diameter of less than 10 nm appearing in the matrix with the increasing of the content of Co and Ti. The thermal stability of Alnico 8 alloys deteriorates with the increasing of the content of Co and Ti, which are caused mainly by the decrease of the degree of particle alignment and particle perfection.

  12. Electrolytic hydriding of LaFe(13-x)Si(x) alloys for energy efficient magnetic cooling.

    PubMed

    Lyubina, Julia; Hannemann, Ullrich; Ryan, Mary P; Cohen, Lesley F

    2012-04-17

    An effective, low-temperature and readily available electrochemical method for tuning the operation temperature of LaFe(13-x)Si(x)-type alloys is demonstrated. Electrolytically hydrided materials have the same high level magnetic properties as in high temperature gas-phase processed materials and offer an advantage of higher hydrogen absorption rate in the ferromagnetic state. PMID:22431476

  13. Nano-crystallization and magnetic mechanisms of Fe85Si2B8P4Cu1 amorphous alloy by ab initio molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Wang, Yaocen; Takeuchi, Akira; Makino, Akihiro; Liang, Yunye; Kawazoe, Yoshiyuki

    2014-05-01

    Iron-based amorphous and nano-crystalline alloys have attracted a growing interest due to their potential in the application of magnetic coil production. However, fundamental understanding of the nano-crystallization mechanisms and magnetic features in the amorphous structure are still lack of knowledge. In the present work, we performed ab initio molecular dynamics simulation to clarify the ionic and electronic structure in atomic scale, and to derive the origin of the good magnetic property of Fe85Si2B8P4Cu1 amorphous alloy. The simulation gave a direct evidence of the Cu-P bonding preference in the amorphous alloy, which may promote nucleation in nano-crystallization process. On the other hand, the electron transfer and the band/orbital features in the amorphous alloy suggests that alloying elements with large electronegativity and the potential to expand Fe disordered matrix are preferred for enhancing the magnetization.

  14. Strongly correlated systems: Magnetic measurements of magnesium diboride and group IV magnetic semiconductor alloys

    NASA Astrophysics Data System (ADS)

    Guchhait, Samaresh

    Nuclear Magnetic Resonance Force Microscopy (NMRFM) is a unique quantum microscopy technique, which combines the three-dimensional imaging capabilities of magnetic resonance imaging (MRI) with the high sensitivity and resolution of atomic force microscopy (AFM). It has potential applications in many different fields. This novel scanning probe instrument holds potential for atomic-scale resolution. MgB2 is a classic example of two-band superconductor. However, the behavior of these two bands below the superconducting transition temperature is not well understood yet. Also, the anisotropic relaxation times of single crystal MgB2 have not been measured because it is not yet possible to grow large enough MgB2 single crystals for conventional NMR. Using our homemade NMRFM probe, we have set out to measure the relaxation times of micron size MgB2 single crystals to answer several questions relating to the anisotropy, multiband behavior, and coherence effects in this unusual superconductor. The goal of a second project is to study the effects of doping on the critical current of MgB2 superconducting wires. Ti-sheathed MgB 2 wires doped with nanosize crystalline-SiC up to a concentration of 15 wt% SiC have been fabricated, and the effects of the SiC doping on the critical current density (Jc) and other superconducting properties studied. In contrast with the previously reported results, our measurements show that SiC doping decreases Jc over almost the whole field range from 0 to 7.3 tesla at all temperatures. Furthermore, it is found that the degradation of Jc becomes stronger at higher SiC doping levels. Our results indicate that these negative effects on Jc could be attributed to the absence of significant effective pinning centers (mainly Mg2Si) due to the high chemical stability of the crystalline-SiC particles. The principle goal of a third project, the study of magnetic semiconductors, is to investigate magnetic properties of Mn-implanted GeC thin films. 20 ke

  15. Joint properties of cast Fe-Pt magnetic alloy laser-welded to Co-Cr alloy.

    PubMed

    Baba, Naoki; Watanabe, Ikuya; Tanaka, Yasuhiro; Hisatsune, Kunihiro; Atsuta, Mitsuru

    2005-12-01

    This study investigated the joint properties of Fe-Pt alloy laser-welded to Co-Cr alloy. Cast plates (0.5 x 3.0 x 10 mm) were prepared with Fe-Pt and Co-Cr alloys. Fe-Pt plates were butted against Co-Cr plates and laser-welded using Nd:YAG laser. Control and homogeneously welded specimens were also prepared. Laser welding was performed with and without argon shielding. Tensile testing was conducted, and both fracture force (Ff: N) and elongation (El: %) were recorded. There were no differences in the Ff value between the specimens with and without argon shielding for the welded Fe-Pt/Co-Cr. Lower Ff value of the welded specimen was obtained in the order of Fe-Pt alloy < Fe-Pt/Co-Cr < Co-Cr alloy. The results indicated that Fe-Pt welded to Co-Cr had Ff values between the values of homogeneously welded Fe-Pt and Co-Cr alloys. Argon shielding, on the other hand, had no effect on the weld strength between Fe-Pt and Co-Cr alloys. PMID:16445017

  16. Preparation, crystallography, magnetic and magnetothermal properties of Ce5SiGe4-x alloys

    SciTech Connect

    Vijayaraghavan, Rangarajan

    2005-05-01

    An investigation of the crystal structure and the phase relationships in the Ce{sub 5}Si{sub 4-x}Ge{sub x} system has been carried out. The crystal structures of the single phase intermetallics were characterized using X-ray powder diffraction and subsequent refinement employing the Rietveld analysis technique was performed. The intermetallic system was found to crystallize in three distinct crystal structures. The Ce{sub 5}Si{sub 4}-based solid solution extends from x = 0 to x = 2.15 and it was found to crystallize in the well-known Zr{sub 5}Si{sub 4}-type tetragonal structure. The germanium rich alloys, where 3.1 {le} x {le} 4, crystallized in the Sm{sub 5}Ge{sub 4}-type orthorhombic structure. The crystal structure of the intermediate phase, when 2.35 {le} x {le} 2.8, was found out to be of the Gd{sub 5}Si{sub 2}Ge{sub 2}-type monoclinic structure. Microhardness tests were conducted on the samples in order to probe the trend in mechanical properties in this alloy system as a function of Ge concentration. The magnetic, thermal and magnetocaloric properties of the Ce{sub 5}Si{sub 4-x}Ge{sub x} alloy system have been investigated for x = 0, 1.0, 1.8, 2.5, 2.8, 3.5, 3.8 and 4.0. The phases with x = 0, 1.0 and 1.8 crystallize in the tetragonal Zr{sub 5}Si{sub 4} structure and those with x = 2.5, 2.8 form in the Gd{sub 5}Si{sub 2}Ge{sub 2}-type monoclinic structure. The alloys with x = 3.5, 3.8 and 4.0 crystallize in the Sm{sub 5}Ge{sub 4}-type orthorhombic structure. The Curie temperature of the tetragonal phases increases with increasing Ge content. The ordering temperatures of the monoclinic and orthorhombic phases remain nearly unaffected by the composition, with the Curie temperatures of the latter slightly higher than those of the former. All the alloys display evidence of antiferromagnetic interactions in the ground state. The orthorhombic and the monoclinic alloys behave as ferromagnets whereas the Si-rich tetragonal phase acts more like an antiferromagnet at

  17. A study of K shell X-ray intensity ratios of NixCr1-x alloys in external magnetic field and determination of effective atomic numbers of these alloys

    NASA Astrophysics Data System (ADS)

    Perişanoğlu, Ufuk; Demir, Lütfü

    2015-05-01

    In this study, the effect of external magnetic field on the Kβ/Kα X-ray intensity ratios of various alloy compositions of Ni-Cr transition metal alloys has been investigated. The Kα and Kβ emission spectra of Ni, Cr and NixCr1-x (x=0.40; 0.50; 0.60; 0.80) alloys were measured by using a Si (Li) solid-state detector. Kβ/Kα X-ray intensity ratios of Ni, Cr and NixCr1-x alloys without magnetic field and in 0.5 and 1 T external magnetic field have been measured following excitation by 59.5 keV γ-rays from a 200 mCi241Am radioisotope point source. When the experimental data obtained in external magnetic field have been compared with data without external magnetic field, deviations have been observed in Kβ/Kα X-ray intensity ratios for Ni and Cr in different alloy compositions. Thus, results of these measurements have shown that Kβ/Kα X-ray intensity ratios of Ni and Cr in NixCr1-x alloys are dependent on the external magnetic field. Also the total mass attenuation coefficients for pure 3d transition metals and their alloys at different compositions were measured and theoretically estimated using mixture rule for selected photon energy. Later on, total atomic and electronic cross-sections and effective atomic number for alloys are determined experimentally and theoretically using these mass attenuation coefficients. When these parameters are examined depending on the alloy compositions, thereof have been found to vary with the alloy composition.

  18. Atomic and magnetic order in the shape memory alloy Mn2NiGa

    NASA Astrophysics Data System (ADS)

    Brown, P. J.; Kanomata, T.; Neumann, K.; Neumann, K. U.; Ouladdiaf, B.; Sheikh, A.; Ziebeck, K. R. A.

    2010-12-01

    Magnetization and high resolution neutron powder diffraction measurements on the magnetic shape memory alloy Mn2NiGa have confirmed that it is ferromagnetic with a Curie temperature above 500 K. The compound undergoes a broad structural phase transformation ΔT ~ 90 K with a mean transition temperature TM ~ 270 K. The high temperature parent phase is cubic (a = 5.937 Å) and has a modified L 21 structure. At 500 K the ordered magnetic moment essentially all on the 4a site is 1.35 μB/Mn. The low temperature martensite has space group I4/mmm and is related to the cubic phase through a Bain transformation atet = (acub + bcub)/2, btet = (acub - bcub) and ctet = ccub in which the change in cell volume is < 2.6%. In this structure at 5 K the ordered moment of ≈2.3 μB is again found to be confined to the sites with full Mn occupation and is aligned parallel to c. Neutron diffraction patterns obtained at 5 K suggested the presence of a weak incommensurate antiferromagnetic phase characterized by either a (\\frac 13 0 \\frac 13) or (0 0 \\frac 13) propagation vector.

  19. Dynamic magnetic characteristics of Fe78Si13B9 amorphous alloy subjected to operating temperature

    NASA Astrophysics Data System (ADS)

    He, Aina; Wang, Anding; Yue, Shiqiang; Zhao, Chengliang; Chang, Chuntao; Men, He; Wang, Xinmin; Li, Run-Wei

    2016-06-01

    The operating temperature dependence of dynamic magnetic characteristics of the annealed Fe78Si13B9 amorphous alloy core was systematically investigated. The core loss, magnetic induction intensity and complex permeability of the amorphous core were analyzed by means of AC B-H loop tracer and impedance analyzer. It is found that the operating temperature below 403 K has little impact on core loss when the induction (B) is less than 1.25 T. As B becomes higher, core loss measured at high temperature becomes higher. For the cores measured at power frequency, the B at 80 A/m and the coercivity (Hc) at 1 T decline slightly as the temperature goes up. Furthermore, the real part of permeability (μ‧) increases with the rise of temperature. The imaginary part of permeability (μ″) maxima shifts to lower frequency side with increasing temperature, indicating the magnetic relaxation behavior in the sample. In addition, with the rise in the operating temperature of the annealed amorphous core, the relaxation time tends to increase.

  20. Magnetic field controlled single crystal growth and surface modification of titanium alloys exposed for biocompatibility

    NASA Astrophysics Data System (ADS)

    Hermann, Regina; Uhlemann, Margitta; Wendrock, Horst; Gerbeth, Gunter; Büchner, Bernd

    2011-03-01

    The aim of this work is growth and characterisation of Ti55Nb45 (wt%) single crystals by floating-zone single crystal growth of intermetallic compounds using two-phase radio-frequency (RF) electromagnetic heating. Thereby, the process and, in particular, the flow field in the molten zone is influenced by additional magnetic fields. The growth of massive intermetallic single crystals is very often unsuccessful due to an unfavourable solid-liquid interface geometry enclosing concave fringes. It is generally known that the crystallization process stability is enhanced if the crystallization interface is convex. For this, a tailored magnetic two-phase stirrer system has been developed, which enables a controlled influence on the melt ranging from intensive inwards to outwards flows. Since Ti is favourably light, strong and biocompatible, it is one of the few materials that naturally match the requirements for implantation in the human body. Therefore, the magnetic system was applied to crystal growth of Ti alloys. The grown crystals were oriented and cut to cubes with the desired crystallographic orientations [1 0 0] and [1 0 1] normally on a plane. The electron backscatter diffraction (EBSD) technique was applied to clearly determine crystal orientation and to localize grain boundaries. The formation of oxidic nanotubes on Ti surfaces in dependence of the grain orientation was investigated, performed electrochemically by anodic oxidation from fluoride containing electrolyte.

  1. Bridgman Growth of GeSi Alloys in a Static Magnetic Field

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Szofran, F. R.; Vujisic, L.; Motakef, S.

    1998-01-01

    Ge(0.95)Si(0.050 alloy crystals have been grown by the vertical Bridgman technique, both with and without an axial 5 Tesla magnetic field. The crystals were processed in a constant axial thermal gradient and the effects of graphite, hot pressed boron nitride, and pyrolitic boron nitride ampoule materials on interface shapes and macrosegregation profiles were investigated. The sample grown in a graphite ampoule at 5 Tesla exhibited a macroscopic axial concentration profile close to that of complete mixing and strong striation patterns. In samples grown in boron nitride ampoules, both with and without a 5 Tesla magnetic field applied, measured macroscopic axial concentration profiles were intermediate between those expected for a completely mixed melt and diffusion-controlled growth, and striation patterns were also observed. Possible explanations for the apparent inability of the magnetic field to reduce the flow velocities to below the growth velocities are discussed, and results of growth experiments in pyrolitic boron nitride ampoules are also described.

  2. Large anisotropic Fe orbital moments in perpendicularly magnetized Co2FeAl Heusler alloy thin films revealed by angular-dependent x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Okabayashi, Jun; Sukegawa, Hiroaki; Wen, Zhenchao; Inomata, Koichiro; Mitani, Seiji

    2013-09-01

    Perpendicular magnetic anisotropy (PMA) in Heusler alloy Co2FeAl thin films sharing an interface with a MgO layer is investigated by angular-dependent x-ray magnetic circular dichroism. Orbital and spin magnetic moments are deduced separately for Fe and Co 3d electrons. In addition, the PMA energies are estimated using the orbital magnetic moments parallel and perpendicular to the film surfaces. We found that PMA in Co2FeAl is determined mainly by the contribution of Fe atoms with large orbital magnetic moments, which are enhanced at the interface between Co2FeAl and MgO. Furthermore, element specific magnetization curves of Fe and Co are found to be similar, suggesting the existence of ferromagnetic coupling between Fe and Co PMA directions.

  3. Effects of age hardening on magnetic and transport properties of Mg-1.3 wt% Ce alloys

    SciTech Connect

    Yamashita, T.; Cavallaro, P.; Kelly, P.M.; Hisa, M.

    1998-05-22

    Magnesium is the lightest structural metal. It has advantages over many other materials in terms of specific strength, machinability and shock absorption. Improvements in magnesium alloy design and more stringent requirements to reduce fuel consumption and air pollution, have recently focused attention on the use of magnesium alloys for automotive components. Here, a Mg-1.3 wt% Ce alloy has been isothermally heat treated at 423 K and the transport and magnetic properties are investigated. This alloy is known to have distinct age hardening behavior and its age hardened microstructure has been studied in detail. The transport properties depend on the early stage of precipitation which is difficult to define by transmission electron microscopy. The scattering sites of electrons are not identical to precipitates, but consist of strain fields induced by the precipitates, solute atoms, dislocations and vacancies. The resistivity was found to increase initially with aging time and then decrease. The highest resistivity was obtained from a specimen aged for 3.6 ks. This aging time is far less than that of 1,800 ks which gives the maximum hardness. On the other hand, magnetic properties correlate with the later stages of the precipitation. In particular, the imaginary part of the magnetic susceptibility is related to macroscopic formation of precipitates. The imaginary part of the magnetic susceptibility of the alloys seems to be generated by eddy current loss. The imaginary part of the magnetic susceptibility increases monotonically with aging time but it may decrease for extensive aging treatments beyond 3,600 ks.

  4. Magnetic and structural characterization of high anisotropy cobalt-rich alloys: Thin films and patterns

    NASA Astrophysics Data System (ADS)

    Zana, Iulica

    In this dissertation the structural and magnetic characterization of high anisotropy Co-rich alloys for magnetic recording and MEMS applications has been carried out. The potential of Co78Sm22 as an ultra-high density recording medium was explored through comprehensive static and dynamic magnetic measurements. It was found out that hard magnetic properties (Hc = 4.5 kOe) can be achieved when CoSm is sputter-deposited on Cr80V 20 underlayer, comparable with those reported for state-of-the-art media at the end of 2002. Furthermore, the chemical stability and reliability of CoSm thin films was studied through combined accelerated aging and electrochemical methods. It was found out that CoSm thin films are more reactive than current recording media (CoPt), and a layer of Si3N4 of at least 6 nm provides satisfactory protection. Electrodeposition of Co80Pt20 onto highly textured Cu seed layer with either {100} or {111} orientation was studied. The influence of Cu texture and plating current density (cd) on the growth, morphology, microstructure, and magnetic properties of the CoPt films was investigated. Epitaxial CoPt thin films with uniform composition across the film thickness were deposited. The microstructure consists in fcc matrix and hcp matrix when plated on Cu(100) and Cu(111), respectively. CoPt hcp single phase films with c-axis normal to the substrate were grown on Cu(111) when plated at cd = 50 mA/cm2. As opposed to the films plated on Cu(100) which show a mostly in-plane magnetic anisotropy, the films plated on Cu(111) develop a well defined perpendicular magnetic anisotropy (PMA) due to the hcp phase with the c-axis normal to the substrate, which yields coercivities as high as 6.1 kOe. The origin of the high PMA was found to lie in the magnetocrystalline anisotropy. CoPt micromagnets have been successfully fabricated by the electrodeposition-through-mask method, which despite the small aspect ratio show a definite PMA. The PMA, together with the hard

  5. Hard Magnetic, Low Neodymium Nd-Fe-B Melt-Spun Alloys Containing Refractory Metals

    SciTech Connect

    Leonowicz, Marcin; Spyra, Marzena; Jezierska, Elzbieta

    2011-06-30

    The effect of selected refractory metals addition on the structure and magnetic properties was studied for the nanocomposite Nd{sub 9}Fe{sub 77-x}B{sub 14}M{sub x}(M = Ti, Mo, Nb, Mn), Nd{sub 8}Fe{sub 78-x}B{sub 14}M{sub x}(M = Ti, Mo, Nb, Mn) and Nd{sub 7}Fe{sub 79-x}B{sub 14}Ti{sub x} systems. It was found that the addition of 2 and 4 at % of refractory metals leads to a substantial increase of the coercivity and maximum energy product for each of the nanocomposite systems while maintaining the remanence unchanged. The highest properties were obtained for the alloys containing 4-5 at% of the refractory metals. The maximum energy product of 143 kJ/m{sup 3} was achieved for the Nd{sub 8}Fe{sub 74}B{sub 14}Ti{sub 4} alloy.

  6. Effect of magnetism on surface segregation in FeNi alloys.

    PubMed

    Sansa, Myriam; Ribeiro, Fabienne; Dhouib, Adnene; Tréglia, Guy

    2016-02-17

    Modelling the segregation of the various chemical species in the vicinity of crystallographic defects in FeNi alloys is essential because it affects the macroscopic properties of these materials, which are widely used in technological applications. We present here a theoretical study of surface segregation, within a mean-field approach based on the tight-binding Ising model grounded on density functional theory calculations. The most important result is that, although FeNi presents none of the driving forces (i.e. surface energy, size mismatch) which generally favour surface enrichment in the same element in the whole range of concentrations, there exists a wide temperature range in which Ni is found to segregate at the surface irrespective of the concentration. This is due to a complex interplay between magnetic and ordering/phase separation effects. PMID:26794606

  7. Study of the effect of magnetic ordering on order-disorder transitions in binary alloys

    NASA Astrophysics Data System (ADS)

    Jena, Ambika Prasad; Sanyal, Biplab; Mookerjee, Abhijit

    2014-06-01

    We set up a mean-field approximation in a random Ising model characterized by two order parameters: the local sublattice magnetization and a mean-field occupation variable which act as an order parameter for the order-disorder transition. In the effective model Hamiltonian the two order-parameters are coupled. We solve the coupled equations arising from this to describe the total phase diagram. The exchange energies for FeCo alloys have then been accurately obtained from first-principles based on the technique of orbital peeling and a Monte Carlo analysis using a coupled Metropolis-Kawasaki updating has been carried out. Our results reasonably successfully agree with earlier experimental data.

  8. Fluctuation induced diamagnetism in the zero magnetic field limit in a low temperature superconducting alloy.

    PubMed

    Mosqueira, J; Carballeira, C; Vidal, F

    2001-10-15

    By using a Pb-18 at. % In alloy, the fluctuation induced diamagnetism was measured in the zero magnetic field limit, never observed until now in a low-T(C) superconductor. This allows us to disentangle the dynamic and the nonlocal electrodynamic effects from the short-wavelength fluctuation effects. The latter may be explained on the grounds of the Gaussian-Ginzburg-Landau approach by introducing a total energy cutoff in the fluctuation spectrum, which strongly suggests the existence of a well-defined temperature in the normal state above which all fluctuating modes vanish. This conclusion may also have implications when describing the superconducting state formation of the high-T(C) cuprates. PMID:11690233

  9. Direct magnetic patterning due to the generation of ferromagnetism by selective ion irradiation of paramagnetic FeAl alloys.

    PubMed

    Menéndez, Enric; Liedke, Maciej Oskar; Fassbender, Jürgen; Gemming, Thomas; Weber, Anja; Heyderman, Laura J; Rao, K V; Deevi, Seetharama C; Suriñach, Santiago; Baró, Maria Dolors; Sort, Jordi; Nogués, Josep

    2009-02-01

    Sub-100-nm magnetic dots embedded in a non-magnetic matrix are controllably generated by selective ion irradiation of paramagnetic Fe(60)Al(40) (atomic %) alloys, taking advantage of the disorder-induced magnetism in this material. The process is demonstrated by sequential focused ion beam irradiation and by in-parallel broad-beam ion irradiation through lithographed masks. Due to the low fluences used, this method results in practically no alteration of the surface roughness. The dots exhibit a range of magnetic properties depending on the size and shape of the structures, with the smallest dots (<100 nm) having square hysteresis loops with coercivities in excess of micro(0)H(C) = 50 mT. Importantly, the patterning can be fully removed by annealing. The combination of properties induced by the direct magnetic patterning is appealing for a wide range of applications, such as patterned media, magnetic separators, or sensors. PMID:19089839

  10. Magnetism and electronic structure of CoFeCrX (X = Si, Ge) Heusler alloys

    NASA Astrophysics Data System (ADS)

    Jin, Y.; Kharel, P.; Lukashev, P.; Valloppilly, S.; Staten, B.; Herran, J.; Tutic, I.; Mitrakumar, M.; Bhusal, B.; O'Connell, A.; Yang, K.; Huh, Y.; Skomski, R.; Sellmyer, D. J.

    2016-08-01

    The structural, electronic, and magnetic properties of CoFeCrX (X = Si, Ge) Heusler alloys have been investigated. Experimentally, the alloys were synthesized in the cubic L21 structure with small disorder. The cubic phase of CoFeCrSi was found to be highly stable against heat treatment, but CoFeCrGe disintegrated into other new compounds when the temperature reached 402 °C (675 K). Although the first-principle calculation predicted the possibility of tetragonal phase in CoFeCrGe, the tetragonal phase could not be stabilized experimentally. Both CoFeCrSi and CoFeCrGe compounds showed ferrimagnetic spin order at room temperature and have Curie temperatures (TC) significantly above room temperature. The measured TC for CoFeCrSi is 790 K but that of CoFeCrGe could not be measured due to its dissociation into new compounds at 675 K. The saturation magnetizations of CoFeCrSi and CoFeCrGe are 2.82 μB/f.u. and 2.78 μB/f.u., respectively, which are close to the theoretically predicted value of 3 μB/f.u. for their half-metallic phases. The calculated band gaps for CoFeCrSi and CoFeCrGe are, respectively, 1 eV and 0.5 eV. These materials have potential for spintronic device applications, as they exhibit half-metallic electronic structures with large band gaps, and Curie temperatures significantly above room temperature.

  11. Electronic and magnetic structure of L10-FePt nanoparticle embedded in FePt random alloy

    SciTech Connect

    Wang, Yang; Stocks, George Malcolm; Rusanu, Aurelian; Nicholson, Don M; Eisenbach, Markus; Zhang, Qiming; Liu, J. P.

    2007-01-01

    One of the grand challenges in the development of nanotechnology is how to synthesize and process "designed nanostructured materials". An important example of these materials is the nanocomposite permanent magnets made of hard and soft magnetic nanoparticles. However, such magnetic nanostructures present substantial theoretical challenges due to the need to treat the electronic interactions quantum-mechanically whilst dealing with a large number of atoms. In this presentation, we show a direct quantum mechanical simulation of magnetic nano-structures made of spherical L10-FePt nanoparticles, with diameter within 2.5 nm 5 nm, embedded in an fct-FePt random alloy. The calculation is performed using the Locally Self-consistent Multiple Scattering (LSMS) method, a linear scaling ab-initio method capable of treating tens of thousands of atoms. We found that there exists a screening region below the surface of each nanoparticle. This screening region essentially screens out the effect of the external random alloy to keep the physical properties of the interior region unchanged from the bulk of L10-FePt. Interestingly, the depth of this screening region is around 4 Angstrom and is independent of the size of the nanoparticles we have investigated. We will discuss the formation of this screening region and the effect of the external random alloy on the electronic and magnetic structure of the nanoparticles.

  12. Magnetic and conventional shape memory behavior of Mn–Ni–Sn and Mn–Ni–Sn(Fe) alloys

    NASA Astrophysics Data System (ADS)

    Turabi, A. S.; Lázpita, P.; Sasmaz, M.; Karaca, H. E.; Chernenko, V. A.

    2016-05-01

    Magnetic and conventional shape memory properties of Mn49Ni42Sn9(at.%) and Mn49Ni39Sn9Fe3(at.%) polycrystalline alloys exhibiting martensitic transformation from ferromagnetic austenite into weakly magnetic martensite are characterized under compressive stress and magnetic field. Magnetization difference between transforming phases drastically increases, while transformation temperature decreases with the addition of Fe. Both Mn49Ni42Sn9 and Mn49Ni39Sn9Fe3 alloys show remarkable superelastic and shape memory properties with recoverable strain of 4% and 3.5% under compression at room temperature, respectively. These characteristics can be counted as extraordinary among the polycrystalline NiMn-based magnetic shape memory alloys. Critical stress for phase transformation was increased by 34 MPa in Mn49Ni39Sn9Fe3 and 21 MPa in Mn49Ni42Sn9 at 9 T, which can be qualitatively understood in terms of thermodynamic Clausius–Clapeyron relationships and in the framework of the suggested physical concept of a volume magnetostress.

  13. Extended investigation of intermartensitic transitions in Ni-Mn-Ga magnetic shape memory alloys: A detailed phase diagram determination

    SciTech Connect

    Çakir, Asli; Aktürk, Selçuk; Righi, Lara

    2013-11-14

    Martensitic transitions in shape memory Ni-Mn-Ga Heusler alloys take place between a high temperature austenite and a low temperature martensite phase. However, intermartensitic transformations have also been encountered that occur from one martensite phase to another. To examine intermartensitic transitions in magnetic shape memory alloys in detail, we carried out temperature dependent magnetization, resistivity, and x-ray diffraction measurements to investigate the intermartensitic transition in Ni{sub 50}Mn{sub 50–x}Ga{sub x} in the composition range 12≤x≤25 at. %. Rietveld refined x-ray diffraction results are found to be consistent with magnetization and resistivity data. Depending on composition, we observe that intermartensitic transitions occur in the sequences 7M→L1{sub 0}, 5M→7M, and 5M→7M→L1{sub 0} with decreasing temperature. The L1{sub 0} non-modulated structure is most stable at low temperature.

  14. The electronic and magnetic properties of defects on half-metallic Ti2NiIn alloy

    NASA Astrophysics Data System (ADS)

    Wei, Xiao-Ping; Zhang, Ya-Ling; Sun, Xiao-Wei; Song, Ting; Guo, Peng

    2016-01-01

    Using full-potential local-orbital minimum-basis method within density functional theory (DFT), we study the electronic and magnetic properties of ideal and defective Ti2NiIn Heusler alloy. The ideal Ti2NiIn exhibits a half-metallic ferromagnetic behavior with a total magnetic moment of 3.000 μB and a band gap 0.394 eV, which is promising for fabricating spin injection devices as the Fermi level is located in the middle of band gap. Among these studied defects, only NiIn antisite as well as Ti(A) and Ti(B) vacancies retain the half-metallicity. However, the remaining defects destroy the half-metallicity. The calculations of formation energy indicate that Ti(A) vacancy can be spontaneously formed during the fabrications of the alloy. In addition, we also discuss the electronic and magnetic properties under different defects.

  15. Analysis of Magnetic Minor Hysteresis Loops in Thermally Aged and Cold-rolled Fe-Cu Alloys

    NASA Astrophysics Data System (ADS)

    Takahashi, F.; Kobayashi, S.; Murakami, T.; Takahashi, S.; Kamada, Y.; Kikuchi, H.

    2011-01-01

    Neutron irradiation causes the formation of Cu precipitate in reactor pressure vessel steel and makes the steel susceptible to rupture. In the present study, we have examined magnetic minor hysteresis loops of Fe-1wt%Cu alloy after thermally ageing at 753 K and subsequent cold rolling to elucidate the effects of Cu precipitation on magnetic properties. Minor-loop coefficients, obtained from scaling power laws between field-dependent parameters of minor hysteresis loops, decrease with ageing time and show a local maximum around 200 min, reflecting the growth of Cu precipitates with ageing. For the alloy cold-rolled after ageing, the minor-loop properties linearly increase with reduction and show a good relationship with mechanical properties such as DBTT and hardness. These observations indicate that the analysis method using magnetic minor loops can be an useful technique of nondestructive evaluation of irradiation embrittlement and subsequent deformation hardening in reactor pressure vessel steels.

  16. Growth temperature dependent structural and magnetic properties of epitaxial Co2FeAl Heusler alloy films

    NASA Astrophysics Data System (ADS)

    Qiao, Shuang; Nie, Shuaihua; Zhao, Jianhua; Zhang, Xinhui

    2013-06-01

    The structural and magnetic properties of a series of Co2FeAl Heusler alloy films grown on GaAs(001) substrate by molecular beam epitaxy have been studied. The epitaxial Co2FeAl films with an ordered L21 structure have been successfully obtained at growth temperature of 433 K, with an in-plane cubic magnetic anisotropy superimposed with an unusual uniaxial magnetic anisotropy. With increasing growth temperature, the ordered L21 structure degrades. Meanwhile, the uniaxial anisotropy decreases and eventually disappears above 673 K. The interfacial bonding between As and Co or Fe atom is suggested to be responsible for the additional uniaxial anisotropy.

  17. Effect of the low magnetic field on the electrodeposition of Co{sub x}Ni{sub 100−x} alloys

    SciTech Connect

    Olvera, S.; Arce Estrada, E.M.; Sanchez-Marcos, J.; Palomares, F.J.; Vazquez, L.; Herrasti, P.

    2015-07-15

    Magnetic, chemical and structural properties of electrosynthesized Co{sub x}Ni{sub 100−x} have been studied. The electrodeposition has been conducted both in the presence and absence of a low magnetic field. The application of a perpendicular magnetic field during the synthesis modified slightly the morphology of the alloys. These changes depend more on the film composition than on the applied field, as demonstrated by AFM images. In the absence of magnetic field, the Co{sub x}Ni{sub 100−x} film grows along the (200) direction. However, when the magnetic field was applied, a preferential orientation along the (111) direction was observed. No important magnetic changes are induced by the presence of the magnetic field during the growth. Based on X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) experiments, the chemical composition of the films was preserved during preparation regardless of whether or not magnetic field is applied. There has been observed an increase in deposition rate in the presence of field even at these low magnetic fields. - Highlights: • CoNi alloys were electrosynthesized in the absence and presence of a low magnetic field. • Application of a magnetic field produced an orientation in the (111) plane of the alloy. • An external field changes the voltammetric curves reducing the energy required for the alloy formation. • The composition and magnetic properties were constant in the absence and presence of magnetic field.

  18. The huge influence of nanograins on the magnetic properties of iron-based Fe Cu Nb B nanocrystalline alloys

    NASA Astrophysics Data System (ADS)

    Bremers, H.; Hupe, O.; Hofmeister, C. E.; Michele, O.; Hesse, J.

    2005-06-01

    In 1995 Skorvanek and O'Handley presented the first experimental evidence for a huge influence of nanograins on the magnetization of a nanostructured alloy. In this contribution experiments are described, performed on as-cast amorphous and nanostructured Fe79Cu1Nb7B13 alloys. In order to get nanostructured samples with different nanograin contents the samples were annealed at different properly chosen temperatures in vacuum. This led to the formation of nanograins embedded in a residual amorphous matrix. These nanograins consist of pure bcc Fe of about 5-6 nm in diameter. Their content can be enhanced without markedly changing their size when annealing at slightly higher temperatures. So an alloy series with the same nominal composition but different nanograin contents and residual amorphous matrices, i.e. a series of nanostructured alloys, was obtained. Our aim was to study the influence of increasing nanograin concentration on the magnetic properties of the coupled system amorphous matrix plus nanograins. We describe magnetization measurements over a wide temperature range, below and above the Curie temperature of the initial amorphous matrix. In a next step these measurements are evaluated in a molecular field approach assuming two different coupled ferromagnetic systems assigned to the amorphous matrix and the nanograins.

  19. Study of the magnetic properties, structure, and phase transformation in the alloys of the Co-Al-W system

    SciTech Connect

    Davidov, D. I. Stepanova, N. N. Kazantseva, N. V. Rigmant, M. B. Shishkin, D. A.

    2015-10-27

    An experimental study of phase transformations in the system of Co-Al-W in the concentration area of the intermetallic compound Co{sub 3}(Al, W) is presented. The structure and phase composition of the Co–9 at % Al–X at % W (X = 4.5, 6.8, 8.5, 10, 12.5) alloys in depending on the tungsten content are analyzed. The Curie temperature and magnetic properties of the alloys with the different phase composition are determined.

  20. Screening on binary Zr-1X (X = Ti, Nb, Mo, Cu, Au, Pd, Ag, Ru, Hf and Bi) alloys with good in vitro cytocompatibility and magnetic resonance imaging compatibility.

    PubMed

    Zhou, F Y; Qiu, K J; Li, H F; Huang, T; Wang, B L; Li, L; Zheng, Y F

    2013-12-01

    In this study, the microstructures, mechanical properties, corrosion behaviors, in vitro cytocompatibility and magnetic susceptibility of Zr-1X alloys with various alloying elements, including Ti, Nb, Mo, Cu, Au, Pd, Ag, Ru, Hf and Bi, were systematically investigated to explore their potential use in biomedical applications. The experimental results indicated that annealed Zr-1X alloys consisted entirely or primarily of α phase. The alloying elements significantly increased the strength and hardness of pure Zr and had a relatively slight influence on elastic modulus. Ru was the most effective enhancing element and Zr-1Ru alloy had the largest elongation. The results of electrochemical corrosion indicated that adding various elements to Zr improved its corrosion resistance, as indicated by the reduced corrosion current density. The extracts of the studied Zr-1X alloys produced no significant deleterious effects on osteoblast-like cells (MG 63), indicating good in vitro cytocompatibility. All except for Zr-1Ag alloy showed decreased magnetic susceptibility compared to pure Zr, and Zr-1Ru alloy had the lowest magnetic susceptibility value, being comparable to that of α' phase Zr-Mo alloy and Zr-Nb alloy and far lower than that of Co-Cr alloy and Ti-6Al-4V alloy. Among the experimental Zr-1X alloys, Zr-1Ru alloy possessing high strength coupled with good ductility, good in vitro cytocompatibility and low magnetic susceptibility may be a good candidate alloy for medical devices within a magnetic resonance imaging environment. PMID:23928334

  1. Ferrimagnetic Tb-Fe Alloy Thin Films: Composition and Thickness Dependence of Magnetic Properties and All-Optical Switching

    NASA Astrophysics Data System (ADS)

    Hebler, Birgit; Hassdenteufel, Alexander; Reinhardt, Patrick; Karl, Helmut; Albrecht, Manfred

    2016-02-01

    Ferrimagnetic rare earth - transition metal Tb-Fe alloy thin films exhibit a variety of different magnetic properties, which depends strongly on composition and temperature. In this study, first the influence of the film thickness (5 - 85 nm) on the sample magnetic properties was investigated in a wide composition range between 15 at.% and 38 at.% of Tb. From our results, we find that the compensation point, remanent magnetization, and magnetic anisotropy of the Tb-Fe films depend not only on the composition but also on the thickness of the magnetic film up to a critical thickness of about 20-30 nm. Beyond this critical thickness, only slight changes in magnetic properties are observed. This behavior can be attributed to a growth-induced modification of the microstructure of the amorphous films, which affects the short range order. As a result, a more collinear alignment of the distributed magnetic moments of Tb along the out-of-plane direction with film thickness is obtained. This increasing contribution of the Tb sublattice magnetization to the total sample magnetization is equivalent to a sample becoming richer in Tb and can be referred to as an “effective” composition. Furthermore, the possibility of all-optical switching, where the magnetization orientation of Tb-Fe can be reversed solely by circularly polarized laser pulses, was analyzed for a broad range of compositions and film thicknesses and correlated to the underlying magnetic properties.

  2. Enhanced magnetic and mechanical properties of die-upset Nd-Fe-B magnets prepared by spark plasma sintering via alloy powder blends

    NASA Astrophysics Data System (ADS)

    Hu, Z. H.; Dong, H.; Ma, D. W.; Luo, C.

    2016-03-01

    Magnetic and mechanical properties of die-upset Nd-Fe-B magnets prepared by spark plasma sintering via alloy powder blends have been investigated. The results showed that the MQP-C powder addition could improve the remanence and maximum energy product of die-upset Nd-Fe-B magnets. The maximum fracture toughness of die-upset Nd-Fe-B magnets was obtained at the MQP-C powder content ratio of 0.4, which indicates the proper MQP-C powder addition contributed to improve the mechanical properties of die-upset Nd-Fe-B magnets. Meanwhile, the MQP-C powder addition could improve the microstructure and crystallographic alignment of die-upset Nd-Fe-B magnets, and we presumed that the intrinsic coercivity of die-upset Nd-Fe-B magnets was mainly determined by the anisotropy field of Nd-Fe-B magnets, and the influence of microstructure defects on the mechanical properties was more sensitive than the magnetic properties of die-upset Nd-Fe-B magnets.

  3. Design, modelling and control of a micro-positioning actuator based on magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Minorowicz, Bartosz; Leonetti, Giuseppe; Stefanski, Frederik; Binetti, Giulio; Naso, David

    2016-07-01

    This paper presents an actuator based on magnetic shape memory alloys (MSMAs) suitable for precise positioning in a wide range (up to 1 mm). The actuator is based on the spring returned operating mode and uses a Smalley wave spring to maintain the same operating parameters of a classical coil spring, while being characterized by a smaller dimension. The MSMA element inside the actuator provides a deformation when excited by an external magnetic field, but its behavior is characterized by an asymmetric and saturated hysteresis. Thus, two models are exploited in this work to represent such a non-linear behavior, i.e., the modified and generalized Prandtl–Ishlinskii models. These models are particularly suitable for control purposes due to the existence of their analytical inversion that can be easily exploited in real time control systems. To this aim, this paper investigates three closed-loop control strategies, namely a classical PID regulator, a PID regulator with direct hysteresis compensation, and a combined PID and feedforward compensation strategy. The effectiveness of both modelling and control strategies applied to the designed MSMA-based actuator is illustrated by means of experimental results.

  4. Perpendicular magnetic anisotropy in Fe2Cr1 - xCoxSi Heusler alloy

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Pu; Qiu, Jin-Jun; Lu, Hui; Ji, Rong; Han, Gu-Chang; Teo, Kie-Leong

    2014-12-01

    Perpendicular magnetic anisotropy (PMA) was achieved in annealed Fe2Cr1 - xCoxSi (FCCS) Heusler alloys with different Co compositions x. The Co composition is varied to tune the Fermi level in order to achieve both higher spin polarization and better thermal stability. The PMA is thermally stable up to 400 oC for FCCS with x = 0, 0.3, 0.5 and 350 oC for FCCS with x = 0.7, 0.9, 1. The thickness of FCCS films with PMA ranges from 0.6 to 1.2 nm. The annealing temperature and FCCS thickness are found to greatly affect the PMA. The magnetic anisotropy energy density KU is 2.8  ×  106 erg cm-3 for 0.8 nm Fe2CrSi, and decreases as the Co composition x increases, suggesting that the PMA induced at the FCCS/MgO interface is dominated by the contribution of Fe atoms. There is a trade-off between high spin polarization and strong PMA by adjusting the Co composition.

  5. Creep Void Detection for Low Alloy Steel Using AC Magnetic Method

    SciTech Connect

    Shiwa, M.; Cheng, W.; Kume, R.

    2004-02-26

    Nondestructive detection of creep void was developed for low alloy steel by using AC magnetic method. Two types of 2.25Cr-1Mo steel specimens, base metal (BM) and simulated heat affected zone (HAZ) under aging and creep damage, were prepared for the tests. A differential type probe was used to detect AC magnetic signals. The exciting and detecting coils were coaxially arranged with a ferrite core. Signals were recorded using a 2-channel waveform recorder. The equivalent hysteresis loss (HL) was analyzed. It was observed that the HL of BM and HAZ changed in opposite direction, that is, HL of BM increased and HL of HAZ decreased with aging time. On the other hand, the HLs of both BM and HAZ decreased with creep time. The HL of creep samples was affected by both aging and stress-induced damage. In order to evaluate creep damage, stress-induced damage (SID) parameter was proposed to remove aging factor of materials from HL. Creep void were observed by scanning electron microscope (SEM) for all creep damage samples of SID value under 0.8.

  6. Macrosegregation of GeSi Alloys Grown in a Static Magnetic Field

    NASA Technical Reports Server (NTRS)

    Ritter, T. M.; Volz, M. P.; Cobb, S. D.; Szofran, F. R.

    1999-01-01

    Axial and radial macrosegregation profiles have been determined for GeSi alloy crystals grown by the vertical Bridgman technique. An axial 5 Tesla magnetic field was applied to several samples during growth to decrease the melt velocities by means of the Lorentz force. Compositions were measured with either energy dispersive X-ray spectroscopy (EDS) on a scanning electron microscope (SEM) or by wavelength dispersive X-ray spectroscopy (WDS) on a microprobe. The crystals were processed in graphite, hot-pressed boron nitride (BN), and pyrolytic boron nitride (PBN) ampoules, which produced various solid-liquid interface shapes during solidification. Those samples grown in a graphite ampoule exhibited radial profiles consistent with a highly concave interface and axial profiles indicative of complete mixing in the melt. The samples grown in BN and PBN ampoules had less radial variation. Axial macrosegregation profiles of these samples fell between the predictions for a completely mixed melt and one where solute transport is dominated by diffusion. Possible explanations for the apparent insufficiency of the magnetic field to achieve diffusion controlled growth conditions are discussed.

  7. Thermodynamics-based models for the magneto-mechanical response of magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    LaMaster, Douglas H.

    Magnetic shape memory alloys (MSMAs) are a relatively new class of smart material that exhibit large recoverable strain (up to 10%) [1] and fast response time (higher than 1 kilohertz) [2]. MSMAs are comprised of martensitic variants arranged as tetragonal unit cells with one short side, denoted by c, and two longer sides, denoted by a. With single crystal MSMAs, these variants align with one of the three Cartesian directions, and the volume fraction of variants with short side aligned in the i-direction is given by ξi. The boundary between two variants, called the twin boundary, moves as one variant volume fraction grows at the expense of the other. Under an applied compressive stress in the i-direction, variants will reorient into the ξi configuration to align the short side of the unit cell with the compressive stress. Each variant has an internal magnetization vector of length Msat that is approximately [3] aligned with the short length of the unit cell in the absence of an external applied magnetic field. This internal magnetization vector tends to align with an externally applied field to minimize the energy in the MSMA. The magnetization vector may align with the external field by: 1) changing internal magnetic domains, 2) rotating magneti- zation vectors away from the easy axis, or 3) variant reorientation . The fraction of the magnetic domains in the ξi variant with easy-axis in the i-direction is denoted by αi, and the domain fraction of the ξi variants with easy axis in the direction opposite to the i-direction is given by (1 - αi). Under an applied field in the i-direction, the αi domain will grow at the expense of the (1 - αi) domain, and vice versa for an applied field in the -i-direction. When the volume fraction αi reaches either 1 or 0, this domain wall motion ceases and the domains are said to be saturated. After domains in ξi have saturated, increasing the magnetic field further may rotate the magnetization vectors in other variants

  8. Excitonic diamagnetic shifts and linewidths in Al_xGa_1-xAs alloys in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Senger, R. T.; Coli, G.; Bajaj, K. K.; Reno, J. L.; Jones, E. D.; Crooker, Scott

    2002-03-01

    We have measured both the diamagnetic shifts and the linewidths of excitonic transitions in Alx Ga_1-xAs alloys as a function of aluminum concentration and magnetic field at 1.4 K using photoluminescence spectroscopy. The aluminum composition in our samples ranged from 0 to 300 to 50 tesla. The samples were grown on GaAs substrates oriented along [001] direction using molecular beam epitaxy at 590ºC. We find that for a given value of alloy composition, both the diamagnetic shift and excitonic linewidth increase as a function of magnetic field. The observed variations of the diamagnetic shifts and excitonic linewidths with magnetic field are considerably smaller than those calculated by Lee and Bajaj [J. Appl. Phys. 73, 1788 (1993)] using a free exciton model. To explain our experimental data we propose that the excitons are localized in a very specific manner. To simulate exciton localization, we assume that the exciton reduced mass is increased and is obtained by using the alloy dependent heavy-hole mass along [001] direction treated isotropically. The calculated values of the variations of the diamagnetic shift and excitonic linewidth as a function of magnetic field obtained using this model agree very well with those reported here. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.

  9. Pulsed high-magnetic-field experiments: New insights into the magnetocaloric effect in Ni-Mn-In Heusler alloys

    SciTech Connect

    Salazar Mejía, C. Nayak, A. K.; Felser, C.; Nicklas, M.; Ghorbani Zavareh, M.; Wosnitza, J.; Skourski, Y.

    2015-05-07

    The present pulsed high-magnetic-field study on Ni{sub 50}Mn{sub 35}In{sub 15} gives an extra insight into the thermodynamics of the martensitic transformation in Heusler shape-memory alloys. The transformation-entropy change, ΔS, was estimated from field-dependent magnetization experiments in pulsed high magnetic fields and by heat-capacity measurements in static fields. We found a decrease of ΔS with decreasing temperature. This behavior can be understood by considering the different signs of the lattice and magnetic contributions to the total entropy. Our results further imply that the magnetocaloric effect will decrease with decreasing temperature and, furthermore, the martensitic transition is not induced anymore by changing the temperature in high magnetic fields.

  10. Effect of the nanocrystallization of amorphous soft magnetic Fe-P-Nb alloys on corrosion resistance in a damp SO2-polluted atmosphere

    NASA Astrophysics Data System (ADS)

    Vavilova, V. V.; Zabolotnyi, V. T.; Korneev, V. P.; Anosova, M. O.; Baldokhin, Yu. V.

    2014-09-01

    The effect of the nanocrystallization of amorphous soft magnetic Fe-P-Nb alloys on their electrochemical behavior in a damp SO2-polluted industrial atmosphere is studied. It is shown that their electro-chemical characteristics shit toward positive values when the phosphorus content in the Fe-P-Nb alloys increases and when they undergo nanocrystallization from an amorphous state.

  11. The First Principles Calculation of Structural, Electronic and Magnetic Properties of MnXY (x = Ru, rh and Y = Ga, Ge, Sb) Alloys

    NASA Astrophysics Data System (ADS)

    Moniri, S. M.; Nourbakhsh, Z.; Mostajabodaavati, M.

    The structural, electronic and magnetic properties of MnXY (X = Ru, Rh and Y = Ga, Ge, Sb) Heusler alloys are studied using density functional theory by the WIEN2k package. These materials are ferromagnetic. Also they have some interesting half-metallic properties. The electron density of states, total and local magnetic moment of these alloys are calculated. We have calculated the effective Coulomb interaction Ueff using the ab initio method. We have compared the magnetic moments of these alloys in GGA and LDA+U with the Slater-Pauling rule. Furthermore the effect of hydrostatic pressure on the magnetic moment of these alloys is studied. The calculated results are fitted with a second order polynomial.

  12. Electronic structure, stability and magnetic properties of small M1-2Cr (M = Fe, Co, and Ni) alloy encapsulated inside a (BN)48 cage

    NASA Astrophysics Data System (ADS)

    Liang, Wenjuan; Jia, Jianfeng; Lv, Jin; Wu, Haishun

    2015-09-01

    The geometrical structure and magnetic properties of M1-2Cr (M = Fe, Co, and Ni) alloy clusters inside a (BN)48 cage were calculated at the BPW91/LANL2DZ level of theory. The doping with Cr significantly changed the magnetic properties of the transition-metal clusters. When M1-2Cr alloys were placed inside a (BN)48 cage, the alloy clusters interacted strongly with the cage, and the M1-2Cr@(BN)48 clusters showed high stability. Moreover, Cr-doped magnetic metal clusters preferably occupied positions off-center and near the hexagonal rings of (BN)48 cages. Thus, the (BN)48 cages can be used to increase the stability of M1-2Cr alloys, and retain their magnetic nature, except for CoCr and Ni2Cr clusters.

  13. Magnetic properties of Ni40+xMn39-xSn21 (x=0, 2, 4, 6 and 8 at.%) Heusler alloys

    SciTech Connect

    Lazpita, P.; Lograsso, T.; Schlagel, D. L.

    2014-01-27

    The low electron concentration region (e/a < 7.75) of the magnetic phase diagram of the off-stoichiometric Ni–Mn–Sn Heusler alloys was investigated in detail by DSC and magnetization measurements of the Ni40+xMn39−xSn21(x = 0, 2, 4, 6 and 8 at.%) alloys. The alloys show a stable austenitic phase without any martensitic transformation down to 5 K even after heat treatment. The Curie temperature exhibits a broad maximum over a large composition range. The evolution of the magnetic moment with the electron concentration fits the data of previous studies and confirms the peak-like dependence in the extended range of e/a values predicted by ab initio calculations. The explored part of the moment versus e/a curve can be explained in terms of a localized magnetic moment model and full atomic order in the alloys.

  14. Structural and magnetic peculiarities of Al86Ni8Sm6 alloy in amorphous, crystalline, and liquid states

    NASA Astrophysics Data System (ADS)

    Uporov, S. A.; Ryl'tsev, R. E.; Uporova, N. S.; Bykov, V. A.; Murzakaev, A. M.; Pryanichnikov, S. V.

    2015-02-01

    Magnetic, structural, and thermal characteristics of the Al86Ni8Sm6 alloy in amorphous, crystalline, and liquid states have been studied over a wide temperature range of 4-1900 K. It has been found that the amorphous alloy has a pronounced cluster structure with an average cluster size of 2-3 nm. The crystallization process occurs in four stages and no apparent thermal effect at the glass-transition temperature is observed. The amorphous ribbon has no magnetic order up to 4 K but demonstrates superparamagneic behavior. An analysis of isothermal magnetization curves indicates a possible correlation between structural and magnetically ordered clusters. Anomalous changes in the magnetic susceptibility in the liquid state have been found at temperatures substantially higher than the liquidus temperature; the anomalies indicate structural changes in the melt. The magnetic susceptibility in the amorphous, crystalline, and liquid states was found to be characterized by a high Van Vleck paramagnetic contribution and can be described adequately in terms of the classic Van Vleck theory with allowance for mixed valence effects. The obtained results are interpreted using a concept on the existence of a specific covalent-metallic interaction between aluminum and rare-earth metal atoms.

  15. Liquid phase electroepitaxial bulk growth of binary and ternary alloy semiconductors under external magnetic field

    NASA Astrophysics Data System (ADS)

    Sheibani, Hamdi

    2002-01-01

    Liquid Phase Electroepitaxy (LPEE) and is a relatively new, promising technique for producing high quality, thick compound semiconductors and their alloys. The main objectives are to reduce the adverse effect of natural convection and to determine the optimum growth conditions for reproducible desired crystals for the optoelectronic and electronic device industry. Among the available techniques for suppressing the adverse effect of natural convection, the application of an external magnetic field seems the most feasible one. The research work in this dissertation consists of two parts. The first part is focused on the design and development of a state of the art LPEE facility with a novel crucible design, that can produce bulk crystals of quality higher than those achieved by the existing LPEE system. A growth procedure was developed to take advantage of this novel crucible design. The research of the growth of InGaAs single crystals presented in this thesis will be a basis for the future LPEE growth of other important material and is an ideal vehicle for the development of a ternary crystal growth process. The second part of the research program is the experimental study of the LPEE growth process of high quality bulk single crystals of binary/ternary semiconductors under applied magnetic field. The compositional uniformity of grown crystals was measured by Electron Probe Micro-analysis (EPMA) and X-ray microanalysis. The state-of-the-art LPEE system developed at University of Victoria, because of its novel design features, has achieved a growth rate of about 4.5 mm/day (with the application of an external fixed magnetic field of 4.5 KGauss and 3 A/cm2 electric current density), and a growth rate of about 11 mm/day (with 4.5 KGauss magnetic field and 7 A/cm2 electric current density). This achievement is simply a breakthrough in LPEE, making this growth technique absolutely a bulk growth technique and putting it in competition with other bulk growth techniques

  16. Theoretical study of magnetic properties and x-ray magnetic circular dichroism of the ordered Fe{sub 0.5}Pd{sub 0.5} alloy

    SciTech Connect

    Galanakis, I.; Ostanin, S.; Alouani, M.; Dreysse, H.; Wills, J. M.

    2000-01-01

    A detailed theoretical study of magnetic and structural properties of Fe{sub 0.5}Pd{sub 0.5} ordered face-centered tetragonal (fct) alloy, using both the local spin density approximation (LSDA) and the generalized gradient approximation (GGA), is presented. The total energy surface as a function of the lattice parameters a and c shows a long valley where stable structures may exist. Our calculation using the GGA predicts a magnetic phase transition from perpendicular to parallel magnetization as a function of the lattice parameter, whereas LSDA favors always the [001] magnetization axis for all values of the lattice parameters. The spin and orbital magnetic moments and x-ray magnetic circular dichroism spectra are calculated for the easy [001] and the hard [100] magnetization axis and for three sets of experimental lattice parameters, and are compared to the available experimental results on these films. A supercell calculation for a 4 monolayer Fe{sub 0.5}Pd{sub 0.5} thin film produced similar results. While the spin magnetic moments are in fair agreement with experiment, the orbital magnetic moments are considerably underestimated. To improve the agreement with experiment we included an atomic orbital polarization term; however, the computed orbital moments scarcely changed. (c) 2000 The American Physical Society.

  17. Nuclear Magnetic Resonance Study of Hydrogen in Niobium-Vanadium Alloys.

    NASA Astrophysics Data System (ADS)

    Lichty, Lyle Raymond

    Proton spin relaxation rates have been measured across the random alloy system Nb_{ rm y}V_{rm 1 - y}H_{rm x} at temperatures from 10 to 800 K and various frequencies from 4.45 to 127.5 MHz. Enhanced spin-lattice relaxation rates found below 100 K in all samples with Nb, including NbH_{0.2}, at frequencies of 40 MHz and below have been explained by a process of dipolar cross relaxation between proton Zeeman energy levels and the combined Zeeman-quadrupole levels of ^ {93}Nb. A semi-quantitative model, applicable in metal-hydrogen as well as other multi-spin systems, has been developed to describe the cross relaxation mechanism. Unusual features found experimentally and interpreted via this model include: (1) cross relaxation in unrotated polycrystalline samples, (2) cross relaxation to spins with pure quadrupole frequencies substantially less than the proton Larmor frequency, and (3) both temperature-dependent and temperature-independent contributions which can vary with frequency. Effects of Zeeman-quadrupole splittings on motional relaxation rates at higher temperatures were also estimated. Phase boundaries between solid solutions and ordered hydrides were found by analyzing non-experimental magnetization recovery curves. The temperature at which hydrides precipitated was lower in all the alloys as compared to pure Nb-H and V-H. Alloys with Nb concentrations of 50 at.% and above could retain substantial amounts of H in solid solution without hydride precipitation, at least down to 10 K. Motional relaxation rates of H in solid solution could in most cases be modeled by hopping rates governed by asymmetric Gaussian distributions of activation energies. The mean activation energies varied from 160 to 280 meV, depending on both V and H composition. A different analysis combined the present NMR results with internal friction data to derive activation energies somewhat smaller than those above, but in closer agreement with previous determinations. The dependence of the

  18. An increase of structural order parameter in Fe{endash}Co{endash}V soft magnetic alloy after thermal aging

    SciTech Connect

    Zhu, Q.; Li, L.; Masteller, M.S.; Del Corso, G.J.

    1996-12-01

    Alloys of Fe{sub 49}Co{sub 49}V{sub 2} (Hiperco Alloy 50) (Hiperco is a registered trademark of CRS Holdings, Inc.), both annealed and thermally aged, were studied using anomalous synchrotron x-ray and neutron powder diffraction. Rietveld and diffraction profile analysis indicated both an {ital increase} in the structural order parameter and a small lattice {ital expansion} ({approximately}0.0004 A) after aging at 450{degree}C for 200 h. In addition, a cubic minority phase ({lt}0.3{percent}) was identified in the {open_quote}{open_quote}annealed{close_quote}{close_quote} sample, which increased noticeably (0.3{percent}{r_arrow}0.8{percent}) as a result of aging. The presence of antiphase domain boundaries in the alloys was also revealed. These results directly correlate with the observed changes in the magnetization behavior and challenge the notion that a {open_quote}{open_quote}fully{close_quote}{close_quote} ordered Fe{endash}Co alloy demonstrates optimum soft magnetic properties. {copyright} {ital 1996 American Institute of Physics.}

  19. Characterization of Alloys with Potential for Application in Cable-in-Conduit Conductors for High-Field Superconducting Magnets

    NASA Astrophysics Data System (ADS)

    Walsh, R. P.; Miller, J. R.; Toplosky, V. J.

    2004-06-01

    Since the introduction of the cable-in-conduit conductor (CICC) concept, a variety of alloys have been proposed for fabricating the jacket. The jacket provides primary containment of the supercritical helium coolant and is typically also the primary structural component for the magnet. These functions create requirements for strength, toughness, weldability, and fabricability in tubular form. When the CICC uses Nb3Sn, there are additional requirements to accommodate the manufacturing and heat-treatment processes for the superconductor as well as its strain-sensitive performance during operation. Both of the present favorite jacket alloys, Incoloy 908 and modified (ultra-low carbon) 316LN, have both demonstrated acceptable functionality as well as a few undesirable features. In this paper, we present data from cryogenic mechanical tests on a group of heat-resistant, high-strength superalloys that appear to offer equal or better mechanical performance (e.g. strength, toughness, and modulus) while mitigating the undesirable aspects (e.g. SAGBO in the case of I908 and thermal-expansion mismatch with Nb3Sn in the case of 316LN). Data are presented for each alloy in the as-received and aged conditions. These alloys are presently being considered as candidates for use in the next-generation hybrid magnet for the NHMFL but may also be of interest to the fusion and energy storage communities.

  20. Characterization of Alloys with Potential for Application in Cable-in-Conduit Conductors for High-Field Superconducting Magnets

    SciTech Connect

    Walsh, R.P.; Miller, J.R.; Toplosky, V.J.

    2004-06-28

    Since the introduction of the cable-in-conduit conductor (CICC) concept, a variety of alloys have been proposed for fabricating the jacket. The jacket provides primary containment of the supercritical helium coolant and is typically also the primary structural component for the magnet. These functions create requirements for strength, toughness, weldability, and fabricability in tubular form. When the CICC uses Nb3Sn, there are additional requirements to accommodate the manufacturing and heat-treatment processes for the superconductor as well as its strain-sensitive performance during operation. Both of the present favorite jacket alloys, Incoloy 908 and modified (ultra-low carbon) 316LN, have both demonstrated acceptable functionality as well as a few undesirable features. In this paper, we present data from cryogenic mechanical tests on a group of heat-resistant, high-strength superalloys that appear to offer equal or better mechanical performance (e.g. strength, toughness, and modulus) while mitigating the undesirable aspects (e.g. SAGBO in the case of I908 and thermal-expansion mismatch with Nb3Sn in the case of 316LN). Data are presented for each alloy in the as-received and aged conditions. These alloys are presently being considered as candidates for use in the next-generation hybrid magnet for the NHMFL but may also be of interest to the fusion and energy storage communities.

  1. Annealing effects on the structural and magnetic properties of off-stoichiometric Fe-Mn-Ga ferromagnetic shape memory alloys

    DOE PAGESBeta

    Chen, Yan; Bei, Hongbin; Dela Cruz, Clarina R; Wang, Yandong; An, Ke

    2016-05-07

    Annealing plays an important role in modifying structures and properties of ferromagnetic shape memory alloys (FSMAs). The annealing effect on the structures and magnetic properties of off-stoichiometric Fe45Mn26Ga29 FSMA has been investigated at different elevated temperatures. Rietveld refinements of neutron diffraction patterns display that the formation of the γ phase in Fe45Mn26Ga29 annealed at 1073 K increases the martensitic transformation temperature and reduces the thermal hysteresis in comparison to the homogenized sample. The phase segregation of a Fe-rich cubic phase and a Ga-rich cubic phase occurs at the annealing temperature of 773 K. The atomic occupancies of the alloys aremore » determined thanks to the neutron's capability of differentiating transition metals. The annealing effects at different temperatures introduce a different magnetic characteristic that is associated with distinctive structural changes in the crystal.« less

  2. Application of the Preisach and Jiles-Atherton models to the simulation of hysteresis in soft magnetic alloys

    NASA Astrophysics Data System (ADS)

    Pasquale, M.; Bertotti, G.; Jiles, D. C.; Bi, Y.

    1999-04-01

    This article describes the advances in unification of model descriptions of hysteresis in magnetic materials and demonstrates the equivalence of two widely accepted models, the Preisach (PM) and Jiles-Atherton (JA) models. Recently it was shown that starting from general energy relations, the JA equation for a loop branch can be derived from PM. The unified approach is here applied to the interpretation of magnetization measured in nonoriented Si-Fe steels with variable grain size , and also in as-cast and annealed Fe amorphous alloys. In the case of NO Fe-Si, the modeling parameter k defined by the volume density of pinning centers is such that k≈A+B/, where the parameters A and B are related to magnetocrystalline anisotropy and grain texture. The value of k in the amorphous alloys can be used to estimate the microstructural correlation length playing the role of effective grain size in these materials.

  3. Time of isothermal holding in the course of in-air heat treatment of soft magnetic Fe-based amorphous alloys and their magnetic properties

    NASA Astrophysics Data System (ADS)

    Skulkina, N. A.; Ivanov, O. A.; Pavlova, I. O.; Minina, O. A.

    2011-12-01

    On the example of soft magnetic Fe81B13Si4C2 and Fe77Ni1Si9B13 amorphous alloys, the relation between the level of magnetic properties and duration of isothermal holding in the course of heat treatment in air has been studied. The optimum temperature-dependent time τ of isothermal holding has been shown to be related to the volume fraction of domains ( V orth) with orthogonal magnetization in the initial (quenched) ribbon by equation V orth = ττ1/3. A temperature dependence of the proportionality coefficient α, which determines the degree of diffusion-process activity, has been determined. The results obtained allow us to substantially simplify the choice of optimum conditions of atmospheric heat treatment of soft magnetic Fe-based amorphous ribbons.

  4. Temperature and field-induced magnetization flips in amorphous Er{endash}Fe alloys evidenced by x-ray magnetic circular dichroism

    SciTech Connect

    Garcia, L.M.; Pizzini, S.; Rueff, J.P.; Vogel, J.; Galera, R.M.; Fontaine, A.; Kappler, J.P.; Krill, G.; Goedkoop, J.

    1996-04-01

    Magnetic properties of amorphous Er{sub 1{minus}{ital x}}Fe{sub {ital x}} alloys with {ital x}{approx_equal}0.7 have been studied. Macroscopic characterization has been performed by measuring temperature- and field-dependent magnetization. Applying a magnetic field the compensation temperature first decreases, but increases again at larger fields. This {open_quote}{open_quote}exotic{close_quote}{close_quote} behavior has been interpreted in terms of the sperimagnetic character of both subnetworks. The suggested scheme has been checked by measuring x-ray circular magnetic dichroism at the Er {ital M}{sub 5}-edge. Using this atom-sensitive technique we have been able to detect temperature-induced as well as field-induced flips of the Er-subnetwork with respect to the direction of the applied field. {copyright} {ital 1996 American Institute of Physics.}

  5. Achievement of high coercivity in sintered R-Fe-B magnets based on misch-metal by dual alloy method

    SciTech Connect

    Niu, E Wang, Zhen-Xi; Chen, Zhi-An; Rao, Xiao-Lei; Hu, Bo-Ping; Chen, Guo-An; Zhao, Yu-Gang; Zhang, Jin

    2014-03-21

    The R-Fe-B (R, rare earth) sintered magnets prepared with different ratio of alloys of MM-Fe-B (MM, misch-metal) and Nd-Fe-B by dual alloy method were investigated. As expected, the high ratio of MM-Fe-B alloy degrades the hard magnetic properties heavily with intrinsic coercivity lower than 5 kOe. When the atomic ratio MM/R ≤ 21.5% the magnetic properties can reach a practical level of B{sub r} ≥ 12.1 kGs, H{sub cj} ≥ 10.7 kOe, and (BH){sub max} ≥ 34.0 MGOe. And the effect of H{sub cj} enhancement by the grain boundary diffusion process is obvious when MM/R ≤ 21.5%. It is revealed that the decrement of intrinsic magnetic properties of R{sub 2}Fe{sub 14}B matrix phase is not the main reason of the degradation of the magnets with high MM ratio. The change of deteriorated microstructure together with phase component plays fundamental roles in low H{sub cj}. In high MM ratio magnets, (a) after annealing, Ce atoms inside main phase are inclined to be segregated in the outer layer of the main phase grains; (b) there is no thin layer of Ce-rich phase as an analogue of Nd-rich phase to separate main phase grains; (c) excessive Ce tends to form CeFe{sub 2} grains.

  6. Magnetic and mechanical properties of rapidly solidified FeSi 6.5 wt% alloys and their interpretation

    NASA Astrophysics Data System (ADS)

    Viala, B.; Degauque, J.; Baricco, M.; Ferrara, E.; Pasquale, M.; Fiorillo, F.

    1996-07-01

    The structural, mechanical and magnetic properties of FeSi 6.5 wt% rapidly solidified alloys have been investigated following recrystallization annealing and different rates of cooling through the B 2 + DO 3 ordering region (1 ≤ T ≤ 1500° C min -1). A transition from ductile to brittle behavior is observed for T < ˜ 1000°C min -1, chiefly due to B 2 ordering and the associated formation of superlattice dislocations, having reduced glide and cross-slip capability. The magnetic behavior appears, however, to be weakly dependent on T, with the energy losses minimized for average grain size around 100-150 μm.

  7. Nanopatterns induced by pulsed laser irradiation on the surface of an Fe-Al alloy and their magnetic properties

    SciTech Connect

    Yoshida, Yutaka; Oosawa, Kazuya; Watanabe, Seiichi; Kaiju, Hideo; Kondo, Kenji; Ishibashi, Akira; Yoshimi, Kyosuke

    2013-05-06

    We have studied nanopatterns induced by nanosecond pulsed laser irradiation on (111) plane surfaces of a polycrystalline iron-aluminum alloy and evaluated their magnetic properties. Multiple nanosecond pulsed laser irradiation induces a wavelength-dependent surface transformation of the lattice structure from a B2-type to a supersaturated body centered cubic lattice. The selective formation of surface nanopatterns consisting of holes, stripes, polygonal networks, and dot-like nanoprotrusions can be observed. Furthermore, focused magneto-optical Kerr effect measurements reveal that the magnetic properties of the resultant nanostructured region changes from a paramagnetic to a ferromagnetic phase in accordance with the number of laser pulses.

  8. All-thermal switching of amorphous Gd-Fe alloys: Analysis of structural properties and magnetization dynamics

    NASA Astrophysics Data System (ADS)

    Chimata, Raghuveer; Isaeva, Leyla; Kádas, Krisztina; Bergman, Anders; Sanyal, Biplab; Mentink, Johan H.; Katsnelson, Mikhail I.; Rasing, Theo; Kirilyuk, Andrei; Kimel, Alexey; Eriksson, Olle; Pereiro, Manuel

    2015-09-01

    In recent years there has been an intense interest in understanding the microscopic mechanism of thermally induced magnetization switching driven by a femtosecond laser pulse. Most of the effort has been dedicated to periodic crystalline structures while the amorphous counterparts have been less studied. By using a multiscale approach, i.e., first-principles density functional theory combined with atomistic spin dynamics, we report here on the very intricate structural and magnetic nature of amorphous Gd-Fe alloys for a wide range of Gd and Fe atomic concentrations at the nanoscale level. Both structural and dynamical properties of Gd-Fe alloys reported in this work are in good agreement with previous experiments. We calculated the dynamic behavior of homogeneous and inhomogeneous amorphous Gd-Fe alloys and their response under the influence of a femtosecond laser pulse. In the homogeneous sample, the Fe sublattice switches its magnetization before the Gd one. However, the temporal sequence of the switching of the two sublattices is reversed in the inhomogeneous sample. We propose a possible explanation based on a mechanism driven by a combination of the Dzyaloshinskii-Moriya interaction and exchange frustration, modeled by an antiferromagnetic second-neighbor exchange interaction between Gd atoms in the Gd-rich region. We also report on the influence of laser fluence and damping effects in the all-thermal switching.

  9. Study on magnetic properties of Ce17Fe78-xZrxB6 (x=0-2.0) alloys

    NASA Astrophysics Data System (ADS)

    Ni, B. J.; Xu, H.; Tan, X. H.; Hou, X. L.

    2016-03-01

    In order to improve the magnetic performances of Ce2Fe14B-type alloys, Ce17Fe78-xZrxB6 (x=0-2.0) were synthesized by a melt spinning method at a quench wheel velocity of 35 m/s. The crystal structure and hard magnetic properties of Ce17Fe78-xZrxB6 (x=0-2.0) alloys were investigated. The glass forming ability and thermal stability of as-spun ribbons were improved by Zr addition. Zr-doped samples had lower Curie temperature for Ce2Fe14B, implying that Zr atoms could substitute directly into Ce2Fe14B phase. Refinement of X-ray diffraction data showed that the lattice constants and volume fraction of Ce2Fe14B phase for Ce17Fe78-xZrxB6 (x=0-2.0) alloys annealed at optimum temperatures decreased gradually with increasing Zr content. Moreover, the mean grain size of the Ce2Fe14B phase decreased gradually with Zr at% increasing from 0 to 2.0. The analysis of Henkel plots verified that proper Zr content improved the microstructure and enhanced the exchange coupling interaction. When x=0.5, the optimum magnetic properties were obtained: iHc=429.9 kA/m, Br=0.48 T and (BH)max=4.5 MGOe.

  10. Crystalline structure and magnetic behavior of the Ni41Mn39In12Co8 alloy demonstrating giant magnetocaloric effect

    NASA Astrophysics Data System (ADS)

    Madiligama, A. S. B.; Ari-Gur, P.; Shavrov, V. G.; Koledov, V. V.; Calder, S.; Mashirov, A. V.; Kamantsev, A. P.; Dilmieva, E. T.; Gonzalez-Legarreta, L.; Grande, B. H.; Vega, V. V.; Kayani, A.

    2016-08-01

    Magnetic cooling is a green cooling technology, which is more energy efficient than existing fluid-compression cooling machines. Ni41Mn39In12Co8 alloy, which demonstrates promising magnetocaloric performances, was investigated using neutron diffraction and thermomagnetic measurements. The austenite structure is cubic L21 (Fm\\bar{3}m), while that of the martensite is a mix of 8 and 6 M modulated monoclinic structures (P\\quad 1\\quad 2/m\\quad 1). The austenitic site occupancy refinements reveal that all substituting Co atoms occupy Ni-sites. Most Mn atoms (65%) are in the Mn-sites and the rest go to In-sites (about 35%) and Ni-sites (less than 5%). This disorder of the magnetic atoms (Mn, Ni and Co) in the austenitic phase remains unchanged during the martensitic transition. The distortions of the interatomic distances due to the modulation of the martensitic structures further enhance the disorder in the magnetic interactions. Thermomagnetic measurements indicate that the austenitic phase is ferromagnetic. Cooling to below 250 K, where the alloy loses its ferromagnetic nature, and down to 50 K, the lack of any antiferromagnetic Bragg peaks suggests no antiferromagnetic ordering in the martensitic phase. At very low temperatures in the martensitic phase, spin glass magnetic nature is identified by magnetic measurements, and the spin-glass transition temperature is ∼19 K.

  11. Microstructural and magnetic properties of Nd-Fe-B alloys processed by equal-channel angular pressing

    NASA Astrophysics Data System (ADS)

    Onal, E.; Lapovok, R.; Kishimoto, H.; Kato, A.; Davies, C. H. J.; Suzuki, K.

    2015-05-01

    Equal-channel angular pressing (ECAP) is a well-established thermo-mechanical processing technique. This technique allows virtually unlimited strain and manipulation of texture by processing route, while the cross-section of the sample remains unchanged during processing. In order to clarify the effectiveness of ECAP on preparing anisotropic permanent magnets, the microstructure and magnetic properties of a melt-spun Nd13.5Fe73.8Co6.7B5.6Ga0.4 alloy processed at 773 K for 300 s by ECAP were investigated. Macrotexture analysis carried out for the exit channel of ECAP shows that the basal plane of the tetragonal Nd2Fe14B crystal aligns parallel to the shear band, i.e., the c-axis texture formation normal to the shear band induced by the ECAP process. Due to this texture formation, the technical magnetization behaviour becomes anisotropic, and the remanent magnetization is clearly enhanced along the direction perpendicular to the shear band. This anisotropic microstructure is realized at a relatively low processing temperature of 773 K, well below the melting point of the Nd-rich intergranular phase. As a consequence of this lower processing temperature, the nanostructure of the melt-spun alloy remains approximately 20 to 30 nm, considerably smaller than the typical grain size obtained after conventional die-upsetting. Our study demonstrates that equal-channel angular pressing has a potential for realising anisotropic nanostructured magnets.

  12. Magnetic and Magnetocaloric Properties in Non-Stoichiometric Gallium Deficient Ni2MnGa1-x Heusler Alloys

    NASA Astrophysics Data System (ADS)

    Madden, Alexander; Corrigan, Mollie; Barton, Linda

    Magnetic data show that off-stoichiometric gallium deficient Heusler alloys of the form Ni2MnGa1-x have structural martensite transition temperatures that increase strongly with x, while their ferromagnetic Curie temperatures remain nearly unchanged. The martensite transition approaches room temperature for x = 0 . 13 . Samples were prepared by rf induction heating. The influence of quenching and post annealing on magnetic properties, as well as structural grain sizes and magnetic domain structure, were investigated. Since the first order structural phase transition can be adjusted to any convenient temperature, these materials offer intriguing possibilities as magnetic refrigerants. Magnetocaloric properties were investigated by direct measurement of ΔT with the application of field ΔH .

  13. Magnetic properties of Ho{sub 1-x}Er{sub x}Al{sub 2} alloys

    SciTech Connect

    Khan, Mahmud; Paudyal, D.; Gschneidner, K. A. Jr.; Pecharsky, V. K.

    2013-05-07

    HoAl{sub 2} exhibits a first order spin reorientation transition at 20 K. Heat capacity measurements showed that when Ho is partially replaced by Er in Ho{sub 1-x}Er{sub x}Al{sub 2}, the spin reorientation transition is gradually suppressed, while slowly shifting to higher temperatures with increasing Er concentration. In this paper, we investigate the magnetic properties of pseudo binary Ho{sub 1-x}Er{sub x}Al{sub 2} alloys by ac and dc magnetization measurements. The magnetization data show that the magnetic interactions below T{sub C} are dramatically modified when Er is added in Ho{sub 1-x}Er{sub x}Al{sub 2}. For a better explanation of the experimental data, results of first principles calculations have been presented as well.

  14. Nanocrystalline Fe88-2xCoxNixZr7B4Cu1 alloys: Soft magnets for vehicle electrification technologies (invited)

    NASA Astrophysics Data System (ADS)

    Knipling, K. E.; Daniil, M.; Willard, M. A.

    2015-05-01

    We report on the effect of substituting Co and Ni for Fe on the crystallization behavior, crystal structure, and magnetic properties of Fe88-2xCoxNixZr7B4Cu1 (x = 0-22.00). The magnetization generally decreases and the coercivity increases with increasing x, whereas the Curie temperature of the amorphous phase increases significantly (from 73 °C at x = 0 to 570 °C at x = 22.00). There is thus an optimum composition near x = 5.50 exhibiting excellent soft magnetic properties at 300-500 °C. The higher magnetization and Curie temperature as compared with Fe-based alloys, and smaller Co content as compared with (Fe,Co)-based alloys, make this alloy attractive as an affordable high-temperature soft magnetic material.

  15. Use of Permanent Magnets in Electromagnetic Facilities for the Treatment of Aluminum Alloys

    NASA Astrophysics Data System (ADS)

    Beinerts, Toms; Bojarevičs, Andris; Bucenieks, Imants; Gelfgat, Yuri; Kaldre, Imants

    2016-06-01

    The possibility of applying the electromagnetic induction pump with permanent magnets for the transportation and stirring of aluminum melts in metallurgical furnaces is investigated. The electromagnetic and hydraulic characteristics of the pump have been investigated theoretically and experimentally with regard to its position in the furnace. The results of the experiments performed with a model in a eutectic InGaSn melt are in good agreement with the calculation data. Extrapolation of the experimental results on the physical characteristics of aluminum melts allows recommending such pumps for contactless control of motion and heat/mass transfer in aluminum melts in different technological processes. A high temperature and the aggressive properties of aluminum alloys make it complicated to use different mechanical devices to solve technological problems, such as liquid metal transportation, dosing, stirring, etc. In this case, any device units or elements moving in or contacting with the melt suffer from corrosion polluting the melt. Therefore, of more importance and topicality are contactless electromagnetic methods for processing of molten metals.

  16. Use of Permanent Magnets in Electromagnetic Facilities for the Treatment of Aluminum Alloys

    NASA Astrophysics Data System (ADS)

    Beinerts, Toms; Bojarevičs, Andris; Bucenieks, Imants; Gelfgat, Yuri; Kaldre, Imants

    2016-03-01

    The possibility of applying the electromagnetic induction pump with permanent magnets for the transportation and stirring of aluminum melts in metallurgical furnaces is investigated. The electromagnetic and hydraulic characteristics of the pump have been investigated theoretically and experimentally with regard to its position in the furnace. The results of the experiments performed with a model in a eutectic InGaSn melt are in good agreement with the calculation data. Extrapolation of the experimental results on the physical characteristics of aluminum melts allows recommending such pumps for contactless control of motion and heat/mass transfer in aluminum melts in different technological processes. A high temperature and the aggressive properties of aluminum alloys make it complicated to use different mechanical devices to solve technological problems, such as liquid metal transportation, dosing, stirring, etc. In this case, any device units or elements moving in or contacting with the melt suffer from corrosion polluting the melt. Therefore, of more importance and topicality are contactless electromagnetic methods for processing of molten metals.

  17. A metallurgical approach toward alloying in rare earth permanen magnet systems

    SciTech Connect

    Branagan, D. J.

    1995-02-23

    The approach was developed to allow microstructural enhancement and control during solidification and processing. Compound additions of Group IVA, VA, or VIA transition metals (TM) and carbon were added to Nd{sub 2}Fe{sub 14}B (2-14-1). Transition metal carbides formed in IVA (TiC, ZrC, HfC) and Group VA (VC, NbC, TaC) systems, but not in the VIA system. The alloying ability of each TM carbide was graded using phase stability, liquid and equilibrium solid solubility, and high temperature carbide stability. Ti with C additions was chosen as the best system. The practically zero equilibrium solid solubility means that the Ti and C additions will ultimately form TiC after heat treatment which allows the development of a composite microstructure consisting of the 2-14-1 phase and TiC. Thus, the excellent intrinsic magnetic properties of the 2-14-1 phase remain unaltered and the extrinsic properties relating to the microstructure are enhanced due to the TiC stabilized microstructure which is much more resistant to grain growth. When Ti + C are dissolved in the liquid melt or solid phases, such as the glass or 2-14-1 phase, the intrinsic properties are changed; favorable changes include increased glass forming ability, reduced optimum cooling rate, increased optimum energy product, and enhanced nucleation kinetics of crystallization.

  18. Hysteresis Modeling of Magnetic Shape Memory Alloy Actuator Based on Krasnosel'skii-Pokrovskii Model

    PubMed Central

    Wang, Shoubin; Gao, Wei

    2013-01-01

    As a new type of intelligent material, magnetically shape memory alloy (MSMA) has a good performance in its applications in the actuator manufacturing. Compared with traditional actuators, MSMA actuator has the advantages as fast response and large deformation; however, the hysteresis nonlinearity of the MSMA actuator restricts its further improving of control precision. In this paper, an improved Krasnosel'skii-Pokrovskii (KP) model is used to establish the hysteresis model of MSMA actuator. To identify the weighting parameters of the KP operators, an improved gradient correction algorithm and a variable step-size recursive least square estimation algorithm are proposed in this paper. In order to demonstrate the validity of the proposed modeling approach, simulation experiments are performed, simulations with improved gradient correction algorithm and variable step-size recursive least square estimation algorithm are studied, respectively. Simulation results of both identification algorithms demonstrate that the proposed modeling approach in this paper can establish an effective and accurate hysteresis model for MSMA actuator, and it provides a foundation for improving the control precision of MSMA actuator. PMID:23737730

  19. Hall Effect in Different Magnetic Phases of Fe-Rich γ-FeNiCr Alloys

    NASA Astrophysics Data System (ADS)

    Sinha, G.; Majudmar, A. K.

    In this paper we present the Hall effect data of Fe80-xNixCr20(14<=x<=30) alloys in four different magnetic phases within the fcc γ-phase. In the spin-glass (SG) phase (x=19) the nonlinear behaviour of the Hall resistivity (ρH) with field arises from the spin-orbit scattering. The temperature variation of ρH shows broad peaks around Tg for lower fields (<0.1 T) but they disappear at higher fields (1 T). We separate the ordinary (OHC) and the extra-ordinary (EHC) Hall coefficients in the ferromagnetic sample (x=30) and show their temperature variation. In the reentrant spin-glass (RSG) (x=26), again ρH shows a nonlinear variation with field. The temperature variation of ρH shows anomaly near both Tg and Tc. In the antiferromagnetic phase (AF) (x=14), ρH increases more or less linearly with field and its temperature variation shows broad peaks around TN for lower fields.

  20. FePtCu alloy thin films: Morphology, L1{sub 0} chemical ordering, and perpendicular magnetic anisotropy

    SciTech Connect

    Brombacher, C.; Schletter, H.; Daniel, M.; Matthes, P.; Joehrmann, N.; Makarov, D.; Hietschold, M.; Albrecht, M.; Maret, M.

    2012-10-01

    Rapid thermal annealing was applied to transform sputter-deposited Fe{sub 51}Pt{sub 49}/Cu bilayers into L1{sub 0} chemically ordered ternary (Fe{sub 51}Pt{sub 49}){sub 100-x}Cu{sub x} alloys with (001) texture on amorphous SiO{sub 2}/Si substrates. It was found that for thin film samples, which were processed at 600 Degree-Sign C for 30 s, the addition of Cu strongly favors the L1{sub 0} ordering and (001) texture formation. Furthermore, it could be revealed by transmission electron microscopy and electron backscatter diffraction that the observed reduction of the ordering temperature with Cu content is accompanied by an increased amount of nucleation sites forming L1{sub 0} ordered grains. The change of the structural properties with Cu content and annealing temperature is closely related to the magnetic properties. While an annealing temperature of 800 Degree-Sign C induces strong perpendicular magnetic anisotropy (PMA) in binary Fe{sub 51}Pt{sub 49} films, the addition of Cu systematically reduces the PMA. However, due to the enhancement of both the A1-L1{sub 0} phase transformation and the development of the (001) texture with increasing Cu content, lowering of the annealing temperature leads to a shift of the maximum perpendicular magnetic anisotropy towards alloys with higher Cu content. Thus, for an annealing temperature of 600 Degree-Sign C, the highest perpendicular magnetic anisotropy energy is found for the (Fe{sub 51}Pt{sub 49}){sub 91}Cu{sub 9} alloy. The smooth surface morphology, adjustable PMA, and high degree of intergranular exchange coupling make these films suitable for post-processing required for specific applications such as for sensorics or magnetic data storage.

  1. Composition-dependent magnetic properties of melt-spun La or/and Ce substituted nanocomposite NdFeB alloys

    NASA Astrophysics Data System (ADS)

    Hussain, M.; Zhao, L. Z.; Zhang, C.; Jiao, D. L.; Zhong, X. C.; Liu, Z. W.

    2016-02-01

    Aiming at high-performance low-cost NdFeB magnets, the magnetic properties and microstructure for melt spun nanocrystalline (Nd1-xMx)10Fe84B6 (M=La, Ce, or La0.5Ce0.5; x=0-0.7) alloys were investigated. Relatively, LaCe-substituted alloys show high values of the remanent magnetization Mr, the maximum energy product (BH)max and the coercivity Hc, up to 114 emu/g (1.07 T), 147 kJ/m3 and 471 kA/m, respectively, at x=0.1. The unusual increase in coercivity for the alloys with 10% La or 10% La0.5Ce0.5 substitution is possibly attributed to the phase segregation in alloys with certain La or LaCe contents. The reduced Curie temperature and spin-reorientation temperature were obtained for La, Ce or LaCe substituted alloys. Transmission electron microscope analysis has revealed that a fine and uniform distributed grain structure leads to remanence enhancement for La0.5Ce0.5 substituted alloys. The present results indicate that partially substituting Nd by La or/and Ce cannot only effectively reduce the cost of nanocrystalline NdFeB based magnetic powders but also can maintain a relatively good combination of magnetic properties.

  2. Complex magnetism of Ho-Dy-Y-Gd-Tb hexagonal high-entropy alloy

    NASA Astrophysics Data System (ADS)

    Lužnik, J.; Koželj, P.; Vrtnik, S.; Jelen, A.; Jagličić, Z.; Meden, A.; Feuerbacher, M.; Dolinšek, J.

    2015-12-01

    Rare earth based equimolar Ho-Dy-Y-Gd-Tb hexagonal high-entropy alloy (HEA) is a prototype of an ideal HEA, stabilized by the entropy of mixing at any temperature with random mixing of elements on the hexagonal close-packed lattice. In order to determine intrinsic properties of an ideal HEA characterized by the enormous chemical (substitutional) disorder on a weakly distorted simple lattice, we have performed measurements of its magnetic and electrical response and the specific heat. The results show that the Ho-Dy-Y-Gd-Tb hexagonal HEA exhibits a rich and complex magnetic field-temperature (H ,T ) phase diagram, as a result of competition among the periodic potential arising from the electronic band structure that favors periodic magnetic ordering, the disorder-induced local random potential that favors spin glass-type spin freezing in random directions, the Zeeman interaction with the external field that favors spin alignment along the field direction, and the thermal agitation that opposes any spin ordering. Three characteristic temperature regions were identified in the (H ,T ) phase diagram between room temperature and 2 K. Within the upper temperature region I (roughly between 300 and 75 K), thermal fluctuations average out the effect of local random pinning potential and the spin system behaves as a pure system of compositionally averaged spins, undergoing a thermodynamic phase transition to a long-range ordered helical antiferromagnetic state at the Néel temperature TN=180 K that is a compositional average of the Néel temperatures of pure Tb, Dy, and Ho metals. Region II (between 75 and 20 K) is an intermediate region where the long-range periodic spin order "melts" and the random ordering of spins in the local random potential starts to prevail. Within the low-temperature region III (below 20 K), the spins gradually freeze in a spin glass configuration. The spin glass phase appears to be specific to the rare earths containing hexagonal HEAs, sharing

  3. Optimization of the microstructure and properties of Co-substituted Fe-Si-B-Nb-Cu nanocrystalline soft magnetic alloys

    NASA Astrophysics Data System (ADS)

    Ohnuma, M.; Ping, D. H.; Abe, T.; Onodera, H.; Hono, K.; Yoshizawa, Y.

    2003-06-01

    The effect of Co replacement for Fe on the microstructure and soft magnetic properties of Fe78.8-xCoxNb2.6Si9B9Cu0.6 (x=5-60) nanocrystalline alloys has been studied for improving the soft magnetic properties of Fe-Si-B-Nb-Cu type alloys at a high frequency range. The magnetic anisotropy constant increases with x, but the coercivity increases when x exceeds 20, indicating that magnetic softness is degraded by replacing Fe with Co. Three-dimensional atom-probe observations have revealed that the number density of Cu-enriched clusters decreases with x, thereby decreasing the number density of the heterogeneous nucleation sites for bcc-Fe primary crystals. In addition, differential scanning calorimetry measurements show that the Cu clustering temperature shifts to a higher temperature with increasing x, suggesting that the kinetics for the Cu clustering decreases as Co content. These experimental results are discussed from the thermodynamical point of view, and the optimized Cu composition to achieve a low coercivity with 40 at % Co has been found. 2003 American Institute of Physics.

  4. Electrodeposition and magnetic characterization of iron and iron-silicon alloys from the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate.

    PubMed

    Giridhar, Pulletikurthi; Weidenfeller, Bernd; El Abedin, Sherif Zein; Endres, Frank

    2014-11-10

    The electrodeposition of soft magnetic iron and iron-silicon alloys for magnetic measurements is presented. The preparation of these materials in 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate, [Py1,4]TfO, at 100 °C with FeCl2 and FeCl2 +SiCl4 was studied by using cyclic voltammetry. Constant-potential electrolysis was carried out to deposit either Fe or FeSi, and deposits of approximately 10 μm thicknesses were obtained. By using scanning electron microscopy and X-ray diffraction, the microstructure and crystallinity of the deposits were investigated. Grain sizes in the nanometer regime (50-80 nm) were found and the presence of iron-silicon alloys was verified. Frequency-dependent magnetic polarizations, coercive forces, and power losses of some deposits were determined by using a digital hysteresis recorder. Corresponding to the small grain sizes, the coercive forces are around 950-1150 A m(-1) and the power losses were at 6000 J m(-3), which is much higher than in commercial Fe(3.2 wt %)Si electrical steel. Below a polarization of 1.8 T, the power losses are mainly caused by domain wall movements and, above 1.8 T, by rotation of magnetic moments as well as domain wall annihilation and recreation. PMID:25146175

  5. The effect of nickel content on the ac magnetic properties of 49Fe-49Co-2V alloys

    NASA Astrophysics Data System (ADS)

    Novotny, P. M.

    1988-04-01

    Experimental alloys containing between 0.03 and 0.67 wt. % nickel were produced to determine the effect of low nickel content on the ac magnetic properties of Carpenter's 49Fe-49Co-2V Hiperco (a registered trademark of Carpenter Technology Corp.) 50A alloy. The alloys were processed into 1.02×10-4 m (0.004 in.) thick strip, wound into tape toroids, annealed then tested for core loss at 60 and 400 Hz for induction levels of 1.0, 1.5, and 2.0 T. Toroids annealed at 885 °C in hydrogen, followed by slow cooling, exhibited a linear increase in core loss as nickel content increased due to the presence of a second phase in the microstructure. When the annealing temperature was decreased to 845 °C the second phase was eliminated and the core loss did not vary with nickel content. STEM examination of the samples determined that the second phase was a heavily dislocated bcc α'1 phase which had martensitically transformed from the fcc γ1 phase despite the slow cooling rate. Thermal expansion testing determined that increasing the Ni content in the range of 0-1 wt. % decreased the α1 +γ1 /α1 transformation temperature of the 49Fe-49Co-2V alloy.

  6. Changes of inclusion, texture and magnetic property of non-oriented Si steel treated by Ca alloy

    NASA Astrophysics Data System (ADS)

    Lv, X.; Zhang, F.; Chen, X.

    2015-04-01

    Based on the industrial production of non-oriented Si steel, Ca treatment by Ca alloy adding during the RH refining process was studied. The changes of inclusion, crystal texture and microstructure, and its effect on magnetic properties of final steel sheets were analyzed. The results showed that, in present work, Ca treatment can improve the texture proportion of {110} and {111} significantly, and the formation of MnS and AlN inclusions were restrained. Meanwhile, the recrystallization effects of hot rolled strip get bad and the fiber structure enhanced obviously. The grain size of finished steel sheets increased as the increase of Ca alloy adding amount quickly, and then decreased. Compared with the non-Ca treatment charge, the numbers of inclusions whose size below 1.0μm will decrease by 68.06%, 87.50% and 94.94%, the texture proportion of {110} and {111} was 30.3%, 39.1%, 17.6% and 2.8%, 5.5%, 20.6%, while the correspondent Ca alloy adding amount is 0.67 kg/t steel, 1.00 kg/t steel and 1.67 kg/t steel, respectively. In addition, the core loss gradually decreases to a stable level as the increasing of Ca added, and the magnetic induction decreases quickly after slow increasing, respectively. The optimal Ca treatment mode depends on the chemical compositions of steel grades.

  7. Influence of Bridgman solidification on microstructures and magnetic behaviors of a non-equiatomic FeCoNiAlSi high-entropy alloy

    SciTech Connect

    Zuo, Tingting; Yang, Xiao; Liaw, Peter K.; Zhang, Yong

    2015-09-07

    The non-equiatomic FeCoNiAlSi alloy is prepared by the Bridgman solidification (BS) technique at different withdrawal velocities (V = 30, 100, and 200 μm/s). Various characterization techniques have been used to study the microstructure and crystal orientation. The morphological evolutions accompanying the crystal growth of the alloy prepared at different withdrawal velocities are nearly the same, from equiaxed grains to columnar crystals. The transition of coercivity is closely related to the local microstructure, while the saturation magnetization changes little at different sites. The coercivity can be significantly reduced from the equiaxed grain area to the columnar crystal area when the applied magnetic field direction is parallel to the crystal growth direction, no matter what is the withdrawal velocity. As a result, the alloy possesses magnetic anisotropy when the applied magnetic field is in different directions.

  8. Influence of Bridgman solidification on microstructures and magnetic behaviors of a non-equiatomic FeCoNiAlSi high-entropy alloy

    DOE PAGESBeta

    Zuo, Tingting; Yang, Xiao; Liaw, Peter K.; Zhang, Yong

    2015-09-07

    The non-equiatomic FeCoNiAlSi alloy is prepared by the Bridgman solidification (BS) technique at different withdrawal velocities (V = 30, 100, and 200 μm/s). Various characterization techniques have been used to study the microstructure and crystal orientation. The morphological evolutions accompanying the crystal growth of the alloy prepared at different withdrawal velocities are nearly the same, from equiaxed grains to columnar crystals. The transition of coercivity is closely related to the local microstructure, while the saturation magnetization changes little at different sites. The coercivity can be significantly reduced from the equiaxed grain area to the columnar crystal area when the appliedmore » magnetic field direction is parallel to the crystal growth direction, no matter what is the withdrawal velocity. As a result, the alloy possesses magnetic anisotropy when the applied magnetic field is in different directions.« less

  9. Magnetic properties of (FeIn{sub 2}S{sub 4}){sub 1-x}(In{sub 2}S{sub 3}){sub x} alloy single crystals

    SciTech Connect

    Bodnar, I. V. Novikova, M. A.; Trukhanov, S. V.

    2013-05-15

    (FeIn{sub 2}S{sub 4}){sub 1-x}(In{sub 2}S{sub 3}){sub x} alloy single crystals are grown by oriented crystallization in the entire range of component concentrations. For the single crystals, studies of the magnetic properties are carried out in the temperature range 4-300 K and the magnetic-field range 0-14 T. It is established that almost all of the alloys are paramagnetic materials at temperatures down to the lowest achievable temperatures ({approx}4 K). It is shown that the ground magnetic phase state of the alloys is the spin-glass state with the freezing temperature steadily increasing with increasing Fe{sup 2+} cation content. The most probable causes and mechanism of formation of the magnetic state of the (FeIn{sub 2}S{sub 4}){sub 1-x}(In{sub 2}S{sub 3}){sub x} crystals are discussed.

  10. A metastable hard magnetic phase in the crystallization process of the Fe75Si11B10Nb3Sn1 alloy

    NASA Astrophysics Data System (ADS)

    Cremaschi, V.; Arcondo, B.; Vázquez, M.; Sirkin, H.

    1999-11-01

    A very interesting characteristic of FeSiB based amorphous alloys is its soft magnetic behavior. Most of these alloys remains soft along the crystallization process up to the nucleation of the iron borides. Examples of this are the widely studied Finemet and the FeSiBSn. In this work the crystallization of Fe76Si11B10Nb3 and Fe75Si11B10Nb3Sn1 is studied by means of X-ray diffraction, Mössbauer spectroscopy and coercive magnetic field measurements after one hour isothermal annealing at different temperatures. In the crystallization process of the latter alloy a hard magnetic phase appeared when the samples were annealed above 773 K. The soft magnetic behavior was recovered after annealing at 873 K. The hyperfine parameters as well as the X-ray diffraction patterns are reported.

  11. Magnetic Tunnel Junctions with Perpendicular Anisotropy Using a Co2FeAl Full-Heusler Alloy

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Sukegawa, Hiroaki; Kasai, Shinya; Hayashi, Masamitsu; Mitani, Seiji; Inomata, Koichiro

    2012-06-01

    We fabricated perpendicularly magnetized magnetic tunnel junctions (p-MTJs) with an ultrathin Co2FeAl (CFA) full-Heusler alloy electrode having large interface magnetic anisotropy of CFA/MgO. An out-of-plane tunnel magnetoresistance (TMR) ratio of 53% at room temperature was observed in CFA/MgO/Co20Fe60B20 p-MTJs. By inserting a 0.1-nm-thick Fe (Co50Fe50) layer between the MgO and Co20Fe60B20 layers, The TMR ratio was significantly enhanced to 91% (82%) due to the improved interface. The bias voltage dependence of differential conductance did not clearly show coherent tunneling characteristics for ultrathin CFA-MTJs, suggesting that a higher TMR ratio may be achieved by improving the B2 ordering of CFA and/or interface structure.

  12. Changes in the magnetic and mechanical properties of thermally aged Fe-Cu alloys due to nano-sized precipitates

    NASA Astrophysics Data System (ADS)

    Li, Yi; Li, Yuanfei; Deng, Shanquan; Xu, Ben; Li, Qiulin; Shu, Guogang; Liu, Wei

    2016-01-01

    The changes in the magnetic properties, mechanical properties, and microstructural parameters of Fe-Cu alloys due to thermal aging have been investigated to improve the fundamental understanding of using magnetic technology for the nondestructive evaluation (NDE) of irradiation embrittlement in the reactor pressure vessel (RPV). Nano-sized Cu particles precipitated from a Fe matrix after thermal aging at 500 °C for various times, and the microstructure parameters were determined. The coercivity, Barkhausen noise (BN), Vickers hardness, and yield stress were also measured for these samples. These properties show the same hardening-softening trend with increasing aging time, which can be interpreted in terms of the microstructure parameters evolution based on the model of the pinning of precipitates on domain walls and dislocations. These results suggest the practicability of using magnetic technology for the NDE of the irradiation embrittlement of the RPV.

  13. Growth temperature dependent structural and magnetic properties of epitaxial Co{sub 2}FeAl Heusler alloy films

    SciTech Connect

    Qiao, Shuang; Nie, Shuaihua; Zhao, Jianhua; Zhang, Xinhui

    2013-06-21

    The structural and magnetic properties of a series of Co{sub 2}FeAl Heusler alloy films grown on GaAs(001) substrate by molecular beam epitaxy have been studied. The epitaxial Co{sub 2}FeAl films with an ordered L{sub 21} structure have been successfully obtained at growth temperature of 433 K, with an in-plane cubic magnetic anisotropy superimposed with an unusual uniaxial magnetic anisotropy. With increasing growth temperature, the ordered L{sub 21} structure degrades. Meanwhile, the uniaxial anisotropy decreases and eventually disappears above 673 K. The interfacial bonding between As and Co or Fe atom is suggested to be responsible for the additional uniaxial anisotropy.

  14. Magnetic Mineralogy of Troilite-Inclusions and their Fe-Ni Host Alloys in IAB Iron Meteorites

    NASA Astrophysics Data System (ADS)

    Kontny, A. M.; Kramar, U.; Luecke, W.

    2011-12-01

    Iron-nickel meteorites often contain isolated, mostly rounded troilite nodules enclosed in a bulk of Fe-Ni alloy. As sulfur has a low solubility in metal, it is excluded from the crystallization of metal during cooling. Therefore troilite nodules are interpreted to be trapped droplets of residual sulfur-enriched melts. Microscopic examinations of the interface (mm-range) between troilite inclusions and Fe-Ni alloy yield clear mineralogical differences compared to the troilite inclusion. Such rims around troilite nodules seem to occur exclusively in Fe-Ni meteorites with slow cooling rates, and therefore might provide interesting clues on segregation, fractional crystallization and reequilibration processes between the Fe-Ni alloy and the sulfide phases. These interfaces however are also highly sensitive to terrestrial weathering. We present microscopic observations in combination with temperature-dependent magnetic susceptibility (k-T curves) in order to identify the magnetic mineralogy of the Morasko (Poland) and Coahuila (Mexico) meteorites, which both geochemically belong to the non-magmatic IAB or IIICD group. In the k-T curves both, rim and troilite nodule are characterized by Curie temperatures (TC) that can be related to magnetite, daubreelite (FeCr2O4), Fe-hydroxide and sometimes cohenite. Therefore the interface seems to be geochemically more similar to the troilite nodule than the Fe-Ni alloy. Optical microscopy in combination with the ferrofluid method revealed complex microstructures of intergrown magnetic (TC = 780-785 °C) and non-magnetic phases in the Fe-Ni alloy, which differ in their Ni-concentration. Towards the rim of the troilite nodule the concentration of magnetic cohenite ((Fe,Ni)3C) and especially schreibersite ((Fe,Ni)3P), which are both intergrown with the metal, increases. Cohenite is easily identified microscopically by a very characteristic stripe-like magnetic domain structure and it shows a TC at about 200 °C. The carbon-rich, dark

  15. Abnormal variation of magnetic properties with Ce content in (PrNdCe)2Fe14B sintered magnets prepared by dual alloy method

    NASA Astrophysics Data System (ADS)

    Xue-Feng, Zhang; Jian-Ting, Lan; Zhu-Bai, Li; Yan-Li, Liu; Le-Le, Zhang; Yong-Feng, Li; Qian, Zhao

    2016-05-01

    Resource-saving (PrNdCe)2Fe14B sintered magnets with nominal composition (PrNd)15‑x Ce x Fe77B8 (x = 0‑10) were prepared using a dual alloy method by mixing (PrNd)5Ce10Fe77B8 with (PrNd)15Fe77B8 powders. For Ce atomic percent of 1% and 2%, coercivity decreases dramatically. With further increase of Ce atomic percent, the coercivity increases, peaks at 6.38 kOe in (PrNd)11Ce4Fe77B8, and then declines gradually. The abnormal dependence of coercivity is likely related to the inhomogeneity of rare earth chemical composition in the intergranular phase, where PrNd concentration is strongly dependent on the additive amount of (PrNd)5Ce10Fe77B8 powders. In addition, for Ce atomic percent of 8%, 7%, and 6% the coercivity is higher than that of magnets prepared by the conventional method, which shows the advantage of the dual alloy method in preparing high abundant rare earth magnets. Project supported by the National Natural Science Foundation of China (Grant Nos. 51461033, 51571126, 51541105, and 11547032), the Natural Science Foundation of Inner Mongolia, China (Grant No. 2013MS0110), and the Inner Mongolia University of Science and Technology Innovation Fund, China.

  16. Glass formation and magnetic properties in the Co and Fe-based amorphous alloy with small Mo or Nb additions

    NASA Astrophysics Data System (ADS)

    Jo, Hye-In; Choi-Yim, Haein

    2012-02-01

    The ferromagnetic metallic glass alloys in the Co-Fe-B-Si-M (M = Mo or Nb) system were investigated. Ingots of [(Co1- x Fe x )0.75B0.2Si0.05]96Mo4 ( x = 0, 0.2, 0.5, 0.8, 1.0) and [(Co1- x Fe x )0.75 B0.2Si0.05]96Nb4 ( x = 0, 0.2, 0.5, 0.8, 1.0) alloys were cast into about 30 µm-thick ribbons by using a melt spinning method. As-spun ribbons were identified as being fully amorphous by using X-ray diffraction (XRD). The thermal stability parameters, such as the supercooled liquid region (Δ T x = T g - T x ) and the exothermic heat (Δ H Exo ), were measured by using differential scanning calorimetry (DSC). For Co-Fe-B-Si-Mo alloys, Δ T x and Δ H Exo were in the range of 41.4-81.7 K and 23.40-104.21 J/g, and for Co-Fe-B-Si-Nb alloys, Δ T x and Δ H Exo were in the range of 60.4-88.0 K and 18.45-62.05 J/g, respectively. These glassy ribbons also exhibited semi-hard magnetic properties, i.e., a coercive force ( H c ) of 67.26-100.68 Oe and a saturation magnetization ( M s ) of 341.288-746.176 emu·cm3.

  17. Synthesis and magnetization studies of nanopowder Fe₇₀Ni₂₀Cr₁₀ alloys prepared by high energy milling

    SciTech Connect

    Chater, R.; Bououdina, M.; Chaanbi, D.; Abbas, H.

    2013-05-01

    Nanocrystalline Fe{sub 1–x–y}NixCry (x=20, y=10% in Wt)) alloy samples were prepared by mechanical alloying process. Fe, Ni and Cr elemental powders have been ball milled in a planetary mill for various periods of time, up to 27 h. XRD analysis allowed the determination of the structure of the mixture, the average crystallite size and the lattice parameter as a function of milling time. The complete formation of FeNiCr is observed after 27 h milling. With increasing milling time from 0 to 27 h, it is observed that the lattice parameter increases from 0.3515 to 0.3593 nm as well as an increase of microstrain from 0.15 to 0.40%, whereas the grain size decreases from 48 to 13 nm. Grain morphology of the powders at different formation stages was examined using SEM. Saturation magnetization and coercive fields derived from the hysteresis curves are discussed as a function of milling time. - Graphical abstract: Fe₇₀Ni₂₀Cr₁₀ nanopowders were prepared using a planetary ball mill. The structure and microstructure vary with milling time; thereby important modifications of the magnetic properties were observed and discussed. Highlights: • Nanocrystalline Fe₇₀Ni₂₀Cr₁₀ alloy were prepared by the mechanical alloying process. • The complete formation of Fe₇₀Ni₂₀Cr₁₀ is observed after 24 h milling. • With increasing milling time, the grain size decreases, while the strain increases. • The SEM images allowed following the morphology of the materials at different stages. • Ms and HC derived from the hysteresis are discussed as a function of milling time.

  18. Magnetization of ternary alloys based on Fe0.65Ni0.35 invar with 3d transition metal additions: An ab initio study

    NASA Astrophysics Data System (ADS)

    Onoue, Masatoshi; Trimarchi, Giancarlo; Freeman, Arthur J.; Popescu, Voicu; Matsen, Marc R.

    2015-01-01

    Smart susceptors are being developed for use as tooling surfaces in molding machines that use apply electro-magnetic induction heating to mold and form plastics or metal powders into structural parts, e.g., on aerospace and automotive manufacturing lines. The optimal magnetic materials for the induction heating process should have large magnetization, high magnetic permeability, but also small thermal expansion coefficient. The Fe0.65Ni0.35 invar alloy with its negligible thermal expansion coefficient is thus a natural choice for this application. Here, we use density functional theory as implemented through the Korringa-Kohn-Rostoker method within the coherent-potential approximation, to design new alloys with the large magnetization desired for smart susceptor applications. We consider the Fe0.65-xNi0.35-yMx+y alloys derived from Fe0.65Ni0.35 invar adding a third element M = Sc, Ti, V, Cr, Mn, or Co with concentration (x + y) reaching up to 5 at. %. We find that the total magnetization depends linearly on the concentration of M. Specifically, the early 3d transition metals from Sc to Cr decrease the magnetization with respect to that of the invar alloy whereas Mn and Co increase it.

  19. Structures and magnetism of two types of c(2x2)-Mn/Pd(001) surface alloys

    SciTech Connect

    Tsuboi, N.; Okuyama, H.; Aruga, T.

    2005-05-15

    Mn/Pd(001) surface alloy was investigated by a tensor low-energy electron diffraction (LEED) analysis. After deposition of Mn on Pd(001) at room temperature, the surface was annealed at 570-620 K, which produced two types of c(2x2) surface alloys, according to the Mn coverage. At a low-Mn coverage, we obtained a Pd-capped c(2x2) surface, in which the first layer was composed of a (1x1)-Pd layer, and the second layer was a c(2x2)-MnPd mixed layer [{alpha}-c(2x2)]. The deposition of greater amounts of Mn followed by annealing resulted in another c(2x2) surface, in which Mn atoms existed in the substitutional sites of the first and third layers [{beta}-c(2x2)]. The first layer consisted of a c(2x2)-MnPd mixed layer, the second layer was a (1x1)-Pd layer, and the third layer was another c(2x2)-MnPd mixed layer. The structure of the {beta}-c(2x2) surface qualitatively agreed with the one previously investigated by LEED. These two types of surface alloys, {alpha}-c(2x2) and {beta}-c(2x2), may be considered as being precursors to the formation of the bulk MnPd{sub 3} alloy. We also investigated the magnetic properties of the {alpha}-c(2x2) and {beta}-c(2x2) surfaces by using surface magneto-optic Kerr effect (MOKE) and self-consistent, total-energy calculations. The MOKE measurements for both surface alloys show no hysterisis loop, even at 10 K. The total-energy calculation shows that Mn atoms have a local-spin moment of 3.9-4.1 {mu}{sub B} and that they are antiferromagnetically ordered in the ground state.

  20. Low temperature magnetization behavior in Co 36Fe 36Si 3Al 1Nb 4B 20 (at%) nanostructured alloy

    NASA Astrophysics Data System (ADS)

    Panda, A. K.; Mohanta, Ojaswini; Basumallick, A.; Mitra, A.

    2010-12-01

    The investigation addresses low temperature magnetization behavior in Co 36Fe 36Si 3Al 1Nb 4B 20 alloy ribbons in their as-spun as well as annealed state. Optimum heat treatment at 875 K led to nanocrystallization whereby bcc-(FeCo)SiAl nanoparticles were dispersed in an amorphous matrix as evidenced from transmission electron microscopy. Low temperature magnetization studies were carried out in the range 77-300 K. Using the method of mathematical fittings, magnetization extrapolated to 0 K was obtained. The dependence of the magnetization with respect to temperature of BT 3/2 was used to determine the Bloch coefficient " B" and spin wave stiffness constant " D". Magnetic softening revealed by lowering in the coercivity in the optimum nanostructured state was also the cause of a drop in the stiffness constant. The range of exchange interaction given by D/ TC was higher in the nanostructured state compared to the as-spun amorphous state. The effect of nanocrystallization and the resulting ferromagnetic coupling was further evidenced by low temperature magnetization studies.

  1. Electronic structures, magnetic properties and half-metallicity in Heusler alloys Zr2CoZ (Z=Al, Ga, In, Sn)

    NASA Astrophysics Data System (ADS)

    Yan, Peng-Li; Zhang, Jian-Min; Xu, Ke-Wei

    2015-10-01

    The electronic structures, magnetic properties, and half-metallicity of full-Heusler alloys Zr2 CoZ (Z=Al, Ga, In, Sn) with the Hg2 CuTi -type structure have been studied by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). The Zr2 CoZ (Z=Al, Ga, In, Sn) are found to be half-metallic ferrimagnets within a certain range of the lattice constant. The total magnetic moments (μt) of the Zr2 CoZ alloys are calculated to be 2 for Z=Al, Ga, In and 3 for Z=Sn, linearly scaled with the total number of valence electrons (Zt) by μt =Zt - 18 . The origin of the band gap for these half-metallic alloys is well understood. These new Zr-based Heusler alloys are the ideal candidates for spintronic devices.

  2. Materials Science Laboratory - Columnar-to-Equiaxed Transition in Solidification Processing and Microstructure Formation in Casting of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions

    NASA Technical Reports Server (NTRS)

    Gandin, Charles-Andre; Ratke, Lorenz

    2008-01-01

    The Materials Science Laboratory - Columnar-to-Equiaxed Transition in Solidification Processing and Microstructure Formation in Casting of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions (MSL-CETSOL and MICAST) are two investigations which supports research into metallurgical solidification, semiconductor crystal growth (Bridgman and zone melting), and measurement of thermo-physical properties of materials. This is a cooperative investigation with the European Space Agency (ESA) and National Aeronautics and Space Administration (NASA) for accommodation and operation aboard the International Space Station (ISS). Research Summary: Materials Science Laboratory - Columnar-to-Equiaxed Transition in Solidification Processing (CETSOL) and Microstructure Formation in Casting of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions (MICAST) are two complementary investigations which will examine different growth patterns and evolution of microstructures during crystallization of metallic alloys in microgravity. The aim of these experiments is to deepen the quantitative understanding of the physical principles that govern solidification processes in cast alloys by directional solidification.

  3. Magnetization kinetics in tension and field annealed Fe-based amorphous alloys

    NASA Astrophysics Data System (ADS)

    Hasegawa, Ryusuke; Takahashi, Kengo; Francoeur, Bruno; Couture, Pierre

    2013-05-01

    Magnetization kinetics in tension-annealed and field-annealed amorphous magnetic materials indicates that strain and magnetic fields are equally effective in inducing and relaxing local structural and magnetic anisotropy changes. This observation is based on the thermomagnetic aging of the magnetic properties obtained in the materials studied.

  4. Thermal and magnetic properties of melt-spun Co-Fe-B-Si-(Cr/Ta) amorphous alloys

    NASA Astrophysics Data System (ADS)

    Jo, Hye-in; Han, Bokyeong; Yim, Haein Choi; Kwon, Woojun

    2013-02-01

    The ferromagnetic amorphous alloys Co-Fe-B-Si-Cr and Co-Fe-B-Si-Ta were systemically investigated. [(Co1- x Fe x )0.75B0.2Si0.05]96Cr4 ( x = 0, 0.1, 0.4, 0.7, 1.0) and [(Co1- x Fe x )0.75B0.2Si0.05]96Ta4 ( x = 0, 0.1, 0.3, 0.5, 1.0) ribbons were prepared by using the melt-spinning technique. Amorphous structures were confirmed by the presence of a broad and halo peak in X-ray diffraction (XRD). The thermal characteristics, such as the glass transition temperature ( T g ), the crystallization temperature ( T x ) and the supercooled liquid region (Δ T x = T x - T g ), were measured by means of a differential scanning calorimeter (DSC). For the Co-Fe-B-Si-Cr alloys, the values of Δ T x were in the range of 51.6-61.4 K, and for Co-Fe-B-Si-Ta alloys, they were in the range of 39.3-55.5 K. The magnetic properties were examined by means of a vibrating sample magnetometer (VSM) at a maximum field strength of 3000 Oe. These glassy ribbons exhibited soft magnetic properties. The saturation magnetization ( M s ) and the coercive force ( H c ) were in the ranges of 307.85-854.52 emu·cm3 and 0.64-0.89 Oe, respectively.

  5. Effect of platinum substitution on the structural and magnetic properties of Ni2MnGa ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Singh, Sanjay; D'Souza, S. W.; Nayak, J.; Caron, L.; Suard, E.; Chadov, S.; Felser, C.

    2016-04-01

    Ni2MnGa exhibits ideal ferromagnetic shape memory properties, however, brittleness and a low-temperature martensite transition hinder its technological applications motivating the search for novel materials showing better mechanical properties as well as higher transition temperatures. In this work, the crystal structure, phase transitions, and the magnetic properties of quaternary Ni2 -xPtxMnGa (0 ≤x ≤1 ) shape memory alloys were studied experimentally by x-ray diffraction, magnetization measurements, and neutron diffraction and compared to ab initio calculations. Compositions within 0 ≤x ≤0.25 exhibit the cubic austenite phase at room temperature. The x ≈0.3 composition exhibits a seven-layer modulated monoclinic martensite structure. Within 0.4 ≤x ≤1 , the system stabilizes in the nonmodulated tetragonal structure. The martensite transition has very narrow thermal hysteresis 0 ≤x ≤0.3 , which is a typical characteristic of a shape memory alloy. By increasing x , the temperature of the martensite transition increases, while that of the magnetic transition decreases. The x =1 composition (NiPtMnGa) in the martensite phase undergoes a para-to-ferrimagnetic transition. The saturation magnetization exhibits a nontrivial behavior with increasing up to x ≈0.25 , above which, it suddenly decreases. Powder neutron diffraction reveals the presence of antisite disorder, with about 17% of the original Ga sites being occupied by Mn. Computations suggest that the antisite disorder triggers an antiferromagnetic coupling between two Mn atoms in different crystallographic positions, resulting into a sudden drop of the saturation magnetization for higher x .

  6. Modelling current-induced magnetization switching in Heusler alloy Co{sub 2}FeAl-based spin-valve nanopillar

    SciTech Connect

    Huang, H. B.; Ma, X. Q.; Liu, Z. H.; Zhao, C. P.; Chen, L. Q.

    2014-04-07

    We investigated the current-induced magnetization switching in a Heusler alloy Co{sub 2}FeAl-based spin-valve nanopillar by using micromagnetic simulations. We demonstrated that the elimination of the intermediate state is originally resulted from the decease of effective magnetic anisotropy constant. The magnetization switching can be achieved at a small current density of 1.0 × 10{sup 4} A/cm{sup 2} by increasing the demagnetization factors of x and y axes. Based on our simulation, we found magnetic anisotropy and demagnetization energies have different contributions to the magnetization switching.

  7. Fe{sub 2-x}Co{sub x}MnSi (x = 0, 1 and 2) Heusler alloys: Structural, magnetic and atomic site disorder properties

    SciTech Connect

    Bhatt, Harsh; Mukadam, M. D.; Meena, S. S.; Yusuf, S. M.

    2015-06-24

    The Heusler alloy series Fe{sub 2-x}Co{sub x}MnSi (x = 0, 1 and 2) is theoretically predicted to be half metallic. We prepared the sample series and determined the structural and magnetic properties to check if these materials are suitable for spintronics applications. The Curie temperatures of two of the alloys have been found to be well above the room temperature. But the presence of elements with atoms of similar size leads to atomic site disorder in these alloys, which may destroy the half metallic nature. The atomic site disorder has been confirmed by Mössbauer spectroscopy.

  8. Magnetic and half-metallic properties of the full-Heusler alloys Co2TiX(X=Al,Ga;Si,Ge,Sn;Sb)

    NASA Astrophysics Data System (ADS)

    Lee, S. C.; Lee, T. D.; Blaha, P.; Schwarz, K.

    2005-05-01

    The electronic structure and magnetic properties of the full-Heusler alloys Co2TiX (X element from groups III, IV and V) were studied by first principle calculations. Previous calculations found Co2TiAl and Co2TiSn not to be half metallic. In this paper, however, it will be shown that the alloys with X =Al,Si,Ge,Sn are half metallic and ferromagnetic. The effect of atomic disorder in the Ti-Al sublattices reduces the half metallicity of the Co2TiAl Heusler alloy.

  9. Comparison of the transformation temperature, microstructure and magnetic properties of Co-Ni-Al and Co-Ni-Al-Cr shape memory alloys

    NASA Astrophysics Data System (ADS)

    Dağdelen, Fethi; Malkoç, Türkan; Kök, Mediha; Ercan, Ercan

    2016-06-01

    In this study, two-phase Co-Ni-Al shape memory alloys that have drawn attention recently due to their technological applications were investigated. Co-Ni-Al and Co-Ni-Al-Cr alloys were produced by melting method in an arc-melter furnace and physical properties between alloys were compared. At the end of experimental measurements it was observed that chromium addition did not change the crystal structure of the Co-Ni-Al alloy, but decreased the martensitic transformation temperature, the most significant property of shape memory alloys. Moreover, there was no significant change in the microstructure of the Co-Ni-Al alloy with chromium addition, and the presence of the two phases determined by X-ray analysis was also determined by optical microscopy. There was no significant change in micro hardness values of the alloys, while important changes in the magnetic properties were determined. It was observed that the Curie temperature decreased by approximately 500 {}^{circ}C with chromium addition and a considerable decrease in the magnetic saturation value was also determined.

  10. Comparison of the transformation temperature, microstructure and magnetic properties of Co-Ni-Al and Co-Ni-Al-Cr shape memory alloys

    NASA Astrophysics Data System (ADS)

    Dağdelen, Fethi; Malkoç, Türkan; Kök, Mediha; Ercan, Ercan

    2016-06-01

    In this study, two-phase Co-Ni-Al shape memory alloys that have drawn attention recently due to their technological applications were investigated. Co-Ni-Al and Co-Ni-Al-Cr alloys were produced by melting method in an arc-melter furnace and physical properties between alloys were compared. At the end of experimental measurements it was observed that chromium addition did not change the crystal structure of the Co-Ni-Al alloy, but decreased the martensitic transformation temperature, the most significant property of shape memory alloys. Moreover, there was no significant change in the microstructure of the Co-Ni-Al alloy with chromium addition, and the presence of the two phases determined by X-ray analysis was also determined by optical microscopy. There was no significant change in micro hardness values of the alloys, while important changes in the magnetic properties were determined. It was observed that the Curie temperature decreased by approximately 500°C with chromium addition and a considerable decrease in the magnetic saturation value was also determined.

  11. Structural and mechanical properties of 7075 alloy strips fabricated by roll-casting in a static magnetic field

    NASA Astrophysics Data System (ADS)

    Su, Xin; Xu, Guang-ming; Jiang, Jiu-wen

    2014-07-01

    The influences of a 0.2 T static magnetic field on the microstructure of 7075 aluminum alloys sheets produced with a twin-roll continuous caster at 675°C were investigated in this paper. Under a uniform magnetic field, the primary dendrites were refined and tended to be equiaxed. The microstructure consisted of an intermediate case between dendritic and equiaxed grains. Moreover, the use of an external static field in the twin-roll casting process can reduce heat discharge, resulting in a decrease in undercooling, and may also account for the abatement of segregation bands. In addition, the static magnetic field effectively improved the solute mixing capacity, and the added atoms more easily diffused from precipitates to the α-Al matrix, which resulted in an increase in the mechanical properties of the rolled sheets. Specimens prepared both in the presence of a static magnetic field and in the absence of a static magnetic field exhibited brittle-fracture characteristics.

  12. Magnetic properties of Sm-Co thin films grown on MgO(100) deposited from a single alloy target

    SciTech Connect

    Verhagen, T. G. A.; Boltje, D. B.; Ruitenbeek, J. M. van; Aarts, J.

    2014-08-07

    We have grown epitaxial Sm-Co thin films by sputter deposition from a single alloy target with a nominal SmCo{sub 5} composition on Cr(100)-buffered MgO(100) single-crystal substrates. By varying the Ar gas pressure, we can change the composition of the film from a SmCo{sub 5}-like to a Sm{sub 2}Co{sub 7}-like phase. The composition, crystal structure, morphology, and magnetic properties of these films have been determined using Rutherford Backscattering, X-ray diffraction, and magnetization measurements. We find that we can grow films with, at room temperature, coercive fields as high as 3.3 T, but with a remanent magnetization which is lower than can be expected from the texturing. This appears to be due to the Sm content of the films, which is higher than expected from the content of the target, even at the lowest possible sputtering pressures. Moreover, we find relatively large variations of film properties using targets of nominally the same composition. At low temperatures, the coercive fields increase, as expected for these hard magnets, but in the magnetization, we observe a strong background signal from the paramagnetic impurities in the MgO substrates.

  13. First-principle investigation of electronic structure, magnetism and phase stability of Heusler-type Pt2-xMn1+xGa alloys

    NASA Astrophysics Data System (ADS)

    Feng, L.; Liu, E. K.; Zhang, W. X.; Wang, W. H.; Wu, G. H.

    2015-03-01

    The electronic structure, magnetism and phase stability of Pt2-xMn1+xGa (x=0, 0.25, 0.5, 0.75, 1) alloys are studied by first-principle calculations. The calculations reveal that a potential magnetic martensitic transformation can be expected in all the series. In addition, a large magnetic-field-induced strain is likely to appear in Pt2-xMn1+xGa (x=0, 0.25, 0.75, 1) alloys. The electronic structure calculations indicate that the tetragonal phase is stabilized upon the distortion because of the pseudogap formation at the Fermi Level. The magnetic structure is also investigated and the total magnetic moment of the tetragonal phase is a little larger than that of the cubic austenite phase in all the series.

  14. EBSD Study on the Effect of a Strong Axial Magnetic Field on the Microstructure and Crystallography of Al-Ni Alloys During Solidification

    NASA Astrophysics Data System (ADS)

    Li, Xi; Fautrelle, Yves; Gagnoud, Annie; Moreau, Rene; Du, Dafan; Ren, Zhongming; Lu, Xionggang

    2016-03-01

    The effect of a strong magnetic field on the microstructure and crystallography of the primary and eutectic Al3Ni phases in Al-Ni alloys was investigated by using EBSD. The results show that the magnetic field significantly affected the microstructures and crystallography during both volume and directional solidification. As a result, the Al3Ni primary phases were aligned with the <001> crystal direction along the magnetic field and formed a layer-like structure. The magnetic field intensity, solidification temperature, growth speed, and alloy composition played important roles during the alignment process of the Al3Ni primary phase. Indeed, the alignment degree increased with the magnetic field and the solidification temperature during normal solidification. Moreover, the effect of the magnetic field on the crystallography of the Al-Al3Ni eutectic in the Al-Ni alloys was also studied. The applied magnetic field modified the orientation of the preferred growth direction of the Al3Ni eutectic fiber and the crystallographic orientation relationship of the Al-Al3Ni eutectic. The orientation of the preferred growth direction of the Al3Ni eutectic fiber depended mainly on the solidification direction and the alignment of the Al3Ni primary phase. Furthermore, a method for controlling the crystallization process by adjusting the angle between the solidification direction and the magnetic field was proposed.

  15. Influence of reduction temperature on composition, particle size, and magnetic properties of CoFe alloy nanomaterials derived from layered double hydroxide precursors.

    PubMed

    Yang, Shuangxia; Wang, Lianying; Yue, Shuang; Lu, Yanluo; He, Jing; Zhao, Dongye

    2014-06-14

    Individual CoFe alloy nanoparticles and CoFe-MgO nanocomposites were prepared through thermal reduction of single-source layered double hydroxide (LDH) precursors at various temperatures. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) analyses to investigate the influence of reduction temperature on the composition, particle size and size distribution, as well as the magnetic properties of the resulting materials. XRD and SEM results show that the as-prepared CoFe alloy nanoparticles and CoFe-MgO nanocomposites display high crystallinity and high purity. The average particle size of individual CoFe nanoparticles increases with the increase of reduction temperature. In the presence of the MgO matrix, uniform CoFe alloy nanoparticles with a narrow diameter distribution (8-11 nm) were obtained. Magnetic measurements indicate that the saturation magnetization strength (Ms) of the resulting materials increases with reduction temperature. The individual CoFe alloy nanoparticles exhibit excellent soft magnetic behavior with an extremely high Ms value (213 emu g(-1) at 800 °C), comparable to that of bulk CoFe alloy (230 emu g(-1)). For CoFe-MgO nanocomposites, small Ms values were obtained due to the small CoFe alloy particle size and low percentage of magnetic component. However, the coercivities are greatly enhanced (663 Oe at 450 °C) for the composites, implying their potential applications in data storage and other magnetic devices. PMID:24695765

  16. Nuclear Magnetic Resonance Study of the Unconventional Kondo Alloy System Uranium COPPER(5-X) Palladium(x)

    NASA Astrophysics Data System (ADS)

    Bernal, Oscar Orlando

    The intermetallic Kondo alloy system UCu _{5-x}Pd_{x } is one of a number of recently-discovered Kondo materials which exhibit deviations from Fermi liquid behavior in their thermodynamic and transport properties down to micro-Kelvin temperatures. Studying local electronic structure by nuclear magnetic resonance techniques (NMR) in this unconventional system, we find anomalous behavior of NMR parameters versus magnetic susceptibility chi in UCu_4Pd and UCu_{3.5}Pd_ {1.5}. Metallic alloys containing magnetic impurities usually display a linear relation between the susceptibility and the Knight shift and its distribution, the magnetic broadening. In UCu_{5 -x}Pd_{x}, as the temperature is lowered, it is found that for both concentrations the magnetic broadening of the ^{63}Cu NMR spectra grows non-linearly with respect to chi, reaching enhancements at the lowest temperatures of ~100% over the values expected from a high-temperature linear relation. Enhancement of the linewidth over the susceptibility might indicate the possibility of U-spin freezing, as observed in some dilute Kondo alloys. The absence of any anomalies in either the specific heat or the magnetic susceptibility of these samples suggests, however, that spin freezing does not account for the observations, and that the enhancement is related to intrinsic behavior of the paramagnetic alloys. Smaller but similar anomalies are found for the isotropic and axial components of the Knight shift {cal K} as functions chi in the two materials. {cal K} presents a linear relation with chi only down to ~30 K. Below this temperature, the absolute value of the Knight-shift components grows more slowly than would be expected from extrapolating their high temperature behavior, suggesting temperature-dependent transferred-hyperfine fields at the Cu sites or a temperature-dependent lineshape asymmetry. We interpret these observations in terms of disorder of the density of conduction-electron states (DOS). A simple model of

  17. Casting Atmosphere Effects on the Precipitates, Magnetism, and Corrosion Resistance of Fe78Si9B13 Glassy Alloys

    NASA Astrophysics Data System (ADS)

    Meng, L. L.; Li, X. Y.; Pang, J.; Wang, L.; An, B.; Yin, L. J.; Song, K. K.; Wang, W. M.

    2013-11-01

    The precipitates, magnetism, and corrosion resistance of Fe78Si9B13 glassy samples fabricated in vacuum and air atmospheres (labeled as VAC and AIR samples, respectively) were studied. The findings show that the fraction of the amorphous phase in VAC samples is lower than that in the AIR counterparts. The Fe phase in VAC samples grows preferentially along the <200> orientation. The distribution of magnetization M 4000 of VAC samples oriented parallel and orthogonal to the field ( H // and H ⊥) at H = 4000 Oe is more scattered than AIR samples. The corrosion resistance of VAC samples is lower than AIR counterparts, which can be attributed to the minor alloying effect of oxygen and the passive effect of silicon atoms supplied from the amorphous phase.

  18. Structural and magnetic properties of ion beam sputtered Co2FeAl full Heusler alloy thin films

    NASA Astrophysics Data System (ADS)

    Husain, Sajid; Kumar, Ankit; Chaudhary, Sujeet; Svedlindh, Peter

    2016-05-01

    Co2FeAl full Heusler alloy thin films grown at different temperatures on Si(100) substrates using ion beam sputtering system have been investigated. X-ray diffraction (XRD) patterns revealed the A2 disordered phase in these films. The deduced lattice parameter slightly increases with increase in the growth temperature. The saturation magnetization it is found to increase with increase in growth temperature. The magnetic anisotropy has been studied using angle dependent magneto-optical Kerr effect. In the room temperature deposited film, the combination of cubic and uniaxial anisotropy have been observed with weak in-plane uniaxial anisotropy which increases with growth temperature. The uniaxial anisotropy is attributed to the anisotropic interfacial bonding in these Co2FeAl /Si(100) heterostructures.

  19. Morphology and magnetic behavior of cobalt rich amorphous/nanocrystalline (Co-Ni)70Ti10B20 alloyed powders

    NASA Astrophysics Data System (ADS)

    Raanaei, Hossein; Mohammad-Hosseini, Vahid

    2016-09-01

    The effect of milling time on microstructural and magnetic behavior of mechanically alloyed Co49Ni21Ti10B20 is investigated by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, differential scanning calorimetry and vibrating sample magnetometer. It is shown, with increasing milling time, the crystallite size decreases and finally reaches to a low value after 190 h of milling time. The increase in microstrain is also observed during the milling process. The results indicate the coexistence between amorphous and nanocrystalline phases after 190 h of milling time. Moreover, the lowest magnetic coercivity of about 39 Oe at the final milling stage is observed. The results of annealed sample reveal structural ordering of constituent elements.

  20. Phase selection and nanocrystallization in Cu-free soft magnetic FeSiNbB amorphous alloy upon rapid annealing

    NASA Astrophysics Data System (ADS)

    Morsdorf, L.; Pradeep, K. G.; Herzer, G.; Kovács, A.; Dunin-Borkowski, R. E.; Povstugar, I.; Konygin, G.; Choi, P.; Raabe, D.

    2016-03-01

    Nucleation of soft magnetic Fe3Si nanocrystals in Cu-free Fe74.5Si15.5Nb3B7 alloy, upon rapid (10 s) and conventional (30 min) annealing, was investigated using x-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy, and atom probe tomography. By employing rapid annealing, preferential nucleation of Fe3Si nanocrystals was achieved, whereas otherwise there is simultaneous nucleation of both Fe3Si and undesired Fe-B compound phases. Analysis revealed that the enhanced Nb diffusivity, achieved during rapid annealing, facilitates homogeneous nucleation of Fe3Si nanocrystals while shifting the secondary Fe-B crystallization to higher temperatures resulting in pure soft magnetic nanocrystallization with very low coercivities of ˜10 A/m.

  1. Magnetic and transport properties of (β+γ) Ni35Co35Al30 ferromagnetic shape memory alloy across the martensitic transition

    NASA Astrophysics Data System (ADS)

    Sokhey, Kanwaljeet S.; Manekar, Meghmalhar; Chattopadhyay, M. K.; Kaul, Rakesh; Roy, S. B.; Chaddah, P.

    2003-06-01

    The results of dc-magnetization, resistivity and ac-susceptibility studies performed on (β+γ) Ni35Co35Al30 magnetic shape memory alloy are presented highlighting the transition between two equilibrium lattice configurations of austenite and martensite phases. The first order nature of this martensitic transition is emphasized by highlighting the presence of thermal hysteresis and phase co-existence. This transition is apparently broadened with the introduction of γ-phase in the pure β-phase Ni35Co35Al30 alloy giving rise to a relatively large thermal hysteresis.

  2. Theoretical investigation of the magnetic and structural transitions of Ni-Co-Mn-Sn metamagnetic shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Li, Chun-Mei; Hu, Qing-Miao; Yang, Rui; Johansson, Börje; Vitos, Levente

    2015-07-01

    The composition-dependent crystal structure, elastic modulus, phase stability, and magnetic property of Ni2 -xCoxMn1.60Sn0.40 (0 ≤x ≤0.50 ) are studied by using first-principles calculations in combination with atomistic spin dynamics method. It is shown that the present lattice parameters and Curie temperature (TC) are in agreement with the available experimental data. The martensitic phase transformation (MPT) occurs for x <0.43 , where the austenite is in the ferromagnetic (FM) state whereas the martensite is in the antiferromagnetic (AFM) one at 0 K. The x dependence of the lattice parameter, elastic modulus, and energy difference between the FM austenite and the AFM martensite well accounts for the decrease of the MPT temperature (TM) with the Co addition. With increasing x , the increase of the magnetic excitation energy between the paramagnetic and FM austenite of these alloys is in line with the TC˜x . The Ni 3 d as well as the Co 3 d electronic states near the Fermi level are confirmed mainly dominating the phase stability of the studied alloys.

  3. Application of the Preisach and Jiles{endash}Atherton models to the simulation of hysteresis in soft magnetic alloys

    SciTech Connect

    Pasquale, M.; Bertotti, G.; Jiles, D.C.; Bi, Y.

    1999-04-01

    This article describes the advances in unification of model descriptions of hysteresis in magnetic materials and demonstrates the equivalence of two widely accepted models, the Preisach (PM) and Jiles{endash}Atherton (JA) models. Recently it was shown that starting from general energy relations, the JA equation for a loop branch can be derived from PM. The unified approach is here applied to the interpretation of magnetization measured in nonoriented Si{endash}Fe steels with variable grain size {l_angle}s{r_angle}, and also in as-cast and annealed Fe amorphous alloys. In the case of NO Fe{endash}Si, the modeling parameter {ital k} defined by the volume density of pinning centers is such that k{approx}A+B/{l_angle}s{r_angle}, where the parameters {ital A} and {ital B} are related to magnetocrystalline anisotropy and grain texture. The value of {ital k} in the amorphous alloys can be used to estimate the microstructural correlation length playing the role of effective grain size in these materials. {copyright} {ital 1999 American Institute of Physics.}

  4. Structural and soft magnetic properties of a new nanocrystalline Fe-based and B-free alloy

    NASA Astrophysics Data System (ADS)

    Long, Jianguo; Laughlin, D. E.; McHenry, M. E.

    2008-04-01

    A new nanocrystalline Fe-based soft magnetic alloy is discussed here. Ingots of nanocrystalline alloys (FeCu)80ZrxSi20-x (x =5, 6, and 8) were prepared by arc melting. The ingots were remelted and cast into 25-30μm thick ribbons by a single roller melt spinning method. X-ray diffraction (XRD) revealed the as-spun ribbons to be amorphous. The structural evolution of these samples was studied by XRD and transmission electron microscopy (TEM) after annealing at 450, 480, and 550°C. XRD shows the primary nanocrystallization product to be the α-Fe(Si ) phase. The grain size was observed by TEM to be ˜10nm after annealing at 480°C for 1h and 14nm after 550°C for 1h. ac soft magnetic properties were measured using a Walker AMH 401 ac permeameter. The core loss at an exciting frequency f =100kHz and maximum induction Bm=1kG was determined to be less than 19W/kg.

  5. Effect of a Transverse Magnetic Field on Solidification Structures in Unmodified and Sr-Modified Al-7wtpctSi Alloys During Directional Solidification

    NASA Astrophysics Data System (ADS)

    Li, Xi; Gagnoud, Annie; Fautrelle, Yves; Moreau, Rene; Du, Dafan; Ren, Zhongming; Lu, Xionggang

    2016-03-01

    The influence of a transverse magnetic field on the microstructures in unmodified and Sr-modified Al-7wtpctSi alloys during directional solidification was investigated. Experimental results indicated that the magnetic field caused the channel and freckle macrosegregations during directional solidification. Comparison of the microstructures in unmodified and Sr-modified Al-7wtpctSi alloys showed that the Sr-addition enhanced the convection effects. Moreover, the EBSD analysis revealed that the magnetic field changed the alignment of the α-Al dendrite and modified the distribution of dendrite fragments in both unmodified and Sr-modified Al-7wtpctSi alloys. Indeed, the application of the magnetic field caused the <001>-crystal direction of the α-Al dendrite to deflect from the solidification direction and induced the formation of dendrite fragments on one side of the sample. Further, the Seebeck signal ( E S) at the liquid/solid interface was measured in situ during directional solidification of Al-7wtpct Si alloy and the results indicated that the value of the E S was of the order of 10 μV and decreased with the increase of the growth speed. The above results may be attributed to the thermoelectric magnetic convection and its effect on the distribution of the solute Si. It is proven that solute effects are primarily responsible for dendrite fragmentation.

  6. Influence of microstructural changes on magnetic refrigeration performance for La(Fe0.94Co0.06)11.8Si1.2 alloys during magnetic field cycling

    NASA Astrophysics Data System (ADS)

    Yuan, Z. M.; He, J.; Yang, L.; Xia, Z. J.; Zhao, D. L.; You, C. Y.; Ren, W. J.

    2015-05-01

    NaZn13-type La(Fe0.94Co0.06)11.8Si1.2 alloys were manufactured to investigate the influence of their microstructural change on magnetic refrigeration performance during magnetic field cycling. The magnetic refrigeration performance measurements indicate that both the large magnetic entropy change value (ΔS = 14.1 J kg-1 K-1) and maximum adiabatic temperature change (ΔT = 2.2 K) are favorable for the alloys to be superior candidate of magnetic refrigerants. However, the alloys exhibit nearly 10% decrease of ΔS and ΔT when they performed cycling ten-thousand times. More than thousand times of cycles induce local stress and grain cleavages presented by the accumulation of irreversible microstructure changes such as micro-cracks and sub-boundaries. According to the domain observation for the alloys with different field cycles, these microstructure characteristics accompany with the reconfiguration of the local magnetic domains and increase of domain wall energy, which are considered to be the reason of the decrease of ΔS.

  7. Magnetic properties of Zn /SUB 3x/ Cd/sub 3/(1-x)P/sub 2/ alloys

    SciTech Connect

    Vitikina, T.Z.; Smolyarenko, E.M.; Trukhan, V.M.

    1985-03-01

    The authors present results of magnetic susceptibility measurements made by the Guy method in solid solutions based on the compounds Zn/sub 3/P/sub 2/ and Cd/sub 3/P/sub 2/. Before measurement, samples were etched in an etchant especially selected for each composition and prepared from hydrochloric and nitric acids, washed in tripledistilled water, and dried. A series of investigations was conducted for revealing the effect of pulverizing on the magnitude of magnetic susceptibility. All investigated alloys were diamagnetic. The magnetic susceptibility of the samples of Zn /SUB 3x/ Cd/sub 3/(1-x)P/sub 2/ solid solutions varied weakly (under 10%) with increasing temperature in the investigated temperature range (170 - 570/sup 0/K), suggesting that the basic contribution to the measured magnetic susceptibility is the susceptibility of the lattice. From the experimentation it is concluded that the dependence x /SUB mol/ = f(x) has a discontinuity at x approx. = 0.16, which apparently is related to the transition from structures with indirect optical transitions to those with direct optical transitions in the cited systems.

  8. On the modeling of equilibrium twin interfaces in a single-crystalline magnetic shape memory alloy sample. II: numerical algorithm

    NASA Astrophysics Data System (ADS)

    Wang, Jiong; Steinmann, Paul

    2016-05-01

    This is part II of this series of papers. The aim of the current paper was to solve the governing PDE system derived in part I numerically, such that the procedure of variant reorientation in a magnetic shape memory alloy (MSMA) sample can be simulated. The sample to be considered in this paper has a 3D cuboid shape and is subject to typical magnetic and mechanical loading conditions. To investigate the demagnetization effect on the sample's response, the surrounding space of the sample is taken into account. By considering the different properties of the independent variables, an iterative numerical algorithm is proposed to solve the governing system. The related mathematical formulas and some techniques facilitating the numerical calculations are introduced. Based on the results of numerical simulations, the distributions of some important physical quantities (e.g., magnetization, demagnetization field, and mechanical stress) in the sample can be determined. Furthermore, the properties of configurational force on the twin interfaces are investigated. By virtue of the twin interface movement criteria derived in part I, the whole procedure of magnetic field- or stress-induced variant reorientations in the MSMA sample can be properly simulated.

  9. Effect of Nb Concentration on Thermal Stability and Glass-Forming Ability of Soft Magnetic (Fe,Co)-Gd-Nb-B Glassy Alloys

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Jia, Fei; Zhang, Xingguo; Xie, Guoqiang; Inoue, Akihisa

    2010-07-01

    Addition of a small amount of Nb to the (Fe,Co)-Gd-B glassy alloy in (Fe0.9Co0.1)71.5- x Nb x Gd3.5B25 increased the stabilization of supercooled liquid. The largest supercooled liquid region of 104 K was obtained for the x = 2 alloy. A distinct two-stage-like glass transition was observed with further incresing Nb content. The nanoscale (Fe,Co)23B6 phase precipitated in the glassy matrix after annealing, while the two-stage-like glass transition disappeared, indicating that the anomalous glass transition behavior originates from the exothermic reaction for the formation of the (Fe,Co)23B6 phase in the supercooled liquid region. The glass-forming ability (GFA) also increased by addition of Nb, leading to formation of the bulk glass form for the Nb-doped alloys. The best GFA with a diameter of over 3 mm was achieved for the x = 4 alloy. The (Fe,Co)-Gd-Nb-B glassy alloys exhibited good magnetic properties, i.e., rather high saturation magnetization of 0.81 to 1.22 T, low coercive force of 2.5 to 5.8 A/m, and low saturated magnetostriction of 9 to 19 × 10-6. In addition, the glassy alloys also possessed very high compressive fracture strength of 3842 to 3916 MPa and high Vickers hardness of 1025 to 1076.

  10. Effect of Cr addition on the glass-forming ability, magnetic properties, and corrosion resistance in FeMoGaPCBSi bulk glassy alloys

    NASA Astrophysics Data System (ADS)

    Shen, Baolong; Akiba, Masahiro; Inoue, Akihisa

    2006-08-01

    The effect of Cr addition on the glass-forming ability (GFA), the magnetic properties, and corrosion resistance in Fe-Mo-Ga-P-C-B-Si glassy alloys was investigated. In addition to a slight increase of supercooled liquid region from 50to55K, the substitution of a small amount of Fe with Cr was found to be effective for approaching alloy to a eutectic point, resulting in an increase in GFA. By copper mold casting, bulk glassy alloy rods with diameters up to 3mm were produced. These glassy alloys exhibit a rather high saturation magnetization of 0.84-1.11T with good soft-magnetic properties, i.e., low coercive force of 2.3-2.9A/m, and high effective permeability of 13 360-15 960 at 1kHz under a field of 1A/m. The passive current density of the glassy alloy rod in 3mass% NaCl solution decreased significantly from 1×102to3×10-1A/m2 with an increase in Cr content, indicating that the addition of Cr is effective in enhancing the corrosion resistance.

  11. Magnetic properties and magnetostriction of PrxNd1-xFe1.9 (0 <= x <= 1.0) alloys at low temperature

    NASA Astrophysics Data System (ADS)

    Wang, Yong; Tang, Shao-Long; Li, Yu-Long; Xie, Ren; Du, You-Wei

    2013-03-01

    The crystal structure, magnetic and magnetostrictive properties of high-pressure synthesized PrxNd1-xFe1.9 (0 <= x <= 1.0) alloys were studied. The alloys exhibit single cubic Laves phase with MgCu2-type structure. The initial magnetization curve reveals that Pr0.2Nd0.8Fe1.9 has a minimum magnetocrystalline anisotropy at 5 K. The magnetostriction curve at 5 K shows that Pr0.2Nd0.8Fe1.9 has a very good low-field magnetostrictive property, and the magnetostriction of the PrxNd1-xFe1.9 alloy in high magnetic field is attributable mainly to Pr. The temperature dependence of the magnetostriction (λ‖) at the field of 5 kOe shows that the substitution of Nd reduces the K1 remarkably, and the values of λ‖ of Pr0.2Nd0.8Fe1.9 and Pr0.8Nd0.2Fe1.9 alloys are nearly five times larger than that of the PrFe1.9 alloy below 50 K; the λ‖ of Pr0.8Nd0.2Fe1.9 reaches up to 1082 ppm at 100 K, which makes it a potential candidate for application in this temperature range.

  12. Temperature and concentration dependent magnetic properties of epitaxial Fe{sub 1−x}Cr{sub x}-alloy films in the high Cr-concentration regime

    SciTech Connect

    Brüssing, F.; Abrudan, R.; Zabel, H.

    2014-07-21

    Soft magnetic materials with a Curie temperature (T{sub c}) close to room temperature are suitable candidates for device applications and for more fundamental aspects of magnetism. Promising candidates are Fe{sub 1−x}Cr{sub x}-alloys with a Fe concentration of about 25%–35%. We have grown by molecular beam epitaxy methods a number of epitaxial Fe{sub 1−x}Cr{sub x} alloys on MgO[100] and MgO[110] substrates, and we report on their structural and magnetic properties in this concentration range, including the dependence of the Curie temperature (T{sub c}) on the concentration, the magnetocrystalline anisotropy, and the development of the magnetic moment.

  13. Effect of Sn and Sb element on the magnetism and functional properties of Ni-Mn-Al ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Agarwal, Sandeep; Mukhopadhyay, P. K.

    2016-03-01

    We have replaced Al partially with Sb and Sn in Ni-Mn-Al systems and investigated its effect on magnetism, entropy change and magnetoresistance in the vicinity of martensitic transformation. Both the samples had identical lattice parameters and Mn contents, which are mostly responsible for magnetism in these systems, yet there were marked changes in magnetic and functional properties of these systems. It was found that the magnetization increased in Sb alloy, while entropy change and magnetoresistance decreased as compared to Sn alloy. These changes are attributed to the change in antiferromagnetic interaction as a result of variation in the Ni d-Mn d hybridization arising due to presence of different sp elements.

  14. Evolution of magnetic properties and microstructure of Hf{sub 2}Co{sub 11}B alloys

    SciTech Connect

    McGuire, Michael A. Rios, Orlando

    2015-02-07

    Amorphous Hf{sub 2}Co{sub 11}B alloys produced by melt-spinning have been crystallized by annealing at 500–800 °C, and the products have been investigated using magnetization measurements, x-ray diffraction, and scanning electron microscopy. The results reveal the evolution of the phase fractions, microstructure, and magnetic properties with both annealing temperature and time. Crystallization of the phase denoted HfCo{sub 7}, which is associated with the development of coercivity, occurs slowly at 500 °C. Annealing at intermediate temperatures produces mixed phase samples containing some of the HfCo{sub 7} phase with the highest values of remanent magnetization and coercivity. The equilibrium structure at 800 °C contains HfCo{sub 3}B{sub 2}, Hf{sub 6}Co{sub 23}, and Co, and displays soft ferromagnetism. Maximum values for the remanent magnetization, intrinsic coercivity, and magnetic energy product among the samples are approximately 5.2 kG, 2.0 kOe, and 3.1 MGOe, respectively, which indicates that the significantly higher values observed in crystalline, melt-spun Hf{sub 2}Co{sub 11}B ribbons are a consequence of the non-equilibrium solidification during the melt-spinning process. Application of high magnetic fields during annealing is observed to strongly affect the microstructural evolution, which may provide access to higher performance materials in Zr/Hf-Co hard ferromagnets. The crystal structure of HfCo{sub 7} and the related Zr analogues is unknown, and without knowledge of atomic positions powder diffraction cannot distinguish among proposed unit cells and symmetries found in the literature.

  15. Effect of magnetism and atomic order on static atomic displacements in the Invar alloy Fe-27 at.% Pt

    NASA Astrophysics Data System (ADS)

    Sax, C. R.; Schönfeld, B.; Ruban, A. V.

    2015-08-01

    Fe-27 at.% Pt was aged at 1123 K and quenched to room temperature (RT) to set up a state of thermal equilibrium. The local atomic arrangement was studied by diffuse x-ray scattering above (at 427 K) and below (at RT) the Curie temperature as well as at RT under a saturating magnetic field. The separated short-range order scattering remained unchanged for all three states, with maxima at 100 positions. Effective pair interaction parameters determined by the inverse Monte Carlo method gave an order-disorder transition temperature of about 1088 K, close to direct experimental findings. The species-dependent static atomic displacements for the first two shells show large differences, with a strong increase in magnitude from the state at 427 K over RT to the state under saturating magnetic field. This outcome is in agreement with an increase in atomic volume of Fe with increasing local magnetic moment. Electronic-structure calculations closely reproduce the values for the static atomic displacements in the ferromagnetic state, and predict their dependence on the atomic configuration. They also reveal a strong dependence of the magnetic exchange interactions in Fe-Pt on the atomic configuration state and lattice parameter. In particular, the increase of the Curie temperature in a random state relative to that in the ordered one is demonstrated to be related to the corresponding change of the magnetic exchange interactions due to the different local atomic chemical environment. There exists a similar strong concentration dependence of the chemical interactions as in the case of magnetic exchange interactions. Theoretical effective interactions for Fe-27 at.% Pt alloy are in good agreement with experimental results, and they also reproduce well the L1 2-A1 transition temperature.

  16. Synthesis, structure and magnetic properties of L10 alloy (FePt)100- x Zn x nanoparticles

    NASA Astrophysics Data System (ADS)

    Zeynali, Hossein; Akbari, Hossein; Bakhshayeshi, Ali

    2016-04-01

    In the present work, alloy (FePt)100- x Zn x nanoparticles have been successfully synthesized by simple wet chemical method with the aid of Pt(acac)2, Fe(acac)3 and Zn(acac)2 as the starting reagents. Oleic acid and oleylamine was used as a surfactant agent. The addition of zinc promoted the face-centered cubic to tetragonal phase transition. Reduction in temperature required for this transition compared with FePt nanoparticles with no additives. This reduction in ordering temperature significantly reduces FePt particle coalescence and enhancing chemical ordering, so magnetic measurements show high coercivity up to 6 kOe of the (FePt)82Zn18 nanoparticles with average size <10 nm after annealing at 500 °C for 60 min. The coercivity increases with the content of zinc up to 18 %, and above this percent, the coercivity starts to decrease. In order to calculate magnetic properties for Zn in FePt: Zn structure, we used density functional theory and GGA approximation. The energy of FePt: Zn structure in which Zn atom replaces Fe ones is lower than other possible structures, so forming of this system is more probable. Calculations show than Zn atoms do not have a significant magnetic momentum when replacing Fe atoms. Curie temperature variation as a function of added Zn atoms is derived. Added Zn atoms replace Fe atoms and previous Fe site is occupied with Zn with approximately zero magnetic momentum. Since these sites are randomly occupied, we have random exchange interactions in the system which can be modeled like spin glass system. Zn atoms have a zero magnetic momentum when replacing Fe atoms, so total magnetic momentum and Curie temperature of FePt: Zn structure decrease with increasing Zn percentage.

  17. Theoretical study of magnetism and superconductivity in three-dimensional transition-metal-MgB2 alloys

    NASA Astrophysics Data System (ADS)

    Singh, Prabhakar P.; Joseph, P. Jiji Thomas

    2002-12-01

    We have studied the electronic structure of three-dimensional transition-metal-MgB2 alloys, Mg0.97TM0.03B2, (TM = Sc, Ti, V, Cr Mn, Fe, Co, Ni, Cu, Zn) using the Korringa-Kohn-Rostoker coherent-potential approximation method in the atomic-sphere approximation. For unpolarized calculations, our results for Mg0.97TM0.03B2 alloys are similar to that of 3d impurities in other s and s-p metals. In particular, the local densities of states (DOS) associated with the 3d impurities are similar to our earlier work on 3d impurities in bulk Al (Singh P P 1991 Phys. Rev. B 43 3975; Singh P P 1991 J. Phys.: Condens. Matter 3 3285). For spin-polarized calculations, we find only the alloys of V, Cr, Mn, Fe and Co with MgB2 to be magnetic of all the 3d elements. We also find that Cr and Mn in MgB2 have a relatively large local magnetic moment of 2.43 and 2.87μB, respectively. We have used the unpolarized, self-consistent potentials of Mg0.97TM0.03B2 alloys, obtained within the coherent-potential approximation, to calculate the electron-phonon coupling constant λ using the Gaspari-Gyorffy formalism and the superconducting transition temperature Tc using the Allen-Dynes equation. We find that the calculated Tc is lowest for Mg0.97Cr0.03B2 and highest for Mg0.97Zn0.03B2, in qualitative agreement with experiment. The calculated trend in variation of Tc from Mn to Zn is also similar to the available experimental data. Our analysis of the variation in Tc, in terms of the DOS and the spectral function along the Γ to A direction, shows the variation to be an interplay between the total DOS at the Fermi energy and the creation/removal of states along the Γ to A direction (Singh P P 2002 Preprint cond-mat/0201093).

  18. High-field magnetization of heusler alloys Fe2 XY ( X = Ti, V, Cr, Mn, Fe, Co, Ni; Y = Al, Si)

    NASA Astrophysics Data System (ADS)

    Kourov, N. I.; Marchenkov, V. V.; Korolev, A. V.; Belozerova, K. A.; Weber, H. W.

    2015-10-01

    The magnetization curves of ferromagnetic Heusler alloys Fe2 XY (where X = Ti, V, Cr, Mn, Fe, Co, Ni are transition 3 d elements and Y = Al, Si are the s and p elements of the third period of the Periodic Table) have been measured at T = 4.2 K in the field range H ≤ 70 kOe. It has been shown that the high-field ( H ≥ 20 kOe) magnetization is described within the Stoner model.

  19. Magnetic properties of Fe73.5Cu1Nb3-xUxSi13.5B9 (x = 1, 2, 3) nanocrystalline alloys

    NASA Astrophysics Data System (ADS)

    Kollár, P.; Füzer, J.; Matta, P.; Švec, T.; Konč, M.

    1996-05-01

    The influence of uranium content and annealing on the magnetic properties and Hall effect of Fe73.5Cu1Nb3-xUxSi13.5B9 (x = 1, 2, 3) nanocrystalline alloys prepared by melt spinning were investigated. Measurements of magnetic properties of surface layers confirmed higher concentration of uranium in the air-side surface layers than in the wheel-side layers.

  20. Ab initio construction of magnetic phase diagrams in alloys: The case of Fe1-xMnxPt

    SciTech Connect

    Pujari, B. S.; Larson, P.; Antropov, V. P.; Belashchenko, K. D.

    2015-07-28

    A first-principles approach to the construction of concentration-temperature magnetic phase diagrams of metallic alloys is presented. The method employs self-consistent total energy calculations based on the coherent potential approximation for partially ordered and noncollinear magnetic states and is able to account for competing interactions and multiple magnetic phases. The application to the Fe1–xMnxPt “magnetic chameleon” system yields the sequence of magnetic phases at T = 0 and the c-T magnetic phase diagram in good agreement with experiment, and a new low-temperature phase is predicted at the Mn-rich end. The importance of non-Heisenberg interactions for the description of the magnetic phase diagram is demonstrated.

  1. Experimental Investigations on Pulsed Nd:YAG Laser Welding of C17300 Copper-Beryllium and 49Ni-Fe Soft Magnetic Alloys

    SciTech Connect

    Mousavi, S. A. A. Akbari; Ebrahimzadeh, H.

    2011-01-17

    Copper-beryllium and soft magnetic alloys must be joined in electrical and electro-mechanical applications. There is a high difference in melting temperatures of these alloys which cause to make the joining process very difficult. In addition, copper-beryllium alloys are of age hardenable alloys and precipitations can brittle the weld. 49Ni-Fe alloy is very hot crack sensitive. Moreover, these alloys have different heat transfer coefficients and reflection of laser beam in laser welding process. Therefore, the control of welding parameters on the formation of adequate weld puddle composition is very difficult. Laser welding is an advanced technique for joining of dissimilar materials since it can precisely control and adjust the welding parameters. In this study, a 100W Nd:YAG pulsed laser machine was used for joining 49Ni-Fe soft magnetic to C17300 copper-beryllium alloys. Welding of samples was carried out autogenously by changing the pulse duration, diameter of beam, welding speed, voltage and frequency. The spacing between samples was set to almost zero. The ample were butt welded. It was required to apply high voltage in this study due to high reflection coefficient of copper alloys. Metallography, SEM analysis, XRD and microhardness measurement was used for survey of results. The results show that the weld strength depends upon the chemical composition of the joints. To change the wells composition and heat input of the welds, it was attempted to deviate the laser focus away from the weld centerline. The best strength was achieved by deviation of the laser beam away about 0.1mm from the weld centerline. The result shows no intermetallic compounds if the laser beam is deviated away from the joint.

  2. Experimental Investigations on Pulsed Nd:YAG Laser Welding of C17300 Copper-Beryllium and 49Ni-Fe Soft Magnetic Alloys

    NASA Astrophysics Data System (ADS)

    Mousavi, S. A. A. Akbari; Ebrahimzadeh, H.

    2011-01-01

    Copper-beryllium and soft magnetic alloys must be joined in electrical and electro-mechanical applications. There is a high difference in melting temperatures of these alloys which cause to make the joining process very difficult. In addition, copper-beryllium alloys are of age hardenable alloys and precipitations can brittle the weld. 49Ni-Fe alloy is very hot crack sensitive. Moreover, these alloys have different heat transfer coefficients and reflection of laser beam in laser welding process. Therefore, the control of welding parameters on the formation of adequate weld puddle composition is very difficult. Laser welding is an advanced technique for joining of dissimilar materials since it can precisely control and adjust the welding parameters. In this study, a 100W Nd:YAG pulsed laser machine was used for joining 49Ni-Fe soft magnetic to C17300 copper-beryllium alloys. Welding of samples was carried out autogenously by changing the pulse duration, diameter of beam, welding speed, voltage and frequency. The spacing between samples was set to almost zero. The ample were butt welded. It was required to apply high voltage in this study due to high reflection coefficient of copper alloys. Metallography, SEM analysis, XRD and microhardness measurement was used for survey of results. The results show that the weld strength depends upon the chemical composition of the joints. To change the wells composition and heat input of the welds, it was attempted to deviate the laser focus away from the weld centerline. The best strength was achieved by deviation of the laser beam away about 0.1mm from the weld centerline. The result shows no intermetallic compounds if the laser beam is deviated away from the joint.

  3. An in-situ study of magnetic domain structures in undercooled Fe-29.5 at. %Pd magnetostrictive alloys by Lorentz microscopy and electron holography

    SciTech Connect

    Sun, Wen; Xu, Xianhui; Liu, Jian E-mail: xiawxing@nimte.ac.cn; Xia, Weixing E-mail: xiawxing@nimte.ac.cn; Yan, Aru

    2015-04-28

    Understanding of correlation between magnetic domain structure and functional properties is of importance for the magnetic field driven phase transition (e.g., martensitic transformation) or microstructure variation (e.g., twin boundary motion) materials. In this work, we report a Fe-29.5 at. %Pd shape memory alloy treated by undercooling processing upon a degree of 320 K below the liquid temperature. The effect of high undercooling on the solidified microstructure and martensitic transformation temperatures was investigated. By in-situ Lorentz transmission electron microscopy and electron holography, magnetic domain structure and the field-induced domain wall motion behavior in as-cast and undercooled samples have been schematically studied. The irregular domain structure can be observed in these alloys. On the application of a field up to 300 Oe, the domain walls for both samples are able to move along the direction of the external magnetic field, but structural transition and rearrangement of variants are not observed in the undercooled alloy. The large magnetostriction of Fe-29.5 at. %Pd undercooled alloy originates from the irregular domain walls motion instead of the rearrangement of martensitic twin variants.

  4. Substitution effect on magnetic and electrical properties of half-Heusler alloy Ni{sub 1−x}Co{sub x}Mn{sub 1−y}Fe{sub y}Sb

    SciTech Connect

    Kushwaha, Varun Sharma, Himanshu Dixit, Dinesh Tomy, C. V.; Tulapurkar, Ashwin

    2014-04-24

    We have studied the effects of Co and Fe doping on the magnetic and electrical properties of half-Heusler compound NiMnSb. The alloys were prepared by arc-melting method in the presence of Argon gas. The powder X-ray diffraction of the each alloy was performed in air at room temperature. The magnetic and electrical properties were performed in the temperature range 2–400 K and in magnetic field up to 1 T.

  5. Self-biased magnetoelectric coupling characteristics of three-phase composite transducers with nanocrystallin soft magnetic alloy

    NASA Astrophysics Data System (ADS)

    Huang, Dongyan; Lu, Caijiang; Bing, Han

    2015-07-01

    This paper reports the self-biased magnetoelectric (ME) effects in composites consisting of high-permeability Fe-based nanocrystalline soft magnetic alloy Fe73.5Cu1Nb3Si13.5B9 (FeCuNbSiB), pure nickel (Ni) and piezoelectric lead zirconate titanate (PZT). The FeCuNbSiB ribbons are fabricated on traditional laminates Ni/PZT/Ni through two modes: the attached mode (F-NPN-F) and the laminated mode (F/NPN/F). The F-NPN-F composite sufficiently reveals that the high-permeability FeCuNbSiB ribbons concentrate more magnetic flux in magnetostrictive Ni, which results in the self-biased ME effects of F-NPN-F. For the F/NPN/F composite, the FeCuNbSiB acts as the dynamic driver to enhance the effective piezomagnetic coefficient of Ni. The giant self-biased ME effects of F/NPN/F are because of the internal magnetic field between Ni and FeCuNbSiB due to their different magnetic characteristics. The influences of the numbers of FeCuNbSiB layers ( L) on the resonant ME voltage coefficients ( α ME ,r ) for F-NPN-F and F/NPN/F composites are investigated in detail. The experiments demonstrate that the maximum α ME ,r at zero-biased field is 80 V/cm Oe for F-NPN-F with L = 2, and 85 V/cm Oe for F/NPN/F with L = 4. This paper demonstrates that these two ME composites are suitable for achieving zero-biased ME transducers, power-free magnetic field sensors and energy harvesters.

  6. Microstructure and magnetic properties of as-cast Ni2MnGa alloys processed by twin roller melt spinning

    NASA Astrophysics Data System (ADS)

    Pozo López, G.; Condó, A. M.; Giordano, R. N.; Urreta, S. E.; Haberkorn, N.; Winkler, E.; Fabietti, L. M.

    2013-06-01

    The magnetism and the microstructure of Ni2MnGa alloys, processed for the first time by twin roller melt spinning at tangential wheel speeds of 10 m/s (V10), 15 m/s (V15) and 20 m/s (V20) are investigated. At room temperature, the major phase in the as-cast alloys is the cubic L21 Ni2MnGa ordered austenitic phase, with a lattice parameter only ˜0.1% larger than the tabulated value. The order domain size in the austenitic phase decreases from (40±1) nm in samples V10 to (19±1) nm in V20. Mn(S,Se) small precipitates are also found uniformly embedded in the ribbons with mean size of (26±2) nm (V10) and (7±2) nm (V20), exhibiting a definite orientation relation with the austenitic matrix, <1 0 0>P// <1 0 0>a. The as-cast alloys transform to an intermediate cubic phase I at about 220-230 K depending on the quenching rate and to a martensitic phase at about 130 K. The high temperature austenitic phase and the low temperature martensitic phase are ferromagnetic; in both cases the saturation polarization is lower in samples quenched at higher rates. The demagnetization curves measured from saturation in the martensitic state show two marked steps: a first one for positive fields in V15 and V10 (˜46 mT) and a larger second one for relatively large inverse fields (˜130-250 mT) in all the samples. These steps are likely to arise from a demagnetization mechanism involving a field induced twin boundary motion in the few martensite variants selected by the crystallographic texture and the quenched stresses in the ribbons.

  7. Quantitative microstructural characterisation of Fe-30Ni alloy after martensitic transformations by means of stereological and magnetic methods

    SciTech Connect

    Ciura, Franciszek . E-mail: ciura@uci.agh.edu.pl; Dubiel, Beata; Satora, Kazimierz

    2006-06-15

    In the Fe-30Ni alloy investigated a martensitic transformation can occur both during quenching or plastic deformation. Martensite formed during plastic deformation, depending on the thermo-mechanical treatment applied, exhibits a different morphology from that achieved during quenching and forms the so-called composite-like structure. The morphology and volume fraction of martensite depends both on strain and temperature. In the present studies Fe-30Ni alloy was deformed by monotonic rolling in one path and perpendicular rolling in the temperature range M {sub D}-M {sub S}. The aim of the investigations was a determination of martensite volume fraction depending on the strain and temperature. To examine the influence of strain, the alloy was deformed by rolling in one path or perpendicular rolling at a temperature of - 30 deg. C, in the strain range of 10-30%. The dependence of temperature was investigated by rolling with 30% strain in a temperature range from - 30 deg. C to - 80 deg. C. The variants of thermo-mechanical treatment performed enabled us to achieve different martensite morphologies and volume fractions. Microstructural analysis was performed by means of light microscopy and transmission electron microscopy. The results of quantitative microstructural analysis of martensite and retained austenite volume fractions formed in different thermo-mechanical treatments were compared with those obtained by magnetic measurements. The fraction of deformation-induced martensite determined varied from 2% to 86%. The partial volume fractions V {sub V} {sup MF} of martensite formed in different deformation directions were also determined. It was found that the influence of the temperature on the martensite volume fraction is more pronounced than the influence of strain.

  8. Microstructure Of Multistage Annealed Nanocrystalline SmCo2Fe2B Alloy With Enhanced Magnetic Properties

    SciTech Connect

    Jiang, Xiujuan; Devaraj, Arun; Balamurugan, B.; Cui, Jun; Shield, Jeffrey E.

    2014-02-11

    The microstructure and chemistry of SmCo2Fe2B melt-spun alloy after multistage annealing was investigated using high resolution transmission electron microscopy (HRTEM) and 3D atom probe tomography. The multistage annealing resulted in an increase in both the coercivity and magnetization. The presence of Sm(Co,Fe)4B (1:4:1) and Sm2(Co,Fe)17Bx (2:17:x) magnetic phases were confirmed using both techniques. Fe2B at a scale of ~ 5 nm was found by HRTEM precipitating within the 1:4:1 phase after the second-stage annealing. Ordering within the 2:17:x phase was directly identified both by the presence of antiphase boundaries observed by TEM and the interconnected isocomposition surface network found in 3D atom probe results in addition to radial distribution function analysis. The variations in the local chemistry after the secondary annealing were considered pivotal in improving the magnetic properties.

  9. Development of a novel shape memory alloy-actuated resettable locking device for magnetic bearing reaction wheel

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoyong; Yan, Xiaojun; Zhang, Shaowei; Nie, Jingxu

    2014-01-01

    The current investigation proposes a shape memory alloy (SMA)-actuated resettable locking device for magnetic bearing reaction wheel. The device employed two SMA wire-based actuators to realize locking and unlocking. Dual-slope mating surfaces were used on one hand to transmit the motion between a moving part and a clamp, and on the other hand to achieve a self-locking linkage in the locking state. Moreover, geometric parameters of the two SMA wires and corresponding bias springs were also designed. Based on the proposed design scheme, four locking devices were manufactured and assembled. Performance and environmental tests were performed to verify the proposed locking device. Test results show that the locking device can protect the magnetic bearing reaction wheel from launch vibration damage, and can withstand the thermal environment in the launch and on-orbit stage. Moreover, the device can be successfully operated for 76 times, and the response time for the locking and unlocking processes under 7 V power supply is 0.9 s and 5.6 s, respectively. Considering the results obtained from these tests, we conclude that the proposed resettable locking device is an attractive alternative technology to conventional motor-driven or pyrotechnics-based technologies, and can be applied reliably in the magnetic bearing reaction wheel.

  10. Microstructure of multistage annealed nanocrystalline SmCo{sub 2}Fe{sub 2}B alloy with enhanced magnetic properties

    SciTech Connect

    Jiang, Xiujuan Shield, Jeffrey E.; Devaraj, Arun; Balamurugan, B.; Cui, Jun

    2014-02-14

    The microstructure and chemistry of SmCo{sub 2}Fe{sub 2}B melt-spun alloy after multistage annealing was investigated using high resolution transmission electron microscopy (HRTEM) and 3D atom probe tomography. The multistage annealing resulted in an increase in both the coercivity and magnetization. The presence of Sm(Co,Fe){sub 4}B (1:4:1) and Sm{sub 2}(Co,Fe){sub 17}B{sub x} (2:17:x) magnetic phases were confirmed using both techniques. Fe{sub 2}B at a scale of ∼5 nm was found by HRTEM precipitating within the 1:4:1 phase after the second-stage annealing. Ordering within the 2:17:x phase was directly identified both by the presence of antiphase boundaries observed by TEM and the interconnected isocomposition surface network found in 3D atom probe results in addition to radial distribution function analysis. The variations in the local chemistry after the secondary annealing were considered pivotal in improving the magnetic properties.

  11. Development of a novel shape memory alloy-actuated resettable locking device for magnetic bearing reaction wheel.

    PubMed

    Zhang, Xiaoyong; Yan, Xiaojun; Zhang, Shaowei; Nie, Jingxu

    2014-01-01

    The current investigation proposes a shape memory alloy (SMA)-actuated resettable locking device for magnetic bearing reaction wheel. The device employed two SMA wire-based actuators to realize locking and unlocking. Dual-slope mating surfaces were used on one hand to transmit the motion between a moving part and a clamp, and on the other hand to achieve a self-locking linkage in the locking state. Moreover, geometric parameters of the two SMA wires and corresponding bias springs were also designed. Based on the proposed design scheme, four locking devices were manufactured and assembled. Performance and environmental tests were performed to verify the proposed locking device. Test results show that the locking device can protect the magnetic bearing reaction wheel from launch vibration damage, and can withstand the thermal environment in the launch and on-orbit stage. Moreover, the device can be successfully operated for 76 times, and the response time for the locking and unlocking processes under 7 V power supply is 0.9 s and 5.6 s, respectively. Considering the results obtained from these tests, we conclude that the proposed resettable locking device is an attractive alternative technology to conventional motor-driven or pyrotechnics-based technologies, and can be applied reliably in the magnetic bearing reaction wheel. PMID:24517805

  12. Influence of Applied Thermal Gradients and a Static Magnetic Field on Bridgman-Grown GeSi Alloys

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Szofran, F. R.; Cobb, S. D.; Ritter, T. M.

    1999-01-01

    The effect of applied axial and radial thermal gradients and an axial static magnetic field on the macrosegregation profiles of Bridgman-grown GeSi alloy crystals has been assessed. The axial thermal gradients were adjusted by changing the control setpoints of a seven-zone vertical Bridgman furnace. The radial thermal gradients were affected by growing samples in ampoules with different thermal conductivities, namely graphite, hot-pressed boron nitride (BN), and pyrolytic boron nitride (PBN). Those samples grown in a graphite ampoule exhibited radial profiles consistent with a highly concave interface and axial profiles indicative of complete mixing in the melt. The samples grown in BN and PBN ampoules had less radial variation. Axial macrosegregation profiles of these samples fell between the predictions for a completely mixed melt and one where solute transport is dominated by diffusion. All of the samples were grown on Ge seeds. This resulted in a period of free growth until the Si concentration in the solid was in equilibrium with the Si concentration in the liquid. The length of crystal grown during this period was inversely proportional to the applied axial thermal gradient. Several samples were grown in an axial 5 Tesla magnetic field. Measured macroscopic segregation profiles on these samples indicate that the magnetic field did not, in general, reduce the melt flow velocities to below the growth velocities.

  13. Competition of magnetization mechanisms in (NdDy)(FeCo)B alloys, doped with samarium

    NASA Astrophysics Data System (ADS)

    Kablov, E. N.; Ospennikova, O. G.; Piskorskii, V. P.; Korolev, D. V.; Kunitsina, E. I.; Dmitriev, A. I.; Morgunov, R. B.

    2016-01-01

    It is found that magnetic hysteresis in sintered magnets (Nd0.62Dy0.33Sm0.05)16.2(Fe0.77Co0.23)78.1B5.7 for the temperature range T = 150-350 K, is caused by a mechanism associated with the displacement of domain walls, which ceases at temperatures below 150 K. In addition, the formation of magnetic hysteresis in this temperature range is affected by the mechanism involving the nucleation of the reverse magnetization phase, which is observed at temperatures down to 36 K.

  14. Magnetocaloric effect over a wide temperature range due to multiple magnetic transitions in GdNi0.8Al1.2 alloy

    NASA Astrophysics Data System (ADS)

    Rashid, T. P.; Nallamuthu, S.; Arun, K.; Curlik, Ivan; Ilkovic, Sergej; Dzubinska, Andrea; Reiffers, Marian; Nagalakshmi, R.

    2016-05-01

    The magnetic properties, magnetocaloric effect (MCE) and refrigerant capacity (RC) of the novel polycrystalline GdNi0.8Al1.2 alloy are investigated. The temperature dependence of magnetization exhibits multiple magnetic transitions at T1=17.7 K, T2=46.7 K and T3=256 K thereby displaying a complex magnetic behaviour. The magnetocaloric effect is calculated in terms of the magnetic entropy change ( -Δ SM), from isothermal magnetization data using Maxwell relations. The maximum magnetic entropy change at major transitions T2 is 9.15 J kg-1K-1 (for a field change of 0-9 T) and 4.20 Jkg-1K-1 (0-5 T) and at T3 is 1.10 Jkg-1K-1 (0-9 T) and 0.67 Jkg-1K-1 (0-5 T). The overlap of the two -Δ SM peaks expeditiously expand the working temperature range of this material with substantial MCE which in turn yields moderate RC value of 120 J/kg for a field change of 0-5T. These results suggest that the GdNi0.8Al1.2 alloy may be a meaningful candidate for magnetic refrigeration working in a wide temperature range.

  15. Undercooling growth and magnetic characterization of ferromagnetic shape memory alloy Ni2FeGa single crystals

    NASA Astrophysics Data System (ADS)

    Qian, J. F.; Zhang, H. G.; Chen, J. L.; Wang, W. H.; Wu, G. H.

    2014-02-01

    Ni2FeGa single crystals have been grown in undercooling conditions provided by a glass-purification method. It has been found that trace amounts of γ phase embededin the single crystalline matrix preferentially orients in the <1 0 0> orientation along the growth direction. This γ phase generates directional residual stress and results in an anisotropic two-way shape memory effect. Large strains of -2.5% in the [0 0 1] and 1.5% in the [0 1 0] directions have been observed. This trace γ phase also improves the ductility of the material, thus the crystals could be plastically deformed at room temperature in the parent phase. The <1 1 0> and <1 1 1> orientations in Ni2FeGa alloy were identified as the easy and hard magnetization directions, respectively, in the parent phase by using low field M-T measurements.

  16. Thermodynamic analysis of binary Fe85B15 to quinary Fe85Si2B8P4Cu1 alloys for primary crystallizations of α-Fe in nanocrystalline soft magnetic alloys

    NASA Astrophysics Data System (ADS)

    Takeuchi, A.; Zhang, Y.; Takenaka, K.; Makino, A.

    2015-05-01

    Fe-based Fe85B15, Fe84B15Cu1, Fe82Si2B15Cu1, Fe85Si2B12Cu1, and Fe85Si2B8P4Cu1 (NANOMET®) alloys were experimental and computational analyzed to clarify the features of NANOMET that exhibits high saturation magnetic flux density (Bs) nearly 1.9 T and low core loss than conventional nanocrystalline soft magnetic alloys. The X-ray diffraction analysis for ribbon specimens produced experimentally by melt spinning from melts revealed that the samples were almost formed into an amorphous single phase. Then, the as-quenched samples were analyzed with differential scanning calorimeter (DSC) experimentally for exothermic enthalpies of the primary and secondary crystallizations (ΔHx1 and ΔHx2) and their crystallization temperatures (Tx1 and Tx2), respectively. The ratio ΔHx1/ΔHx2 measured by DSC experimentally tended to be extremely high for the Fe85Si2B8P4Cu1 alloy, and this tendency was reproduced by the analysis with commercial software, Thermo-Calc, with database for Fe-based alloys, TCFE7 for Gibbs free energy (G) assessments. The calculations exhibit that a volume fraction (Vf) of α-Fe tends to increase from 0.56 for the Fe85B15 to 0.75 for the Fe85Si2B8P4Cu1 alloy. The computational analysis of the alloys for G of α-Fe and amorphous phases (Gα-Fe and Gamor) shows that a relationship Gα-Fe ˜ Gamor holds for the Fe85Si2B12Cu1, whereas Gα-Fe < Gamor for the Fe85Si2B8P4Cu1 alloy at Tx1 and that an extremely high Vf = 0.75 was achieved for the Fe85Si2B8P4Cu1 alloy by including 2.8 at. % Si and 4.5 at. % P into α-Fe. These computational results indicate that the Fe85Si2B8P4Cu1 alloy barely forms amorphous phase, which, in turn, leads to high Vf and resultant high Bs.

  17. Bulk CoNiFe-SiB Amorphous and Nanostructured Alloys Produced by Plasma Spray Deposition and Dynamic Compaction: Formation of Soft Magnetic Properties

    NASA Astrophysics Data System (ADS)

    Denisova, Elena; Kuzovnikova, Ludmila; Iskhakov, Rauf; Kuzovnikov, Aleksandr; Lepeshev, Anatoly; Nemtsev, Ivan; Saunin, Viktor; Telegin, Sergey; Bondarenko, Galina; Mal`tsev, Vadim

    The bulk nanostructured Co58Ni10Fe5B16Si11 alloys were prepared by dynamic compaction and plasma spray deposition techniques. The investigation of structure and magnetic properties of bulk samples was carried out by X-ray diffraction, electron microscopy and correlation magnetometry. The bulk samples produced by both methods can be characterized as a heterophase system. The highest value of permeability 20 · 103 for plasma spraying coating is achieved when volume fraction of nanocrystalline phase with Curie temperature Tc ∼ 640 K is increased to 30%. The magnetic characteristics, such as the saturation magnetization, the Bloch constant, the local magnetic anisotropy field, the ferromagnetic resonance linewidth, and the coercivity remain unchanged after both compaction techniques. It was shown that the plasma spraying method allows to obtain bulk magnetically soft materials with magnetic parameters that are not inferior to the characteristics of a thermally treated rapidly quenched ribbon with the same composition.

  18. Magnetic transitions of single-component molecular metal [Au(tmdt)2] and its alloy systems.

    PubMed

    Zhou, Biao; Shimamura, Mina; Fujiwara, Emiko; Kobayashi, Akiko; Higashi, Takeshi; Nishibori, Eiji; Sakata, Makoto; Cui, Hengbo; Takahashi, Kazuyuki; Kobayashi, Hayao

    2006-03-29

    A single-component molecular conductor [Au(tmdt)2] (tmdt = trimethylenetetrathiafulvalenedithiolate) undergoes an antiferromagnetic phase transition at unprecedentedly high temperature (TN = 110 K). Black microcrystals of alloys, [Ni1-xAux(tmdt)2] (0.0 < x < 1.0) were prepared. The Au-rich system exhibited an antiferromagnetic transition. Metallic single crystal was obtained for x = 0.25. PMID:16551070

  19. High Frequency Properties of Ferrite/Fe-Si-Al Alloy Soft Magnetic Composites

    NASA Astrophysics Data System (ADS)

    Stergiou, Charalampos A.; Zaspalis, Vassilios

    The inclusion of Fe-Si-Al alloy particles in NiCuZn ferrite matrix was investigated with regard to the high frequency electromagnetic properties (complex permeability and permittivity). The resultant composites of relatively low density exhibit a shift of the permeability spectra to higher frequencies and an increase of dielectric polarization, which finally favour the electromagnetic wave attenuation at microwave frequencies. Thus, wider band return loss peaks are attained at frequencies above 6 GHz by thinner composite materials.

  20. Formation of bcc non-equilibrium La, Gd, and Dy alloys and the magnetic structure of Mg-stabilized. beta. Gd and. beta. Dy

    SciTech Connect

    Herchenroeder, J.W.

    1988-01-01

    The high temperature bcc allotrope of a rare earth metal has the potential for substantially different magnetic properties than the room temperature hexagonal (hcp or dcp) counterpart because of its more symmetrical crystal field. The stabilization by alloying and quenching of this bcc phase was studied for La-M alloys where M is a non-rare earth metal from Group II or III. The factors influencing the stabilization, such as size of M and quench rate, are discussed. {gamma}La (bcc) could be retained over a composition range around the eutectoid composition by Mg or Cd alloying. A comparison of T{sub o} curves of the various alloy systems suggest that the eutectoid temperature of the La-M system must be approximately equal to or less than a critical T{sub o} temperature of 515{degree}C if the bcc phase is to be retained by quenching. The thermal stability of {beta}Gd (bcc) was investigated by DTA and isothermal annealing. It was found to transform to an intermediate phase before reverting to the equilibrium phases in contrast to {gamma}La alloys which decompose directly on heating to the equilibrium phases. Bcc {beta}Gd and {beta}Dy stabilized by Mg additions exhibit spin glass-like behavior. Both systems show field cooling effects in the magnetic susceptibility which is indicative of spin freezing reactions.

  1. The elastic, electronic and magnetism structure of the MAl and M3Al (M=Fe and Ni) alloy with and without hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Mubarak, A. A.

    2016-03-01

    The energetic stability, electronic and magnetism of the MAl, M3Al alloy (M=Fe, Ni) and variant surfaces of MAl (001) with and without hydrogen atoms are investigated by utilizing DFT and GGA as the exchange-correlation potential. All presented alloys with and without the H atom absorption is found elastically and thermodynamically stable. The calculated absorption energy shows that H is more energetically stable in the bridge and octahedral site in MAl and M3Al alloys, respectively. Hydrogen atoms absorption is expanded and brittle the studied host alloys. The ability of absorption of H atom at more than one site in the MAl alloy is found energetically and thermodynamically stable. The H adsorption on the variant surfaces of MAl (001) is predicted too. Fourfold and top sites are found more energetically stable to adsorbed the H atom on the above surface layer of H/MAl-M and H/MAl-Al, respectively. The obvious changes are observed in the interlayer spacing for studied surfaces which yields to decrease the LDOS and magnetic moments of the surface and subsurface layers.

  2. Structural and magnetic investigations in the vicinity of first-order transformations in Ni-Mn-Ga-Co ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Satish Kumar, A.; Ramudu, M.; Seshubai, V.

    2012-12-01

    Among the series of alloys derived from Ni50Mn29Ga21 on selective substitution of Co for Ni and Mn, two alloys Ni49.8Mn27.2Ga21.2Co1.8 and Ni46.9Mn28.8Ga21Co3.3 referred to as CoMn-1.8 and CoNi-3.3, respectively, are found to exhibit an additional first-order transformation below their martensitic transformation temperatures. Systematic studies on temperature and field dependence of magnetic properties of these alloys are carried out, through the transformations, to understand their origin. An examination of these results in conjunction with those from structural investigations reveals that the transformation in the CoMn-1.8 alloy is an intermartensitic transformation and has a structural origin, while that in the CoNi-3.3 alloy is not of the structural origin and is attributed to local spin inversion of Co moments, which is of the magnetic origin.

  3. Relaxation of bending stresses and the reversibility of residual stresses in amorphous soft magnetic alloys

    SciTech Connect

    Kekalo, I. B.; Mogil’nikov, P. S.

    2015-06-15

    The reversibility of residual bending stresses is revealed in ribbon samples of cobalt- and iron-based amorphous alloys Co{sub 69}Fe{sub 3.7}Cr{sub 3.8}Si{sub 12.5}B{sub 11} and Fe{sub 57}Co{sub 31}Si{sub 2.9}B{sub 9.1}: the ribbons that are free of applied stresses and bent under the action of residual stresses become completely or incompletely straight upon annealing at the initial temperatures. The influence of annealing on the relaxation of bending stresses is studied. Preliminary annealing is found to sharply decrease the relaxation rate of bending stresses, and the initial stage of fast relaxation of these stresses is absent. Complete straightening of preliminarily annealed ribbons is shown to occur at significantly higher temperatures than that of the initial ribbons. Incomplete straightening of the ribbons is explained by the fact that bending stresses relaxation at high annealing temperatures proceeds due to both reversible anelastic deformation and viscous flow, which is a fully irreversible process. Incomplete reversibility is also caused by irreversible processes, such as the release of excess free volume and clustering (detected by small-angle X-ray scattering). The revealed differences in the relaxation processes that occur in the cobalt- and iron-based amorphous alloys are discussed in terms of different atomic diffusion mobilities in these alloys.

  4. Effect of niobium addition on the martensitic transformation and magnetocaloric effect in low hysteresis NiCoMnSn magnetic shape memory alloys

    SciTech Connect

    Emre, Baris; Bruno, Nickolaus M.; Yuce Emre, Suheyla; Karaman, Ibrahim

    2014-12-08

    The effect of Nb substitution for Ni in Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} magnetic shape memory alloys on their magnetic properties, martensitic transformation characteristics, transformation hysteresis, and magnetocaloric properties was studied using wavelength-dispersive X-ray spectroscopy, differential scanning calorimetry, and the temperature and field dependence of the magnetization. Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloy has a very low transformation hysteresis; however, the martensitic transformation temperatures are notably above room temperature, which is not desirable for magnetic refrigeration applications. In this study, small quantities of Nb substitution were shown to drastically shift the transformation temperatures to lower temperatures, at a rate of 68 K/at. % Nb, which is needed for household refrigeration. The austenite Curie temperature also decreased with increasing Nb content. However, a decrease in the latent heat of the martensitic transition was observed, which negatively affects the magnetic field-induced adiabatic temperature change capability. Still, the relatively large transformation entropy and the low transformation hysteresis make the Nb-doped Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloys potential candidates for solid state refrigeration near room temperature.

  5. Effect of niobium addition on the martensitic transformation and magnetocaloric effect in low hysteresis NiCoMnSn magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Emre, Baris; Bruno, Nickolaus M.; Yuce Emre, Suheyla; Karaman, Ibrahim

    2014-12-01

    The effect of Nb substitution for Ni in Ni45Co5Mn40Sn10 magnetic shape memory alloys on their magnetic properties, martensitic transformation characteristics, transformation hysteresis, and magnetocaloric properties was studied using wavelength-dispersive X-ray spectroscopy, differential scanning calorimetry, and the temperature and field dependence of the magnetization. Ni45Co5Mn40Sn10 alloy has a very low transformation hysteresis; however, the martensitic transformation temperatures are notably above room temperature, which is not desirable for magnetic refrigeration applications. In this study, small quantities of Nb substitution were shown to drastically shift the transformation temperatures to lower temperatures, at a rate of 68 K/at. % Nb, which is needed for household refrigeration. The austenite Curie temperature also decreased with increasing Nb content. However, a decrease in the latent heat of the martensitic transition was observed, which negatively affects the magnetic field-induced adiabatic temperature change capability. Still, the relatively large transformation entropy and the low transformation hysteresis make the Nb-doped Ni45Co5Mn40Sn10 alloys potential candidates for solid state refrigeration near room temperature.

  6. Low temperature diffusion process using rare earth-Cu eutectic alloys for hot-deformed Nd-Fe-B bulk magnets

    SciTech Connect

    Akiya, T. Sepehri-Amin, H.; Ohkubo, T.; Liu, J.; Hono, K.; Hioki, K.; Hattori, A.

    2014-05-07

    The low temperature grain boundary diffusion process using RE{sub 70}Cu{sub 30} (RE = Pr, Nd) eutectic alloy powders was applied to sintered and hot-deformed Nd-Fe-B bulk magnets. Although only marginal coercivity increase was observed in sintered magnets, a substantial enhancement in coercivity was observed when the process was applied to hot-deformed anisotropic bulk magnets. Using Pr{sub 70}Cu{sub 30} eutectic alloy as a diffusion source, the coercivity was enhanced from 1.65 T to 2.56 T. The hot-deformed sample expanded along c-axis direction only after the diffusion process as RE rich intergranular layers parallel to the broad surface of the Nd{sub 2}Fe{sub 14}B are thickened in the c-axis direction.

  7. Tailoring of the magnetic properties of SmCo{sub 5}:Nb{sub 0.33}Cr{sub 0.67} nanocomposites using mechanical alloying

    SciTech Connect

    Schalek, R.L.; Leslie-Pelecky, D.L.; Knight, J.; Sellmyer, D.J.; Axtell, S.C.

    1995-11-01

    Nanocomposite structures composed of ferromagnetic particles dispersed in a matrix are systems in which the magnetic properties can be tailored by varying the size and spacing of the ferromagnetic particles. Nanocomposites of SmCo{sub 5} in a non-magnetic Nb{sub 0.33}Cr{sub 0.67} matrix exhibit a wide variety of magnetic properties. SmCo{sub 5} powder is premilled prior to mechanical alloying. The premilling results in a maximum coercivity of 16 kOe after 2 hours of milling, and an enhanced remanence ratio. Both features may be due to exchange anisotropy and/or exchange coupling between hard and soft ferromagnetic phases. The nanocomposite samples show that, when the SmCo{sub 5} particulates are small enough, the primary effect of alloying is to disperse them throughout the matrix with no further refinement of size.

  8. Structural and magnetic properties of Co2Ti1-xFexAl (0 ≤ x ≤ 0.5) alloys

    NASA Astrophysics Data System (ADS)

    Pal, Lakhan; Gupta, Sachin; Suresh, K. G.

    2014-04-01

    In this work we studied the effect of partial Fe substitution for Ti on the structural and magnetic properties of the Co2TiAl. X-ray diffraction analysis indicates the presence of B2 type disorder for x > 0, (111) reflections are absent for x > 0 which is the characteristic of B2 type disorder. XRD analysis also shows presence of second phase. Magnetization measurements also confirm the presence of dual phase. Curie temperature of the alloys increases with increase in Fe concentration. Saturation magnetic moments agree very well with those calculated by Slater-Pauling rule.

  9. Influence of the static high magnetic field on the liquid-liquid phase separation during solidifying the hyper-monotectic alloys

    NASA Astrophysics Data System (ADS)

    Wang, J.; Zhong, Y. B.; Fautrelle, Y.; Zheng, T. X.; Li, F.; Ren, Z. M.; Debray, F.

    2013-09-01

    Magnetic in-situ quenching refers to fixing and quenching the sample at a static high magnetic field (SHMF) up to 18 T; it has been achieved by a specially designed facility. Zn-7wt%Bi and Zn-10wt%Bi hyper-monotectic melts were quenched under different magnetic flux densities to investigate the influence of SHMF on the liquid-liquid phase separation process in solidifying hyper-monotectic alloys. Because this separation is mainly caused by the growth of minority phase droplets (Bi droplets in the present study), and such growth is attributed to the diffusion of Bi element and the coalescence between the droplets, the influence of SHMF on the growth of Bi droplets was analyzed. Results show that the imposed SHMF prevented the formation of layered structure in the Zn-10wt%Bi alloy and refined the Bi particles in the Zn-7wt%Bi alloy, which indicates that the SHMF retarded the liquid-liquid phase separation during solidifying the hyper-monotectic alloys. Indeed, the two motions of droplets in determining the coalescence, Marangoni migration and Stocks sedimentation, were slowed down by the applied SHMF. Analytical estimations of the magnitude of such damping effect have been made and show that the 18 T SHMF could reduce the speed of Stokes sedimentation and Marangoni migration of the minority phase droplets by about 95.5 % and 62.4 %, respectively.

  10. The effects of substituting B for Cu on the magnetic and shape memory properties of CuAlMnB alloys

    NASA Astrophysics Data System (ADS)

    Aydogdu, Y.; Turabi, A. S.; Aydogdu, A.; Vance, E. D.; Kok, M.; Kirat, G.; Karaca, H. E.

    2016-07-01

    The effects of B addition on the magnetization, mechanical and shape memory properties in Cu70- x Al24Mn6B x at.% ( x = 0, 1, 2, 3, 4) alloys have been investigated. The ductility was decreased, while the strength was improved with B addition. Transformation temperatures were increased with B content due to increased e/ a ratio. Martensite start temperature of B-free CuAlMn was found to be 37.3 °C and increased to 218.8 °C with 4 % B addition. B-free CuAlMn exhibited shape memory effect with a recoverable strain of 2.25 % under 200 MPa and a perfect superelasticity with a recoverable strain of 2.5 % at 163 °C. B addition degraded the shape memory properties and eventually resulted in the lack of recoverable strain. In addition, saturation magnetization was increased with B content. Moreover, the addition of B slightly decreased the ductility of the alloy. It was found that the magnetization, mechanical and shape memory properties CuAlMn alloys can be tailored by quaternary alloying with B.

  11. Effect of boron on the structural and magnetic properties of Co2FeSi1-xBx Heusler alloys

    NASA Astrophysics Data System (ADS)

    Ramudu, M.; Raja, M. Manivel; Kamat, S. V.

    2016-05-01

    The partial substitution of Si with B on the structural and magnetic properties of Co2FeSi1-xBx (x = 0-0.5) alloys was systematically investigated. X-ray and microstructural investigations show the presence of second phase at the grain boundaries which increases with increasing boron content. From thermal analysis studies, it was observed that L21-B2 ordering temperature remain constant whereas the melting point decreases with increase in boron addition and merges with ordering temperature at x = 0.5. The increase in TC for the alloys x ≥ 0.25 was attributed to the increase in second phase due to boron.

  12. Study of magnetic behavior in ball-milled nanocrystalline Fe-50 at.%Al alloy as a function of milling time

    NASA Astrophysics Data System (ADS)

    Rajan, S.; Shukla, R.; Kumar, A.; Vyas, A.; Brajpuriya, R.

    2015-04-01

    Ball milling technique has been extensively used to prepare different metastable states with nanocrystalline microstructures from intermetallic compounds. The present study was made on the identification of the changes in magnetic and electronic properties as a result of high-energy ball milling of Fe-50 at.%Al alloy samples. The phase formation and physical properties of the alloys were determined as a function of milling time by means of Mössbauer and X-ray photoelectron spectroscopy (XPS). The Mössbauer results show the formation of nanostructured body-centered cubic (BCC) FeAl alloy only after 5 h of mechanical milling and the same is also confirmed by Scanning electron microscope (SEM) and Transmission electron microscopy (TEM) studies. Mössbauer studies further confirm that there is magnetic behavior retention in the FeAl alloy samples even after 5 h of milling but magnetization decreases as the milling time increases. The reason for the same is due to the shocks and fracturing of the Al atoms embedded in the sites of Fe and as a result of which Fe-Fe nearest neighbors decreases. Secondly, with the increase in milling time, the particle size and the number density of equiatomic BCC Fe50Al50 grains decrease while the volume of grain boundary containing a solid solution of BCC FeAl and concentration of Al in a solid solution of BCC FeAl at the grain boundary increases as a result of which magnetization decreases. The shift in the binding energy of Fe2p and Al2p core level towards higher binding energy also supports the alloy formation after milling.

  13. Magnetic and structural anisotropies in laser ablated epitaxial thin films of full-Heusler alloy Co2MnSi on SrTiO3

    NASA Astrophysics Data System (ADS)

    Pandey, Himanshu; Rout, P. K.; Budhani, R. C.

    2013-03-01

    We present the thickness dependent magnetic properties of laser ablated epitaxial Co2MnSi (CMS)Heusler alloy thin films grown on (001) oriented SrTiO3 substrate. In order to study the intrinsic magnetic anisotropy, a highly ordered single crystal thin film of Heusler alloys is necessary. This provides a unique opportunity to determine the behavior of magnetization reversal, and affect important properties such as the coercive field and remanence. The two important sources of the magnetic anisotropy are the magnetic dipolar interaction and the spin-orbit interaction. The strain in films due to the lattice mismatch with the substrate affects the shape anisotropy while spin-orbit coupling changes magneto-crystalline anisotropy. We have observed an in-plane biaxial compressive strain in the films which relaxes with increasing film thickness. Although the hysteresis loops show an in-plane easy axis for all films, the single-domain phase diagram reveals a gradual transition from in-plane to out-of-plane transition of magnetization as the film thickness is decreased. The magnetization starts to cant as film thickness start to decrease and we found a canting angle of ~ 31.8° with respect to the film plane for our thinnest 5 nm CMS films. We acknowledge support from DIT, DST, CSIR and IIT Kanpur.

  14. Effects of the interplay between atomic and magnetic order on the properties of metamagnetic Ni-Co-Mn-Ga shape memory alloys

    SciTech Connect

    Seguí, C.

    2014-03-21

    Ni-Co-Mn-Ga ferromagnetic shape memory alloys show metamagnetic behavior for a range of Co contents. The temperatures of the structural and magnetic transitions depend strongly on composition and atomic order degree, in such a way that combined composition and thermal treatment allows obtaining martensitic transformation between any magnetic state of austenite and martensite. This work presents a detailed analysis of the effect of atomic order on Ni-Co-Mn-Ga alloys through the evolution of structural and magnetic transitions after quench from high temperatures and during post-quest ageing. It is found that the way in which the atomic order affects the martensitic transformation temperatures and entropy depends on the magnetic order of austenite and martensite. The results can be explained assuming that improvement of atomic order decreases the free energy of the structural phases according to their magnetic order. However, it is assumed in this work that changes in the slope—that is, the entropy—of the Gibbs free energy curves are also decisive to the stability of the two-phase system. The experimental transformation entropy values have been compared with a phenomenological model, based on a Bragg–Williams approximation, accounting for the magnetic contribution. The excellent agreement obtained corroborates the magnetic origin of changes in transformation entropy brought about by atomic ordering.

  15. Coercivity and thermal stability improvement in sintered Nd-Fe-B permanent magnets by intergranular addition of Dy-Mn alloy

    NASA Astrophysics Data System (ADS)

    Li, Xiangbin; Liu, Shuo; Cao, Xuejing; Zhou, Beibei; Chen, Ling; Yan, Aru; Yan, Gaolin

    2016-06-01

    To increase coercivity and thermal stability of sintered Nd-Fe-B magnets for high temperature applications, Dy88Mn12 (wt%) alloy powders were intergranular added into (Pr0.25Nd0.75)30.6Cu0.15FebalB1 (wt%) starting magnet. The magnetic properties, microstructure and thermal stability of the sintered magnets with different amounts of Dy88Mn12 were investigated. By adding a small amount of Dy88Mn12, the coercivity was significantly increased from 12.56 kOe to 17.49 kOe. Microstructure analysis showed that a optimized microstructure, i.e. continuous, uniform grain boundary phase was achieved with Dy88Mn12 alloy addition, and Dy was enriched in the outer region of the Nd2Fe14B matrix grains during the sintering process, which favored to substitute for Nd in matrix grains to form the (Nd,Dy)2Fe14B core-shell phase. The greatly increased magnetocrystalline anisotropy of the core-shell phase and the improved decoupling by the continuous grain boundary phase accounted for the coercivity enhancement. Furthermore, by adding 0-4 wt% Dy88Mn12, the reversible temperature coefficients of remanence (α) and coercivity (β) of the magnet were improved from -0.115%/ºC to -0.107%/ºC and -0.744%/ºC to -0.696%/ºC in the range of 20-100 °C, respectively. In addition, the irreversible flux loss of magnetic flow (hirr) decreased sharply as Dy88Mn12 addition. The temperature-dependent magnetic properties results indicated that with intergranular addition of Dy88Mn12 alloy, the thermal stability of the magnets was effectively improved.

  16. Magnetic properties of bulk nanocomposite permanent magnets based on NdDyFeB alloys with additions

    NASA Astrophysics Data System (ADS)

    Marinescu, M.; Chiriac, H.; Grigoras, M.

    2005-04-01

    NdFeB-based bulk nanocomposite permanent magnets with addition of Mo, Ti, Zr, Cu, Nb, V, respectively, Dy substitution for Nd and Co substitution for Fe, in form of rods with diameters ranging from 0.5 to 0.8 mm, have been prepared by devitrification annealing of amorphous and partly-amorphous precursors produced by injection die casting. A fully amorphous structure was obtained for rods with the diameter as large as 0.6 mm. The best-achieved magnetic properties have been obtained for the optimum devitrification annealed Nd 3Dy 1Fe 66Co 10B 20 rods with 0.6 mm diameter and are: iH c=296 kA/m, μ0Mr=0.86 T, Mr/ Mmax=0.65 and ( BH) max=74 kJ/m 3.

  17. Magnetism of CoPd self-organized alloy clusters on Au(111)

    NASA Astrophysics Data System (ADS)

    Ohresser, P.; Otero, E.; Wilhelm, F.; Rogalev, A.; Goyhenex, C.; Joly, L.; Bulou, H.; Romeo, M.; Speisser, V.; Arabski, J.; Schull, G.; Scheurer, F.

    2013-12-01

    Magnetic properties of gold-encapsulated CoxPd1-x self-organized nano-clusters on Au(111) are analyzed by x-ray magnetic circular dichroism for x = 0.5, 0.7, and 1.0. The clusters are superparamagnetic with a blocking temperature decreasing with increasing Pd concentration, due to a reduction of the out-of-plane anisotropy strength. No magnetic moment is detected on Pd in these clusters, within the detection limit, contrary to thick CoPd films. Both reduction of anisotropy and vanishing Pd moment are attributed to strain.

  18. New alnico magnets fabricated from pre-alloyed gas-atomized powder through diverse consolidation techniques

    DOE PAGESBeta

    Tang, W.; Zhou, L.; Kassen, A. G.; Palasyuk, A.; White, E. M.; Dennis, K. W.; Kramer, M. J.; McCallum, R. W.; Anderson, I. E.

    2015-05-25

    Fine Alnico 8 spherical powder produced by gas atomization was consolidated through hot pressing (HP), hot isostatic pressing (HIP), and compression molding and subsequent sintering (CMS) techniques. The effects of different fabrication techniques and processing parameters on microstructure and magnetic properties were analyzed and compared. The HP, HIP, and CMS magnets exhibited different features in microstructures and magnetic properties. Magnetically annealed at 840°C for 10 min and subsequently tempered at 650°C for 5h and 580°C for 15h, the HIP sample achieved the best coercivity (Hcj =1845 Oe) due to spinodally decomposed (SD) phases with uniform and well-faceted mosaic morphology. Asmore » a result, the CMS sample had a lower Hcj than HIP and HP samples, but a higher remanence and thus the best energy product (6.5 MGOe) due to preferential grain alignment induced by abnormal grain growth.« less

  19. New alnico magnets fabricated from pre-alloyed gas-atomized powder through diverse consolidation techniques

    SciTech Connect

    Tang, W.; Zhou, L.; Kassen, A. G.; Palasyuk, A.; White, E. M.; Dennis, K. W.; Kramer, M. J.; McCallum, R. W.; Anderson, I. E.

    2015-05-25

    Fine Alnico 8 spherical powder produced by gas atomization was consolidated through hot pressing (HP), hot isostatic pressing (HIP), and compression molding and subsequent sintering (CMS) techniques. The effects of different fabrication techniques and processing parameters on microstructure and magnetic properties were analyzed and compared. The HP, HIP, and CMS magnets exhibited different features in microstructures and magnetic properties. Magnetically annealed at 840°C for 10 min and subsequently tempered at 650°C for 5h and 580°C for 15h, the HIP sample achieved the best coercivity (Hcj =1845 Oe) due to spinodally decomposed (SD) phases with uniform and well-faceted mosaic morphology. As a result, the CMS sample had a lower Hcj than HIP and HP samples, but a higher remanence and thus the best energy product (6.5 MGOe) due to preferential grain alignment induced by abnormal grain growth.

  20. Xenon-ion Induced Magnetic and Structural Modifications of Ferromagnetic Alloys

    NASA Astrophysics Data System (ADS)

    Gupta, Ratnesh; Lieb, K. P.; Müller, G. A.; Schaaf, P.; Zhang, K.

    2005-01-01

    Thin polycrystalline films of permalloy (Ni79Fe21) and permendur (Co50Fe50) have been irradiated with Xe-ions to fluences of 1014 1016 ions/cm2. Ion-induced structural and magnetic modifications have been measured by grazing angle X-ray diffraction, Rutherford backscattering and magneto-optical Kerr effect. In the case of permendur, the Xe-ion implantation first reduced the coercivity, because of stress relaxation, while higher ion fluences increased the coercivity due to pinning centers generated in the film. The ion irradiation aligned the in-plane easy axis of the magnetization along the direction of the external magnetic field during implantation. Phase shifts obtained from magnetic force microscopy confirmed these modifications. The effects of Xe-ion irradiation in permalloy films are much weaker and underline the importance of magnetostriction in the variation of the coercivity and anisotropy.

  1. Optical and magneto-optical studies of martensitic transformation in Ni-Mn-Ga magnetic shape memory alloys

    SciTech Connect

    Beran, L.; Cejpek, P.; Kulda, M.; Antos, R.; Holy, V.; Veis, M.; Straka, L.; Heczko, O.

    2015-05-07

    Optical and magneto-optical properties of single crystal of Ni{sub 50.1}Mn{sub 28.4}Ga{sub 21.5} magnetic shape memory alloy during its transformation from martensite to austenite phase were systematically studied. Crystal orientation was approximately along (100) planes of parent cubic austenite. X-ray reciprocal mapping confirmed modulated 10 M martensite phase. Temperature depended measurements of saturation magnetization revealed the martensitic transformation at 335 K during heating. Magneto-optical spectroscopy and spectroscopic ellipsometry were measured in the sample temperature range from 297 to 373 K and photon energy range from 1.2 to 6.5 eV. Magneto-optical spectra of polar Kerr rotation as well as the spectra of ellipsometric parameter Ψ exhibited significant changes when crossing the transformation temperature. These changes were assigned to different optical properties of Ni-Mn-Ga in martensite and austenite phases due to modification of electronic structure near the Fermi energy during martensitic transformation.

  2. Optical and magneto-optical studies of martensitic transformation in Ni-Mn-Ga magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Beran, L.; Cejpek, P.; Kulda, M.; Antos, R.; Holy, V.; Veis, M.; Straka, L.; Heczko, O.

    2015-05-01

    Optical and magneto-optical properties of single crystal of Ni50.1Mn28.4Ga21.5 magnetic shape memory alloy during its transformation from martensite to austenite phase were systematically studied. Crystal orientation was approximately along {100} planes of parent cubic austenite. X-ray reciprocal mapping confirmed modulated 10 M martensite phase. Temperature depended measurements of saturation magnetization revealed the martensitic transformation at 335 K during heating. Magneto-optical spectroscopy and spectroscopic ellipsometry were measured in the sample temperature range from 297 to 373 K and photon energy range from 1.2 to 6.5 eV. Magneto-optical spectra of polar Kerr rotation as well as the spectra of ellipsometric parameter Ψ exhibited significant changes when crossing the transformation temperature. These changes were assigned to different optical properties of Ni-Mn-Ga in martensite and austenite phases due to modification of electronic structure near the Fermi energy during martensitic transformation.

  3. Resonant magnetoelectric coupling in trilayers of ferromagnetic alloys and piezoelectric lead zirconate titanate: The influence of bias magnetic field

    NASA Astrophysics Data System (ADS)

    Srinivasan, G.; de Vreugd, C. P.; Laletin, V. M.; Paddubnaya, N.; Bichurin, M. I.; Petrov, V. M.; Filippov, D. A.

    2005-05-01

    We present the first data and theory for the bias magnetic field dependence of magnetoelectric coupling in the electromechanical resonance (EMR) region for ferromagnetic-piezoelectric heterostructures. Trilayers of Permendur, a Co-Fe-V alloy, and lead zirconate titanate were studied. Measurements of the magnetoelectric (ME) voltage coefficient αE indicate a strong ME coupling in the low-frequency range and a giant ME effect due to EMR at 200-300kHz for radial modes and at ˜2.7MHz for thickness modes. Data were obtained for the bias field H dependence of two key parameters, the EMR frequency fr and the ME coefficient αE,R at resonance. With increasing H , an increase in fr and a rapid rise and fall in αE,R are measured. In our model we consider two mechanisms for the magnetic field influence on ME interactions: (i) a shift in the EMR frequency due to changes in compliance coefficients ( ΔE effect) and (ii) variation in the piezomagnetic coefficient that manifests as a change in αE,R . Theoretical profiles of αE vs frequency and estimates of frequency shift based on the ΔE effect are in excellent agreement with the data.

  4. Influence of Pt Doping on Gilbert Damping in Permalloy Films and Comparison with the Perpendicularly Magnetized Alloy Films

    NASA Astrophysics Data System (ADS)

    Mizukami, Shigemi; Kubota, Takahide; Zhang, Xianmin; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Miyazaki, Terunobu

    2011-10-01

    Effects of Pt doping on magnetic properties and Gilbert damping are investigated for Ni80Fe20 permalloy films to compare with damping in alloy films containing Pt with a large perpendicular anisotropy. Gilbert damping constant α and g-factor g for (Ni80Fe20)100-xPtx (x = 0-34 at. %) are evaluated from out-of-plane angular variations of ferromagnetic resonance (FMR) linewidth and resonance field with an analysis based on the Landau-Lifshitz-Gilbert equation. Data of angular dependence of the FMR linewidth are fitted reasonably well by a theoretical model without having to take into account any extrinsic influences on linewidth, thereby allowing us to determine precise values of α. The α values show variation with increasing Pt concentration rising by ˜0.06 at a Pt concentration of 34 at. %, which is very close to those in perpendicularly magnetized CoCrPt and FePt film reported recently. Nevertheless, Gilbert damping rate G for the Pt doped permalloy films is smaller than those in CoCrPt and FePt films. These experimental results are discussed with a spin-orbit torque theory.

  5. The effect of mechanical milling on the soft magnetic properties of amorphous FINEMET alloy

    NASA Astrophysics Data System (ADS)

    Gheiratmand, T.; Hosseini, H. R. Madaah; Davami, P.; Gjoka, M.; Song, M.

    2015-05-01

    The effect of milling time on the magnetic properties of FINEMET amorphous ribbons has been investigated using X-ray diffraction, Mössbauer spectroscopy, thermo-magnetic measurements, transmission electron microscopy and SQUID magnetometery. Ribbons were melt-spun at a wheel speed of 38 ms-1 and then mechanically milled for different periods up to 45 min. The results showed that the partially crystallization of the amorphous powder occurs during milling. TEM observations confirmed the formation of small volume fraction of the crystalline phase with ~9 nm crystallite size in the amorphous matrix for the ribbon milled for 45 min. Thermo-magnetic measurements indicated the enhancement of the Curie temperature of amorphous phase during milling which is due to the annihilation of free volumes and microstructural ordering. The Hopkinson effect led to the monotonic increase of magnetization with respect to the temperature before reaching the Curie temperature of the milled samples. Moreover; the magnetization increased with the formation of the Fe(Si) phase while the coercivity decreased. Mössbauer spectroscopy and thermo-magnetic measurements revealed the existence of 13% Fe in crystalline phase. The composition of crystalline phase was determined as Fe-16.5Si. Hyperfine field values increased with milling time, suggesting the ordering of the structure and enhancement of the number of Fe-Fe atomic pairs in the crystalline phase comparing to the primary amorphous ribbon.

  6. Large magnetic entropy change and magnetoresistance in a Ni41Co9Mn40Sn10 magnetic shape memory alloy

    SciTech Connect

    Huang, L.; Cong, D. Y.; Ma, L.; Nie, Z. H.; Wang, M. G.; Wang, Z. L.; Suo, H. L.; Ren, Y.; Wang, Y. D.

    2015-07-02

    A polycrystalline Ni41Co9Mn40Sn10 (at. %) magnetic shape memory alloy was prepared by arc melting and characterized mainly by magnetic measurements, in-situ high-energy X-ray diffraction (HEXRD), and mechanical testing. A large magnetoresistance of 53.8% (under 5 T) and a large magnetic entropy change of 31.9 J/(kg K) (under 5 T) were simultaneously achieved. Both of these values are among the highest values reported so far in Ni-Mn-Sn-based Heusler alloys. The large magnetic entropy change, closely related to the structural entropy change, is attributed to the large unit cell volume change across martensitic transformation as revealed by our in-situ HEXRD experiment. Furthermore, good compressive properties were also obtained. Lastly, the combination of large magnetoresistance, large magnetic entropy change, and good compressive properties, as well as low cost makes this alloy a promising candidate for multifunctional applications.

  7. Structure and magnetism in Fe/FexPd1-x core/shell nanoparticles formed by alloying in Pd-embedded Fe nanoparticles

    NASA Astrophysics Data System (ADS)

    Baker, S. H.; Lees, M.; Roy, M.; Binns, C.

    2013-09-01

    We have investigated atomic structure and magnetism in Fe nanoparticles with a diameter of 2 nm embedded in a Pd matrix. The samples for these studies were prepared directly from the gas phase by co-deposition, using a gas aggregation source and an MBE-type source for the Fe nanoparticles and Pd matrix respectively. Extended absorption fine structure (EXAFS) measurements indicate that there is an appreciable degree of alloying at the nanoparticle/matrix interface; at dilute nanoparticle concentrations, more than half of the Fe atoms are alloyed with Pd. This leads to a core/shell structure in the embedded nanoparticles, with an FexPd1-x shell surrounding a reduced pure Fe core. Magnetism in the nanocomposite samples was probed by means of magnetometry measurements, which were interpreted in the light of their atomic structure. These point to a magnetized cloud of Pd atoms surrounding the embedded nanoparticles which is significantly larger than around single Fe atoms in Pd. The coercivities in the Fe/Pd nanocomposite samples are larger than in FexPd1-x atomic alloys of corresponding composition, which is consistent with exchange coupling between the magnetically harder and softer regions in the nanocomposite samples.

  8. Low temperature magnetic and electrical transport behavior of Co{sub 58.5}Ga{sub 41.5} alloy

    SciTech Connect

    Yasin, Sk Mohammad Srinivas, V.; Kasiviswanathan, S.; Saha, Ritwik; Nigam, A. K.; Rao, T. V. Chandrasekhar

    2015-06-24

    The electrical transport and magnetic properties of Co{sub 58.5}Ga{sub 41.5} binary alloy have been investigated in the temperature range 2-300 K. Analysis of field and temperatures dependence magnetization data suggests a reentrant magnetic behavior with Curie temperature (T{sub C}) ∼90 K. Temperature dependence of resistivity shows large residual resistivity values which is sensitive to the applied magnetic field. The temperature and field dependent resistivity behavior indicates the presence of spin fluctuations at low temperature. Magnetoresistance (MR) of 17 % has been observed at 2 K in 90 kOe field, which follows a power law with exponent varying form 0.5 at low temperature to linear behavior at higher temperature. The temperature variation of magnetization and MR can be understood on the basis of ferromagnetic matrix with finite spin clusters.

  9. Small-angle neutron scattering study of magnetic ordering and inhomogeneity across the martensitic phase transformation in Ni50–xCoxMn₄₀Sn₁₀ alloys

    DOE PAGESBeta

    Bhatti, Kanwal Preet; El-Khatib, S.; Srivastava, Vijay; James, R. D.; Leighton, C.

    2012-04-27

    The Heusler-derived multiferroic alloy Ni50–xCoxMn₄₀Sn₁₀ has recently been shown to exhibit, at just above room temperature, a highly reversible martensitic phase transformation with an unusually large magnetization change. In this work the nature of the magnetic ordering above and below this transformation has been studied in detail in the critical composition range x = 6–8 via temperature-dependent (5–600 K) magnetometry and small-angle neutron scattering (SANS). We observe fairly typical paramagnetic to long-range-ordered ferromagnetic phase transitions on cooling to 420–430 K, with the expected critical spin fluctuations, followed by first-order martensitic phase transformations to a nonferromagnetic state below 360–390 K. Themore » static magnetization reveals complex magnetism in this low-temperature nonferromagnetic phase, including a Langevin-like field dependence, distinct spin freezing near 60 K, and significant exchange bias effects, consistent with superparamagnetic blocking of ferromagnetic clusters of nanoscopic dimensions. We demonstrate that these spin clusters, whose existence has been hypothesized in a variety of martensitic alloys exhibiting competition between ferromagnetic and antiferromagnetic exchange interactions, can be directly observed by SANS. The scattering data are consistent with a liquidlike spatial distribution of interacting magnetic clusters with a mean center-to-center spacing of 12 nm. Considering the behavior of the superparmagnetism, cooling-field and temperature-dependent exchange bias, and magnetic SANS, we discuss in detail the physical form and origin of these spin clusters, their intercluster interactions, the nature of the ground-state magnetic ordering in the martensitic phase, and the implications for our understanding of such alloy systems.« less

  10. Correlation of the energy product with evolution of the nanostructure in Y,Dy,Nd-(Fe,Co)-B magnetic alloy

    SciTech Connect

    Wu, Y.Q; Tang, W.; Kramer, M.J.; Dennis, K.W.; Oster, N.; McCallum, R.W.; Anderson, I.E.

    2009-07-24

    The devitrification behavior of nanocrystalline MRE{sub 2}(Fe,Co){sub 14}B+ZrC (MRE = Nd+Y+Dy) was studied using differential scanning calorimetry (DSC), synchrotron high temperature x-ray diffraction, and analytical transmission electron microscopy (TEM) techniques. Alloy ribbons were melt spun at 25 m/s to obtain an amorphous structure. Optimum hard magnetic properties (B{sub r} = 7.2 kG, H{sub c} = 12.7 kOe and (BH){sub max} = 10.8 MG Oe) were obtained in ribbons annealed at 750 C for 15 min. A reduced annealing temperature of 638 C and holding time from 0 to 11 min were chosen based on DSC analysis. Large changes in both microstructure and hard magnetic properties were found in a narrow window of annealing time, 4.5-6 min, resulting in a dramatic increase in energy product, remanence and coercivity: 0.96 MG Oe, 5.2 kG, 2.7 kOe to 5.7 MG Oe, 7.2 kG, 8.5 kOe for (BH){sub max}, B{sub r} and H{sub c}, respectively. Energy dispersive x-ray spectroscopy and energy filtered TEM analyses indicate that Zr- and C-rich particles ({approx} 5 nm) and thin grain boundary layers (1-2 nm thick) are formed surrounding 2-14-1 hard phase grains when the annealing time is over 6 min. Further annealing resulted in a more distinct hard phase surrounded by a nonmagnetic grain boundary phase {approx} 1 nm in thickness. The thin grain boundary layer phase starts to disappear with annealing time over 11 min. The partitioning behavior of various elements at different annealing conditions appears to be associated with significant changes in magnetic properties, leading to an improved optimum microstructure.

  11. Changes in cluster magnetism and suppression of local superconductivity in amorphous FeCrB alloy irradiated by Ar+ ions

    NASA Astrophysics Data System (ADS)

    Okunev, V. D.; Samoilenko, Z. A.; Szymczak, H.; Szewczyk, A.; Szymczak, R.; Lewandowski, S. J.; Aleshkevych, P.; Malinowski, A.; Gierłowski, P.; Więckowski, J.; Wolny-Marszałek, M.; Jeżabek, M.; Varyukhin, V. N.; Antoshina, I. A.

    2016-02-01

    We show that cluster magnetism in ferromagnetic amorphous Fe67Cr18B15 alloy is related to the presence of large, D=150-250 Å, α-(Fe Cr) clusters responsible for basic changes in cluster magnetism, small, D=30-100 Å, α-(Fe, Cr) and Fe3B clusters and subcluster atomic α-(Fe, Cr, B) groupings, D=10-20 Å, in disordered intercluster medium. For initial sample and irradiated one (Φ=1.5×1018 ions/cm2) superconductivity exists in the cluster shells of metallic α-(Fe, Cr) phase where ferromagnetism of iron is counterbalanced by antiferromagnetism of chromium. At Φ=3×1018 ions/cm2, the internal stresses intensify and the process of iron and chromium phase separation, favorable for mesoscopic superconductivity, changes for inverse one promoting more homogeneous distribution of iron and chromium in the clusters as well as gigantic (twice as much) increase in density of the samples. As a result, in the cluster shells ferromagnetism is restored leading to the increase in magnetization of the sample and suppression of local superconductivity. For initial samples, the temperature dependence of resistivity ρ(T)~T2 is determined by the electron scattering on quantum defects. In strongly inhomogeneous samples, after irradiation by fluence Φ=1.5×1018 ions/cm2, the transition to a dependence ρ(T)~T1/2 is caused by the effects of weak localization. In more homogeneous samples, at Φ=3×1018 ions/cm2, a return to the dependence ρ(T)~T2 is observed.

  12. Ab initio study of structural, electronic, magnetic alloys: XTiSb (X = Co, Ni and Fe)

    SciTech Connect

    Ibrir, M. Berri, S.; Lakel, S.; Alleg, S.; Bensalem, R.

    2015-03-30

    Structural, electronic and magnetic properties of three semi-Heusler compounds of CoTiSb, NiTiSb and FeTiSb were calculated by the method (FP-LAPW) which is based on the DFT code WIEN2k. We used the generalized gradient approximation (GGA (06)) for the term of the potential exchange and correlation (XC) to calculate structural properties, electronic properties and magnetic properties. Structural properties obtained as the lattice parameter are in good agreement with the experimental results available for the electronic and magnetic properties was that: CoTiSb is a semiconductor NiTiSb is a metal and FeTiSb is a half-metal ferromagnetic.

  13. Development of Cu-Nb alloy microcomposite conductors for high field pulsed magnets. Final report

    SciTech Connect

    Pantsyrnyi, V.I.; Shikov, A.K.; Nikulin, A.D.; Belyiakov, N.M.; Potapenko, I.I.; Vorob`ova, A.E.; Silaev, A.G.; Kozlenkova, N.I.; Zinov`ev, V.G.; Drobyshev, V.A.

    1995-12-31

    Primary goal is to develop high strength-high conductivity composite wires with enhanced cross section. The following research areas were started: melting, deformation, TEM, SEM, and mechanical/electrical characterization of in-situ Cu-Nb microcomposites. Consumable arc melting using initial composite electrodes produced by cold deformation was chosen for preparing initial ingots of Cu-(16- 18)wt%Nb alloy. The deformation process including extrusion, drawing with intermediate heat treatments, and rolling was analyzed. Structure of Cu-Nb composite was investigated at all stages of its fabrication. Rebundling was successfully used to manufacture conductors with enhanced cross sections. Wire with 3x7mm{sup 2} cross section and 50m length was produced with UTS (20 C) = 1000 MPa and electroconductivity 70% IACS.

  14. Formation of bcc non-equilibrium La, Gd and Dy alloys and the magnetic structure of Mg-stabilized. beta. Gd and. beta. Dy

    SciTech Connect

    Herchenroeder, J.W.

    1989-02-01

    The high temperature bcc allotrope of a rare earth metal has the potential for substantially different magnetic properties than the room temperature hexagonal (hcp or dhcp) counterpart because of its more symmetrical crystal field. The stabilization by alloying and quenching of this bcc phase was studied for La-M alloys where M is an non-rare earth metal from Group II or III. The factors influencing the stabilization, such as size of M and quench rate, are discussed. ..gamma..La (bcc) could be retained over a composition range around the eutectoid composition by Mg or Cd alloying. A comparison of T/sub o/ curves of the various alloy systems suggest that the eutectoid temperature of the La-M system must be approximately equal to or less than a critical T/sub o/ temperature of 515/degree/C if the bcc phase is to be retained by quenching. The thermal stability of ..beta..Gd (bcc) was investigated by DTA and isothermal annealing. It was found to transform to an intermediate phase before reverting to the equilibrium phases in contrast to ..gamma..La alloys which decompose directly on heating to the equilibrium phases. 71 refs., 52 figs., 7 tabs.

  15. Comparison of the Crystallization Behavior of Fe-Si-B-Cu and Fe-Si-B-Cu-Nb-Based Amorphous Soft Magnetic Alloys

    NASA Astrophysics Data System (ADS)

    Smith, Casey; Katakam, Shravana; Nag, Soumya; Zhang, Y. R.; Law, J. Y.; Ramanujan, Raju V.; Dahotre, Narendra B.; Banerjee, Rajarshi

    2014-06-01

    The role of the solute elements, copper, and niobium, on the different stages of de-vitrification or crystallization of two amorphous soft magnetic alloys, Fe73.5Si13.5B9Nb3Cu1, also referred to as FINEMET, and a Fe76.5Si13.5B9Cu1 alloy, a model composition without Nb, has been investigated in detail by coupling atom probe tomography and transmission electron microscopy. The effects of copper clustering and niobium pile-up at the propagating interface between the α-Fe3Si nanocrystals and the amorphous matrix, on the nucleation and growth kinetics have been addressed. The results demonstrate that while Cu clustering takes place in both alloys in the early stages, the added presence of Nb in FINEMET severely restricts the diffusivity of solute elements such as Cu, Si, and B. Therefore, the kinetics of solute partitioning and mobility of the nanocrystal/amorphous matrix interface is substantially slower in FINEMET as compared to the Fe76.5Si13.5B9Cu1 alloy. Consequently, the presence of Nb limits the growth rate of the α-Fe3Si nanocrystals in FINEMET and results in the activation of a larger no. of nucleation sites, leading to a substantially more refined microstructure as compared to the Fe76.5Si13.5B9Cu1 alloy.

  16. Heat capacities, magnetic properties, and resistivities of ternary RPdBi alloys where R = La, Nd, Gd, Dy, Er, and Lu

    SciTech Connect

    Riedemann, T.M.

    1996-05-01

    Over the past four and a half decades research on the rare earths, their compounds, and their alloys has yielded significant insights into the nature of materials. The rare earths can be used to systematically study a series of alloys or compounds. Magnetic ordering, crystalline fields, spin fluctuations, the magnetocaloric effect, and magnetostriction are a small sample of phenomena studied that are exhibited by the rare earth family. A significant portion of research has been conducted on the abundant RM{sub 2} and RM phases, where R is the rare earth and M is a transition metal. The natural progression of science has led to the study of related RMX ternary phases, where X is either another transition metal or semimetal. There are now over 1,000 known RMX phases. The focus of this study is on RPdBi where R = La, Nd, Gd, Dy, Er, and Lu. Their heat capacities, magnetic properties, and resistivities are studied.

  17. Low temperature and magnetic field behaviour of the (Cr{sub 84}Re{sub 16}){sub 89.6}V{sub 10.4} alloy

    SciTech Connect

    Jacobs, B. S. Sheppard, C. J.; Prinsloo, A. R. E.; Lodya, L.

    2014-05-07

    Measurements of the temperature (T) dependence of the magnetic susceptibility (χ) and electrical resistance (R) on an antiferromagnetic (AFM) (Cr{sub 84}Re{sub 16}){sub 89.6}V{sub 10.4} alloy are reported in order to probe the existence of quantum critical behaviour (QCB) utilizing static magnetic fields (H) as a tuning parameter. The results indicate that an increase in H suppresses T{sub N} in such a way that it varies exponentially with increasing H. R(T) measurements show evidence of possible superconducting (SC) behaviour below 1 K at H = 0 T. These results therefore indicate the coexistence of the AFM and SC phases in the (Cr{sub 84}Re{sub 16}){sub 89.6}V{sub 10.4} alloy.

  18. Stability of metastable phase and soft magnetic properties of bulk Fe-B nano-eutectic alloy prepared by undercooling solidification combined with CU-mold chilling

    NASA Astrophysics Data System (ADS)

    Yang, Changlin; Zhang, Jun; Huang, Huili; Song, Qijiao; Liu, Feng

    2015-11-01

    Bulk Fe83B17 nano-eutectic alloys were prepared by undercooling solidification combined with Cu-mold chilling method. Stable phase Fe2B and metastable phase Fe3B were found to coexist in the as-solidified microstructure. The soft magnetic properties were improved significantly by the nano-lamellar eutectic and the metastable phase and, were increased further by annealing at 1173 K for 1.5 h after which the metastable phase was decomposed completely.

  19. Interface magnetism of Co{sub 2}FeGe Heusler alloy layers and magnetoresistance of Co{sub 2}FeGe/MgO/Fe magnetic tunnel junctions

    SciTech Connect

    Tanaka, M. A. Maezaki, D.; Ishii, T.; Okubo, A.; Mibu, K.; Hiramatsu, R.; Ono, T.

    2014-10-28

    The interface magnetism between Co{sub 2}FeGe Heusler alloy layers and MgO layers was investigated using {sup 57}Fe Mössbauer spectroscopy. Interface-sensitive samples, where the {sup 57}Fe isotope was used only for the interfacial atomic layer of the Co{sub 2}FeGe layer on the MgO layer, were prepared using atomically controlled alternate deposition. The {sup 57}Fe Mössbauer spectra of the interface-sensitive samples at room temperature were found similar to those of the bulk-sensitive Co{sub 2}FeGe films in which the {sup 57}Fe isotope was distributed throughout the films. On the other hand, the tunnel magnetoresistance effect of magnetic tunnel junctions with Co{sub 2}FeGe layers as the ferromagnetic electrodes showed strong reduction at room temperature. These results indicate that the strong temperature dependence of the tunneling magnetoresistance of magnetic tunnel junctions using Heusler alloy electrodes cannot be attributed simply to the reduction of the magnetization at the interfaces between the Heusler alloy and insulator layers.

  20. Electric and magnetic properties of Al86Ni8R6 (R=Sm, Gd, Ho) alloys in liquid and amorphous states

    NASA Astrophysics Data System (ADS)

    Sidorov, V.; Svec, P.; Svec, P.; Janickovic, D.; Mikhailov, V.; Sidorova, E.; Son, L.

    2016-06-01

    Electrical resistivity and magnetic susceptibility of Al86Ni8Sm6, Al86Ni8Gd6 and Al86Ni8Ho6 alloys are studied in a wide temperature range including amorphous, crystalline and liquid states. The negative value of resistivity temperature coefficient in amorphous ribbons is explained by the structural separation starting much before the beginning of their crystallization. The effective magnetic moments per Gd and Ho atoms are found to be essentially lower than for R3+ ions. The results are discussed in supposition of directed bonds between rare earth and aluminum atoms.

  1. Low-temperature magnetization of amorphous and nanocrystalline Fe 76.5- xU xCu 1Si 13.5B 9 alloys

    NASA Astrophysics Data System (ADS)

    Duša, O.; Kováč, J.; Konč, M.; Švec, T.; Kavečanský, V.

    1996-03-01

    The low-temperature magnetization of amorphous and nanocrystalline Fe 76.5- xU xCu 1Si 13.5B 9 alloys ( x = 0-11) has been studied in the 4.2-300 K range. All examined magnetic parameters (exchange integral J, range of exchange interactions < r2>, magnetic moment per Fe atom, μFe, spin wave stiffness constant D) are markedly influenced by the uranium substitution for iron. Both the μFe and D are found to increase with decreasing Fe content in amorphous alloys for x = 0 up to about 4. The noncollinear spin structures as a result of competing interactions are supposed to explain this behaviour. Some samples (with U contents of 2-6 at%) annealed for 1 h at 813 K appear to be nanocrystalline. Uranium seems to inhibit grain growth in the investigated FeUCuSiB system, just as Nb does in FeNbCuSiB nanocrystalline alloys.

  2. Effect of a transverse magnetic field on solidification morphology and microstructures of pure Sn and Sn-15 wt% Pb alloys grown by a Czochralski method

    NASA Astrophysics Data System (ADS)

    Shen, Zhe; Zhong, Yunbo; Wang, Huai; Ren, Weili; Lei, Zuosheng; Ren, Zhongming

    2015-12-01

    The pure Sn and Sn-15 wt% Pb alloys were grown by a Czochralski method under various magnetic flux densities in this paper. The influence of thermoelectric magnetic (TEM) flows and buoyancy flows on solidification morphology, macrosegregation and microstructures had been investigated experimentally, and the velocity magnitude of TEM flows and buoyancy flows had been studied by 3D numerical simulations. The experimental results indicate that the modification of solidification morphology and microstructures is attributed to the unidirectional Pb solutes transport caused by TEM flows. The 3D numerical simulations results show that the buoyancy flows dominate the flows in the melt under a weak transverse magnetic field (B≤0.43 T), and the unidirectional TEM flows at the vicinity of solid-liquid interface become the dominant flows in the melt with the increase of magnetic field. The interaction of TEM flows and buoyancy flows affecting solidification morphology and microstructures during directional solidification of alloys by the Czochralski method under various magnetic flux densities has been discussed and a corresponding simple evolution mechanism of dendritic growth has been proposed.

  3. Observation of magnetic-field-induced transformation in MnCo0.78Fe0.22Ge alloys with colossal strain output and large magnetocaloric effect

    NASA Astrophysics Data System (ADS)

    Wang, Zilong; Xiu, Pengyuan; Huang, Lian; Nie, Zhihua; Zeng, Junxi; Brown, Dennis E.; Ren, Yang; Wang, Yandong

    2016-05-01

    The thermal, structural and magnetic properties were studied for the hexagonal MnCo0.78Fe0.22Ge alloys, which undergoes a first-order phase transformation from paramagnetic hexagonal phase into ferromagnetic orthorhombic martensite on cooling. Owing to the magnetostructural coupling, large magnetocaloric effect (∆SM=-10.97 J kg-1 K-1) was obtained at 254 K. In-situ synchrotron high-energy X-ray diffraction experiments were conducted to reveal the detailed change in crystallographic structure of phases and the effect of applied magnetic field on phase transformation behaviors. An anomalously huge strain of 11.89% and volume expansion of 4.35% in unit-cell were obtained between martensite and parent phase across the transformation. Furthermore, the magnetic field-induced martensitic transformation was directly evidenced at 250 K, which eventually demonstrates the possibility to achieve magnetic-field-induced strain and large magnetocaloric effect simultaneously.

  4. Magnetic and structural anisotropies of Co2FeAl Heusler alloy epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Gabor, M. S.; Petrisor, T., Jr.; Tiusan, C.; Hehn, M.; Petrisor, T.

    2011-10-01

    This paper shows the correlation between chemical order, lattice strains, and magnetic properties of Heusler Co2FeAl films epitaxially grown on MgO(001). A detailed magnetic characterization is performed using vector-field magnetometery combined with a numerical Stoner-Wohlfarth analysis. We demonstrate the presence of three types of in-plane anisotropies: one biaxial, as expected for the cubic symmetry, and two uniaxial. The three anisotropies show different behavior with the annealing temperature. The biaxial anisotropy shows a monotonic increase. The uniaxial anisotropy that is parallel to the hard biaxial axes (related to chemical homogeneity) decreases, while the anisotropy that is supposed to have a magnetostatic origin remains constant.

  5. Magnetic anisotropy of C and N doped bulk FeCo alloy: A first principles study

    NASA Astrophysics Data System (ADS)

    Khan, Imran; Hong, Jisang

    2015-08-01

    Using the full potential linearized augmented plane wave (FLAPW) method, we investigated the magnetocrystalline anisotropy of carbon and nitrogen doped FeCo in the interstitial site. Here, we have considered 3.125% impurity doping concentration. The impurity doping induces a tetragonal distortion in the FeCo lattice, and both carbon and nitrogen impurities play a similar role for lattice distortion. The local magnetic moment of Fe atom around the impurity site was greatly reduced, whereas the Co had rather robust magnetic moment. We found a uniaxial magnetocrystalline anisotropy constant of 0.65 and 0.58 MJ/m3 for C and N doped bulk FeCo, and this was mainly due to the tetragonal distortion induced by C and N impurity, not from the hybridization effect with Fe or Co. Additionally, the estimated maximum energy product and coercive field were 81.4, 72.5 MGOe and 600, 530 kA m-1 for C and N doped bulk FeCo, respectively. These results may imply that the interstitial C or N doped FeCo can be used for potential rare earth free permanent magnet although those values are likely to be suppressed in real samples due to micromagnetic factors such as structural defects, geometrical effect, or grain boundary effect.

  6. Hydrogen-mediated long-range magnetic ordering in Pd-rich alloy film

    SciTech Connect

    Lin, Wen-Chin Tsai, Cheng-Jui; Huang, Han-Yuan; Mudinepalli, Venkata Ramana; Chiu, Hsiang-Chih; Wang, Bo-Yao

    2015-01-05

    The effect of hydrogenation on a 14 nm Co{sub 14}Pd{sub 86}/Al{sub 2}O{sub 3}(0001) thin film was investigated on the basis of the magnetooptical Kerr effect. After exposure to H{sub 2} gas, the squareness of the hysteresis loop showed a large transition from approximately 10% to 100% and the saturation Kerr signal was reduced to nearly 30% of the pristine value. The reversibility of the transition was verified and the response time was within 2–3 s. These observations indicate that the hydride formation transformed the short-range coupled and disordered magnetic state of the Co{sub 14}Pd{sub 86} film to a long-range-ordered ferromagnetic state and induced appreciable decrease in the magnetic moment. The enhanced long-range-ordering and the reduction of the magnetic moment were attributed to the change of electronic structure in Co{sub 14}Pd{sub 86} with hydrogen uptake.

  7. Magnetic properties of Fe5SiB2 and its alloys with P, S, and Co

    NASA Astrophysics Data System (ADS)

    Werwiński, Mirosław; Kontos, Sofia; Gunnarsson, Klas; Svedlindh, Peter; Cedervall, Johan; Höglin, Viktor; Sahlberg, Martin; Edström, Alexander; Eriksson, Olle; Rusz, Ján

    2016-05-01

    Fe5SiB2 has been synthesized and magnetic measurements have been carried out, revealing that Msat=0.92 MA/m at T =300 K. The M versus T curve shows a broad peak around T =160 K. The anisotropy constant K1, estimated at T =300 K, is 0.25 MJ/m3. Theoretical analysis of Fe5SiB2 system has been carried out and extended to the full range of Fe5Si1 -xPxB2 ,Fe5P1 -xSxB2 , and (Fe1 -xCox )5SiB2 compositions. The electronic band structures have been calculated using the full-potential local-orbital minimum-basis scheme (FPLO-14). The calculated total magnetic moments are 9.20, 9.15, 9.59, and 2.42 μB per formula units of Fe5SiB2 ,Fe5PB2 ,Fe5SB2 , and Co5SiB2 , respectively. In agreement with experiment, magnetocrystalline anisotropy energies (MAE's) calculated for T =0 K change from a negative (easy-plane) anisotropy -0.28 MJ/m3 for Fe5SiB2 to the positive (easy-axis) anisotropy 0.35 MJ/m3 for Fe5PB2 . Further increase of the number of p electrons in Fe5P1 -xSxB2 leads to an increase of MAE up to 0.77 MJ/m3 for the hypothetical Fe5P0.4S0.6B2 composition. Volume variation and fixed spin moment calculations (FSM) performed for Fe5SiB2 show an inverse relation between MAE and magnetic moment in the region down to about 15% reduction of the spin moment. The alloying of Fe5SiB2 with Co is proposed as a practical realization of magnetic moment reduction, which ought to increase MAE. MAE calculated in virtual crystal approximation (VCA) for a full range of (Fe1 -xCox )5SiB2 compositions reaches the maximum value of 1.16 MJ/m3 at Co concentration x =0.3 , with the magnetic moment 7.75 μB per formula unit. Thus, (Fe0.7Co0.3 )5SiB2 is suggested as a candidate for a rare-earth free permanent magnet. For the stoichiometric Co5SiB2 there is an easy-plane magnetization, with the value of MAE=-0.15 MJ/m3.

  8. Electric field tunability of microwave soft magnetic properties of Co2FeAl Heusler alloy film

    NASA Astrophysics Data System (ADS)

    Li, Shandong; Xu, Jie; Xue, Qian; Du, Honglei; Li, Qiang; Chen, Caiyun; Yang, Ru; Xie, Shiming; Liu, Ming; Nan, Tianxiang; Sun, Nian X.; Shao, Weiquan

    2015-05-01

    Co2FeAl Heusler alloy film with 100 nm in thickness was sputtered on (011)-cut lead zinc niobate-lead titanate (PZN-PT) single crystal slabs. It was revealed that this multiferroic laminate shows very large electric field (E-field) tunability of microwave soft magnetic properties. With the increase of electric field from 0 to 8 kV/cm on PZN-PT, the anisotropy field, HK, of the Co2FeAl film along [100] direction of PZN-PT is dramatically enhanced from 65 to 570 Oe due to the strong magnetoelectric (ME) coupling between ferromagnetic Co2FeAl film and ferroelectric substrate. At the same time, the damping constant α of Co2FeAl film dramatically decreases from 0.20 to 0.029. As a result, a significantly shift of self-biased ferromagnetic resonance frequency, fFMR, from 1.86 to 6.68 GHz with increment of 3.6 times was obtained. These features demonstrate that Co2FeAl/PZN-PT multiferroic laminate is promising in fabrication of E-field tunable microwave components.

  9. Temperature dependence of tunneling magnetoresistance in epitaxial magnetic tunnel junctions using a Co2FeAl Heusler alloy electrode

    NASA Astrophysics Data System (ADS)

    Wang, Wenhong; Sukegawa, Hiroaki; Inomata, Koichiro

    2010-09-01

    Spin-valve-type epitaxial magnetic tunnel junctions (MTJs) consisting of a full-Heusler alloy Co2FeAl (CFA) and a MgO tunnel barrier were fabricated on a single-crystal MgO(001) substrate using sputtering method for all the layers. Experimental temperature-dependent tunnel magnetoresistance in the MTJs was revealed to be fitted well using spin wave excitation model for tunneling spin polarization, P(T)=P0(1-αT3/2) up to room temperature, where P0 is the spin polarization at 0 K and α is a fitting parameter. The determined P and α are shown to be significantly different between bottom and top CFA electrodes facing a MgO barrier. It is demonstrated that the bottom CFA deposited on a Cr buffer has a low α and behaves as a half-metal with P˜1 in terms of the Δ1 symmetry due to the coherent tunneling through a MgO barrier.

  10. Magnetism of Ho1-xTbxAl₂ alloys: Critical dependence of a first-order transition on Tb concentration

    DOE PAGESBeta

    Khan, Mahmud; Mudryk, Ya.; Gschneidner, K. A.; Pecharsky, V. K.

    2011-12-27

    HoAl₂ exhibits a first-order spin reorientation transition at 20 K, which is manifested as a sharp peak in the heat capacity. When Ho is partially replaced by only 5% of Tb, the sharp heat-capacity peak in Ho1-xTbxAl₂ (x = 0.05) disappears, and then reappears again for x ≥ 0.07. For x = 0.05, the anomaly corresponding to the spin reorientation transition is barely seen in the heat capacity, but as x exceeds 0.07 the weak anomaly transforms to a sharp peak. The spin reorientation transition temperature increases to 29 K for x = 0.05, and as x increases further themore » transition shifts to lower temperature and returns to ~20 K for x = 0.25. The transition is no longer observed when x exceeds 0.60. Temperature-dependent x-ray powder-diffraction data confirm the first-order nature of the spin reorientation transition for the alloy with x = 0.40, and indicate that the compound retains the room-temperature cubic structure within the sensitivity of the technique. Experimental observations are discussed considering the easy magnetization directions of HoAl₂ and TbAl₂.« less

  11. Effect of a low axial magnetic field on the primary Al 2 Cu phase growth in a directionally solidified Al-Cu hypereutectic alloy

    NASA Astrophysics Data System (ADS)

    Shen, Yu; Ren, Zhongming; Li, Xi; Ren, Weili; Xi, Yan

    2011-12-01

    Effect of a low axial magnetic field on the growth behavior of the primary Al 2Cu phase in the Al-40 wt% Cu hypereutectic alloy during directional solidification at a low growth speed has been investigated experimentally. The results show that the application of a low magnetic field (≤1 T) causes the primary Al 2Cu phase to become deformed and irregular opposed to the well developed strip-like primary phase in the absence of the field. The deformation of the primary phase is maximum when a 0.5 T magnetic field is applied. Moreover, it has been found that the magnetic field promotes a transition of the primary phase morphology from faceted growth to irregular cellular structure and makes the primary phase spacing decrease with the increase of the magnetic field intensity. From the macroscopic scale, the magnetic field causes the occurrence of a considerable radial macrosegregation. These experimental results may be attributed to the effects of thermoelectric magnetic force (TEMF) in the solid and thermoelectromagnetic convection (TEMC) in the liquid. Further, the model of these effects is presented and evaluated numerically. The results indicate that the numerical magnitude of the TEMF during directional solidification under a 0.5 T low axial magnetic field can be of the order of 10 3 N/m 3. The force causes TEMC at different scales to modify the distribution of solute at the interface and should be responsible for the deformation, fracture and deflection of the primary phase.

  12. Magnetic ordering and exchange interactions in structural modifications of M n3Ga alloys: Interplay of frustration, atomic order, and off-stoichiometry

    NASA Astrophysics Data System (ADS)

    Khmelevskyi, Sergii; Ruban, Andrei V.; Mohn, Peter

    2016-05-01

    Mn-Ga alloys close to the M n3Ga stoichiometry can be synthesized in three different crystal modifications: hexagonal, tetragonal, and face-centered cubic, both in bulk and in thin-film forms. The magnetic ordering of these modifications is varying from noncollinear antiferromagnetic in the hexagonal case to ferrimagnetic order in the tetragonal one, whereas it is still unknown for the atomically disordered fcc structure. Here we study the onset of magnetic order at finite temperatures in these systems on a first-principles basis calculating the interatomic magnetic exchange interactions in the high-temperature paramagnetic regime. We employ the disordered local moment formalism and the magnetic force theorem within the framework of the local spin-density approximation and Monte Carlo simulations taking also the effects of atomic disorder in fcc alloys into account. In particular we find the origin of the stabilization of the noncollinear 3 k structure in competition between antiferromagnetic inter- and in-plane couplings of frustrated kagome planes in hexagonal M n3Ga and predict the antiferromagnetic-1 collinear order due to frustration in fcc alloys. Special attention is paid to the effects of the off-stoichiometry and the consequences of atomic disorder. We calculate the site-preference energy of Ga antisite atoms in the tetragonal structures in the range of the compositions from M n3Ga to M n2Ga and slightly beyond and confirm the earlier explanation of the effect of magnetization increase due to Ga preferentially occupying one of the Mn sites.

  13. Effect of external magnetic field on valence-electron structures of Fe and Ni in Invar, Permalloy and the other Fe-Ni alloys by using Kβ-to-Kα X-ray intensity ratios.

    PubMed

    Alım, Bünyamin; Han, İbrahim; Demir, Lütfü

    2016-06-01

    The effect of external magnetic field on the valence-electron structures of Fe and Ni in various Fe-Ni alloy compositions was investigated by using X-ray fluorescence spectroscopy. Firstly, Kβ-to-Kα X-ray intensity ratios of Fe and Ni in Invar (Fe0.64Ni0.36), Permalloy (Fe0.20Ni0.80) and FexNi1-x (x=0, 0.40, 0.52, 0.55, 0.61, and 1) alloys were measured without any magnetic field and under 0.5 and 1T external magnetic fields, separately. Later, the valence-electron structures of Fe and Ni in both pure form and alloys were obtained by comparison of measured X-ray intensity ratios with the results of multi-configurations Dirac-Fock (MCDF) calculations. The results obtained for valence-electron structures of Fe and Ni in various Fe-Ni alloys were evaluated in terms of magnetic field effect, delocalization and/or charge transfer phenomena. The results have shown that valence electron structure of Fe and Ni in Fe-Ni alloys are dependent on both external magnetic field and concentration of alloy elements. PMID:26974486

  14. EXAFS Studies and Microwave Magnetic Properties of FeGaB Thin Films and FeCuZr Ball-Milled Alloys

    NASA Astrophysics Data System (ADS)

    Gao, Jinsheng

    X-ray absorption fine structure (XAFS) is a spectroscopic technique which can investigate the physical and chemical structure of materials at the atomic scale. X-rays are applied in this technique to be near and above the binding energy of a particular core electronic level of a particular atomic species. Over the last decades, XAFS has emerged as a highly informative probe of the local structure around selected atomic species in solids, liquids, and molecular gases. It offers both element specificity and local structure sensitivity. Foremost among its strengths are its ability to probe the local atomic environments of different elements in the sample by selecting the corresponding incident X-ray energy. In the first part of this thesis, FeGaB alloys, which are of value as soft magnetic materials having relatively large magnetostriction coefficient, were fabricated in which varying amounts of boron were added to the host FeGa alloy to investigate its impact upon local atomic structure and magnetic and microwave properties. The impact of B upon the local atomic structure in FeGaB films were investigated by extended X-ray absorption fine structure (EXAFS) analysis. EXAFS fitting results revealed a contraction of lattice parameters with the introduction of B. The Debye-Waller factor determined from EXAFS fitting gradually increases as a function of boron addition and abruptly increases during the structural evolution from crystalline to amorphous. Upon the onset of this transition the static and microwave magnetic properties became exceptionally softer, with values of coercivity and ferromagnetic linewidth reducing dramatically. In the second part of this thesis, metastable alloys of the composition FeCuZr were synthesized by high energy ball milling and measured by EXAFS . The fitting results demonstrate that nanocrystalline or amorphous alloys have been obtained depending on the Zr content.

  15. Magnetic damping constant of Co{sub 2}FeSi Heusler alloy thin film

    SciTech Connect

    Oogane, Mikihiko; Yilgin, Resul; Shinano, Masatsugu; Yakata, Satoshi; Sakuraba, Yuya; Ando, Yasuo; Miyazaki, Terunobu

    2007-05-01

    Co{sub 2}FeSi films were prepared using magnetron sputtering technique on Cr buffer layers and MgO(001) substrates at various annealing temperatures. We investigated the crystal structures, magnetic properties (M{sub s} and H{sub c}), surface roughness, and magnetic damping constants ({alpha}) of the prepared Co{sub 2}FeSi films. Out-of-plane angular dependences of the resonance field and the linewidth of the ferromagnetic resonance spectra were measured and fitted using the Landau-Lifshitz-Gilbert equation to determine the damping constant. The as-deposited Co{sub 2}FeSi film exhibited an amorphous and disordered structure; the {alpha} value was 0.008. In contrast, the Co{sub 2}FeSi films annealed over 300 degree sign C showed epitaxial growth and had a (001)-oriented and L2{sub 1} ordered structure. Both disordered and L2{sub 1} ordered Co{sub 2}FeSi films showed similar {alpha} values.

  16. Structural, electronic and magnetic properties of Fe2-based full Heusler alloys: A first principle study

    NASA Astrophysics Data System (ADS)

    Dahmane, F.; Mogulkoc, Y.; Doumi, B.; Tadjer, A.; Khenata, R.; Bin Omran, S.; Rai, D. P.; Murtaza, G.; Varshney, Dinesh

    2016-06-01

    Using the first-principles density functional calculations, the structural, electronic and magnetic properties of the Fe2XAl (X=Cr, Mn, Ni) compounds in both the Hg2CuTi and Cu2MnAl-type structures were studied by the full-potential linearized augmented plane waves (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) where the results show that the Cu2MnAl-type structure is energetically more stable than the Hg2CuTi-type structure for the Fe2CrAl and Fe2MnAl compounds at the equilibrium volume. The full Heusler compounds Fe2XAl (X=Cr, Mn) are half-metallic in the Cu2MnAl-type structure. Fe2NiAl has a metallic character in both CuHg2Ti and AlCu2Mn-type structures. The total magnetic moments of the Fe2CrAl and Fe2MnAl compounds are 1.0 and 2.0 μB, respectively, which are in agreement with the Slater-Pauling rule Mtot=Ztot- 24.

  17. Ultrasoft magnetic properties in nanocrystalline alloy Finemet with Au substituted for Cu

    NASA Astrophysics Data System (ADS)

    Chau, N.; Hoa, N. Q.; The, N. D.; Niem, P. Q.

    2006-09-01

    The amorphous ribbon Fe 73.5Si 13.5B 9Nb 3Au 1 has been prepared by rapid cooling on a copper wheel. The ribbon is 16.8 μm thick and 7 mm wide. The DSC curves show the first peak at 547-579 °C (corresponds to the crystallization of α-Fe(Si) phase) depending on heating rate from 10 to 50 °C/min which is a little higher than that of pure Finemet (542-570 °C, respectively). From the Kissinger plot, the crystallization activation energy is determined and shown to be 2.8 eV for α-Fe(Si) phase, less than that of Finemet ( E=3.25 eV). By annealing at 530 °C for 30, 60 and 90 min, the crystallization volume fraction of α-Fe(Si) phase increased from 73% to 78% and 84%, respectively. After appropriate annealing, the ultrasoft magnetic properties are achieved. The maximum magnetic entropy change, ∣Δ Sm∣ max, showed a giant value of 7.8 J/kg K which occurred at around Curie temperature of amorphous phase of the ribbon.

  18. Al3+ ions dependent structural and magnetic properties of Co-Ni nano-alloys.

    PubMed

    Kadam, R H; Alone, Suresh T; Gaikwad, Anil S; Birajdar, A P; Shirsath, Sagar E

    2014-06-01

    Ferrite samples with a chemical formula Co0.5Ni0.5Al(x)Fe(2-x)O4 (where x = 0.0, 0.25, 0.5, 0.75 and 1.0) were synthesized by sol-gel auto-combustion method. The synthesized samples were annealed at 600 degrees C for 4 h. An analysis of X-ray diffraction (XRD) patterns reveals the formation of single phase cubic spinel structure. The lattice parameter decreased linearly with the increasing Al content x. Nano size of the powders were confirmed by the transmission electron micrographs (TEM). Particle size, bulk density decreased whereas specific surface area and porosity of the samples increased with the Al substitution. Cation distribution of constituent ions shows linear dependence of Al substitution. Based on the cation distribution obtained from XRD data, structural parameters such as lattice parameters, ionic radii of available sites and the oxygen parameter 'u' is calculated. Saturation magnetization (M(s)), magneton number (n(B)) and coercivity (H(c)) decreased with the Al substitution. Possible explanation for the observed structural and magnetic behavior with various Al content are discussed. PMID:24738358

  19. On the synthesis of copper-nickel binary alloy nanoparticles and binding silane coupling agents to magnetic ferrite nanoparticles

    NASA Astrophysics Data System (ADS)

    Pritchett, Jeremy Scott

    This dissertation addresses the creation of a multifunctional nanoplatform for cancer targeting, imaging, and therapy. Magnetic oxide nanoparticles were labeled with silane coupling agents that could be used for targeting. The magnetic oxides have application as contrast enhancing agents for magnetic resonance imaging. Copper-nickel binary alloy nanoparticles were prepared for possible use in Curie temperature limited hyperthermia therapy. Spherical, single crystal iron oxide nanoparticles with average diameters of 4 nm, 6 nm, 8 nm, 11 nm, or 16 nm were prepared using published procedures. The iron oxide particle chemistry was extended to synthesize 13 nm diameter CoFe2O4, 9 nm diameter MnFe2O4, and 12 nm diameter NiFe2O4. The particles had a coating of oleic acid and oleylamine ligands. Silane coupling chemistry was used to displace these ligands with either beta-aminoethyl-gamma-aminopropyl-trimethoxysilane, triethoxysilane-PEG, or triethoxysilane-biotin. The silane ligands would allow the particles to be conjugated with a targeting group. New chemistry was developed to synthesize fcc CuNi nanoparticles with the objective of finding methods that give particles with an average size less than 50 nm, a narrow distribution of particle sizes, and control of particle composition. The particle synthesis involves the reduction of a mixture of copper(II) and nickel(II) and the reduction conditions included diol reduction, polyol synthesis, seeding by diol reduction, and oleate reduction. One of the main issues is the formation of hcp nickel particles as a containment in the method. The factors that avoided the formation of hcp nickel particles and allow only fcc particles to form were the choice of reducing agent, ratio of surfactants, and heating time. Both the oleate reduction and diol reduction gave a mixture of the hcp and fcc phases. By controlling certain reaction conditions, such as keeping the ratio of oleic acid to oleylamine 1:1 and slowly heating to reflux for

  20. In-plane/out-of-plane disorder influence on the magnetic anisotropy of Fe1-yMnyPt-L10 bulk alloy

    NASA Astrophysics Data System (ADS)

    Cuadrado, R.; Liu, Kai; Klemmer, Timothy J.; Chantrell, R. W.

    2016-03-01

    The random substitution of a non-magnetic species instead of Fe atoms in FePt-L10 bulk alloy will permit to tune the magnetic anisotropy energy of this material. We have performed by means of first principles calculations a study of Fe1-yMnyPt-L10 (y = 0.0, 0.08, 0.12, 0.17, 0.22, and 0.25) bulk alloy for a fixed Pt concentration when the Mn species have ferro-/antiferromagnetic (FM,AFM) alignment at the same(different) atomic plane(s). This substitution will promote several in-plane lattice values for a fixed amount of Mn. Charge hybridization will change compared to the FePt-L10 bulk due to this lattice variation leading to a site resolved magnetic moment modification. We demonstrate that this translates into a total magnetic anisotropy reduction for the AFM phase and an enhancement for the FM alignment. Several geometric configurations were taken into account for a fixed Mn concentration because of different possible Mn positions in the simulation cell.

  1. Effect of bending stresses on the high-frequency magnetic properties and their time stability in a cobalt-based amorphous alloy with an extremely low magnetostriction

    NASA Astrophysics Data System (ADS)

    Kekalo, I. B.; Mogil'nikov, P. S.

    2015-12-01

    An unusual effect of the stresses of bending (toroidal sample diameter D) on the hysteretic magnetic properties ( H c , μ5) of an amorphous Co69Fe3.7Cr3.8Si12B11 alloy with an extremely low magnetostriction (|λ s | ≤ 10-7) is revealed. These properties are measured in a dynamic regime at a magnetic-field frequency f = 0.1-20 kHz. The coercive force of the alloy H c weakly depends on D at low frequencies ( f < 1 kHz), and permeability μ5 ( H = 5 mOe), in contrast, is independent of D at high frequencies and is dependent on D at low frequencies. The samples subjected to high-temperature (390°C) annealing followed by water quenching exhibit "anomalous" dependences: permeability μ5 increases with decreasing toroidal sample radius, i.e., with increasing bending stresses. The detected dependences are related to the fact that magnetization reversal via the displacement of rigid domain walls is predominant at low frequencies and during static measurements and magnetization reversal via the displacement of flexible domain walls is predominant at high frequencies.

  2. Magnetic anisotropy graded media and iron-platinum alloy thin films

    NASA Astrophysics Data System (ADS)

    Lu, Zhihong

    Anisotropy graded media are promising to overcome the writability problem in achieving ultrahigh areal density for magnetic recording media. To more conveniently study and compare various media with regard to a particular figure of merit, a new energy landscape method of analysis is suggested. Using this method, the theoretical limit of the figure of merit for a graded medium is found to be 4. This limit can be approached by a graded medium with anisotropy quadratically increasing from zero to its maximum value. In order to characterize the anisotropy distribution of a graded medium, hard axis loops of graded media with various anisotropy profiles are simulated and analyzed. It is found that the second derivative of the hard axis loop can give useful information on the anisotropy distribution in a graded medium. Fe50Pt 50 with the L10 structure, as one of the magnetically hardest materials, has great potential for media application. By using a first-principles calculation method, the magnetic and electronic structures of L10 structured Fe50Pt50 have been studied. These calculations show that although the ferromagnetic phase is the most stable phase for Fe 50Fe50 with the L10 structure, there is a competition between the antiferromagnetic and the ferromagnetic phases when the ratio of lattice constants, c/a, decreases. Experimental investigations of Fe 50Pt50 films with graded order parameter fabricated by varying the growth temperature during deposition demonstrate that these films have much smaller switching field than fully ordered Fe50Pt50, which suggests it is possible to make graded media by using this kind of films. Fe100-xPtx films with compositional gradient were also studied; however, the large easy axis dispersion in these films makes them unsuitable for the fabrication of graded media. Films with [FePt3(ordered)/FePt 3(disordered)]n superlattices were deposited on MgO substrates and sapphire substrates. It was found that the superlattices deposited on Mg

  3. Experimental and ab initio studies on sub-lattice ordering and magnetism in Co{sub 2}Fe(Ge{sub 1−x}Si{sub x}) alloys

    SciTech Connect

    Deka, Bhargab; Kundu, Ashis; Ghosh, Subhradip; Srinivasan, A.

    2015-10-07

    Crystallographic and magnetic properties of bulk Co{sub 2}Fe(Ge{sub 1−x}Si{sub x}) alloys with 0 ≤ x ≤ 1, synthesized by arc melting method, have been studied. Co{sub 2}FeSi alloy has been found to crystallize with L2{sub 1} structure, but the super-lattice peaks are absent in the X-ray diffraction patterns of alloys containing high Ge concentration. Unit cell volume of this series of alloys decreased from 185.2 to 178.5 Å{sup 3} as Si content was increased from 0 to 1.00. All alloy compositions exhibit ferromagnetic behavior with a high Curie temperature (T{sub C}). T{sub C} showed a systematic variation with x. A comparison between the values of saturation magnetization (M{sub s}) and effective moment per magnetic atom p{sub c} estimated from the temperature dependent susceptibility data above T{sub C}, shows that the alloys have half-metallic character. The alloy with x = 0 follows Slater-Pauling (S-P) rule with M{sub s} of 5.99μ{sub B}. However, M{sub s} for the alloy with x = 1.00 was found to be 5.42μ{sub B}, which is lower than the value of 6.0μ{sub B} predicted by S-P rule. Since atomic disorder is known to affect the M{sub s} and electronic structure of these alloys, ab initio calculations were carried out to explain the deviation in observed M{sub s} from S-P rule prediction and the half-metallic character of the alloys. Ab initio calculations reveal that alloys with L2{sub 1} structure have M{sub s} value as predicted by S-P rule. However, introduction of 12.5% DO{sub 3} disorder, which occurs due to swapping of Co and Fe atoms in the unit cell, decreases M{sub s} of alloys with x > 0 from the S-P prediction to values obtained experimentally. The results analyzed from the view point of electronic structure of the alloys in different ordered states bring out the influence of disorder on the observed magnetic properties of these technologically important alloys.

  4. Antiferromagnetism in R u2Mn Z (Z =Sn ,Sb ,Ge ,Si ) full Heusler alloys: Effects of magnetic frustration and chemical disorder

    NASA Astrophysics Data System (ADS)

    Khmelevskyi, Sergii; Simon, Eszter; Szunyogh, László

    2015-03-01

    We present systematic theoretical investigations to explore the microscopic mechanisms leading to the formation of antiferromagnetism in R u2Mn Z (Z =Sn ,Sb ,Ge ,Si ) full Heusler alloys. Our study is based on first-principles calculations of interatomic Mn-Mn exchange interactions to set up a suitable Heisenberg spin model and on subsequent Monte Carlo simulations of the magnetic properties at finite temperature. The exchange interactions are derived from the paramagnetic state, while a realistic account of long-range chemical disorder is made in the framework of the coherent potential approximation. We find that in the case of the highly ordered alloys (Z =Sn and Sb), the exchange interactions derived from the perfectly ordered L 21 structure lead to Néel temperatures in excellent agreement with the experiments, whereas, in particular in the case of Si, the consideration of chemical disorder is essential to reproduce the experimental Néel temperatures. Our numerical results suggest that by improving a heat treatment of the samples to suppress the intermixing between the Mn and Si atoms, the Néel temperature of the Si-based alloys can potentially be increased by more than 30%. Based on calculated biquadratic exchange couplings, we evidence a lifting of degeneracy of the antiferromagnetic ground states on a frustrated face-centered-cubic lattice in the fully ordered compounds. Furthermore, we show that in strongly disordered R u2MnSi alloys, a distinct change in the antiferromagnetic ordering occurs.

  5. Electronic properties, magnetic properties and phase stability of alloyed cementite (Fe,M) 3C (M=Co,Ni) from density-functional theory calculations

    NASA Astrophysics Data System (ADS)

    Wang, C. X.; Lv, Z. Q.; Fu, W. T.; Li, Y.; Sun, S. H.; Wang, B.

    2011-08-01

    First-principles calculations have been performed to investigate the magnetic properties and phase stability of alloyed cementite with Co or Ni. The calculations show Co and Ni reduce the stability of cementite and (Fe,M) 3C (X = Co/Ni) form more difficultly than cementite. We predict that Ni and Co additions in high Co and Ni alloyed steels will promote the dissolution of the cementite. The magnetic moments (Ms) of Fe 2CoC, Co 2FeC, Fe 2NiC and Ni 2FeC are 4.86, 4.23, 3.95 and 2.41 μ B/f.u, respectively. The Ms of Co in Fe 2CoC (1.03 μ B) and Co 2FeC (1.09 μ B) are different due to replacing different Fe atoms. The Ms of Ni in Fe 2NiC and Ni 2FeC are 0.14 μ B and 0.15 μ B, respectively. The Ms of alloyed cementite are mainly contributed by 3d electrons of metal atoms.

  6. Crystallographic, magnetic, and electronic structures of ferromagnetic shape memory alloys Ni2XGa (X=Mn,Fe,Co) from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Bai, J.; Raulot, J. M.; Zhang, Y. D.; Esling, C.; Zhao, X.; Zuo, L.

    2011-01-01

    The crystallographic, magnetic and electronic structures of the ferromagnetic shape memory alloys Ni2XGa (X=Mn, Fe, and Co), are systematically investigated by means of the first-principles calculations within the framework of density functional theory using the VIENNA AB INITIO SOFTWARE PACKAGE. The lattice parameters of both austenitic and martensitic phases in Ni2MnGa have been calculated. The formation energies of the cubic phase of Ni2XGa are estimated, and show a destabilization tendency if Mn atom is substituted by Fe or Co. From Ni2MnGa to Ni2CoGa, the down spin total density of states (DOS) at Fermi level is gradually increasing, whereas that of the up spin part remains almost unchanged. This is the main origin of the difference of the magnetic moment in these alloys. The partial DOS is dominated by the Ni and Mn 3d states in the bonding region below EF. There are two bond types existing in Ni2XGa: one is between neighboring Ni atoms in Ni2MnGa; the other is between Ni and X atoms in Ni2FeGa and Ni2CoGa alloys.

  7. Effect of heat treatment on the crystal structure, martensitic transformation and magnetic properties of Mn53Ni25Ga22 ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Dong, G. F.; Gao, Z. Y.

    2016-02-01

    In this study, the effect of heat treatment on crystal structure, martensitic transformation, thermodynamic behavior and magnetic properties of polycrystalline Mn53Ni25Ga22 ferromagnetic shape memory alloy was systematically investigated. The results show that the heat treatment has obvious effect on martensitic transformation temperatures, crystal structure and hysteresis loops. Heat treatment greatly effects on transformation temperatures due to modified composition of the matrix. Martensitic transformation temperature, saturation magnetization decreased with the increase heat treatment temperature, reaching their minimum values at the heat treatment temperature of 1173 K for 12 h. Curie temperature of maximum values obtained at solution-treated of 1173 K for 12 h. In other word, increasing heat treatment temperature and time has an effect on Curie temperature. In addition, the annealed alloy Mn53Ni25Ga22 may completely dissolve in vacuum tubes at 1173 K for 12 h. It is found that the studied alloys have some (Mn,Ni)4 Ga-type compound precipitates, which can be seen dispersing both in grain interiors and on grain boundaries at other heat treatment process. Lastly, Rietveld analysis shows the good agreement between experiment and calculated data of XRD patterns.

  8. Residual stress induced stabilization of martensite phase and its effect on the magnetostructural transition in Mn-rich Ni-Mn-In/Ga magnetic shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Singh, Sanjay; Kushwaha, Pallavi; Scheibel, F.; Liermann, Hanns-Peter; Barman, S. R.; Acet, M.; Felser, C.; Pandey, Dhananjai

    2015-07-01

    The irreversibility of the martensite transition in magnetic shape memory alloys (MSMAs) with respect to the external magnetic field is one of the biggest challenges that limits their application as giant caloric materials. This transition is a magnetostructural transition that is accompanied with a steep drop in magnetization (i.e.,Δ M ) around the martensite start temperature (Ms) due to the lower magnetization of the martensite phase. In this Rapid Communication, we show that Δ M around Ms in Mn-rich Ni-Mn-based MSMAs gets suppressed by two orders of magnitude in crushed powders due to the stabilization of the martensite phase at temperatures well above Ms and the austenite finish (Af) temperatures due to residual stresses. Analysis of the intensities and the FWHM of the x-ray powder-diffraction patterns reveals stabilized martensite phase fractions as 97 % , 75 % , and 90 % with corresponding residual microstrains as 5.4 % , 5.6 % , and 3 % in crushed powders of the three different Mn-rich Ni-Mn alloys, namely, M n1.8N i1.8I n0.4 , M n1.75N i1.25Ga , and M n1.9N i1.1Ga , respectively. Even after annealing at 773 K, the residual stress stabilized martensite phase does not fully revert to the equilibrium cubic austenite phase as the magnetostructural transition is only partially restored with a reduced value of Δ M . Our results have a very significant bearing on the application of such alloys as inverse magnetocaloric and barocaloric materials.

  9. Effects of coexisting spin disorder and antiferromagnetism on the magnetic behavior of nanostructured (Fe{sub 79}Mn{sub 21}){sub 1−x}Cu{sub x} alloys

    SciTech Connect

    Mizrahi, M. E-mail: cabrera@fisica.unlp.edu.ar; Cabrera, A. F. E-mail: cabrera@fisica.unlp.edu.ar; Desimoni, J.; Stewart, S. J.

    2014-06-07

    We report a magnetic study on nanostructured (Fe{sub 79}Mn{sub 21}){sub 1−x}Cu{sub x} (0.00 ≤ x ≤ 0.30) alloys using static magnetic measurements. The alloys are mainly composed by an antiferromagnetic fcc phase and a disordered region that displays a spin-glass-like behavior. The interplay between the antiferromagnetic and magnetically disordered phases establishes an exchange anisotropy that gives rise to a loop shift at temperatures below the freezing temperature of moments belonging to the disordered region. The loop shift is more noticeable as the Cu content increases, which also enhances the spin-glass-like features. Further, in the x = 0.30 alloy the alignment imposed by applied magnetic fields higher than 4 kOe prevail over the configuration determined by the frustration mechanism that characterizes the spin glass-like phase.

  10. Magnetization Dynamics Through Magnetoimpedance Effect in Isotropic Co2FeAl/Au/Co2FeAl Full-Heusler Alloy Trilayer Films

    NASA Astrophysics Data System (ADS)

    Assolin Corrêa, Marcio; Montardo Escobar, Vivian; Trigueiro-Neto, Osvaldo; Bohn, Felipe; Daiane Sossmeier, Kelly; Gomes Bezerra, Claudionor; Chesman, Carlos; Pearson, John; Hoffmann, Axel

    2013-09-01

    We investigate the magnetization dynamics in low damping parameter α systems by measuring the magnetoimpedance effect over a wide range of frequencies, from 0.1 to 3.0 GHz, in Co2FeAl/Au/Co2FeAl full-Heusler alloy trilayer films grown by magnetron sputtering on glass and MgO substrates. We show that the film produced on the glass substrate presents high magnetoimpedance performance, while that grown on the MgO substrate has low magnetoimpedance performance. Since both films are polycrystalline and have isotropic in-plane magnetic properties, we interpret the magnetoimpedance results in terms of the low damping parameter α and strain effects in the films. Thus, we verified that our films present good magnetoimpedance performance and showed that high performance can be achieved even in films with isotropic in-plane magnetic properties, since they present low damping parameter α.

  11. High strain in polycrystalline Ni48.8Mn31.4Ga19.8 Heusler alloys under overlapped static and oscillating magnetic fields

    NASA Astrophysics Data System (ADS)

    Montanher, D. Z.; Pereira, J. R. D.; Cótica, L. F.; Gotardo, R. A. M.; Viana, D. S. F.; Garcia, D.; Eiras, J. A.; Santos, I. A.

    2014-09-01

    Martensitic polycrystalline Ni48.8Mn31.4Ga19.8 Heusler alloys, with a stacking period of 14 atomic planes at room temperature, were innovatively processed by combining high-energy ball milling and powder metallurgy. Bulk samples were mechanically coupled to a piezoelectric material in a parallel configuration, and the mechanical deformation of the studied system due to the twin's variant motion was investigated under overlapped static and oscillating magnetic fields. A reversible and high mechanical deformation is observed when the frequency of the oscillating magnetic field is tuned with the natural vibration frequency of this system. In this condition, a linear deformation as a function of the static magnetic field amplitude occurs in the ±4 kOe range, and a mechanical deformation of 2% at 10 kOe is observed.

  12. First-principles investigation of possible martensitic transformation and magnetic properties of Heusler-type Pt2-xMn1+xIn alloys

    NASA Astrophysics Data System (ADS)

    Feng, Lin; Zhang, Wenxing; Liu, Enke; Wang, Wenhong; Wu, Guangheng

    2015-06-01

    The phase stability, electronic structure and magnetism of Pt2-xMn1+xIn (x = 0, 0.25, 0.5, 0.75, 1) alloys are studied by first-principles calculations. The possible magnetic martensitic transformation in this series has been investigated. For all the five compounds, the energy minimums occur around c/a = 1.30, and the energy differences between the austenitic and martensitic phases are large enough to overcome the resistance of phase transformation. By comparing the electronic structures of austenitic and martensitic phases, we can find that the phase stability is enhanced by the martensitic transformation. The magnetic structures of the austenitic and martensitic phases are also discussed.

  13. Annealing effect on soft magnetic properties and magnetoimpedance of Finemet Fe 73.5Si 13.5B 9Nb 3Au 1 alloy

    NASA Astrophysics Data System (ADS)

    Tho, N. D.; Chau, N.; Yu, S. C.; Lee, H. B.; The, N. D.; Tuan, L. A.

    2006-09-01

    Effect of annealing on the soft magnetic properties of Fe 73.5Si 13.5B 9Nb 3Au 1 amorphous ribbon has been investigated by means of structure examination, magnetoimpedance ratio (MIR) and incremental permeability ratio (PR) spectra measured in the frequency range of 1-10 MHz at a fixed current of 10 mA X-ray diffraction analysis showed that the as-cast sample was amorphous and it became nanocrystalline under a proper heat treatment. When annealing amorphous alloy at 530 °C for 30, 60, 90 min, soft magnetic properties have been improved drastically. Among the samples investigated, the sample annealed at 530 °C for 90 min showed the softest magnetic behavior. The MIR and PR curves revealed the desirable changes in anisotropy field depending upon annealing.

  14. Low-temperature anomaly of the magnetization in alloys (Pr,Dy, M)2(Fe,Co)14B ( M = Gd, Sm, Nd)

    NASA Astrophysics Data System (ADS)

    Kablov, E. N.; Ospennikova, O. G.; Rezchikova, I. I.; Valeev, R. A.; Cherednichenko, I. V.; Kunitsyna, E. I.; Morgunov, R. B.; Piskorskii, V. P.

    2016-03-01

    It has been found that temperature dependences of the saturation magnetization of sintered hard magnetic (Pr,Dy, M)2(Fe,Co)14B ( M = Gd, Sm, Nd) alloys demonstrate an increase at a temperature lower than a critical temperature (150 K for Sm and Nd and 70 K for Gd). An additive of copper does not influence the critical temperature. It has been assumed that there is a low-temperature phase in which cobalt is replaced with boron that diffuses from the (Pr,Dy,Gd)(Fe,Co)4B phase to the near-surface region of grains of the main magnetic (Pr,Dy,Gd)2(Fe,Co)14B phase.

  15. Synthesis and characterization of magnetically hard Fe-Pt alloy nanoparticles and nano-islands

    NASA Astrophysics Data System (ADS)

    Hu, Xiaocao

    In this dissertation, we explored the fabrication of FePt nanoparticles and nano-islands with the face-centered tetragonal (fct, L10) phase prepared by both chemical synthesis routes and physical vapor deposition. Microstructure and magnetic properties characterizations were used to gain a fundamental understanding of the nano-structure formation and atomic ordering behavior and determine the possible applications in the next generation ultra-high density magnetic storage media. FePt nanoparticles prepared by thermal decomposition of iron pentacarbonyl [Fe(CO)5] have been widely investigated and by tuning the processing procedure monodispersed FePt nanoparticles with good assembly can be obtained. The as-made FePt nanoparticles are usually in the magnetically soft face-centered cubic (fcc) phase. To transformation to the fct phase, post-annealing at above 600°C is needed which, however, introduces undesirable agglomeration and sintering. To address this problem, we used three different fabrication processes which are discussed below. In the first fabrication experiment, the FePt nanoparticles were fabricated by a novel environmental friendly method involving crystalline saline complex hexaaquairon (II) hexachloroplatinate ([Fe(H2O)6]PtCl 6) with a special layered structure. Then the precursor was ball milled with NaCl and annealed at temperatures above 400°C under a reducing atmosphere of forming gas (95% Ar and 5% H2) FePt nanoparticles were obtained after washing away NaCl with deionized water. This method avoids the use of the very poisonous Fe(CO)5 and other organic solvents such as oleylamine and oleic acid. Instead, environmentally friendly NaCl and water were used. The size of FePt nanoparticles was controlled by varying the proportion of precursor and NaCl (from 10mg/20g to 50mg/20g). Particles with size in the range of 6.2--13.2 nm were obtained. All the nanoparticles annealed above 400°C are in the highly ordered fct phase with a coercivity range of 4

  16. Synthesis and characterization of magnetically hard Fe-Pt alloy nanoparticles and nano-islands

    NASA Astrophysics Data System (ADS)

    Hu, Xiaocao

    In this dissertation, we explored the fabrication of FePt nanoparticles and nano-islands with the face-centered tetragonal (fct, L10) phase prepared by both chemical synthesis routes and physical vapor deposition. Microstructure and magnetic properties characterizations were used to gain a fundamental understanding of the nano-structure formation and atomic ordering behavior and determine the possible applications in the next generation ultra-high density magnetic storage media. FePt nanoparticles prepared by thermal decomposition of iron pentacarbonyl [Fe(CO)5] have been widely investigated and by tuning the processing procedure monodispersed FePt nanoparticles with good assembly can be obtained. The as-made FePt nanoparticles are usually in the magnetically soft face-centered cubic (fcc) phase. To transformation to the fct phase, post-annealing at above 600°C is needed which, however, introduces undesirable agglomeration and sintering. To address this problem, we used three different fabrication processes which are discussed below. In the first fabrication experiment, the FePt nanoparticles were fabricated by a novel environmental friendly method involving crystalline saline complex hexaaquairon (II) hexachloroplatinate ([Fe(H2O)6]PtCl 6) with a special layered structure. Then the precursor was ball milled with NaCl and annealed at temperatures above 400°C under a reducing atmosphere of forming gas (95% Ar and 5% H2) FePt nanoparticles were obtained after washing away NaCl with deionized water. This method avoids the use of the very poisonous Fe(CO)5 and other organic solvents such as oleylamine and oleic acid. Instead, environmentally friendly NaCl and water were used. The size of FePt nanoparticles was controlled by varying the proportion of precursor and NaCl (from 10mg/20g to 50mg/20g). Particles with size in the range of 6.2--13.2 nm were obtained. All the nanoparticles annealed above 400°C are in the highly ordered fct phase with a coercivity range of 4

  17. Electronic structure, magnetic properties and electrical resistivity of the Fe2V1-xTixAl Heusler alloys: experiment and calculation

    NASA Astrophysics Data System (ADS)

    Slebarski, A.; Goraus, J.; Deniszczyk, J.; Skoczen, L.

    2006-11-01

    The aim of this work is to investigate electronic structure, magnetic properties and electrical resistivity of Fe2V1-xTixAl Heusler alloys. Numerical calculations give a pseudogap at the Fermi level for the majority-spin band of Fe2TiAl and a magnetic moment larger than 0.9 μB, whereas the ground state of Fe2VAl is calculated as a nonmagnetic semimetal with a very low total density of states at the Fermi level. In our calculations the remaining alloys of the Fe2V1-xTixAl series are nonmagnetic for x<0.1 and weakly magnetic for 0.1magnetic moment μ of the series of Fe2V1-xTixAl compounds scales with the number of valence electrons and fits well to the Slater-Pauling curve. We also present a study of the electronic transport properties and magnetic susceptibility. The resistivities ρ(T) of Fe2VAl and Fe2V0.9Ti0.1Al are large and exhibit a negative temperature coefficient dρ/dT of the resistivity between 2 and 300 K. Below 20 K, ρ(T) also shows an activated character. The magnetic susceptibility of Fe2VAl and Fe2V0.9Ti0.1Al shows a maximum at ~2 K which could reflect either the disorder effect or the hybridization gap, characteristic of Kondo insulators.

  18. Electronic structure, magnetic properties and electrical resistivity of the Fe(2)V(1-x)Ti(x)Al Heusler alloys: experiment and calculation.

    PubMed

    Slebarski, A; Goraus, J; Deniszczyk, J; Skoczeń, L

    2006-11-22

    The aim of this work is to investigate electronic structure, magnetic properties and electrical resistivity of Fe(2)V(1-x)Ti(x)Al Heusler alloys. Numerical calculations give a pseudogap at the Fermi level for the majority-spin band of Fe(2)TiAl and a magnetic moment larger than 0.9 μ(B), whereas the ground state of Fe(2)VAl is calculated as a nonmagnetic semimetal with a very low total density of states at the Fermi level. In our calculations the remaining alloys of the Fe(2)V(1-x)Ti(x)Al series are nonmagnetic for x<0.1 and weakly magnetic for 0.1magnetic moment μ of the series of Fe(2)V(1-x)Ti(x)Al compounds scales with the number of valence electrons and fits well to the Slater-Pauling curve. We also present a study of the electronic transport properties and magnetic susceptibility. The resistivities ρ(T) of Fe(2)VAl and Fe(2)V(0.9)Ti(0.1)Al are large and exhibit a negative temperature coefficient dρ/dT of the resistivity between 2 and 300 K. Below 20 K, ρ(T) also shows an activated character. The magnetic susceptibility of Fe(2)VAl and Fe(2)V(0.9)Ti(0.1)Al shows a maximum at ∼2 K which could reflect either the disorder effect or the hybridization gap, characteristic of Kondo insulators. PMID:21690920

  19. A first principle study of phase stability, electronic structure and magnetic properties for Co2-xCrxMnAl Heusler alloys

    NASA Astrophysics Data System (ADS)

    Rached, H.; Rached, D.; Khenata, R.; Abidri, B.; Rabah, M.; Benkhettou, N.; Omran, S. Bin

    2015-04-01

    The structural stabilities, electronic and magnetic properties of Co2-xCrxMnAl alloys with (x=0,1 and 2) were investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method, in the framework of the density functional theory (DFT) within the generalized gradient approximation (GGA) for the exchange correlation functional. The ground state properties including lattice parameter, bulk modulus for the two considered crystal structures Hg2CuTi-Type (X-Type) and Cu2MnAl-Type (L21-Type) are calculated. The half-metallicity within ferromagnetic ground state starts to appear in CoCrMnAl and Cr2MnAl. In the objective for the proposition of the new HM-FM in the Full-Heusler alloys, our results classified CoCrMnAl as new HM-FM material with high spin polarization.

  20. Microstructure and magnetic properties of melt-spun Alnico-5 alloys

    NASA Astrophysics Data System (ADS)

    Löwe, Konrad; Dürrschnabel, Michael; Molina-Luna, Leopoldo; Madugundo, Rajasekhar; Frincu, Bianca; Kleebe, Hans-Joachim; Gutfleisch, Oliver; Hadjipanayis, George C.

    2016-06-01

    The aim of this work is to investigate the effect of very fine grain sizes on the spinodal decomposition in the Alnico system. Commercial Alnico 5 was melted and melt-spun with varying copper wheel speeds, which led to a grain size of 1-2 μm. This value was further reduced to sub-micrometer size by a small addition of Boron (1 at%). The spinodal decomposition was induced through a two-step annealing treatment under magnetic field in the range of 600-900 °C. It was found that the size of the spinodal structures is not influenced much by increased wheel speeds but becomes smaller with the addition of Boron. However, the difference in coercivity between the samples with and without Boron is only 50 Oe (4 kA/m). To study the influence of the annealing treatment two sets of samples are compared, one with the highest coercivity (366 Oe/29 kA/m) and the other one with lower coercivity (180 Oe/14.5 kA/m). We found with Scanning transmission electron microscopy Energy-dispersive X-ray spectroscopy (STEM EDX) a much sharper chemical interface between the α1 and α2 precipitates in the former sample, which we attribute to be the main reason for the higher coercivity.