Single particle excitations in itinerant antiferromagnets
Brenig, W.; Kampf, A.P.
1994-04-01
The authors present a self-consistent strong coupling scheme to evaluate the single-particle Green`s function for the two dimensional Hubbard model in the spin-density-wave state. The authors analyze the single quasihole properties including its dispersion and its spectral weight factor. Significant incoherent contributions to the spectral function are found resulting from multi spin wave processes in accordance with similar results for the t-J model and small Hubbard clusters.
NASA Astrophysics Data System (ADS)
Cuchet, Léa; Rodmacq, Bernard; Auffret, Stéphane; Sousa, Ricardo C.; Prejbeanu, Ioan L.; Dieny, Bernard
2015-06-01
The magnetic properties of double tunnel junctions with perpendicular anisotropy were investigated. Two synthetic antiferromagnetic references are used, while the middle storage magnetic layer can be either a single ferromagnetic or a synthetic antiferromagnetic FeCoB-based layer, with a critical thickness as large as 3.0 nm. Among the different achievable magnetic configurations in zero field, those with either antiparallel references, and single ferromagnetic storage layer, or parallel references, and synthetic antiferromagnetic storage layer, are of particular interest since they allow increasing the efficiency of spin transfer torque writing and the thermal stability of the stored information as compared to single tunnel junctions. The latter configuration can be preferred when stray fields would favour a parallel orientation of the reference layers. In this case, the synthetic antiferromagnetic storage layer is also less sensitive to residual stray fields.
Cuchet, Léa; Rodmacq, Bernard; Auffret, Stéphane; Sousa, Ricardo C.; Prejbeanu, Ioan L.; Dieny, Bernard
2015-06-21
The magnetic properties of double tunnel junctions with perpendicular anisotropy were investigated. Two synthetic antiferromagnetic references are used, while the middle storage magnetic layer can be either a single ferromagnetic or a synthetic antiferromagnetic FeCoB-based layer, with a critical thickness as large as 3.0 nm. Among the different achievable magnetic configurations in zero field, those with either antiparallel references, and single ferromagnetic storage layer, or parallel references, and synthetic antiferromagnetic storage layer, are of particular interest since they allow increasing the efficiency of spin transfer torque writing and the thermal stability of the stored information as compared to single tunnel junctions. The latter configuration can be preferred when stray fields would favour a parallel orientation of the reference layers. In this case, the synthetic antiferromagnetic storage layer is also less sensitive to residual stray fields.
On the exchange bias in single and polycrystalline ferro/antiferromagnetic bilayers
Li, Zhanjie; Zhang, Shufeng
2001-06-01
By incorporating a random interfacial exchange interaction into the Landau{endash}Lifshitz{endash}Gilbert equation, a unified picture of exchange bias for single crystals, textured crystals, twin structures, and polycrystals of antiferromagnets is presented. It is found that the lateral interaction in the antiferromagnet is a key element governing the exchange bias and magnetization reversal of the ferromagnet. {copyright} 2001 American Institute of Physics.
Multicritical points in the three-dimensional XXZ antiferromagnet with single-ion anisotropy
NASA Astrophysics Data System (ADS)
Selke, Walter
2013-01-01
The classical Heisenberg antiferromagnet with uniaxial exchange anisotropy, the XXZ model, and competing planar single-ion anisotropy in a magnetic field on a simple cubic lattice is studied with the help of extensive Monte Carlo simulations. The biconical (supersolid) phase, bordering the antiferromagnetic and spin-flop phases, is found to become thermally unstable well below the onset of the disordered, paramagnetic phase, leading to interesting multicritical points.
NASA Astrophysics Data System (ADS)
Pires, A. S. T.
2016-08-01
I study the spin-1 Heisenberg antiferromagnet on the two dimensional honeycomb lattice at zero temperature, with first J1, second J2 and third J3 neighbors exchange interactions and single ion easy plane anisotropy, using the SU(3) Schwinger boson formalism. The phase diagram is shown. The results show the existence of a region in the intermediate frustrated regime where the system does not have quantum magnetic order.
Antiferromagnetic phase transition in a single MnTe monolayer
NASA Astrophysics Data System (ADS)
Prechtl, G.; Heiss, W.; Bonanni, A.; Sitter, H.; Jantsch, W.; Mackowski, S.; Karczewski, G.
2000-05-01
We investigate a quantum-well sample containing a monolayer of MnTe in its center. The exciton Zeeman splitting is measured as a function of temperature by polarization-dependent photoluminescence excitation experiments. The dependence of the inverse Zeeman splitting shows a kink at a critical temperature of 50 K. Simultaneously, a peak in the linewidth of the e1- hh1 transition is observed at the same temperature. The critical temperature agrees very well with the predicted Nèel temperature obtained within the mean-field approximation for a single monolayer MnTe. After annealing the sample, the Zeeman splitting drastically increases and no critical phenomena are observed anymore.
Deng, Qingming; Zhao, Lina; Luo, Youhua; Zhang, Meng; Jing, Long; Zhao, Yuliang
2011-09-01
We theoretically studied the ferromagnetism/antiferromagnetism (FM/AFM) transition between single-wall carbon nanotubes (SWCNTs) induced by chemical modifications of semihydrogenation (SH-) and full-amination (NH(2)-). We found that armchairs with large diameters of SH-CNTs (n > 3) possess FM functions with intense magnetic moments, while armchair NH(2)-CNTs (n = 4, 6, 8) are antiferromagnetic semiconductors. The FM/AFM transition is mainly dominated by different chemical modifications and sizes of SWCNTs whose distance between carbon atoms of unpaired electrons can regulate the intensity of p-p spin interactions. Moreover, the zigzag SH-CNTs and NH(2)-CNTs are NM semiconductors. Thus, the electronic and magnetic properties of the SH- or NH(2)-CNTs can be precisely modulated by controlling the hydrogenation or amination on the different types and diameters of CNTs, which provides a new and also simple process for magnetism optimization design in SWCNTs. PMID:21804988
NASA Astrophysics Data System (ADS)
Deng, Qingming; Zhao, Lina; Luo, Youhua; Zhang, Meng; Jing, Long; Zhao, Yuliang
2011-09-01
We theoretically studied the ferromagnetism/antiferromagnetism (FM/AFM) transition between single-wall carbon nanotubes (SWCNTs) induced by chemical modifications of semihydrogenation (SH-) and full-amination (NH2-). We found that armchairs with large diameters of SH-CNTs (n > 3) possess FM functions with intense magnetic moments, while armchair NH2-CNTs (n = 4, 6, 8) are antiferromagnetic semiconductors. The FM/AFM transition is mainly dominated by different chemical modifications and sizes of SWCNTs whose distance between carbon atoms of unpaired electrons can regulate the intensity of p-p spin interactions. Moreover, the zigzag SH-CNTs and NH2-CNTs are NM semiconductors. Thus, the electronic and magnetic properties of the SH- or NH2-CNTs can be precisely modulated by controlling the hydrogenation or amination on the different types and diameters of CNTs, which provides a new and also simple process for magnetism optimization design in SWCNTs.
Zhou, Biao; Kobayashi, Akiko; Okano, Yoshinori; Cui, HengBo; Graf, David; Brooks, James S; Nakashima, Takeshi; Aoyagi, Shinobu; Nishibori, Eiji; Sakata, Makoto; Kobayashi, Hayao
2009-11-01
The crystal structure of the single-component molecular metal [Au(tmdt)(2)] was examined by performing powder X-ray diffraction experiments in the temperature range of 9-300 K using a synchrotron radiation source installed at SPring-8. The structural anomalies associated with antiferromagnetic transition were observed around the transition temperature (T(N) = 110 K). The continuous temperature dependence of the unit cell volume and the discontinuous change in the thermal expansion coefficient at T(N) suggested that the antiferromagnetic transition of [Au(tmdt)(2)] is a second-order transition. Au(tmdt)(2) molecules are closely packed in the (021) plane with two-dimensional lattice vectors of a and l (= 2a + b + 2c). The shortest intermolecular S...S distance along the a axis shows a sharp decrease at around T(N), while the temperature dependence of l exhibits a characteristic peak in the same temperature region. A distinct structure anomaly was not observed along the direction perpendicular to the (021) plane. These results suggest that the molecular arrangement in only the (021) plane changes significantly at T(N). Thus, the intermolecular spacing shows anomalous temperature dependence at around T(N) only along that direction where the neighboring tmdt ligands have opposite spins in the antiferromagnetic spin structure model recently derived from ab initio band structure calculations. The results of single-crystal four-probe resistance measurements on extremely small crystals (approximately 25 microm) did not show a distinct resistance anomaly at T(N). The resistance anomaly associated with antiferromagnetic transition, if at all present, is very small. The Au-S bond length decreases sharply at around 110 K; this is consistent with the proposed antiferromagnetic spin distribution model, where the left and right ligands of the same molecule possess opposite spin polarizations. The tendency of the Au-S bond to elongate with decreasing temperature is ascribed to the
Uniaxial anisotropy and low-temperature antiferromagnetism of Mn2BO4 single crystal
NASA Astrophysics Data System (ADS)
Kazak, N. V.; Platunov, M. S.; Knyazev, Yu. V.; Ivanova, N. B.; Bayukov, O. A.; Vasiliev, A. D.; Bezmaternykh, L. N.; Nizhankovskii, V. I.; Gavrilkin, S. Yu.; Lamonova, K. V.; Ovchinnikov, S. G.
2015-11-01
The Mn2BO4 single crystals have been grown by the flux technique. A careful study of the crystal structure and magnetic properties have been carried out. The antiferromagnetic transition at TN=26 K has been traced through the dc magnetization and specific heat temperature dependences. Magnetic uniaxial anisotropy has been found with easy axis magnetization lying in the ab-plane. The obtained value of effective magnetic moment is assigned to the non-quenched orbital moment of Jahn-Teller Mn3+ ions. The discussion of magnetic properties is based on the superexchange interaction calculations.
Polar Order and Frustrated Antiferromagnetism in Perovskite Pb2MnWO6 Single Crystals.
Ivanov, Sergey A; Bush, Alexander A; Stash, Adam I; Kamentsev, Konstantin E; Shkuratov, Valerii Ya; Kvashnin, Yaroslav O; Autieri, Carmine; Di Marco, Igor; Sanyal, Biplab; Eriksson, Olle; Nordblad, Per; Mathieu, Roland
2016-03-21
Single crystals of the multiferroic double-perovskite Pb2MnWO6 have been synthesized and their structural, thermal, magnetic and dielectric properties studied in detail. Pure perovskite-phase formation and stoichiometric chemical composition of the as-grown crystals are confirmed by X-ray single-crystal and powder diffraction techniques as well as energy-dispersive X-ray and inductively coupled plasma mass spectrometry. Detailed structural analyses reveal that the crystals experience a structural phase transition from the cubic space group (s.g.) Fm3̅m to an orthorhombic structure in s.g. Pn21a at about 460 K. Dielectric data suggest that a ferrielectric phase transition takes place at that same temperature, in contrast to earlier results on polycrystalline samples, which reported a transition to s.g. Pnma and an antiferroelectric low-temperature phase. Magnetic susceptibility measurements indicate that a frustrated antiferromagnetic phase emerges below 8 K. Density functional theory based calculations confirm that the cationic order between Mn and W is favorable. The lowest total energy was found for an antiferromagnetically ordered state. However, analyses of the calculated exchange parameters revealed strongly competing antiferromagnetic interactions. The large distance between the magnetic atoms, together with magnetic frustration, is shown to be the main reason for the low value of the ordering temperature observed experimentally. We discuss the structure-property relationships in Pb2MnWO6 and compare these observations to reported results on related Pb2BWO6 perovskites with different B cations. PMID:26954581
Polarized Neutron Studies on Antiferromagnetic Single Crystals: Technical Report No. 4
DOE R&D Accomplishments Database
Nathans, R.; Riste, T.; Shirane, G.; Shull, C.G.
1958-11-26
The theory of neutron scattering by magnetic crystals as given by Halpern and Johnson predicts changes in the polarization state of the neutron beam upon scattering which depend upon the relative orientation of the neutron polarization vector and the crystal magnetic axis. This was investigated experimentally with a polarized beam spectrometer using single crystals of Cr{sub 2}O{sub 3} and alpha - Fe{sub 2}O{sub 3} in which reside unique antiferromagnetic axes. Studies were made on several different reflections in both crystals for a number of different temperatures both below and above the Neel point. Results support the theoretical predictions and indicate directions for the moments in these crystals consistent with previous work. A more detailed study of the polarization changes in the (111) reflection in alpha - Fe{sub 2}O{sub 3} at room temperature on application of a magnetic field was carried out, The results indicate that the principal source of the parasitic ferromagnetism in hematite is essentially independent of the orientation of the antiferromagnetic domains within the crystal.
Conductance of ferro- and antiferro-magnetic single-atom contacts: A first-principles study
Tan, Zhi-Yun; Zheng, Xiao-long; Ye, Xiang; Xie, Yi-qun; Ke, San-Huang
2013-08-14
We present a first-principles study on the spin dependent conductance of five single-atom magnetic junctions consisting of a magnetic tip and an adatom adsorbed on a magnetic surface, i.e., the Co-Co/Co(001) and Ni-X/Ni(001) (X = Fe, Co, Ni, Cu) junctions. When their spin configuration changes from ferromagnetism to anti-ferromagnetism, the spin-up conductance increases while the spin-down one decreases. For the junctions with a magnetic adatom, there is nearly no spin valve effect as the decreased spin-down conductance counteracts the increased spin-up one. For the junction with a nonmagnetic adatom (Ni-Cu/Ni(001)), a spin valve effect is obtained with a variation of 22% in the total conductance. In addition, the change in spin configuration enhances the spin filter effect for the Ni-Fe/Ni(001) junction but suppresses it for the other junctions.
Antiferromagnetic Ordering in the Single-Component Molecular Conductor [Pd(tmdt)2].
Ogura, Satomi; Idobata, Yuki; Zhou, Biao; Kobayashi, Akiko; Takagi, Rina; Miyagawa, Kazuya; Kanoda, Kazushi; Kasai, Hidetaka; Nishibori, Eiji; Satoko, Chikatoshi; Delley, Bernard
2016-08-01
Crystals of [Pd(tmdt)2] (tmdt = trimethylenetetrathiafulvalenedithiolate) were prepared in order to investigate their physical properties. The electrical resistivity of [Pd(tmdt)2] was measured on single crystals using two-probe methods and showed that the room-temperature conductivity was 100 S·cm(-1). The resistivity behaviors implied that [Pd(tmdt)2] was a semimetal at approximately room temperature and became narrow-gap semiconducting as the temperature was decreased to the lowest temperature. X-ray structural studies on small single crystals of [Pd(tmdt)2] at temperatures of 20-300 K performed using synchrotron radiation at SPring-8 showed no distinct structural change over this temperature region. However, small anomalies were observed at approximately 100 K. Electron spin resonance (ESR) spectra were measured over the temperature range of 2.7-301 K. The ESR intensity increased as the temperature decreased to 100 K and then decreased linearly as the temperature was further decreased to 50 K, where an abrupt decrease in the intensity was observed. To investigate the magnetic state, (1)H nuclear magnetic resonance (NMR) measurements were performed in the temperature range of 2.5-271 K, revealing broadening below 100 K. The NMR relaxation rate gradually increased below 100 K and formed a broad peak at approximately 50 K, followed by a gradual decrease down to the lowest temperature. These results suggest that most of the sample undergoes the antiferromagnetic transition at approximately 50 K with the magnetic ordering temperatures distributed over a wide range up to 100 K. These electric and magnetic properties of [Pd(tmdt)2] are quite different from those of the single-component molecular (semi)metals [Ni(tmdt)2] and [Pt(tmdt)2], which retain their stable metallic states down to extremely low temperatures. The experimental results and the band structure calculations at the density functional theory level showed that [Pd(tmdt)2] may be an antiferromagnetic Mott
Paramagnetism and antiferromagnetic interactions in single-phase Fe-implanted ZnO.
Pereira, L M C; Wahl, U; Correia, J G; Van Bael, M J; Temst, K; Vantomme, A; Araújo, J P
2013-10-16
As the intrinsic origin of the high-temperature ferromagnetism often observed in wide-gap dilute magnetic semiconductors becomes increasingly debated, there is a growing need for comprehensive studies on the single-phase region of the phase diagram of these materials. Here we report on the magnetic and structural properties of Fe-doped ZnO prepared by ion implantation of ZnO single crystals. A detailed structural characterization shows that the Fe impurities substitute for Zn in ZnO in a wurtzite Zn(1-x)Fe(x)O phase which is coherent with the ZnO host. In addition, the density of beam-induced defects is progressively decreased by thermal annealing up to 900 ° C, from highly disordered after implantation to highly crystalline upon subsequent annealing. Based on a detailed analysis of the magnetometry data, we demonstrate that isolated Fe impurities occupying Zn-substitutional sites behave as localized paramagnetic moments down to 2 K, irrespective of the Fe concentration and the density of beam-induced defects. With increasing local concentration of Zn-substitutional Fe, strong nearest-cation-neighbor antiferromagnetic interactions favor the antiparallel alignment of the Fe moments. PMID:24025311
Paramagnetism and antiferromagnetic interactions in single-phase Fe-implanted ZnO
NASA Astrophysics Data System (ADS)
Pereira, L. M. C.; Wahl, U.; Correia, J. G.; Van Bael, M. J.; Temst, K.; Vantomme, A.; Araújo, J. P.
2013-10-01
As the intrinsic origin of the high-temperature ferromagnetism often observed in wide-gap dilute magnetic semiconductors becomes increasingly debated, there is a growing need for comprehensive studies on the single-phase region of the phase diagram of these materials. Here we report on the magnetic and structural properties of Fe-doped ZnO prepared by ion implantation of ZnO single crystals. A detailed structural characterization shows that the Fe impurities substitute for Zn in ZnO in a wurtzite Zn1-xFexO phase which is coherent with the ZnO host. In addition, the density of beam-induced defects is progressively decreased by thermal annealing up to 900 ° C, from highly disordered after implantation to highly crystalline upon subsequent annealing. Based on a detailed analysis of the magnetometry data, we demonstrate that isolated Fe impurities occupying Zn-substitutional sites behave as localized paramagnetic moments down to 2 K, irrespective of the Fe concentration and the density of beam-induced defects. With increasing local concentration of Zn-substitutional Fe, strong nearest-cation-neighbor antiferromagnetic interactions favor the antiparallel alignment of the Fe moments.
Quantum Monte-Carlo simulation of spin-one antiferromagnets with single-ion anisotropy
NASA Astrophysics Data System (ADS)
Kato, Yasuyuki; Wierschem, Keola; Nishida, Yusuke; Batista, Cristian; Sengupta, Pinaki
2013-03-01
We study a spin-one Heisenberg model with uniaxial single-ion anisotropy, D, and Zeeman coupling to a magnetic field, B, parallel to the symmetry axis. We compute the (D / J , B / J) quantum phase diagram for square and simple cubic lattices by combining analytical and Quantum Monte Carlo approaches, and find a transition between XY-antiferromagnetic and ferronematic phases that spontaneously break the U(1) symmetry of the model. In the language of bosonic gases, this is a transition between a Bose-Einstein condensate (BEC) of single bosons and a BEC of pairs. For the efficient simulation of ferronematic phase, we developed and implemented a new multi-discontinuity algorithm based on the directed-loop algorithm. The ordinary quantum Monte-Carlo methods fall into freezing problems when we apply them to this system at large D / J and finite B / J ~ 1 . The new method does not suffer from the freezing problems. This research used resources of the NERSCC (DOE Contract No. DE-AC02-05CH11231). Work at LANL was performed under the auspices of a J. Robert Oppenheimer Fellowship and the U.S. DOE contract No. DE-AC52-06NA25396 through the LDRD program.
NASA Astrophysics Data System (ADS)
Huang, C. L.; Fritsch, V.; Pilawa, B.; Yang, C. C.; Merz, M.; Löhneysen, H. v.
2015-04-01
We present measurements of the magnetization M , specific heat C , resistivity ρ , and magnetoresistance MR of single-crystalline hexagonal CeAuSn for temperature down to T =1.6 K and in magnetic field up to B =12 T . Antiferromagnetic ordering at TN=4.4 K is observed as previously found for polycrystalline samples. A strong magnetic easy-plane anisotropy of M for B perpendicular and parallel to the c direction is found with M⊥/M||≈15 in B =0.1 T around TN, which is attributed to crystal-electric-field anisotropy. The analysis of the magnetic susceptibility indicates ferromagnetic correlations above TN. Measurements of M (T ) under hydrostatic pressure P show that TN(P ) increases linearly with P at a small rate of 0.035 K/kbar up to 4 kbar and gradually saturates approaching P =16 kbar . Zero-field Δ C /T , the phonon contribution to C being subtracted, is proportional to T2 below TN indicating a gapless spin-wave spectrum. It is found that all Δ C (T ,B )/T curves for B =0 -9 T cross at the same temperature, providing an example of a particularly well defined isosbestic point in a very narrow region around Tiso=6.6 K . Finally, ρ (T ) and MR experiments with current perpendicular and parallel to B allow us to separate orbital effects from the Zeeman splitting.
NaCaCo2F7: A single-crystal high-temperature pyrochlore antiferromagnet
NASA Astrophysics Data System (ADS)
Krizan, J. W.; Cava, R. J.
2014-06-01
We report the magnetic characterization of the frustrated transition metal pyrochlore NaCaCo2F7. This material has high spin Co2+ in CoF6 octahedra in a pyrochlore lattice and disordered nonmagnetic Na and Ca on the large-atom sites in the structure. Large crystals grown by the floating zone method were studied. The magnetic susceptibility is isotropic; the Co moment is larger than the spin-only value; and in spite of the large Curie Weiss theta (-140 K), freezing of the spin system, as characterized by peaks in the ac and dc susceptibility and specific heat, does not occur until around 2.4 K. This yields a frustration index of f=-θCW/Tf≈56, an indication that the system is highly frustrated. The observed entropy loss at the freezing transition is low, indicating that magnetic entropy remains present in the system at 0.6 K. The compound may be the realization of a frustrated pyrochlore antiferromagnet with weak bond disorder. The high magnetic interaction strength, strong frustration, and the availability of large single crystals makes NaCaCo2F7 an interesting alternative to rare earth oxide pyrochlores for the study of geometric magnetic frustration in pyrochlore lattices.
Collinear antiferromagnetism in trigonal SrMn2As2 revealed by single crystal neutron diffraction
NASA Astrophysics Data System (ADS)
Kreyssig, A.; Das, P.; Sangeetha, N. S.; Benson, Z. A.; Heitman, T.; Johnston, D. C.; Goldman, A. I.
FeAs-based compounds and related materials have been an area of intense research in understanding the complex interplay between magnetism and superconductivity. Here we report on the magnetic structure of SrMn2As2 that crystallizes in a trigonal structure (P 3 m1) and undergoes an antiferromagnetic (AFM) transition at TN ~ 120 K. The temperature dependence of the magnetic susceptibility remains nearly constant below TN with H ∥ c while it decreases significantly with H ∥ ab . This shows that the local Mn moments order and lie in the ab plane instead of aligning along the c axis as in BaMn2As2. Single crystal neutron diffraction measurements on SrMn2As2 determined that the Mn moments are collinearly aligned in a G-type AFM order with AFM alignments between a moment and all nearest neighbors in the basal plane and also perpendicular to it. This manifests that G-type AFM order is robust for Mn122 systems despite different symmetries, i.e. tetragonal for BaMn2As2 and trigonal for SrMn2As2.Work at Ames Laboratory was supported by the DOE, BES, Division of Materials Sciences & Engineering, through DE-AC02-07CH11358. This research used resources at University of Missouri Research Reactor.
Spin wave dynamics in Heisenberg ferromagnetic/antiferromagnetic single-walled nanotubes
NASA Astrophysics Data System (ADS)
Mi, Bin-Zhou
2016-09-01
The spin wave dynamics, including the magnetization, spin wave dispersion relation, and energy level splitting, of Heisenberg ferromagnetic/antiferromagnetic single-walled nanotubes are systematically calculated by use of the double-time Green's function method within the random phase approximation. The role of temperature, diameter of the tube, and wave vector on spin wave energy spectrum and energy level splitting are carefully analyzed. There are two categories of spin wave modes, which are quantized and degenerate, and the total number of independent magnon branches is dependent on diameter of the tube, caused by the physical symmetry of nanotubes. Moreover, the number of flat spin wave modes increases with diameter of the tube rising. The spin wave energy and the energy level splitting decrease with temperature rising, and become zero as temperature reaches the critical point. At any temperature, the energy level splitting varies with wave vector, and for a larger wave vector it is smaller. When pb=π, the boundary of first Brillouin zone, spin wave energies are degenerate, and the energy level splittings are zero.
Signatures of filamentary superconductivity in antiferromagnetic BaFe2As2 single crystals
NASA Astrophysics Data System (ADS)
Moseley, D.; Yates, K. A.; Branford, W. R.; Sefat, A. S.; Mandrus, D.; Stuard, S. J.; Salem-Sugui, S.; Ghivelder, L.; Cohen, L. F.
2015-08-01
In this paper, we present ac susceptibility and magnetotransport measurements on aged single crystals of the ferropnictide parent compound, BaFe2As2 with a paramagnetic-to-antiferromagnetic transition temperature of 134 K. The ac susceptibility shows the clear onset of a partial diamagnetic response with an onset temperature, commensurate with a subtle downturn in resistivity at approximately 20 K. Below 20 K the magnetotransport shows in-plane anisotropy, magnetic-field history dependence and a hysteretic signature. Above 20 K the crystals show the widely reported high-field linear magnetoresistance. An enhanced noise signature in ac susceptibility is observed above 20 K, which varies in character with amplitude and frequency of the ac signal. The hysteresis in magnetoresistance and the observed sensitivity of the superconducting phase to the amplitude of the ac signal are indicative characteristics of granular or weakly linked filamentary superconductivity. These features taken together with the observed noise signature above T{c} suggests a link between the formation of the superconducting filamentary phase and the freezing of antiphase domain walls, known to exist in these materials.
Antiferromagnetic order and Kondo-lattice behavior in single-crystalline Ce2RhSi3
NASA Astrophysics Data System (ADS)
Szlawska, M.; Kaczorowski, D.; Ślebarski, A.; Gulay, L.; Stępień-Damm, J.
2009-04-01
Single crystal of Ce2RhSi3 was investigated by means of x-ray diffraction, magnetization, electrical resistivity, and heat-capacity measurements. Moreover, its electronic structure was studied by cerium core-level x-ray photoemission spectroscopy. The results revealed that Ce2RhSi3 is an antiferromagnetic Kondo lattice due to the presence of stable trivalent Ce ions.
NASA Astrophysics Data System (ADS)
Duan, T. F.; Ren, W. J.; Liu, W.; Zhang, Z. D.
2016-08-01
The magnetic structure of MnSn2 and magnetic phase transitions in this compound have been investigated by magnetic measurements on single crystals. The results show that two antiferromagnetic (AFM) states exist below 325 K and that a transition between these two phases occurs at 74 K. Applying a magnetic field (H) has great influence on the transition temperature. An anomalous magnetization process at low fields occurs when the magnetic field applied along the [110] direction, which is ascribed to the contribution of the basal anisotropy. Based on the data for the magnetization processes and the phase transition of the present single crystal, the H-T phase diagram has been established.
Antiferromagnetic spintronics.
Jungwirth, T; Marti, X; Wadley, P; Wunderlich, J
2016-03-01
Antiferromagnetic materials are internally magnetic, but the direction of their ordered microscopic moments alternates between individual atomic sites. The resulting zero net magnetic moment makes magnetism in antiferromagnets externally invisible. This implies that information stored in antiferromagnetic moments would be invisible to common magnetic probes, insensitive to disturbing magnetic fields, and the antiferromagnetic element would not magnetically affect its neighbours, regardless of how densely the elements are arranged in the device. The intrinsic high frequencies of antiferromagnetic dynamics represent another property that makes antiferromagnets distinct from ferromagnets. Among the outstanding questions is how to manipulate and detect the magnetic state of an antiferromagnet efficiently. In this Review we focus on recent works that have addressed this question. The field of antiferromagnetic spintronics can also be viewed from the general perspectives of spin transport, magnetic textures and dynamics, and materials research. We briefly mention this broader context, together with an outlook of future research and applications of antiferromagnetic spintronics. PMID:26936817
NASA Astrophysics Data System (ADS)
Jungwirth, T.; Marti, X.; Wadley, P.; Wunderlich, J.
2016-03-01
Antiferromagnetic materials are internally magnetic, but the direction of their ordered microscopic moments alternates between individual atomic sites. The resulting zero net magnetic moment makes magnetism in antiferromagnets externally invisible. This implies that information stored in antiferromagnetic moments would be invisible to common magnetic probes, insensitive to disturbing magnetic fields, and the antiferromagnetic element would not magnetically affect its neighbours, regardless of how densely the elements are arranged in the device. The intrinsic high frequencies of antiferromagnetic dynamics represent another property that makes antiferromagnets distinct from ferromagnets. Among the outstanding questions is how to manipulate and detect the magnetic state of an antiferromagnet efficiently. In this Review we focus on recent works that have addressed this question. The field of antiferromagnetic spintronics can also be viewed from the general perspectives of spin transport, magnetic textures and dynamics, and materials research. We briefly mention this broader context, together with an outlook of future research and applications of antiferromagnetic spintronics.
Antiferromagnetic order in single crystals of the S =2 quasi-one-dimensional chain MnCl3(bpy)
NASA Astrophysics Data System (ADS)
Shinozaki, Shin-ichi; Okutani, Akira; Yoshizawa, Daichi; Kida, Takanori; Takeuchi, Tetsuya; Yamamoto, Shoji; Risset, Olivia N.; Talham, Daniel R.; Meisel, Mark W.; Hagiwara, Masayuki
2016-01-01
A suite of experimental tools, including high-field magnetization and electron spin resonance (ESR) studies in magnetic fields of up to 50 T and heat capacity studies up to 9 T, have revealed antiferromagnetic order in single crystals of the Heisenberg S =2 chain compound MnCl3(bpy), where bpy is 2 ,2'-bipyridine . The Néel temperature, which depends on the strength of the applied magnetic field and its orientation with respect to the crystalline axes that was revealed by heat capacity measurements, is near 11.5 K in zero field. The spin-flop transition is identified in the magnetization curve acquired at 1.7 K and at μoHSFc=24 T along the c axis. The transition field HSF is lower than that expected from the previous antiferromagnetic resonance (AFMR) studies on a powder sample. The identification of the long-range antiferromagnetic order resolves an earlier report by Granroth et al. [Phys. Rev. Lett. 77, 1616 (1996)], 10.1103/PhysRevLett.77.1616 that identified MnCl3(bpy) as an S =2 Haldane system down to 40 mK. The ESR studies identify a wide range of antiferromagnetic resonance modes that provide additional microscopic information about the g values (ga*=2.09 , gb=1.92 , and gc=2.07 ), the zero-field splitting constants, D /kB=-1.5 K and E /kB=-0.17 K when the nearest-neighbor spin interaction J /kB=31.2 K, which is evaluated from fitting the susceptibility, and the anisotropy of this compound (easy axis is the c axis, the second easy-axis is the b axis, and the hard axis is the a* axis), when using a standard (two-sublattice) AFMR analysis that does not quantitatively reproduce the observed HSFc value. The observed resonance mode indicates the frequency minimum at HSFc.
Hardy, Will J; Yuan, Jiangtan; Guo, Hua; Zhou, Panpan; Lou, Jun; Natelson, Douglas
2016-06-28
With materials approaching the 2D limit yielding many exciting systems with intriguing physical properties and promising technological functionalities, understanding and engineering magnetic order in nanoscale, layered materials is generating keen interest. One such material is V5S8, a metal with an antiferromagnetic ground state below the Néel temperature TN ∼ 32 K and a prominent spin-flop signature in the magnetoresistance (MR) when H∥c ∼ 4.2 T. Here we study nanoscale-thickness single crystals of V5S8, focusing on temperatures close to TN and the evolution of material properties in response to systematic reduction in crystal thickness. Transport measurements just below TN reveal magnetic hysteresis that we ascribe to a metamagnetic transition, the first-order magnetic-field-driven breakdown of the ordered state. The reduction of crystal thickness to ∼10 nm coincides with systematic changes in the magnetic response: TN falls, implying that antiferromagnetism is suppressed; and while the spin-flop signature remains, the hysteresis disappears, implying that the metamagnetic transition becomes second order as the thickness approaches the 2D limit. This work demonstrates that single crystals of magnetic materials with nanometer thicknesses are promising systems for future studies of magnetism in reduced dimensionality and quantum phase transitions. PMID:27163511
Phase diagrams of a classical two-dimensional Heisenberg antiferromagnet with single-ion anisotropy
NASA Astrophysics Data System (ADS)
Leidl, R.; Selke, W.
2004-11-01
A classical variant of the two-dimensional anisotropic Heisenberg model reproducing inelastic neutron scattering experiments on La5Ca9Cu24O41 [M. Matsuda , Phys. Rev. B 68, 060406(R) (2003)] is analyzed using mostly Monte Carlo techniques. Phase diagrams with external fields parallel and perpendicular to the easy axis of the anisotropic interactions are determined, including antiferromagnetic and spin-flop phases. Mobile spinless defects, or holes, are found to form stripes which bunch, debunch, and break up at a phase transition. A parallel field can lead to a spin-flop phase.
Neto, Minos A; de Sousa, J Ricardo; Branco, N S
2015-05-01
We have studied the presence of plateaus on the low-temperature magnetization of an antiferromagnetic spin-1 chain, as an external uniform magnetic field is varied. A crystal-field interaction is present in the model and the exchange constants follow a random quenched (Bernoulli or Gaussian) distribution. Using a transfer-matrix technique we calculate the largest Lyapunov exponent and, from it, the magnetization at low temperatures as a function of the magnetic field, for different values of the crystal field and the width of the distributions. For the Bernoulli distribution, the number of plateaus increases, with respect to the uniform case [Litaiff et al., Solid State Commun. 147, 494 (2008)] and their presence can be linked to different ground states, when the magnetic field is varied. For the Gaussian distributions, the uniform scenario is maintained, for small widths, but the plateaus structure disappears as the width increases. PMID:26066165
NASA Astrophysics Data System (ADS)
Juan-Juan, Liu; Jin-Chen, Wang; Wei, Luo; Jie-Ming, Sheng; Zhang-Zhen, He; A. Danilkin, S.; Wei, Bao
2016-03-01
The magnetic structure of the spin-chain antiferromagnet SrCo2V2O8 is determined by single-crystal neutron diffraction experiment. The system undergoes magnetic long range order below T_N = 4.96 K. The moment of 2.16{\\mu}_B per Co at 1.6 K in the screw chain running along the c axis alternates in the c-axis. The moments of neighboring screw chains are arranged antiferromagnetically along one in-plane axis and ferromagnetically along the other in-plane axis. This magnetic configuration breaks the 4-fold symmetry of the tetragonal crystal structure and leads to two equally populated magnetic twins with antiferromagnetic vector in the a or b axis. The very similar magnetic state to the isostructural BaCo2V2O8 warrants SrCo2V2O8 another interesting half-integer spin-chain antiferromagnet for investigation on quantum antiferromagnetism.
Antiferromagnetic order induced by gadolinium substitution in Bi{sub 2}Se{sub 3} single crystals
Kim, S. W.; Jung, M. H.; Vrtnik, S.; Dolinšek, J.
2015-06-22
Magnetic topological insulators can serve as a fundamental platform for various spin-based device applications. We report the antiferromagnetic order induced by the magnetic impurity dopants of Gd in Gd{sub x}Bi{sub 2−x}Se{sub 3} and the systematic results with varying the Gd concentration x ( = 0.14, 0.20, 0.30, and 0.40). The antiferromagnetic order is demonstrated by the magnetic susceptibility, electrical resistivity, and specific heat measurements. The anomaly observed at T{sub N} = 6 K for x ≥ 0.30 shifts towards lower temperature with increasing the magnetic field, indicative of antiferromagnetic ground state. The Gd substitution into Bi{sub 2}Se{sub 3} enables not only tuning the magnetism from paramagnetic to antiferromagnetic for high x (≥ 0.30) but also giving a promising candidate for antiferromagnetic topological insulators.
NASA Astrophysics Data System (ADS)
Tretiakov, Oleg; Barker, Joseph
Skyrmions are topologically protected entities in magnetic materials which have the potential to be used in spintronics for information storage and processing. However, skyrmions in ferromagnets have some intrinsic difficulties which must be overcome to use them for spintronic applications, such as the inability to move straight along current. We show that skyrmions can also be stabilized and manipulated in antiferromagnetic materials. An antiferromagnetic skyrmion is a compound topological object with a similar but of opposite sign spin texture on each sublattice, which e.g. results in a complete cancelation of the Magnus force. We find that the composite nature of antiferromagnetic skyrmions gives rise to different dynamical behavior, both due to an applied current and temperature effects. O.A.T. and J.B. acknowledge support by the Grants-in-Aid for Scientific Research (Nos. 25800184, 25247056, 25220910 and 15H01009) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan and SpinNet.
NASA Astrophysics Data System (ADS)
Kaczorowski, D.; Pikul, A. P.; Gnida, D.; Tran, V. H.
2009-07-01
Single crystals of Ce2PdIn8 were studied by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. The compound was found to be a heavy fermion clean-limit superconductor with Tc=0.68K. Most remarkably, the superconductivity in this system emerges out of the antiferromagnetic state that sets in at TN=10K, and both cooperative phenomena coexist in a bulk at ambient pressure conditions.
Kaczorowski, D; Pikul, A P; Gnida, D; Tran, V H
2009-07-10
Single crystals of Ce2PdIn8 were studied by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. The compound was found to be a heavy fermion clean-limit superconductor with Tc=0.68 K. Most remarkably, the superconductivity in this system emerges out of the antiferromagnetic state that sets in at TN=10 K, and both cooperative phenomena coexist in a bulk at ambient pressure conditions. PMID:19659236
Motion of a single hole in a quantum antiferromagnet at finite temperatures
Igarashi, J. ); Fulde, P. )
1993-07-01
Motion of a single hole is studied at finite temperatures in the [ital t]-[ital J] model on a slave-fermion Schwinger-boson representation. The spin fluctuation is treated with the mean-field theory of Arovas and Auerbach. The Green's function for the slave fermion is calculated within the self-consistent Born approximation. A sharp quasiparticle peak is found to be separated from a broad spectrum of incoherence in the spectral function for low temperatures. The Green's function for the physical hole is calculated by taking account of the multiple scattering between the slave fermion and the Schwinger boson. A bound state of the slave fermion and the Schwinger boson is found at low temperatures, suggesting that the spin and the charge cannot be separated into a simple form. The energy of the bound state is minimized at momenta ([plus minus][pi]/2, [plus minus][pi]/2), indicating that a small pocketlike Fermi surface is formed around the momenta for low concentrations of dopant holes.
Cell dimensions and antiferromagnetism of lunar and terrestrial ilmenite single crystals
Thorpe, A.N.; Minkin, J.A.; Senftle, F.E.; Alexander, Corrine; Briggs, Charles; Evans, H.T., Jr.; Nord, G.L., Jr.
1977-01-01
X-Ray diffraction and anisotropic magnetic measurements have been made on single crystals of lunar ilmenite and on terrestrial ilmenite from Bancroft, Ontario, Canada and the Ilmen Mountains, U.S.S.R. The elongated c-axis of lunar ilmenite, previously reported, is confirmed by new measurements. The shorter c-axis found in terrestrial specimens is ascribed to Fe3+ substitution for Ti4+ in the titanium layer. Magnetic measurements on the same specimens show that, in agreement with the Ishikawa-Shirane et al. model, the initial shortening of the c-axis by the above substitution of small amounts of Fe3+ (<8%) causes an increase in Fe2+-Fe2+ exchange coupling through Fe3+ in the titanium layer that lowers the Ne??el transition temperature. The Weiss temperatures and other magnetic parameters confirm this model proposed by Ishikawa and Shirane et al. Additional transitions found in one of the terrestrial specimens (Bancroft) have been ascribed to a small amount of an exsolved spinel phase, possibly a solid solution phase of magnetite-u??lvospinel. The spinel phase is localized in hematite-rich blebs which exsolved from the host ilmenite-rich phase. ?? 1977.
Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4
NASA Astrophysics Data System (ADS)
Zaharko, O.; Christensen, N. B.; Cervellino, A.; Tsurkan, V.; Maljuk, A.; Stuhr, U.; Niedermayer, C.; Yokaichiya, F.; Argyriou, D. N.; Boehm, M.; Loidl, A.
2011-09-01
We study the evidence for spin liquid in the frustrated diamond lattice antiferromagnet CoAl2O4 by means of single-crystal neutron scattering in zero and applied magnetic fields. The magnetically ordered phase appearing below TN=8 K remains nonconventional down to 1.5 K. The magnetic Bragg peaks at the q=0 positions are broad and their line shapes have strong Lorentzian contributions. Additionally, the peaks are connected by weak diffuse streaks oriented along the <111> directions. The observed short-range magnetic correlations are explained within the spiral spin-liquid model. The specific shape of the energy landscape of the system, with an extremely flat energy minimum around q=0 and many low-lying excited spiral states with q=<111>, results in thermal population of this manifold at finite temperatures. The agreement between the experimental results and the spiral spin-liquid model is only qualitative, indicating that microstructure effects might be important to achieve quantitative agreement. Application of a magnetic field significantly perturbs the spiral spin-liquid correlations. The magnetic peaks remain broad but acquire more Gaussian line shapes and increase in intensity. The 1.5 K static magnetic moment increases from 1.58 μB/Co at zero field to 2.08 μB/Co at 10 T. The magnetic excitations appear rather conventional at zero field. Analysis using classical spin-wave theory yields values of the nearest- and next-nearest-neighbor exchange parameters J1=0.92(1) meV and J2=0.101(2) meV and an additional anisotropy term D=-0.0089(2) meV for CoAl2O4. In the presence of a magnetic field, the spin excitations broaden considerably and become nearly featureless at the zone center.
Antiferromagnetic resonance in charge ordering state of Pr 0.5Ca 0.5MnO 3- δ single crystal
NASA Astrophysics Data System (ADS)
Kawamata, S.; Noguchi, S.; Okuda, K.; Nojiri, H.; Motokawa, M.
2001-05-01
An antiferromagnetic resonance (AFMR) is observed in the charge ordered antiferromagnetic phase of Pr 0.5Ca 0.5MnO 3- δ single crystal for the first time. Above the Néel temperature, TN=173 K, a paramagnetic resonance with g=2.0 is observed. There is no significant change of the resonance spectra at the charge ordering transition temperature, TCO=242 K. Below TN, a branch of AFMR is found. Since the resonance field of this mode increases linearly as the frequency is decreased, this branch is assigned as the spin-flop mode. Below 60 K, the critical fields, BC, evaluated as the extrapolation of this mode to zero frequency agree well with the insulator-metal transition fields, BCO, at which the melting of the charge-ordering phase occurs. Present results indicate that the temperature dependence of BCO is affected by the temperature dependence of BC.
Antiferromagnetism in EuCu2As2 and EuCu1.82Sb2 single crystals
Anand, V. K.; Johnston, D. C.
2015-05-07
Single crystals of EuCu2As2 and EuCu2Sb2 were grown from CuAs and CuSb self-flux, respectively. The crystallographic, magnetic, thermal, and electronic transport properties of the single crystals were investigated by room-temperature x-ray diffraction (XRD), magnetic susceptibility χ versus temperature T, isothermal magnetization M versus magnetic field H, specific heat Cp(T), and electrical resistivity ρ(T) measurements. EuCu2As2 crystallizes in the body-centered tetragonal ThCr2Si2-type structure (space group I4/mmm), whereas EuCu2Sb2 crystallizes in the related primitive tetragonal CaBe2Ge2-type structure (space group P4/nmm). The energy-dispersive x-ray spectroscopy and XRD data for the EuCu2Sb2 crystals showed the presence of vacancies on the Cu sites, yielding themore » actual composition EuCu1.82Sb2. The ρ(T) and Cp(T) data reveal metallic character for both EuCu2As2 and EuCu1.82Sb2. Antiferromagnetic (AFM) ordering is indicated from the χ(T),Cp(T), and ρ(T) data for both EuCu2As2 (TN = 17.5 K) and EuCu1.82Sb2 (TN = 5.1 K). In EuCu1.82Sb2, the ordered-state χ(T) and M(H) data suggest either a collinear A-type AFM ordering of Eu+2 spins S = 7/2 or a planar noncollinear AFM structure, with the ordered moments oriented in the tetragonal ab plane in either case. This ordered-moment orientation for the A-type AFM is consistent with calculations with magnetic dipole interactions. As a result, the anisotropic χ(T) and isothermal M(H) data for EuCu2As2, also containing Eu+2 spins S = 7/2, strongly deviate from the predictions of molecular field theory for collinear AFM ordering and the AFM structure appears to be both noncollinear and noncoplanar.« less
Antiferromagnetism in EuCu2As2 and EuCu1.82Sb2 single crystals
NASA Astrophysics Data System (ADS)
Anand, V. K.; Johnston, D. C.
2015-05-01
Single crystals of EuCu2As2 and EuCu2Sb2 were grown from CuAs and CuSb self-flux, respectively. The crystallographic, magnetic, thermal, and electronic transport properties of the single crystals were investigated by room-temperature x-ray diffraction (XRD), magnetic susceptibility χ versus temperature T , isothermal magnetization M versus magnetic field H , specific heat Cp(T ) , and electrical resistivity ρ (T ) measurements. EuCu2As2 crystallizes in the body-centered tetragonal ThCr2Si2 -type structure (space group I 4 /m m m ), whereas EuCu2Sb2 crystallizes in the related primitive tetragonal CaBe2Ge2 -type structure (space group P 4 /n m m ). The energy-dispersive x-ray spectroscopy and XRD data for the EuCu2Sb2 crystals showed the presence of vacancies on the Cu sites, yielding the actual composition EuCu1.82Sb2 . The ρ (T ) and Cp(T ) data reveal metallic character for both EuCu2As2 and EuCu1.82Sb2 . Antiferromagnetic (AFM) ordering is indicated from the χ (T ) ,Cp(T ) , and ρ (T ) data for both EuCu2As2 (TN=17.5 K) and EuCu1.82Sb2 (TN=5.1 K). In EuCu1.82Sb2 , the ordered-state χ (T ) and M (H ) data suggest either a collinear A-type AFM ordering of Eu+2 spins S =7/2 or a planar noncollinear AFM structure, with the ordered moments oriented in the tetragonal a b plane in either case. This ordered-moment orientation for the A-type AFM is consistent with calculations with magnetic dipole interactions. The anisotropic χ (T ) and isothermal M (H ) data for EuCu2As2 , also containing Eu+2 spins S =7/2 , strongly deviate from the predictions of molecular field theory for collinear AFM ordering and the AFM structure appears to be both noncollinear and noncoplanar.
Li, Hai-Feng; Cao, Chongde; Wildes, Andrew; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Löser, Wolfgang; Roth, Georg
2015-01-01
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q± = (H ± 0.557(1), 0, L ± 0.150(1)) and QC = (H ± 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature- and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q± modulation may be attributed to localized 4f moments while the QC correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix. PMID:25608949
NASA Astrophysics Data System (ADS)
Mukuda, H.; Abe, M.; Kitaoka, Y.; Kotegawa, H.; Tokiwa, K.; Watanabe, T.; Iyo, A.; Kito, H.; Tanaka, Y.; Kodama, Y.
2007-09-01
We report systematic Cu-NMR studies on five-layered cuprates from under-doped HgBa2Ca4Cu5O12+δ (Hg-1245(UD)) to slightly overdoped Tl-1245(OVD), and compare with optimally-doped Hg-1245(OPT). In the under-doped Hg-1245(UD), antiferromagnetism (AFM) has been found to take place at TN = 290 K, exhibiting a large antiferromagnetic moment of 0.67-0.69 μB at three inner planes (IP's). These values are comparable to that reported for non-doped cuprates, suggesting that the IP's may be in a nearly non-doped regime. Most surprisingly, the AFM order is also detected with MAFM(OP) = 0.1 μB even at two outer planes (OP's) that are responsible for the onset of superconductivity (SC) with Tc = 72 K. The high-Tc SC at Tc = 72 K can uniformly coexist on a microscopic level with the AFM at OP's. This is the first microscopic evidence for the uniformly mixed phase of AFM and SC on a single CuO2 plane. Although, the AFM/SC mixed CuO2 planes are significantly separated by three non-doped AFM layers, the onset of AFM does not prevent the occurrence of SC with the high value of Tc = 72 K.
Li, Hai-Feng; Cao, Chongde; Wildes, Andrew; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Löser, Wolfgang; Roth, Georg
2015-01-01
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q± = (H ± 0.557(1), 0, L ± 0.150(1)) and QC = (H ± 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature- and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q± modulation may be attributed to localized 4f moments while the QC correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix. PMID:25608949
Single antiferromagnetic MnTe (sub)monolayers in CdTe/CdMgTe quantum wells
NASA Astrophysics Data System (ADS)
Prechtl, G.; Heiss, W.; Mackowski, S.; Bonanni, A.; Karczewski, G.; Sitter, H.; Jantsch, W.
2000-06-01
Antiferromagnetic MnTe (sub)monolayers inserted into nonmagnetic CdTe/CdMgTe quantum wells are investigated by magneto-optical spectroscopy. In particular, the Zeeman splitting is determined from polarization dependent photoluminescence excitation experiments. Rapid thermal annealing (RTA) is applied to diffuse Mn out of the (sub)monolayer barriers into the quantum well. The resulting Mn diffusion leads to a substantial increase of the Zeeman splitting. Furthermore, the annealing induced broadening of the MnTe (sub)monolayer barrier in the well is accompanied by a decrease of the barrier height, leading to a blue shift or a red shift of the e1-hh1 transition, depending on the detailed sample structure. A comparison of the observed energy shifts with model calculations allows us to estimate the thickness of the MnTe barriers. These are found to be very close to their nominal values before annealing, regardless of the chosen MnTe band offset and effective masses.
Kondo lattice and antiferromagnetic behavior in quaternary CeTAl4Si2 (T = Rh, Ir) single crystals
Maurya, Arvind; Kulkarni, Ruta; Thamizhavel, Arumugam; Paudyal, Durga; Dhar, Sudesh Kumar
2016-02-26
Here, we have explored in detail the anisotropic magnetic properties of CeRhAl4Si2 and CeIrAl4Si2, which undergo two antiferromagnetic transitions, at TN1 = 12.6 and 15.5 K, followed by a second transition at TN2 = 9.4 and 13.8 K, respectively, with the [001]-axis as the relatively easy axis of magnetization. The electrical resistivity at ambient and applied pressure provides evidence of Kondo interaction in both compounds, further supported by a reduced value of the entropy associated with the magnetic ordering. The Sommerfeld coefficient γ is inferred to be 195.6 and 49.4 mJ/(mol K2) for CeRhAl4Si2 and CeIrAl4Si2, respectively, classifying these materialsmore » as moderate heavy-fermion compounds. The crystal electric field energy levels are derived from the peak seen in the Schottky heat capacity. Furthermore, we have also performed electronic structure calculations by using the local spin density approximation + U [LSDA+U] approach, which provide physical insights on the observed magnetic behavior of these two compounds.« less
Tancharakorn, Somchai; Fabbiani, Francesca P A; Allan, David R; Kamenev, Konstantin V; Robertson, Neil
2006-07-19
The magnetic susceptibility and single-crystal X-ray structure of the one-dimensional Heisenberg antiferromagnetic chain tetramethylammonium manganese trichloride (TMMC) have been studied under pressure as a facile route to develop structure-property relationships. The X-ray structure of TMMC was determined at 0, 2.1, 3.8, 6.8, 12.2, and 17.0 kbar using diamond-anvil cell techniques and synchrotron radiation. The space group is confirmed to be P6(3)/m up to 17 kbar, and structural refinement shows that the Mn-Mn separations between and along the chains change by about 3.4 and 2.5%, respectively, over 17 kbar. A structural transition from hexagonal to monoclinic symmetry possibly occurs at 17 kbar, associated with a loss of crystal quality. Variable-temperature magnetic susceptibility data were taken at 0, 0.3, 1.5, 2.9, 4.0, 5.2, and 6.5 kbar and show that the intrachain coupling constant changes from -6.85 to -7.81 K over this range. The interchain coupling constant of -0.54 K can also be extracted from the Fisher model modified for interacting chains. The pressure-temperature diagram shows the slope of the intrachain antiferromagnetic coupling with pressure, DeltaT(IAF)/DeltaP, changes from 0.5 to 1.6 K/kbar at 2 kbar where the structure changes from P2(1)/a to P2(1)/m. Comparison of the magnetic and structural data are consistent with the power-law relationship developed by Bloch where J proportional, variant r-n, r = Mn...Mn separation and n approximately 10. PMID:16834394
Electrical switching of an antiferromagnet
NASA Astrophysics Data System (ADS)
Jungwirth, Tomas
Louis Néel pointed out in his Nobel lecture that while abundant and interesting from theoretical viewpoint, antiferromagnets did not seem to have any applications. Indeed, the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization make antiferromagnets hard to control by tools common in ferromagnets. Strong coupling would be achieved if the externally generated field had a sign alternating on the scale of a lattice constant at which moments alternate in AFMs. However, generating such a field has been regarded unfeasible, hindering the research and applications of these abundant magnetic materials. We have recently predicted that relativistic quantum mechanics may offer staggered current induced fields with the sign alternating within the magnetic unit cell which can facilitate a reversible switching of an antiferromagnet by applying electrical currents with comparable efficiency to ferromagnets. Among suitable materials is a high Néel temperature antiferromagnet, tetragonal-phase CuMnAs, which we have recently synthesized in the form of single-crystal epilayers structurally compatible with common semiconductors. We demonstrate electrical writing and read-out, combined with the insensitivity to magnetic field perturbations, in a proof-of-concept antiferromagnetic memory device. We acknowledge support from European Research Council Advanced Grant No. 268066.
Adelnia, Fatemeh; Chiesa, Alessandro; Bordignon, Sara; Carretta, Stefano; Ghirri, Alberto; Candini, Andrea; Cervetti, Christian; Evangelisti, Marco; Affronte, Marco; Sheikin, Ilya; Winpenny, Richard; Timco, Grigore; Borsa, Ferdinando; and others
2015-12-28
A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr{sub 8}Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ{sub 0}H{sub c1} = 2.15 T is found to be an almost true LC while the second LC at μ{sub 0}H{sub c2} = 6.95 T has an anti-crossing gap of Δ{sub 12} = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ{sub 0}H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ∼ 10{sup 10} rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.
NASA Astrophysics Data System (ADS)
Adelnia, Fatemeh; Chiesa, Alessandro; Bordignon, Sara; Carretta, Stefano; Ghirri, Alberto; Candini, Andrea; Cervetti, Christian; Evangelisti, Marco; Affronte, Marco; Sheikin, Ilya; Winpenny, Richard; Timco, Grigore; Borsa, Ferdinando; Lascialfari, Alessandro
2015-12-01
A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr8Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ0Hc1 = 2.15 T is found to be an almost true LC while the second LC at μ0Hc2 = 6.95 T has an anti-crossing gap of Δ12 = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ0H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ˜ 1010 rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.
NASA Astrophysics Data System (ADS)
Chikara, S.; Korneta, O. B.; Qi, T. F.; Parkin, S.; Cao, G.; Song, W. P.; Crummett, W. P.
2009-03-01
Bilayered Ca3Ru2O7 is a highly anisotropic system [1] characterized by orbitally-driven colossal magnetoresistance^2 and an unusual antiferromagnetic metallic (AFM-M) state [2]. We report transport and thermodynamic properties of (Ca1-x Ax)3Ru2O7 (A = Sr, Ba) single crystals as a function of temperature and applied magnetic field. While Ba doping shows a far stronger impact, both Sr and Ba substitution for Ca induce a large array of interesting phenomena. Among them, a bulk spin-valve effect occurs in the AFM-M range, which is largely broadened due to the doping. This effect in bulk crystals is a novel phenomenon first observed in Ca3(Ru1-xCrx)2O7 single crystals [3]. The spin-valve effect in (Ca1-xAx)3Ru2O7 single crystals opens new avenues to understand the underlying physics and realize the potential of spin valves in practical devices.[0pt] [1] G. Cao et al., PRL 78, 1751 (1997)[0pt] [2] X. N. Lin et al., PRL 95, 017203 (2005)[0pt] [3] G. Cao et al., PRL 100, 016604 (2008)
Magnetic coupling between Sm3+ and the canted spin in an antiferromagnetic SmFeO3 single crystal
Cheng, J G; Zhou, J.-S.; Mandrus, D.; Goodenough, J; Marshall, L; Yan, Jiaqiang
2012-01-01
The perovskite SmFeO3 exhibits type-G AF ordering at TN 670 K and an easy axis rotation transition at TSR 480 K. Owing to the peculiar site anisotropy of rare-earth Sm3+, the moment on Sm3+ is oriented antiparallel to the canted spin from the Fe3+ sublattice along the a axis at T < TSR. Development of the magnetic moment on Sm3+ as temperature decreases makes it possible to balance the two magnetic moments at Tcomp. Application of a moderate external magnetic field along the a axis can trigger an abrupt reversal of the moment on Sm3+ and the canted spin relative to the external field at a temperature around Tcomp. We report here a study of the field-induced magnetic-moment reversal in a single crystal SmFeO3 by measuring the magnetization and specific heat with the external field along different crystallographic axes.
NASA Astrophysics Data System (ADS)
Zheng, H.; Terzic, J.; Ye, Feng; Wan, X. G.; Wang, D.; Wang, Jinchen; Wang, Xiaoping; Schlottmann, P.; Yuan, S. J.; Cao, G.
2016-06-01
The orthorhombic perovskite SrIr O3 is a semimetal, an intriguing exception in iridates where the strong spin-orbit interaction coupled with electron correlations tends to impose an insulating state. We report results of our investigation of bulk single-crystal S r0.94I r0.78O2.68 or Ir-deficient, orthorhombic perovskite SrIr O3 . It retains the same crystal structure as stoichiometric SrIr O3 but exhibits a sharp, simultaneous antiferromagnetic (AFM) and metal-insulator (MI) transition occurring in the basal-plane resistivity at 185 K. Above it, the basal-plane resistivity features an extended regime of almost linear temperature dependence up to 800 K but the strong electronic anisotropy renders an insulating behavior in the out-of-plane resistivity. The Hall resistivity undergoes an abrupt sign change and grows below 40 K, which along with the Sommerfeld constant of 20 mJ /mol K2 suggests a multiband effect. All results including our first-principles calculations underscore a delicacy of the paramagnetic, metallic state in SrIr O3 that is in close proximity to an AFM insulating state. The contrasting ground states in isostructural S r0.94I r0.78O2.68 and SrIr O3 illustrate a critical role of lattice distortions and Ir deficiency in rebalancing the ground state in the iridates. Finally, the concurrent AFM and MI transitions reveal a direct correlation between the magnetic transition and formation of an activation gap in the iridate, which is conspicuously absent in S r2Ir O4 .
Niazi, A.; Bud'ko, S.L.; Schlagel, D.L.; Yan, J.Q.; Lograsso, T.A.; Kreyssig, A.; Das, S.; Nandi, S.; Goldman, A.I.; Honecker, A.; McCallum, R.W.; Reehuis, M.; Pieper, O.; Lake, B.; Johnston, D.C.
2009-05-01
The compound CaV{sub 2}O{sub 4} contains V{sup +3} cations with spin S=1 and has an orthorhombic structure at room temperature containing zigzag chains of V atoms running along the c axis. We have grown single crystals of CaV{sub 2}O{sub 4} and report crystallography, static magnetization, magnetic susceptibility x, ac magnetic susceptibility, heat capacity C{sub p}, and thermal expansion measurements in the temperature T range of 1.8--350 K on the single crystals and on polycrystalline samples. An orthorhombic-to-monoclinic structural distortion and a long-range antiferromagnetic (AF) transition were found at sample-dependent temperatures T{sub S}{approx}108--145 K and T{sub N}{approx}51--76 K, respectively. In two annealed single crystals, another transition was found at {approx}200 K. In one of the crystals, this transition is mostly due to V{sub 2}O{sub 3} impurity phase that grows coherently in the crystals during annealing. However, in the other crystal the origin of this transition at 200 K is unknown. The x(T) shows a broad maximum at {approx}300 K associated with short-range AF ordering and the anisotropy of x above T{sub N} is small. The anisotropic x(T{yields}0) data below T{sub N} show that the (average) easy axis of the AF magnetic structure is the b axis. The C{sub p}(T) data indicate strong short-range AF ordering above T{sub N}, consistent with the x(T) data. We fitted our x data by a J{sub 1}-J{sub 2} S=1 Heisenberg chain model, where J{sub 1}(J{sub 2}) is the (next)-nearest-neighbor exchange interaction. We find J{sub 1}{approx}230 K and surprisingly, J{sub 2}/J{sub 1}{approx}0 (or J{sub 1}/J{sub 2}{approx}0). The interaction J{sub {perpendicular}} between these S=1 chains leading to long-range AF ordering at T{sub N} is estimated to be J{sub {perpendicular}}/J{sub 1}{approx_equal}0.04.
Itoh, S.; Nakayama, T.; Kajimoto, R.; Adams, M. A.; Materials Science Division; High Energy Accelerator Research Organization; Rutherford Appleton Lab.
2009-01-01
The dynamic structure factors S(q,w) of an ideal percolating network, the three-dimensional (3d) dilute Heisenberg antiferromagnet RbMn{sub 0.4}Mg{sub 0.6}F{sub 3}, obtained from high resolution ({Delta}E = 17.5 {micro}eV) inelastic neutron scattering (INS) experiments are analyzed for the first time within the framework of the single-length-scaling postulate (SLSP). The analysis confirms the validity of the SLSP and is also used to extract the values of the key exponents governing the spin dynamics, the dynamic exponent (z{sub AF} = D{sub f}/tilded{sub AF}) being 2.5 {+-} 0.1 and the spectral dimension tilded{sub AF} for antiferromagnetic (AFM) fractons taking a value of unity.
Spintronics in antiferromagnets
Soh, Yeong-Ah; Kummamuru, Ravi K.
2012-05-10
Magnetic domains and the walls between are the subject of great interest because of the role they play in determining the electrical properties of ferromagnetic materials and as a means of manipulating electron spin in spintronic devices. However, much less attention has been paid to these effects in antiferromagnets, primarily because there is less awareness of their existence in antiferromagnets, and in addition they are hard to probe since they exhibit no net magnetic moment. In this paper, we discuss the electrical properties of chromium, which is the only elemental antiferromagnet and how they depend on the subtle arrangement of the antiferromagnetically ordered spins. X-ray measurement of the modulation wavevector Q of the incommensurate antiferromagnetic spin-density wave shows thermal hysteresis, with the corresponding wavelength being larger during cooling than during warming. The thermal hysteresis in the Q vector is accompanied with a thermal hysteresis in both the longitudinal and Hall resistivity. During cooling, we measure a larger longitudinal and Hall resistivity compared with when warming, which indicates that a larger wavelength at a given temperature corresponds to a smaller carrier density or equivalently a larger antiferromagnetic ordering parameter compared to a smaller wavelength. This shows that the arrangement of the antiferromagnetic spins directly influences the transport properties. In thin films, the sign of the thermal hysteresis for Q is the same as in thick films, but a distinct aspect is that Q is quantized.
Antiferromagnetic magnonic crystals
NASA Astrophysics Data System (ADS)
Troncoso, Roberto E.; Ulloa, Camilo; Pesce, Felipe; Nunez, A. S.
2015-12-01
We describe the features of magnonic crystals based upon antiferromagnetic elements. Our main results are that with a periodic modulation of either magnetic fields or system characteristics, such as the anisotropy, it is possible to tailor the spin-wave spectra of antiferromagnetic systems into a band-like organization that displays a segregation of allowed and forbidden bands. The main features of the band structure, such as bandwidths and band gaps, can be readily manipulated. Our results provide a natural link between two steadily growing fields of spintronics: antiferromagnetic spintronics and magnonics.
Ferromagnetic response of a ``high-temperature'' quantum antiferromagnet
NASA Astrophysics Data System (ADS)
Wang, Xin
2014-03-01
We study the antiferromagnetic phase of the ionic Hubbard model at finite temperature using dynamical mean-field theory. We find that the ionic potential plays a dual role in determining the antiferromagnetic order. A small ionic potential (compared to the Hubbard repulsion) increases the super-exchange coupling, thereby implying an increase of the Neel temperature of the system, which should facilitate observation of antiferromagnetic ordering experimentally. On the other hand, for large ionic potential, the antiferromagnetic ordering is killed and the system becomes a charge density wave with electron occupancies alternating between 0 and 2. This novel way of degrading antiferromagnetism leads to spin polarization of the low energy single particle density of states. The dynamic response of the system thus mimics ferromagnetic behavior, although the system is still an antiferromagnet in terms of the static spin order. Work done in collaboration with Rajdeep Sensarma and Sankar Das Sarma, and supported by NSF-JQI-PFC, AFOSR MURI, and ARO MURI.
Antiferromagnetism in CaAl2Si2-type CaMn2As2 and SrMn2As2 single crystals
NASA Astrophysics Data System (ADS)
Sangeetha, N. S.; Pandey, Abhishek; Benson, Zackery A.; Johnston, D. C.
Magnetic susceptibility versus temperature χ (T) measurements of CaMn2As2 and SrMn2As2 crystals show clear antiferromagnetic (AFM) transitions at TN ~ 65 K and 120 K,1 respectively. The anisotropic behaviors in χ (T <=TN) suggest that both compounds are noncollinear antiferromagnets which may result either from an intrinsic noncollinear structure or from multiple collinear AFM domains that are not aligned collinearly.2 The χ (T) data at T >TN reveal that both compounds exhibit strong short-range AFM ordering, evidently associated with quasi-two-dimensional spin lattices. The electrical resistivities show insulating ground states with activation energies of ~ 63 meV in CaMn2As2 and 44 meV in SrMn2As2 . The experimental results thus reveal that both (Ca , Sr) Mn2As2 materials are AFM insulators at low temperatures and in analogy with the high Tc cuprates, may be potential parent compounds for CaAl2Si2-type superconductors. Work was supported by the USDOE under Contract No. DE-AC02-07CH11358.
Antiferromagnetic hedgehogs with superconducting cores
NASA Astrophysics Data System (ADS)
Goldbart, Paul M.; Sheehy, Daniel E.
1998-09-01
Excitations of the antiferromagnetic state that resemble antiferromagnetic hedgehogs at large distances but are predominantly superconducting inside a core region are discussed within the context of Zhang's SO(5)-symmetry-based approach to the physics of high-temperature superconducting materials. Nonsingular, in contrast with their hedgehog cousins in pure antiferromagnetism, these texture excitations are what hedgehogs become when the antiferromagnetic order parameter is permitted to ``escape'' into superconducting directions. The structure of such excitations is determined in a simple setting, and a number of their experimental implications are examined.
Antiferromagnetic hedgehogs with superconducting cores
Goldbart, P.M.; Sheehy, D.E.
1998-09-01
Excitations of the antiferromagnetic state that resemble antiferromagnetic hedgehogs at large distances but are predominantly superconducting inside a core region are discussed within the context of Zhang{close_quote}s SO(5)-symmetry-based approach to the physics of high-temperature superconducting materials. Nonsingular, in contrast with their hedgehog cousins in pure antiferromagnetism, these texture excitations are what hedgehogs become when the antiferromagnetic order parameter is permitted to {open_quotes}escape{close_quotes} into superconducting directions. The structure of such excitations is determined in a simple setting, and a number of their experimental implications are examined. {copyright} {ital 1998} {ital The American Physical Society}
Spin reorientation via antiferromagnetic coupling
Ranjbar, M.; Sbiaa, R.; Dumas, R. K.; Åkerman, J.; Piramanayagam, S. N.
2014-05-07
Spin reorientation in antiferromagnetically coupled (AFC) Co/Pd multilayers, wherein the thickness of the constituent Co layers was varied, was studied. AFC-Co/Pd multilayers were observed to have perpendicular magnetic anisotropy even for a Co sublayer thickness of 1 nm, much larger than what is usually observed in systems without antiferromagnetic coupling. When similar multilayer structures were prepared without antiferromagnetic coupling, this effect was not observed. The results indicate that the additional anisotropy energy contribution arising from the antiferromagnetic coupling, which is estimated to be around 6 × 10{sup 6} ergs/cm{sup 3}, induces the spin-reorientation.
From local to nonlocal Fermi liquid in doped antiferromagnets
Prelovsek, P. |; Jaklic, J.; Bedell, K.
1999-07-01
The variation of single-particle spectral functions with doping is studied numerically within the t-J model. Results suggest that the corresponding self-energies change from local ones at the intermediate doping to strongly nonlocal ones for a weakly doped antiferromagnet. The nonlocality shows up most clearly in the pseudogap emerging in the density of states, due to the onset of short-range antiferromagnetic correlations. {copyright} {ital 1999} {ital The American Physical Society}
Spectral function and photoemission spectra in antiferromagnetically correlated metals
Kampf, A.P.; Schrieffer, J.R. )
1990-11-01
Antiferromagnetic spin fluctuations in a two-dimensional metal, such as doped high-{Tc} superconductors, lead to a pseudogap in the electronic spectrum. In the spectral function weight is shifted from the single quasiparticle peak of the Fermi-liquid regime to the incoherent particle and hole backgrounds, which evolve into the upper and lower Mott-Hubbard bands of the antiferromagnetic insulator. Precursors of these split bands show up as shadow bands'' in angle-resolved photoemission spectra.
Antiferromagnetic Spin Seebeck Effect.
Wu, Stephen M; Zhang, Wei; Kc, Amit; Borisov, Pavel; Pearson, John E; Jiang, J Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand
2016-03-01
We report on the observation of the spin Seebeck effect in antiferromagnetic MnF_{2}. A device scale on-chip heater is deposited on a bilayer of MnF_{2} (110) (30 nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF_{2} (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF_{2} through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9 T) are applied parallel to the easy axis of the MnF_{2} thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected. PMID:26991198
Electrical switching of an antiferromagnet.
Wadley, P; Howells, B; Železný, J; Andrews, C; Hills, V; Campion, R P; Novák, V; Olejník, K; Maccherozzi, F; Dhesi, S S; Martin, S Y; Wagner, T; Wunderlich, J; Freimuth, F; Mokrousov, Y; Kuneš, J; Chauhan, J S; Grzybowski, M J; Rushforth, A W; Edmonds, K W; Gallagher, B L; Jungwirth, T
2016-02-01
Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 10(6) ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics. PMID:26841431
Electrical switching of an antiferromagnet
NASA Astrophysics Data System (ADS)
Wadley, P.; Howells, B.; Železný, J.; Andrews, C.; Hills, V.; Campion, R. P.; Novák, V.; Olejník, K.; Maccherozzi, F.; Dhesi, S. S.; Martin, S. Y.; Wagner, T.; Wunderlich, J.; Freimuth, F.; Mokrousov, Y.; Kuneš, J.; Chauhan, J. S.; Grzybowski, M. J.; Rushforth, A. W.; Edmonds, K. W.; Gallagher, B. L.; Jungwirth, T.
2016-02-01
Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 106 ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.
Magnetic field tuning of antiferromagnetic Yb3Pt4
NASA Astrophysics Data System (ADS)
Wu, L. S.; Janssen, Y.; Marques, C.; Bennett, M. C.; Kim, M. S.; Park, K.; Chi, Songxue; Lynn, J. W.; Lorusso, G.; Biasiol, G.; Aronson, M. C.
2011-10-01
We present measurements of the specific heat, magnetization, magnetocaloric effect, and magnetic neutron diffraction carried out on single crystals of antiferromagnetic Yb3Pt4, where highly localized Yb moments order at TN=2.4 K in zero field. The antiferromagnetic order was suppressed to TN→0 by applying a field of 1.85 T in the ab plane. Magnetocaloric effect measurements show that the antiferromagnetic phase transition is always continuous for TN>0, although a pronounced step in the magnetization is observed at the critical field in both neutron diffraction and magnetization measurements. These steps sharpen with decreasing temperature, but the related divergences in the magnetic susceptibility are cut off at the lowest temperatures, where the phase line itself becomes vertical in the field-temperature plane. As TN→0, the antiferromagnetic transition is increasingly influenced by a quantum critical end point, where TN ultimately vanishes in a first-order phase transition.
Antiferromagnetic inclusions in lunar glass
Thorpe, A.N.; Senftle, F.E.; Briggs, Charles; Alexander, Corrine
1974-01-01
The magnetic susceptibility of 11 glass spherules from the Apollo 15, 16, and 17 fines and two specimens of a relatively large glass spherical shell were studied as a function of temperature from room temperature to liquid helium temperatures. All but one specimen showed the presence of antiferromagnetic inclusions. Closely spaced temperature measurements of the magnetic susceptibility below 77 K on five of the specimens showed antiferromagnetic temperature transitions (Ne??el transitions). With the exception of ilmenite in one specimen, these transitions did not correspond to any transitions in known antiferromagnetic compounds. ?? 1974.
Yeninas, Steven; Pandey, Abhishek; Ogloblichev, V.; Mikhalev, K.; Johnston, David C.; Furukawa, Yuji
2013-12-23
The magnetic structure and metal-insulator transition in antiferromagnetic (AFM) BaMn2As2 and Ba1−xKxMn2As2 single crystals have been investigated by 55Mn and 75As nuclear magnetic resonance (NMR) measurements. In the parent AFM insulator BaMn2As2 with a Néel temperature TN=625 K, we observed a 55Mn zero-field NMR (ZFNMR) spectrum and confirmed the G-type AFM structure from the field dependence of the 55Mn spectra and 75As NMR spectra below TN. In hole-doped crystals with x>0.01, similar 55Mn ZFNMR spectra were observed and the AFM state was revealed to be robust up to x=0.4 with the ordered moment nearly independent of x. The nuclear spin-lattice relaxation rates (1/T1) for both nuclei in the doped samples follow the Korringa relation T1T=const, indicating a metallic state. This confirms the coexistence of AFM ordered localized Mn spins and conduction carriers from a microscopic point of view. From the x dependence of (T1T)−1/2 for both nuclei, we conclude that this transition is caused by vanishing of the hole concentration as the transition is approached from the metallic side.
NASA Astrophysics Data System (ADS)
Torikai, E.; Ishihara, H.; Nagamine, K.; Kitazawa, H.; Tanaka, I.; Kojima, H.; Sulaiman, S. B.; Srinivas, S.; Das, T. P.
1993-03-01
By using a monodomain single crystal La2CuO4 grown by the travelling solvent floating zone method, the strength and direction of the local hyperfine field vector at positive muon sites were determined. Combining with the μ+ location determined separately, we found the importance of the local hyperfine field contributions with dipolar symmetry as well as the distant dipolar field from surrounding point dipoles of Cu atomic moments.
Thermophoresis of an antiferromagnetic soliton
NASA Astrophysics Data System (ADS)
Kim, Se Kwon; Tchernyshyov, Oleg; Tserkovnyak, Yaroslav
2015-07-01
We study the dynamics of an antiferromagnetic soliton under a temperature gradient. To this end, we start by phenomenologically constructing the stochastic Landau-Lifshitz-Gilbert equation for an antiferromagnet with the aid of the fluctuation-dissipation theorem. We then derive the Langevin equation for the soliton's center of mass by the collective coordinate approach. An antiferromagentic soliton behaves as a classical massive particle immersed in a viscous medium. By considering a thermodynamic ensemble of solitons, we obtain the Fokker-Planck equation, from which we extract the average drift velocity of a soliton. The diffusion coefficient is inversely proportional to a small damping constant α , which can yield a drift velocity of tens of m/s under a temperature gradient of 1 K/mm for a domain wall in an easy-axis antiferromagnetic wire with α ˜10-4 .
Quantification of quantum discord in a antiferromagnetic Heisenberg compound
Singh, H. Chakraborty, T. Mitra, C.
2014-04-24
An experimental quantification of concurrence and quantum discord from heat capacity (C{sub p}) measurement performed over a solid state system has been reported. In this work, thermodynamic measurements were performed on copper nitrate (CN, Cu(NO{sub 3}){sub 2}⋅2.5H{sub 2}O) single crystals which is an alternating antiferromagnet Heisenberg spin 1/2 system. CN being a weak dimerized antiferromagnet is an ideal system to investigate correlations between spins. The theoretical expressions were used to obtain concurrence and quantum discord curves as a function of temperature from heat capacity data of a real macroscopic system, CN.
Intrinsic magnetization of antiferromagnetic textures
NASA Astrophysics Data System (ADS)
Tveten, Erlend G.; Müller, Tristan; Linder, Jacob; Brataas, Arne
2016-03-01
Antiferromagnets (AFMs) exhibit intrinsic magnetization when the order parameter spatially varies. This intrinsic spin is present even at equilibrium and can be interpreted as a twisting of the homogeneous AFM into a state with a finite spin. Because magnetic moments couple directly to external magnetic fields, the intrinsic magnetization can alter the dynamics of antiferromagnetic textures under such influence. Starting from the discrete Heisenberg model, we derive the continuum limit of the free energy of AFMs in the exchange approximation and explicitly rederive that the spatial variation of the antiferromagnetic order parameter is associated with an intrinsic magnetization density. We calculate the magnetization profile of a domain wall and discuss how the intrinsic magnetization reacts to external forces. We show conclusively, both analytically and numerically, that a spatially inhomogeneous magnetic field can move and control the position of domain walls in AFMs. By comparing our model to a commonly used alternative parametrization procedure for the continuum fields, we show that the physical interpretations of these fields depend critically on the choice of parametrization procedure for the discrete-to-continuous transition. This can explain why a significant amount of recent studies of the dynamics of AFMs, including effective models that describe the motion of antiferromagnetic domain walls, have neglected the intrinsic spin of the textured order parameter.
Antiferromagnetic ordering in MnF(salen)
NASA Astrophysics Data System (ADS)
Čižmár, Erik; Risset, Olivia N.; Wang, Tong; Botko, Martin; Ahir, Akhil R.; Andrus, Matthew J.; Park, Ju-Hyun; Abboud, Khalil A.; Talham, Daniel R.; Meisel, Mark W.; Brown, Stuart E.
2016-06-01
Antiferromagnetic order at {{T}\\text{N}}=23 K has been identified in Mn(III)F(salen), salen = H14C16N2O2, an S = 2 linear-chain system. Using single crystals, specific heat studies performed in magnetic fields up to 9 T revealed the presence of a field-independent cusp at the same temperature where 1H NMR studies conducted at 42 MHz observed dramatic changes in the spin-lattice relaxation time, T 1, and in the linewidths. Low-field (less than 0.1 T) magnetic susceptibility studies of single crystals and randomly-arranged microcrystalline samples reveal subtle features associated with the transition.
Strong correlation induced charge localization in antiferromagnets
Zhu, Zheng; Jiang, Hong-Chen; Qi, Yang; Tian, Chushun; Weng, Zheng-Yu
2013-01-01
The fate of a hole injected in an antiferromagnet is an outstanding issue of strongly correlated physics. It provides important insights into doped Mott insulators closely related to high-temperature superconductivity. Here, we report a systematic numerical study of t-J ladder systems based on the density matrix renormalization group. It reveals a surprising result for the single hole's motion in an otherwise well-understood undoped system. Specifically, we find that the common belief of quasiparticle picture is invalidated by the self-localization of the doped hole. In contrast to Anderson localization caused by disorders, the charge localization discovered here is an entirely new phenomenon purely of strong correlation origin. It results from destructive quantum interference of novel signs picked up by the hole, and since the same effect is of a generic feature of doped Mott physics, our findings unveil a new paradigm which may go beyond the single hole doped system. PMID:24002668
Antiferromagnetic ordering in MnF(salen).
Čižmár, Erik; Risset, Olivia N; Wang, Tong; Botko, Martin; Ahir, Akhil R; Andrus, Matthew J; Park, Ju-Hyun; Abboud, Khalil A; Talham, Daniel R; Meisel, Mark W; Brown, Stuart E
2016-06-15
Antiferromagnetic order at [Formula: see text] K has been identified in Mn(III)F(salen), salen = H14C16N2O2, an S = 2 linear-chain system. Using single crystals, specific heat studies performed in magnetic fields up to 9 T revealed the presence of a field-independent cusp at the same temperature where (1)H NMR studies conducted at 42 MHz observed dramatic changes in the spin-lattice relaxation time, T 1, and in the linewidths. Low-field (less than 0.1 T) magnetic susceptibility studies of single crystals and randomly-arranged microcrystalline samples reveal subtle features associated with the transition. PMID:27160792
Magnetoelectric effect in simple collinear antiferromagnetic spinels
NASA Astrophysics Data System (ADS)
Saha, Rana; Ghara, Somnath; Suard, Emmanuelle; Jang, Dong Hyun; Kim, Kee Hoon; Ter-Oganessian, N. V.; Sundaresan, A.
2016-07-01
We report the discovery of the linear magnetoelectric effect in a family of spinel oxides, C o3O4 and Mn B2O4 (B =Al ,Ga) with simple collinear antiferromagnetic spin structure. An external magnetic field induces a dielectric anomaly at TN, accompanied by the generation of electric polarization that varies linearly with magnetic field. Magnetization and magnetoelectric measurements on a single crystal of MnG a2O4 together with a phenomenological theory suggest that the easy axis direction is [111] with the corresponding magnetic symmetry R 3¯'m' . The proposed theoretical model of single-ion contribution of magnetic ions located in a noncentrosymmetric crystal environment stands for a generic mechanism for observing magnetoelectric effects in these and other similar materials.
Antiferromagnetism in EuCu_{2}As_{2} and EuCu_{1.82}Sb_{2} single crystals
Anand, V. K.; Johnston, D. C.
2015-05-07
Single crystals of EuCu_{2}As_{2} and EuCu_{2}Sb_{2} were grown from CuAs and CuSb self-flux, respectively. The crystallographic, magnetic, thermal, and electronic transport properties of the single crystals were investigated by room-temperature x-ray diffraction (XRD), magnetic susceptibility χ versus temperature T, isothermal magnetization M versus magnetic field H, specific heat C_{p}(T), and electrical resistivity ρ(T) measurements. EuCu_{2}As_{2} crystallizes in the body-centered tetragonal ThCr_{2}Si_{2}-type structure (space group I4/mmm), whereas EuCu_{2}Sb_{2} crystallizes in the related primitive tetragonal CaBe_{2}Ge_{2}-type structure (space group P4/nmm). The energy-dispersive x-ray spectroscopy and XRD data for the EuCu_{2}Sb_{2} crystals showed the presence of vacancies on the Cu sites, yielding the actual composition EuCu_{1.82}Sb_{2}. The ρ(T) and C_{p}(T) data reveal metallic character for both EuCu_{2}As_{2} and EuCu_{1.82}Sb_{2}. Antiferromagnetic (AFM) ordering is indicated from the χ(T),C_{p}(T), and ρ(T) data for both EuCu_{2}As_{2} (T_{N} = 17.5 K) and EuCu_{1.82}Sb_{2} (T_{N} = 5.1 K). In EuCu_{1.82}Sb_{2}, the ordered-state χ(T) and M(H) data suggest either a collinear A-type AFM ordering of Eu^{+2} spins S = 7/2 or a planar noncollinear AFM structure, with the ordered moments oriented in the tetragonal ab plane in either case. This ordered-moment orientation for the A-type AFM is consistent with calculations with magnetic dipole interactions. As a result, the anisotropic χ(T) and isothermal M(H) data for EuCu_{2}As_{2}, also containing Eu^{+2} spins S = 7/2, strongly deviate from the predictions of molecular field theory for collinear AFM ordering and the
NASA Astrophysics Data System (ADS)
Bandiera, S.; Sousa, R. C.; Auffret, S.; Rodmacq, B.; Dieny, B.
2012-08-01
Synthetic antiferromagnets are of great interest as reference layers in magnetic tunnel junctions since they allow decreasing the dipolar coupling between the two magnetic electrodes and exhibit larger pinning fields than single reference layers. In this letter, we investigate the effect of the insertion of an ultrathin Pt layer in contact with the Ru spacer in synthetic antiferromagnets with perpendicular magnetic anisotropy. Surprisingly, for Ru thickness below 0.75 nm, the antiferromagnetic coupling amplitude through Ru first increases upon Pt insertion up to a critical Pt thickness (˜0.25 nm) above which coupling decreases. In addition, the corresponding increase of perpendicular magnetic anisotropy enhances the thermal stability of the structure.
Antiferromagnetism in Pr3In: Singlet/triplet physics withfrustration
Christianson, A.D.; Lawrence, J.M.; Zarestky, J.L.; Suzuki, H.; Thompson, J.D.; Hundley, M.F.; Sarrao, J.L.; Booth, C.H.; Antonio, D.; Cornelius, A.L.
2004-11-18
We present neutron diffraction, magnetic susceptibility and specific heat data for a single-crystal sample of the cubic (Cu{sub 3}Au structure) compound Pr{sub 3}In. This compound is believed to have a singlet ({Lambda}{sub 1}) groundstate and a low-lying triplet ({Lambda}{sub 4}) excited state. In addition, nearest-neighbor antiferromagnetic interactions are frustrated in this structure. Antiferromagnetic order occurs below T{sub N} = 12K with propagation vector (0, 0, 0.5 {center_dot}{delta}) where {delta} {approx} 1/12. The neutron diffraction results can be approximated with the following model: ferromagnetic sheets from each of the three Pr sites alternate in sign along the propagation direction with a twelve-unit-cell square-wave modulation. The three moments of the unit cell of 1 {micro}{sub B} magnitude are aligned so as to sum to zero as expected for nearest-neighbor antiferromagnetic interactions on a triangle. The magnetic susceptibility indicates that in addition to the antiferromagnetic transition at 12K, there is a transition near 70K below which there is a small (0.005 {micro}{sub B}) ferromagnetic moment. There is considerable field and sample dependence to these transitions. The specific heat data show almost no anomaly at T{sub N} = 12K. This may be a consequence of the induced moment in the {Lambda}{sub 1} singlet, but may also be a sample-dependent effect.
Electric voltage generation by antiferromagnetic dynamics
NASA Astrophysics Data System (ADS)
Yamane, Yuta; Ieda, Jun'ichi; Sinova, Jairo
2016-05-01
We theoretically demonstrate dc and ac electric voltage generation due to spin motive forces originating from domain wall motion and magnetic resonance, respectively, in two-sublattice antiferromagnets. Our theory accounts for the canting between the sublattice magnetizations, the nonadiabatic electron spin dynamics, and the Rashba spin-orbit coupling, with the intersublattice electron dynamics treated as a perturbation. This work suggests a way to observe and explore the dynamics of antiferromagnetic textures by electrical means, an important aspect in the emerging field of antiferromagnetic spintronics, where both manipulation and detection of antiferromagnets are needed.
Quantum Optomechanics of a Bose-Einstein Antiferromagnet
Jing, H.; Goldbaum, D. S.; Buchmann, L.; Meystre, P.
2011-06-03
We investigate the cavity optomechanical properties of an antiferromagnetic Bose-Einstein condensate, where the role of the mechanical element is played by spin-wave excitations. We show how this system can be described by a single rotor that can be prepared deep in the quantum regime under realizable experimental conditions. This system provides a bottom-up realization of dispersive rotational optomechanics, and opens the door to the direct observation of quantum spin fluctuations.
Antiferromagnetism and Kondo screening on a honeycomb lattice
NASA Astrophysics Data System (ADS)
Lin, Heng-Fu; Hong-Shuai, Tao; Guo, Wen-Xiang; Liu, Wu-Ming
2015-05-01
Magnetic adatoms in the honeycomb lattice have received tremendous attention due to the interplay between Ruderman-Kittel-Kasuya-Yosida interaction and Kondo coupling leading to very rich physics. Here we study the competition between the antiferromagnetism and Kondo screening of local moments by the conduction electrons on the honeycomb lattice using the determinant quantum Monte Carlo method. While changing the interband hybridization V, we systematically investigate the antiferromagnetic-order state and the Kondo singlet state transition, which is characterized by the behavior of the local moment, antiferromagnetic structure factor, and the short range spin-spin correlation. The evolution of the single particle spectrum are also calculated as a function of hybridization V, we find that the system presents a small gap in the antiferromagnetic-order region and a large gap in the Kondo singlet region in the Fermi level. We also find that the localized and itinerant electrons coupling leads to the midgap states in the conduction band in the Fermi level at very small V. Moreover, the formation of antiferromagnetic order and Kondo singlet are studied as on-site interaction U or temperature T increasing, we have derived the phase diagrams at on-site interaction U (or temperature T) and hybridization V plane. Project supported by the National Key Basic Research Special Foundation of China (Grants Nos. 2011CB921502 and 2012CB821305), the National Natural Science Foundation of China (Grants Nos. 61227902, 61378017, and 11434015), the State Key Laboratory for Quantum Optics and Quantum Optical Devices, China (Grant No. KF201403).
Spatially anisotropic Heisenberg kagome antiferromagnet
NASA Astrophysics Data System (ADS)
Apel, W.; Yavors'kii, T.; Everts, H.-U.
2007-04-01
In the search for spin-1/2 kagome antiferromagnets, the mineral volborthite has recently been the subject of experimental studies (Hiroi et al 2001 J. Phys. Soc. Japan 70 3377; Fukaya et al 2003 Phys. Rev. Lett. 91 207603; Bert et al 2004 J. Phys.: Condens. Matter 16 S829; Bert et al 2005 Phys. Rev. Lett. 95 087203). It has been suggested that the magnetic properties of this material are described by a spin-1/2 Heisenberg model on the kagome lattice with spatially anisotropic exchange couplings. We report on investigations of the {\\mathrm {Sp}}(\\mathcal {N}) symmetric generalization of this model in the large \\mathcal {N} limit. We obtain a detailed description of the dependence of possible ground states on the anisotropy and on the spin length S. A fairly rich phase diagram with a ferrimagnetic phase, incommensurate phases with and without long-range order and a decoupled chain phase emerges.
Incommensurate to commensurate antiferromagnetism in CeRhAl4Si2 : An 27Al NMR study
NASA Astrophysics Data System (ADS)
Sakai, H.; Hattori, T.; Tokunaga, Y.; Kambe, S.; Ghimire, N. J.; Ronning, F.; Bauer, E. D.; Thompson, J. D.
2016-01-01
27Al nuclear magnetic resonance (NMR) experiments have been performed on a single crystal of CeRhAl4Si2 , which is an antiferromagnetic Kondo-lattice compound with successive antiferromagnetic transitions of TN 1=14 K and TN 2=9 K at zero external field. In the paramagnetic state, the Knight shifts, quadrupolar frequency, and asymmetric parameter of electrical field gradient on the Al sites have been determined, which have local orthorhombic symmetry. The transferred hyperfine coupling constants are also determined. Analysis of the NMR spectra indicates that a commensurate antiferromagnetic structure exists below TN 2, but an incommensurate modulation of antiferromagnetic moments is present in the antiferromagnetic state between TN 1 and TN 2. The spin-lattice relaxation rate suggests that the 4 f electrons behave as local moments at temperatures above TN 1.
Magnetostatic interactions in antiferromagnetically coupled patterned media.
Deng, S; Aung, K O; Piramanayagam, S N; Sbiaa, R
2011-03-01
In an array of closely spaced magnetic islands as in patterned media, magnetostatic interactions play a major role in widening the switching field distribution and reducing the thermal stability. Patterned antiferromagnetically coupled (AFC) media provide interesting systems for studying the effect of magnetostatic interactions on the reversal of closely spaced AFC bits in an array, as AFC structure helps to reduce the remanent magnetization (M(r)), leading to reduced magnetostatic interactions. Here, we study the magnetic reversal of single domain-patterned AFC CoCrPt:oxide bilayer system with perpendicular magnetic anisotropy, by imaging the remanence state of the bits after the application of a magnetic field with magnetic force microscopy (MFM). The influence of magnetostatic fields from the neighboring bits on the switching field distribution (SFD) for an entity in a patterned media is studied by varying the stabilizing layer thickness of the AFC structure and bit spacing. We observe a distinct increase in stability and coercivity with an increase in stabilizing layer thickness for the 40 nm spaced bits. This demonstrates the effectiveness of the AFC structure for reducing magnetostatic interactions in patterned media, such that high thermal stability can be achieved by the reduced M(r), without writability issues. PMID:21449425
Solitonlike magnetization textures in noncollinear antiferromagnets
NASA Astrophysics Data System (ADS)
Ulloa, Camilo; Nunez, A. S.
2016-04-01
We show that proper control of magnetization textures can be achieved in noncollinear antiferromagnets. This opens the versatile toolbox of domain-wall manipulation in the context of a different family of materials. In this way, we show that noncollinear antiferromagnets are a good prospect for applications in the context of antiferromagnetic spintronics. As in many noncollinear antiferromagnets, the order parameter field takes values in SO(3). By performing a gradient expansion in the energy functional we derive an effective theory that accounts for the physics of the magnetization of long-wavelength excitations. We apply our formalism to static and dynamic textures such as domain walls and localized oscillations, and identify topologically protected textures that are spatially localized. Our results are applicable to the exchange-bias materials Mn3X , with X =Ir,Rh,Pt .
Spin-Hall effects in metallic antiferromagnets
NASA Astrophysics Data System (ADS)
Zhang, Wei
Materials possessing new parameters for efficient and tunable spin Hall effects are being explored, among which antiferromagnets have become one of the most promising candidates. Two distinct properties of antiferromagnets are the microscopic spin magnetic moment ordering and the intrinsic anisotropy. Thus the natural question arises whether these two unique features of antiferromagnets can become new degrees of freedom for tuning their spin Hall effects. We performed experimental studies using spin pumping and inverse spin Hall detection on prototypical CuAu-I-type metallic antiferromagnets, PtMn, IrMn, PdMn, and FeMn, in which we observed increasing spin Hall effects for the alloys with heavier elements included. In particular, PtMn shows a large spin Hall effect that is comparable to Pt. We also demonstrated that the spin transfer torques from the antiferromagnets are large enough to excite ferromagnetic resonance of an adjacent ferromagnetic layer. We conclude that the sign and magnitude of the spin Hall effects in these antiferromagnets are determined by the atomic spin-orbit coupling of the heavy elements (e.g. Pt and Ir) as well as the large spin magnetic moments of Mn. In addition, by using epitaxial growth, we investigated the influence of the different crystalline and magnetic orientations on the anisotropic spin Hall effects of these antiferromagnets. Most of the experimental results were further corroborated by first-principles calculations, which determine the intrinsic spin Hall effect contribution and suggest pronounced anisotropies. Thus metallic antiferromagnets may become an active component for manipulating spin dependent transport properties in spintronic concepts. Work at Argonne was supported by the U.S. DOE, OS, Materials Sciences and Engineering Division. Work at Center for Nanoscale Materials was supported by DOE, OS-BES (DE-AC02-06CH11357). Work at Julich was supported by SPP 1538 Programme of the DFG.
Constructing a magnetic handle for antiferromagnetic manganites
NASA Astrophysics Data System (ADS)
Glavic, Artur; Dixit, Hemant; Cooper, Valentino R.; Aczel, Adam A.
2016-04-01
An intrinsic property of antiferromagnetic materials is the compensation of the magnetic moments from the individual atoms that prohibits the direct interaction of the spin lattice with an external magnetic field. To overcome this limitation we have created artificial spin structures by heteroepitaxy between two bulk antiferromagnets SrMnO3 and NdMnO3. Here, we demonstrate that charge transfer at the interface results in the creation of thin ferromagnetic layers adjacent to A -type antiferromagnetism in thick NdMnO3 layers. A novel interference based neutron diffraction technique and polarized neutron reflectometry are used to confirm the presence of ferromagnetism in the SrMnO3 layers and to probe the relative alignment of antiferromagnetic spins induced by the coupling at the ferro- to antiferromagnet interface. A density functional theory analysis of the driving forces for the exchange reveals strong ferromagnetic interfacial coupling through quantifiable short range charge transfer. These results confirm a layer-by-layer control of magnetic arrangements that constitutes a promising step on a path towards isothermal magnetic control of antiferromagnetic arrangements as would be necessary in spin-based heterostructures like multiferroic devices.
Roughness effects in uncompensated antiferromagnets
Charilaou, M.; Hellman, F.
2015-02-28
Monte Carlo simulations show that roughness in uncompensated antiferromagnets decreases not just the surface magnetization but also the net magnetization and particularly strongly affects the temperature dependence. In films with step-type roughness, each step creates a new compensation front that decreases the global net magnetization. The saturation magnetization decreases non-monotonically with increasing roughness and does not scale with the surface area. Roughness in the form of surface vacancies changes the temperature-dependence of the magnetization; when only one surface has vacancies, the saturation magnetization will decrease linearly with surface occupancy, whereas when both surfaces have vacancies, the magnetization is negative and exhibits a compensation point at finite temperature, which can be tuned by controlling the occupancy. Roughness also affects the spin-texture of the surfaces due to long-range dipolar interactions and generates non-collinear spin configurations that could be used in devices to produce locally modified exchange bias. These results explain the strongly reduced magnetization found in magnetometry experiments and furthers our understanding of the temperature-dependence of exchange bias.
Anomalous Hall effect in the noncollinear antiferromagnet Mn5Si3
NASA Astrophysics Data System (ADS)
Sürgers, Christoph; Kittler, Wolfram; Wolf, Thomas; Löhneysen, Hilbert v.
2016-05-01
Metallic antiferromagnets with noncollinear orientation of magnetic moments provide a playground for investigating spin-dependent transport properties by analysis of the anomalous Hall effect. The intermetallic compound Mn5Si3 is an intinerant antiferromagnet with collinear and noncollinear magnetic structures due to Mn atoms on two inequivalent lattice sites. Here, magnetotransport measurements on polycrstalline thin films and a single crystal are reported. In all samples, an additional contribution to the anomalous Hall effect attributed to the noncollinear arrangment of magnetic moments is observed. Furthermore, an additional magnetic phase between the noncollinear and collinear regimes above a metamagnetic transition is resolved in the single crystal by the anomalous Hall effect.
An itinerant antiferromagnetic metal without magnetic constituents
Svanidze, E.; Wang, Jiakui K.; Besara, T.; Liu, L.; Huang, Q.; Siegrist, T.; Frandsen, B.; Lynn, J. W.; Nevidomskyy, Andriy H.; Gamża, Monika B.; Aronson, M. C.; Uemura, Y. J.; Morosan, E.
2015-07-13
The origin of magnetism in metals has been traditionally discussed in two diametrically opposite limits: itinerant and local moments. Surprisingly, there are very few known examples of materials that are close to the itinerant limit, and their properties are not universally understood. In the case of the two such examples discovered several decades ago, the itinerant ferromagnets ZrZn_{2} and Sc_{3}In, the understanding of their magnetic ground states draws on the existence of 3d electrons subject to strong spin fluctuations. Similarly, in Cr, an elemental itinerant antiferromagnet with a spin density wave ground state, its 3d electron character has been deemed crucial to it being magnetic. Here, we report evidence for an itinerant antiferromagnetic metal with no magnetic constituents: TiAu. Antiferromagnetic order occurs below a Néel temperature of 36 K, about an order of magnitude smaller than in Cr, rendering the spin fluctuations in TiAu more important at low temperatures. In conclusion, this itinerant antiferromagnet challenges the currently limited understanding of weak itinerant antiferromagnetism, while providing insights into the effects of spin fluctuations in itinerant–electron systems.
An itinerant antiferromagnetic metal without magnetic constituents
Svanidze, E.; Wang, Jiakui K.; Besara, T.; Liu, L.; Huang, Q.; Siegrist, T.; Frandsen, B.; Lynn, J. W.; Nevidomskyy, Andriy H.; Gamża, Monika B.; et al
2015-07-13
The origin of magnetism in metals has been traditionally discussed in two diametrically opposite limits: itinerant and local moments. Surprisingly, there are very few known examples of materials that are close to the itinerant limit, and their properties are not universally understood. In the case of the two such examples discovered several decades ago, the itinerant ferromagnets ZrZn2 and Sc3In, the understanding of their magnetic ground states draws on the existence of 3d electrons subject to strong spin fluctuations. Similarly, in Cr, an elemental itinerant antiferromagnet with a spin density wave ground state, its 3d electron character has been deemedmore » crucial to it being magnetic. Here, we report evidence for an itinerant antiferromagnetic metal with no magnetic constituents: TiAu. Antiferromagnetic order occurs below a Néel temperature of 36 K, about an order of magnitude smaller than in Cr, rendering the spin fluctuations in TiAu more important at low temperatures. In conclusion, this itinerant antiferromagnet challenges the currently limited understanding of weak itinerant antiferromagnetism, while providing insights into the effects of spin fluctuations in itinerant–electron systems.« less
An itinerant antiferromagnetic metal without magnetic constituents
Svanidze, E.; Wang, Jiakui K.; Besara, T.; Liu, L.; Huang, Q.; Siegrist, T.; Frandsen, B.; Lynn, J. W.; Nevidomskyy, Andriy H.; Gamża, Monika B.; Aronson, M. C.; Uemura, Y. J.; Morosan, E.
2015-01-01
The origin of magnetism in metals has been traditionally discussed in two diametrically opposite limits: itinerant and local moments. Surprisingly, there are very few known examples of materials that are close to the itinerant limit, and their properties are not universally understood. In the case of the two such examples discovered several decades ago, the itinerant ferromagnets ZrZn2 and Sc3In, the understanding of their magnetic ground states draws on the existence of 3d electrons subject to strong spin fluctuations. Similarly, in Cr, an elemental itinerant antiferromagnet with a spin density wave ground state, its 3d electron character has been deemed crucial to it being magnetic. Here, we report evidence for an itinerant antiferromagnetic metal with no magnetic constituents: TiAu. Antiferromagnetic order occurs below a Néel temperature of 36 K, about an order of magnitude smaller than in Cr, rendering the spin fluctuations in TiAu more important at low temperatures. This itinerant antiferromagnet challenges the currently limited understanding of weak itinerant antiferromagnetism, while providing insights into the effects of spin fluctuations in itinerant–electron systems. PMID:26166042
Antiferromagnetic Domain Wall Motion Driven by Spin-Orbit Torques.
Shiino, Takayuki; Oh, Se-Hyeok; Haney, Paul M; Lee, Seo-Won; Go, Gyungchoon; Park, Byong-Guk; Lee, Kyung-Jin
2016-08-19
We theoretically investigate the dynamics of antiferromagnetic domain walls driven by spin-orbit torques in antiferromagnet-heavy-metal bilayers. We show that spin-orbit torques drive antiferromagnetic domain walls much faster than ferromagnetic domain walls. As the domain wall velocity approaches the maximum spin-wave group velocity, the domain wall undergoes Lorentz contraction and emits spin waves in the terahertz frequency range. The interplay between spin-orbit torques and the relativistic dynamics of antiferromagnetic domain walls leads to the efficient manipulation of antiferromagnetic spin textures and paves the way for the generation of high frequency signals from antiferromagnets. PMID:27588878
Antiferromagnetic phases of the Kondo lattice
NASA Astrophysics Data System (ADS)
Eder, R.; Grube, K.; Wróbel, P.
2016-04-01
We discuss the paramagnetic and Néel-ordered phases of the Kondo lattice Hamiltonian on the two-dimensional square lattice by means of bond fermions. In the doped case we find two antiferromagnetic solutions, the first one with small ordered moment, heavy bands, and an antiferromagnetically folded large Fermi surface—i.e., including the localized spins—the second one with large ordered moment, light bands, and an antiferromagnetically folded conduction electron-only Fermi surface. The zero temperature phase diagram as a function of Kondo coupling and conduction electron density shows first- and second-order transition lines between the three different phases and agrees qualitatively with previous numerical studies. We compare to experiments on CeRh1 -xCoxIn5 and find qualitative agreement.
Antiferromagnetic Spin Wave Field-Effect Transistor.
Cheng, Ran; Daniels, Matthew W; Zhu, Jian-Gang; Xiao, Di
2016-01-01
In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field-effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. Our findings open up the exciting possibility of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale. PMID:27048928
Spinon dynamics in quantum integrable antiferromagnets
NASA Astrophysics Data System (ADS)
Vlijm, R.; Caux, J.-S.
2016-05-01
The excitations of the Heisenberg antiferromagnetic spin chain in zero field are known as spinons. As pairwise-created fractionalized excitations, spinons are important in the understanding of inelastic neutron scattering experiments in (quasi-)one-dimensional materials. In the present paper, we consider the real space-time dynamics of spinons originating from a local spin flip on the antiferromagnetic ground state of the (an)isotropic Heisenberg spin-1/2 model and the Babujan-Takhtajan spin-1 model. By utilizing algebraic Bethe ansatz methods at finite system size to compute the expectation value of the local magnetization and spin-spin correlations, spinons are visualized as propagating domain walls in the antiferromagnetic spin ordering with anisotropy dependent behavior. The spin-spin correlation after the spin flip displays a light cone, satisfying the Lieb-Robinson bound for the propagation of correlations at the spinon velocity.
Quantized spin waves in antiferromagnetic Heisenberg chains.
Wieser, R; Vedmedenko, E Y; Wiesendanger, R
2008-10-24
The quantized stationary spin wave modes in one-dimensional antiferromagnetic spin chains with easy axis on-site anisotropy have been studied by means of Landau-Lifshitz-Gilbert spin dynamics. We demonstrate that the confined antiferromagnetic chains show a unique behavior having no equivalent, neither in ferromagnetism nor in acoustics. The discrete energy dispersion is split into two interpenetrating n and n' levels caused by the existence of two sublattices. The oscillations of individual sublattices as well as the standing wave pattern strongly depend on the boundary conditions. Particularly, acoustical and optical antiferromagnetic spin waves in chains with boundaries fixed (pinned) on different sublattices can be found, while an asymmetry of oscillations appears if the two pinned ends belong to the same sublattice. PMID:18999780
Ferroelectric polarization in antiferromagnetically coupled ferromagnetic film
NASA Astrophysics Data System (ADS)
Gareeva, Z. V.; Mazhitova, F. A.; Doroshenko, R. A.
2016-09-01
We report the influence of interface antiferromagnetic coupling on magnetoelectric properties of ferromagnetic bi-layers. Electric polarization arising at magnetic ingomogeneity in bi-layered ferromagnetic structure with antiferromagnetic coupling at interface in applied magnetic field has been explored. Diagrams representing dependences of electric polarization on magnetic field P(H) have been constructed for two magnetic field geometries (in-plane and out-of plane fields). It has been found out that P(H) dependences demonstrate non-monotonic behavior. Peculiarities of polarization in an in-plane-oriented magnetic field have been explained by magnetization processes. It has been shown that a variety of magnetic configurations of Bloch, Neel and mixed Bloch-Neel types can be realized in antiferromagnetically coupled film due to cubic anisotropy contribution. In the area of Bloch magnetic configuration electric polarization vanishes. The critical values of magnetic fields suppressing polarization have been estimated.
Antiferromagnetic Spin Wave Field-Effect Transistor
Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; Xiao, Di
2016-04-06
In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. In conclusion, our findings open up the exciting possibilitymore » of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale.« less
Antiferromagnetic Spin Wave Field-Effect Transistor
Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; Xiao, Di
2016-01-01
In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field-effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. Our findings open up the exciting possibility of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale. PMID:27048928
Antiferromagnetic Spin Wave Field-Effect Transistor
NASA Astrophysics Data System (ADS)
Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; Xiao, Di
2016-04-01
In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field-effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. Our findings open up the exciting possibility of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale.
Paramagnetic and Antiferromagnetic Spin Seebeck Effect
NASA Astrophysics Data System (ADS)
Wu, Stephen
We report on the observation of the longitudinal spin Seebeck effect in both antiferromagnetic and paramagnetic insulators. By using a microscale on-chip local heater, it is possible to generate a large thermal gradient confined to the chip surface without a large increase in the total sample temperature. This technique allows us to easily access low temperatures (200 mK) and high magnetic fields (14 T) through conventional dilution refrigeration and superconducting magnet setups. By exploring this regime, we detect the spin Seebeck effect through the spin-flop transition in antiferromagnetic MnF2 when a large magnetic field (>9 T) is applied along the easy axis direction. Using the same technique, we are also able to resolve a spin Seebeck effect from the paramagnetic phase of geometrically frustrated antiferromagnet Gd3Ga5O12 (gadolinium gallium garnet) and antiferromagnetic DyScO3 (DSO). Since these measurements occur above the ordering temperatures of these two materials, short-range magnetic order is implicated as the cause of the spin Seebeck effect in these systems. The discovery of the spin Seebeck effect in these two materials classes suggest that both antiferromagnetic spin waves and spin excitations from short range magnetic order may be used to generate spin current from insulators and that the spin wave spectra of individual materials are highly important to the specifics of the longitudinal spin Seebeck effect. Since insulating antiferromagnets and paramagnets are far more common than the typical insulating ferrimagnetic materials used in spin Seebeck experiments, this discovery opens up a large new class of materials for use in spin caloritronic devices. All authors acknowledge support of the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division. The use of facilities at the Center for Nanoscale Materials, was supported by the U.S. DOE, BES under Contract No. DE-AC02-06CH11357.
Nonequilibrium dynamics in the antiferromagnetic Hubbard model
NASA Astrophysics Data System (ADS)
Sandri, Matteo; Fabrizio, Michele
2013-10-01
We investigate by means of the time-dependent Gutzwiller variational approach the out-of-equilibrium dynamics of an antiferromagnetic state evolved with the Hubbard model Hamiltonian after a sudden change of the repulsion strength U. We find that magnetic order survives more than what is expected on the basis of thermalization arguments, in agreement with recent dynamical mean field theory calculations. In addition, we find evidence of a dynamical transition for quenches to large values of U between a coherent antiferromagnet characterized by a finite quasiparticle residue to an incoherent one with vanishing residue, which finally turns into a paramagnet for even larger U.
Ground-state candidate for the classical dipolar kagome Ising antiferromagnet
NASA Astrophysics Data System (ADS)
Chioar, I. A.; Rougemaille, N.; Canals, B.
2016-06-01
We have investigated the low-temperature thermodynamic properties of the classical dipolar kagome Ising antiferromagnet using Monte Carlo simulations, in the quest for the ground-state manifold. In spite of the limitations of a single-spin-flip approach, we managed to identify certain ordering patterns in the low-temperature regime and we propose a candidate for this unknown state. This configuration presents some intriguing features and is fully compatible with the extrapolations of the at-equilibrium thermodynamic behavior sampled so far, making it a very likely choice for the dipolar long-range ordered state of the classical kagome Ising antiferromagnet.
Giant Anomalous Hall Effect in the Chiral Antiferromagnet Mn3Ge
NASA Astrophysics Data System (ADS)
Kiyohara, Naoki; Tomita, Takahiro; Nakatsuji, Satoru
2016-06-01
The external field control of antiferromagnetism is a significant subject both for basic science and technological applications. As a useful macroscopic response to detect magnetic states, the anomalous Hall effect (AHE) is known for ferromagnets, but it has never been observed in antiferromagnets until the recent discovery in Mn3Sn . Here we report another example of the AHE in a related antiferromagnet, namely, in the hexagonal chiral antiferromagnet Mn3Ge . Our single-crystal study reveals that Mn3Ge exhibits a giant anomalous Hall conductivity |σx z|˜60 Ω-1 cm-1 at room temperature and approximately 380 Ω-1 cm-1 at 5 K in zero field, reaching nearly half of the value expected for the quantum Hall effect per atomic layer with Chern number of unity. Our detailed analyses on the anisotropic Hall conductivity indicate that in comparison with the in-plane-field components |σx z| and |σz y|, which are very large and nearly comparable in size, we find |σy x| obtained in the field along the c axis to be much smaller. The anomalous Hall effect shows a sign reversal with the rotation of a small magnetic field less than 0.1 T. The soft response of the AHE to magnetic field should be useful for applications, for example, to develop switching and memory devices based on antiferromagnets.
Complex antiferromagnetic order in the Cd6 R approximants to the i- R-Cd quasicrystals
NASA Astrophysics Data System (ADS)
Kreyssig, A.; Beutier, G.; Hoffmann, J.-U.; Kong, T.; Kim, M. G.; Tucker, G. S.; Ueland, B. G.; Hiroto, T.; Liu, D.; Yamada, T.; Boissieu, M. De; Tamura, R.; Bud'Ko, S. L.; Canfield, P. C.; Goldman, A. I.
2014-03-01
The observation of antiferromagnetic order in the Cd6 R (R = rare earths) approximants to the recently discovered related i- R-Cd quasicrystals provides new and exciting opportunities to unravel the nature of magnetism in these materials. We present single-crystal studies employing x-ray and neutron scattering that revealed complex antiferromagnetism in the Cd6 R approximants. Resolution-limited magnetic Bragg peaks have been observed at lattice points forbidden by the center-symmetry and at incommensurate positions demonstrating long-range antiferromagnetic correlations between the R moments. The work at the Ames Laboratory was supported by US DOE, Office of Basic Energy Sciences, DMSE, contract DE-AC02-07CH11358. Work at the Tokyo University of Science was supported by KAKENHI (Grant No. 20045017).
NaSrCo2F7, a Co(2+) pyrochlore antiferromagnet.
Krizan, J W; Cava, R J
2015-07-29
We report the crystal growth, by the Bridgeman-Stockbarger method, and the basic magnetic properties of a new cobalt-based pyrochlore, NaSrCo2F7. Single-crystal structure determination shows that Na and Sr are completely disordered on the non-magnetic large atom A sites, while magnetic [Formula: see text] Co(2+) fully occupies the pyrochlore lattice B sites. NaSrCo2F7 displays strong antiferromagnetic interactions ([Formula: see text]), a large effective moment ([Formula: see text]), and no spin freezing until 3 K. Thus, NaSrCo2F7 is a geometrically frustrated antiferromagnet with a frustration index [Formula: see text]. Ac susceptibility, dc susceptibility, and heat capacity are utilized to characterize the spin freezing. We argue that NaSrCo2F7 and the related material NaCaCo2F7 are examples of frustrated pyrochlore antiferromagnets with weak bond disorder. PMID:26154596
NASA Astrophysics Data System (ADS)
Merodio, P.; Kalitsov, A.; Chshiev, M.; Velev, J.
2016-06-01
Based on model calculations, we predict a magnetoelectric tunneling electroresistance effect in multiferroic tunnel junctions consisting of ferromagnetic electrodes and magnetoelectric antiferromagnetic barriers. Switching of the antiferromagnetic order parameter in the barrier in applied electric field by means of the magnetoelectric coupling leads to a substantial change of the resistance of the junction. The effect is explained in terms of the switching of the orientations of local magnetizations at the barrier interfaces affecting the spin-dependent interface transmission probabilities. Magnetoelectric multiferroic materials with finite ferroelectric polarization exhibit an enhanced resistive change due to polarization-induced spin-dependent screening. These results suggest that devices with active barriers based on single-phase magnetoelectric antiferromagnets represent an alternative nonvolatile memory concept.
Direct measurement of antiferromagnetic domain fluctuations.
Shpyrko, O G; Isaacs, E D; Logan, J M; Feng, Yejun; Aeppli, G; Jaramillo, R; Kim, H C; Rosenbaum, T F; Zschack, P; Sprung, M; Narayanan, S; Sandy, A R
2007-05-01
Measurements of magnetic noise emanating from ferromagnets owing to domain motion were first carried out nearly 100 years ago, and have underpinned much science and technology. Antiferromagnets, which carry no net external magnetic dipole moment, yet have a periodic arrangement of the electron spins extending over macroscopic distances, should also display magnetic noise. However, this must be sampled at spatial wavelengths of the order of several interatomic spacings, rather than the macroscopic scales characteristic of ferromagnets. Here we present a direct measurement of the fluctuations in the nanometre-scale superstructure of spin- and charge-density waves associated with antiferromagnetism in elemental chromium. The technique used is X-ray photon correlation spectroscopy, where coherent X-ray diffraction produces a speckle pattern that serves as a 'fingerprint' of a particular magnetic domain configuration. The temporal evolution of the patterns corresponds to domain walls advancing and retreating over micrometre distances. This work demonstrates a useful measurement tool for antiferromagnetic domain wall engineering, but also reveals a fundamental finding about spin dynamics in the simplest antiferromagnet: although the domain wall motion is thermally activated at temperatures above 100 K, it is not so at lower temperatures, and indeed has a rate that saturates at a finite value-consistent with quantum fluctuations-on cooling below 40 K. PMID:17476263
Indirect control of antiferromagnetic domain walls with spin current.
Wieser, R; Vedmedenko, E Y; Wiesendanger, R
2011-02-11
The indirect controlled displacement of an antiferromagnetic domain wall by a spin current is studied by Landau-Lifshitz-Gilbert spin dynamics. The antiferromagnetic domain wall can be shifted both by a spin-polarized tunnel current of a scanning tunneling microscope or by a current driven ferromagnetic domain wall in an exchange coupled antiferromagnetic-ferromagnetic layer system. The indirect control of antiferromagnetic domain walls opens up a new and promising direction for future spin device applications based on antiferromagnetic materials. PMID:21405493
Antiferromagnetism and superconductivity in the half-Heusler semimetal HoPdBi
Pavlosiuk, Orest; Kaczorowski, Dariusz; Fabreges, Xavier; Gukasov, Arsen; Wiśniewski, Piotr
2016-01-01
We observed the coexistence of superconductivity and antiferromagnetic order in the single-crystalline ternary pnictide HoPdBi, a plausible topological semimetal. The compound orders antiferromagnetically at TN = 1.9 K and exhibits superconductivity below Tc = 0.7 K, which was confirmed by magnetic, electrical transport and specific heat measurements. The specific heat shows anomalies corresponding to antiferromagnetic ordering transition and crystalline field effect, but not to superconducting transition. Single-crystal neutron diffraction indicates that the antiferromagnetic structure is characterized by the propagation vector. Temperature variation of the electrical resistivity reveals two parallel conducting channels of semiconducting and metallic character. In weak magnetic fields, the magnetoresistance exhibits weak antilocalization effect, while in strong fields and temperatures below 50 K it is large and negative. At temperatures below 7 K Shubnikov-de Haas oscillations with two frequencies appear in the resistivity. These oscillations have non-trivial Berry phase, which is a distinguished feature of Dirac fermions. PMID:26728755
Antiferromagnetism and superconductivity in the half-Heusler semimetal HoPdBi.
Pavlosiuk, Orest; Kaczorowski, Dariusz; Fabreges, Xavier; Gukasov, Arsen; Wiśniewski, Piotr
2016-01-01
We observed the coexistence of superconductivity and antiferromagnetic order in the single-crystalline ternary pnictide HoPdBi, a plausible topological semimetal. The compound orders antiferromagnetically at TN = 1.9 K and exhibits superconductivity below Tc = 0.7 K, which was confirmed by magnetic, electrical transport and specific heat measurements. The specific heat shows anomalies corresponding to antiferromagnetic ordering transition and crystalline field effect, but not to superconducting transition. Single-crystal neutron diffraction indicates that the antiferromagnetic structure is characterized by the propagation vector. Temperature variation of the electrical resistivity reveals two parallel conducting channels of semiconducting and metallic character. In weak magnetic fields, the magnetoresistance exhibits weak antilocalization effect, while in strong fields and temperatures below 50 K it is large and negative. At temperatures below 7 K Shubnikov-de Haas oscillations with two frequencies appear in the resistivity. These oscillations have non-trivial Berry phase, which is a distinguished feature of Dirac fermions. PMID:26728755
Order and topology in antiferromagnets with surfaces
NASA Astrophysics Data System (ADS)
Charilaou, Michalis; Hellman, Frances
2014-03-01
We show using Monte Carlo simulations and mean-field theory that the antiferromagnetic (AFM) magnetization, arising from uncompensated spins, exhibits a unique thermodynamic behavior that differs from that of ferromagnets or of the Néel vector. More importantly, the net uncompensated magnetization is lower than that of the surface due to finite size effects. This phenomenon can be is manifested in thin films but it is in fact the same even in infinite systems with free surfaces, suggesting a topological order in uncompensated antiferromagnets. Moreover, we investigate the effects of defects and roughness on the magnetization of AFM and show that with increasing roughness the magnetization decreases non-monotonically and reaches values of only a few percent. Thanks to DOE BES LBNL magnetism program and Swiss Federation for support.
Skyrmions in square-lattice antiferromagnets
NASA Astrophysics Data System (ADS)
Keesman, Rick; Raaijmakers, Mark; Baerends, A. E.; Barkema, G. T.; Duine, R. A.
2016-08-01
The ground states of square-lattice two-dimensional antiferromagnets with anisotropy in an external magnetic field are determined using Monte Carlo simulations and compared to theoretical analysis. We find a phase in between the spin-flop and spiral phase that shows strong similarity to skyrmions in ferromagnetic thin films. We show that this phase arises as a result of the competition between Zeeman and Dzyaloshinskii-Moriya interaction energies of the magnetic system. Moreover, we find that isolated (anti-)skyrmions are stabilized in finite-sized systems, even at higher temperatures. The existence of thermodynamically stable skyrmions in square-lattice antiferromagnets provides an appealing alternative over skyrmions in ferromagnets as data carriers.
Dimensional Reduction in Quantum Dipolar Antiferromagnets
NASA Astrophysics Data System (ADS)
Babkevich, P.; Jeong, M.; Matsumoto, Y.; Kovacevic, I.; Finco, A.; Toft-Petersen, R.; Ritter, C.; Mânsson, M.; Nakatsuji, S.; Rønnow, H. M.
2016-05-01
We report ac susceptibility, specific heat, and neutron scattering measurements on a dipolar-coupled antiferromagnet LiYbF4 . For the thermal transition, the order-parameter critical exponent is found to be 0.20(1) and the specific-heat critical exponent -0.25 (1 ) . The exponents agree with the 2D X Y /h4 universality class despite the lack of apparent two-dimensionality in the structure. The order-parameter exponent for the quantum phase transitions is found to be 0.35(1) corresponding to (2 +1 )D . These results are in line with those found for LiErF4 which has the same crystal structure, but largely different TN, crystal field environment and hyperfine interactions. Our results therefore experimentally establish that the dimensional reduction is universal to quantum dipolar antiferromagnets on a distorted diamond lattice.
Dimensional Reduction in Quantum Dipolar Antiferromagnets.
Babkevich, P; Jeong, M; Matsumoto, Y; Kovacevic, I; Finco, A; Toft-Petersen, R; Ritter, C; Månsson, M; Nakatsuji, S; Rønnow, H M
2016-05-13
We report ac susceptibility, specific heat, and neutron scattering measurements on a dipolar-coupled antiferromagnet LiYbF_{4}. For the thermal transition, the order-parameter critical exponent is found to be 0.20(1) and the specific-heat critical exponent -0.25(1). The exponents agree with the 2D XY/h_{4} universality class despite the lack of apparent two-dimensionality in the structure. The order-parameter exponent for the quantum phase transitions is found to be 0.35(1) corresponding to (2+1)D. These results are in line with those found for LiErF_{4} which has the same crystal structure, but largely different T_{N}, crystal field environment and hyperfine interactions. Our results therefore experimentally establish that the dimensional reduction is universal to quantum dipolar antiferromagnets on a distorted diamond lattice. PMID:27232040
Antiferromagnetic Ising Model in Hierarchical Networks
NASA Astrophysics Data System (ADS)
Cheng, Xiang; Boettcher, Stefan
2015-03-01
The Ising antiferromagnet is a convenient model of glassy dynamics. It can introduce geometric frustrations and may give rise to a spin glass phase and glassy relaxation at low temperatures [ 1 ] . We apply the antiferromagnetic Ising model to 3 hierarchical networks which share features of both small world networks and regular lattices. Their recursive and fixed structures make them suitable for exact renormalization group analysis as well as numerical simulations. We first explore the dynamical behaviors using simulated annealing and discover an extremely slow relaxation at low temperatures. Then we employ the Wang-Landau algorithm to investigate the energy landscape and the corresponding equilibrium behaviors for different system sizes. Besides the Monte Carlo methods, renormalization group [ 2 ] is used to study the equilibrium properties in the thermodynamic limit and to compare with the results from simulated annealing and Wang-Landau sampling. Supported through NSF Grant DMR-1207431.
Heisenberg antiferromagnet on the Husimi lattice
NASA Astrophysics Data System (ADS)
Liao, H. J.; Xie, Z. Y.; Chen, J.; Han, X. J.; Xie, H. D.; Normand, B.; Xiang, T.
2016-02-01
We perform a systematic study of the antiferromagnetic Heisenberg model on the Husimi lattice using numerical tensor-network methods based on projected entangled simplex states. The nature of the ground state varies strongly with the spin quantum number S . For S =1/2 , it is an algebraic (gapless) quantum spin liquid. For S =1 , it is a gapped, nonmagnetic state with spontaneous breaking of triangle symmetry (a trimerized simplex-solid state). For S =2 , it is a simplex-solid state with a spin gap and no symmetry breaking; both integer-spin simplex-solid states are characterized by specific degeneracies in the entanglement spectrum. For S =3/2 , and indeed for all spin values S ≥5/2 , the ground states have 120∘ antiferromagnetic order. In a finite magnetic field, we find that, irrespective of the value of S , there is always a plateau in the magnetization at m =1/3 .
Terahertz Antiferromagnetic Spin Hall Nano-Oscillator
NASA Astrophysics Data System (ADS)
Cheng, Ran; Xiao, Di; Brataas, Arne
2016-05-01
We consider the current-induced dynamics of insulating antiferromagnets in a spin Hall geometry. Sufficiently large in-plane currents perpendicular to the Néel order trigger spontaneous oscillations at frequencies between the acoustic and the optical eigenmodes. The direction of the driving current determines the chirality of the excitation. When the current exceeds a threshold, the combined effect of spin pumping and current-induced torques introduces a dynamic feedback that sustains steady-state oscillations with amplitudes controllable via the applied current. The ac voltage output is calculated numerically as a function of the dc current input for different feedback strengths. Our findings open a route towards terahertz antiferromagnetic spin-torque oscillators.
Terahertz Antiferromagnetic Spin Hall Nano-Oscillator.
Cheng, Ran; Xiao, Di; Brataas, Arne
2016-05-20
We consider the current-induced dynamics of insulating antiferromagnets in a spin Hall geometry. Sufficiently large in-plane currents perpendicular to the Néel order trigger spontaneous oscillations at frequencies between the acoustic and the optical eigenmodes. The direction of the driving current determines the chirality of the excitation. When the current exceeds a threshold, the combined effect of spin pumping and current-induced torques introduces a dynamic feedback that sustains steady-state oscillations with amplitudes controllable via the applied current. The ac voltage output is calculated numerically as a function of the dc current input for different feedback strengths. Our findings open a route towards terahertz antiferromagnetic spin-torque oscillators. PMID:27258884
Diffusive magnonic spin transport in antiferromagnetic insulators
NASA Astrophysics Data System (ADS)
Rezende, S. M.; Rodríguez-Suárez, R. L.; Azevedo, A.
2016-02-01
It has been shown recently that a layer of the antiferromagnetic insulator (AFI) NiO can be used to transport spin current between a ferromagnet (FM) and a nonmagnetic metal (NM). In the experiments one uses the microwave-driven ferromagnetic resonance in a FM layer to produce a spin pumped spin current that flows through an AFI layer and reaches a NM layer where it is converted into a charge current by means of the inverse spin Hall effect. Here we present a theory for the spin transport in an AFI that relies on the spin current carried by the diffusion of thermal antiferromagnetic magnons. The theory explains quite well the measured dependence of the voltage in the NM layer on the thickness of the NiO layer.
Itinerant antiferromagnetism of TiAl alloys
NASA Astrophysics Data System (ADS)
Petrişor, T.; Pop, I.; Giurgiu, A.; Farbaş, N.
1986-06-01
Magnetic susceptibility measurements of TiAl alloys are reported. Aluminium, by alloying, acts on the Néel temperature of pure titanium giving rise to a complicated phase diagram. A theoretical model, based on the itinerant antiferromagnetism model of chromium is proposed in order to explain the magnetic phase diagram of TiAl alloys. The experimental and theoretical magnetic phase diagram are in good agreement.
NASA Astrophysics Data System (ADS)
Jiang, Shan; Liu, Lian; Schütt, Michael; Hallas, Alannah M.; Shen, Bing; Tian, Wei; Emmanouilidou, Eve; Shi, Aoshuang; Luke, Graeme M.; Uemura, Yasutomo J.; Fernandes, Rafael M.; Ni, Ni
2016-05-01
We report the transport, thermodynamic, muon spin relaxation, and neutron study of the Ca0.74 (1 )La0.26 (1 ) (Fe1 -xCox )As2 single crystals, mapping out the temperature-doping level phase diagram. Upon Co substitution on the Fe site, the structural and magnetic phase transitions in this 112 compound are suppressed and superconductivity up to 20 K occurs. Our measurements of the superconducting and magnetic volume fractions show that these two phases coexist microscopically in the underdoped region, in contrast to the related Ca10(Pt3As8 )((Fe1 -xPtx )2As2 )5 (10-3-8) compound, where coexistence is absent. Supported by model calculations, we discuss the differences in the phase diagrams of the 112 and 10-3-8 compounds in terms of the FeAs interlayer coupling, whose strength is affected by the character of the spacer layer, which is metallic in the 112 compound and insulating in the 10-3-8 compound.
Enhanced ordering temperatures in antiferromagnetic manganite superlattices
May, Stephen J.; Robertson, Lee; Ryan, P J; Kim, J.-W.; Santos, Tiffany S.; Karapetrova, Evgenia; Zarestky, Jerel L.; Zhai, X.; Te velthuis, Suzanne G.; Eckstein, James N.; Bader, S. D.; Bhattacharya, Anand
2009-01-01
The disorder inherent to doping by cation substitution in the complex oxides can have profound effects on collective ordered states. Here, we demonstrate that cation-site ordering achieved via digital synthesis techniques can dramatically enhance the antiferromagnetic ordering temperatures of manganite films. Cation-ordered (LaMnO3)m/(SrMnO3)2m superlattices exhibit N el temperatures (TN) that are the highest of any La1-xSrxMnO3 compound, ~70 K greater than compositionally equivalent randomly doped La1/3Sr2/3MnO3. The antiferromagnetic order is A-type, consisting of in-plane double-exchange-mediated ferromagnetic sheets coupled antiferromagnetically along the out-of-plane direction. Via synchrotron x-ray scattering, we have discovered an in-plane structural modulation that reduces the charge itinerancy and hence the ordering temperature within the ferromagnetic sheets, thereby limiting TN. This modulation is mitigated and driven to long wavelengths by cation ordering, enabling the higher TN values of the superlattices. These results provide insight into how cation-site ordering can enhance cooperative behavior in oxides through subtle structural phenomena.
Enhanced ordering temperatures in antiferromagnetic manganite superlattices.
May, S. J.; Ryan, P. J.; Robertson, J. L.; Kim, J.-W.; Santos, T. S.; Karapetrova, E.; Zaresty, J. L.; Zhai, X.; te Velthuis, S. G. E.; Eckstein, J. N.; Bader, S. D.; Bhattacharya, A.; Iowa State Univ.; ORNL; Univ. of Illinois
2009-01-01
The disorder inherent to doping by cation substitution in the complex oxides can have profound effects on collective-ordered states. Here, we demonstrate that cation-site ordering achieved through digital-synthesis techniques can dramatically enhance the antiferromagnetic ordering temperatures of manganite films. Cation-ordered (LaMnO{sub 3}){sub m}/(SrMnO{sub 3}){sub 2m} superlattices show Neel temperatures (TN) that are the highest of any La{sub 1-x}Sr{sub x}MnO{sub 3} compound, {approx}70 K greater than compositionally equivalent randomly doped La{sub 1/3}Sr{sub 2/3}MnO{sub 3}. The antiferromagnetic order is A-type, consisting of in-plane double-exchange-mediated ferromagnetic sheets coupled antiferromagnetically along the out-of-plane direction. Through synchrotron X-ray scattering, we have discovered an in-plane structural modulation that reduces the charge itinerancy and hence the ordering temperature within the ferromagnetic sheets, thereby limiting TN. This modulation is mitigated and driven to long wavelengths by cation ordering, enabling the higher TN values of the superlattices. These results provide insight into how cation-site ordering can enhance cooperative behavior in oxides through subtle structural phenomena.
Barlowite as a canted antiferromagnet: Theory and experiment
NASA Astrophysics Data System (ADS)
Jeschke, Harald O.; Salvat-Pujol, Francesc; Gati, Elena; Hoang, Nguyen Hieu; Wolf, Bernd; Lang, Michael; Schlueter, John A.; Valentí, Roser
2015-09-01
We investigate the structural, electronic, and magnetic properties of the newly synthesized mineral barlowite Cu4(OH) 6FBr which contains Cu2 + ions in a perfect kagome arrangement. In contrast to the spin-liquid candidate herbertsmithite ZnCu3(OH)6Cl 2, kagome layers in barlowite are perfectly aligned due to the different bonding environments adopted by F- and Br- compared to Cl-. With the synthesis of this material we unveil a design strategy for layered kagome systems with possible exotic magnetic states. Density functional theory calculations and effective model considerations for Cu4(OH) 6FBr , which has a Cu2 + site coupling the kagome layers, predict a three-dimensional network of exchange couplings, which together with a substantial Dzyaloshinskii-Moriya coupling lead to canted antiferromagnetic ordering of this compound in excellent agreement with magnetic susceptibility measurements on single crystals yielding TN=15 K .
NASA Astrophysics Data System (ADS)
Shick, A. B.; Khmelevskyi, S.; Mryasov, O. N.; Wunderlich, J.; Jungwirth, T.
2010-06-01
Magnetic anisotropy phenomena in bimetallic antiferromagnets Mn2Au and MnIr are studied by first-principles density-functional theory calculations. We find strong and lattice-parameter-dependent magnetic anisotropies of the ground-state energy, chemical potential, and density of states, and attribute these anisotropies to combined effects of large moment on the Mn3d shell and large spin-orbit coupling on the 5d shell of the noble metal. Large magnitudes of the proposed effects can open a route towards spintronics in compensated antiferromagnets without involving ferromagnetic elements.
Room temperature spin-polarizations of Mn-based antiferromagnetic nanoelectrodes
Yamada, Toyo Kazu; Vazquez de Parga, Amadeo L.
2014-11-03
Antiferromagnets produce no stray field, and therefore, a tip electrode made of antiferromagnetic material has been considered to be the most suitable choice to measure such as magnetoresistance (MR) through single isolated magnetic nanoparticles, molecules, and ultrathin films. Spin polarizations (P) of antiferromagnetic 3-nm, 6-nm, and annealed 3-nm Mn films grown on W tips with a bcc(110) apex as well as bulk-NiMn tips were obtained at 300 K by measuring MR in ultrahigh vacuum by means of spin-polarized scanning tunneling microscopy using a layerwise antiferromagnetically stacking bct-Mn(001) film electrode. The Mn-coated tips with coverages of 3 and 6 nm exhibited P values of 1 ± 1% and 3 ± 2%, respectively, which tips likely contain α- or strained Mn. With a thermal assist, the crystalline quality and the magnetic stability of the film could increase. The annealed tip exhibited P = 9 ± 2%. The bulk-NiMn tips exhibit spin polarizations of 0 or 6 ± 2% probably depending on the chemical species (Mn or Ni) present at the apex of the tip. Fe-coated W tips were used to estimate the bct-Mn(001) film spin polarization.
Dynamic magnetic hysteresis and nonlinear susceptibility of antiferromagnetic nanoparticles
NASA Astrophysics Data System (ADS)
Kalmykov, Yuri P.; Ouari, Bachir; Titov, Serguey V.
2016-08-01
The nonlinear ac stationary response of antiferromagnetic nanoparticles subjected to both external ac and dc fields of arbitrary strength and orientation is investigated using Brown's continuous diffusion model. The nonlinear complex susceptibility and dynamic magnetic hysteresis (DMH) loops of an individual antiferromagnetic nanoparticle are evaluated and compared with the linear regime for extensive ranges of the anisotropy, the ac and dc magnetic fields, damping, and the specific antiferromagnetic parameter. It is shown that the shape and area of the DMH loops of antiferromagnetic particles are substantially altered by applying a dc field that permits tuning of the specific magnetic power loss in the nanoparticles.
Half-Quantum Vortices in an Antiferromagnetic Spinor Bose-Einstein Condensate.
Seo, Sang Won; Kang, Seji; Kwon, Woo Jin; Shin, Yong-il
2015-07-01
We report on the observation of half-quantum vortices (HQVs) in the easy-plane polar phase of an antiferromagnetic spinor Bose-Einstein condensate. Using in situ magnetization-sensitive imaging, we observe that pairs of HQVs with opposite core magnetization are generated when singly charged quantum vortices are injected into the condensate. The dynamics of HQV pair formation is characterized by measuring the temporal evolutions of the pair separation distance and the core magnetization, which reveals the short-range nature of the repulsive interactions between the HQVs. We find that spin fluctuations arising from thermal population of transverse magnon excitations do not significantly affect the HQV pair formation dynamics. Our results demonstrate the instability of a singly charged vortex in the antiferromagnetic spinor condensate. PMID:26182102
Goetsch, R. J.; Ananad, V. K.; Johnston, David C.
2013-02-07
The synthesis and crystallographic and physical properties of polycrystalline EuNiGe3 are reported. EuNiGe3 crystallizes in the noncentrosymmetric body-centered tetragonal BaNiSn3-type structure (space group I4mm), in agreement with previous reports, with the Eu atoms at the corners and body center of the unit cell. The physical property data consistently demonstrate that this is a metallic system in which Eu spins S = 7/2 order antiferromagnetically at a temperature TN = 13.6 K.Magnetic susceptibility χ data forT >TN indicate that the Eu atoms have spin 7/2 with g = 2, that the Ni atoms are nonmagnetic, and that the dominant interactions between the Eu spins are ferromagnetic. Thus we propose that EuNiGe3 has a collinear A-type antiferromagnetic structure, with the Eu ordered moments in the ab plane aligned ferromagnetically and with the moments in adjacent planes along the c axis aligned antiferromagnetically. A fit of χ(T TN) by our molecular field theory is consistent with a collinear magnetic structure. Electrical resistivity ρ data from TN to 350 K are fitted by the Bloch-Gr¨uneisen model for electron-phonon scattering, yielding a Debye temperature of 265(2) K.Astrong decrease in ρ occurs belowTN due to loss of spin-disorder scattering. Heat capacity data at 25 K T 300Kare fitted by the Debye model, yielding the same Debye temperature 268(2) K as found from ρ(T ). The extracted magnetic heat capacity is consistent with S = 7/2 and shows that significant short-range dynamical spin correlations occur above TN. The magnetic entropy at TN = 13.6 K is 83% of the expected asymptotic high-T value, with the remainder recovered by 30 K.
Doping an antiferromagnetic insulator : A route to an antiferromagnetic metallic phase
NASA Astrophysics Data System (ADS)
Mahadevan, Priya; Pandey, Shishir; Sarma, D. D.
Usually antiferromagnetism is accompanied by an insulating character of the ground state, while ferromagnetism is accompanied by metallicity. In the limit of half-filling, the Hubbard model yields an antiferromagnetic insulator as the ground state. From the Nagaoka theorem we expect ferromagnetism at any finite electron doping of this half filled state. Numerical studies on the other hand, have however shown, that at low doping concentrations one has a narrow region of an antiferromagnetic metallic phase. The question is whether this is realizable in real materials. Among the 3d transition metal oxides, this antiferromagnetic metallic phase has remained elusive as strong electron-phonon coupling results in a different phase diagram. The 5d transition metal oxides are therefore more suitable. In this work we solve a multiband Hubbard model relevant for a 5d transition metal oxide within a mean-field approach and show that the large bandwidth and the small intra-atomic Hund's exchange associated with this limit gives us a robust AFM-M ground state for 25% electron doping. The conclusions are supported by ab-initio electronic structure calculations for NaOsO3.
NASA Astrophysics Data System (ADS)
Gu, Bo; Su, Gang; Gao, Song
2006-04-01
The magnetization process, the susceptibility, and the specific heat of the spin- 1/2 antiferromagnet (AF)-AF-ferromagnet (F) and F-F-AF trimerized quantum Heisenberg chains have been investigated by means of the transfer matrix renormalization group (TMRG) technique as well as the modified spin-wave (MSW) theory. A magnetization plateau at m=1/6 for both trimerized chains is observed at low temperature. The susceptibility and the specific heat show various behaviors for different ferromagnetic and antiferromagnetic interactions and in different magnetic fields. The TMRG results of susceptibility and the specific heat can be nicely fitted by a linear superposition of double two-level systems, where two fitting equations are proposed. Three branch excitations, one gapless excitation and two gapful excitations, for both systems are found within the MSW theory. It is observed that the MSW theory captures the main characteristics of the thermodynamic behaviors at low temperatures. The TMRG results are also compared with the possible experimental data.
Ferrimagnetism in a transverse Ising antiferromagnet
NASA Astrophysics Data System (ADS)
Kaneyoshi, T.
2016-05-01
The phase diagrams and temperature dependences of total magnetization mT in a transverse Ising antiferromagnet consisting of alternating two (A and B) layers are studied by the uses of the effective-field theory with correlations and the mean-field-theory. A lot of characteristic phenomena, namely ferrimagnetic behaviors, have been found in the mT, when the crystallographically equivalent conditions between the A and B layers are broken. The appearance of a compensation point has been found below its transition temperature.
Frustrated 3×3 Heisenberg antiferromagnets
NASA Astrophysics Data System (ADS)
Moustanis, P. N.
2016-08-01
The full energy spectrum and the exact thermodynamic results of the antiferromagnetic Heisenberg Hamiltonian of the 3×3 triangular and the frustrated square lattice with periodic boundary conditions and s=1/2 are obtained. To this end the method of hierarchy of algebras is employed. It was found that the ground state of the 3×3 frustrated square lattice is a Resonating Valence Bond (RVB) state. Thermodynamic properties, like the specific heat, magnetic susceptibility, the thermal average of the square of the total Sz and entropy, for these two lattices are presented.
Switching of antiferromagnetic chains with magnetic pulses
NASA Astrophysics Data System (ADS)
Tao, Kun; Polyakov, Oleg P.; Stepanyuk, Valeri S.
2016-04-01
Recent experimental studies have demonstrated the possibility of information storage in short antiferromagnetic chains on an insulator substrate [S. Loth et al., Science 335, 196 (2012), 10.1126/science.1214131]. Here, using the density functional theory and atomistic spin dynamics simulations, we show that a local magnetic control of such chains with a magnetic tip and magnetic pulses can be used for fast switching of their magnetization. Furthermore, by changing the position of the tip one can engineer the magnetization dynamics of the chains.
Dynamic critical curve of a synthetic antiferromagnet
NASA Astrophysics Data System (ADS)
Pham, Huy; Cimpoesu, Dorin; Plamadǎ, Andrei-Valentin; Stancu, Alexandru; Spinu, Leonard
2009-11-01
In this letter, a dynamic generalization of static critical curves (sCCs) for synthetic antiferromagnet (SAF) structures is presented, analyzing the magnetization switching of SAF elements subjected to pulsed magnetic fields. The dependence of dynamic critical curves (dCCs) on field pulse's shape and length, on damping, and on magnetostatic coupling is investigated. Comparing sCCs, which are currently used for studying the switching in toggle magnetic random access memories, with dCCs, it is shown that a consistent switching can be achieved only under specific conditions that take into account the dynamics of the systems. The study relies on the Landau-Lifshitz-Gilbert equation.
Antiferromagnetic Ordering of Mn(III)F(salen)
NASA Astrophysics Data System (ADS)
Meisel, M. W.; Wang, Tong; Brown, S. E.; Botko, M.; Čižmár, E.; Risset, O. N.; Talham, D. R.
2014-03-01
Due to a report suggesting Mn(III)F(salen), salen = H14C16N2O2, is an S = 2 Haldane system with J /kB = 50 K and no long-range order down to 2 K based on standard magnetometry studies,[2] specific heat and NMR measurements were performed. Using small single crystals, specific heat studies revealed the presence of an anomaly near 23 K, and this response was robust in fields up to 9 T. The 1H NMR results performed on a single crystal in 1 T revealed a sharp transition characteristic of antiferromagnetic ordering at 22.5 K. Measuring the magnetic response of the same single crystal in a commercial magnetometer reveals the presence of a subtle feature, near 23 K, that is not resolved with as-grown, randomlly oriented microcrystalline samples. These findings provide insight into the results obtained in torque magnetometry, EPR, and neutron scattering data.[3] Supported by NSF via DMR-1202033 (MWM), DMR-1105531 (SEB), DMR-1005581 (DRT), and DMR-1157490 (NHMFL), by the Slovak Agency for Research and Development via APVV-0132-11 (EČ), and by the Fulbright Commission of the Slovak Republic (MWM).
Shuaibu, A.; Rahman, M. M.
2014-03-05
We study the low temperature behavior of a triangular lattice quantum spin-1 Heisenberg antiferromagnet with single-site anisotropy by using coordinate Bethe ansatz method. We compute the standard two-particle Hermitian Hamiltonian, and obtain the eigenfunctions and eigenvalue of the system. The obtained results show a number of advantages in comparison with many results.
Microscopic theory of dynamical matrix in itinerant model of antiferromagnetism
NASA Astrophysics Data System (ADS)
Ami, Seiju; Cade, N. A.; Young, W.
1983-02-01
The dynamical matrix and the elastic constants are derived for an itinerant antiferromagnet. An orbital representation is used which bypasses the problem of large matrix inversion in reciprocal space. We show that exchange enhancement and antiferromagnetic ordering leads to softening of some of the elastic constants.
Charge Stripes and Antiferromagnetism in Copper-Oxide Superconductors
Tranquada, J.M.
1997-12-31
Superconducting cuprate compounds are obtained by doping holes into antiferromagnetic insulators. Neutron scattering studies have provided evidence that the doped holes tend to segregate into charge stripes, which act like domain walls between antiferromagnetic regions. The interaction between the spatially segregated holes and the magnetic domains may be responsible for the strong pairing interaction found in the cuprates.
"Quasi-Antiferromagnetic" Ordering in the R-Mg-Zn Icosahedral Alloys? The Case of Tb-Mg-Zn
NASA Astrophysics Data System (ADS)
Goldman, A. I.; Islam, Z.; Fisher, I. R.; Panchula, A. F.; Cheon, K. O.; Canfield, P. C.; Stassis, C.; Zarestky, J.
1998-03-01
Recently, it was reported that long-range magnetic ordering was observed in several of the new rare earth containing icosahedral alloys, R-Mg-Zn (R=Tb, Dy, Ho, Er) (B. Charrier et al., Phys. Rev. Lett. 78, 4637, 1997.). At low temperatures, the antiferromagnetic Bragg peaks, while weak, could be indexed to the icosahedral parent phase with good accuracy. In addition, significant magnetic diffuse scattering, indicating only short-range magnetic order, was also observed. However, bulk magnetization measurements have evidenced only a spin-glass transition at low temperatures, and no antiferromagnetic transition. We will report on new neutron scattering measurements of the magnetic order in Tb-Mg-Zn powder samples produced from crushed single-crystals, used to improve sample purity. Our results for these samples show only the diffuse component of the magnetic scattering at low temperature, and no antiferromagnetic Bragg peaks. We will discuss several possibilities for the discrepencies between the two experiments.
Activation of antiferromagnetic domain switching in exchange-coupled Fe/CoO/MgO(001) systems
NASA Astrophysics Data System (ADS)
Li, Q.; Chen, G.; Ma, T. P.; Zhu, J.; N'Diaye, A. T.; Sun, L.; Gu, T.; Huo, Y.; Liang, J. H.; Li, R. W.; Won, C.; Ding, H. F.; Qiu, Z. Q.; Wu, Y. Z.
2015-04-01
In contrast to the extensive study of domain reversal in ferromagnetic materials, the domain switching process in antiferromagnets is much less studied due to the difficulty of probing antiferromagnetic spins. Using a combination of hysteresis loop, Kerr microscope, and x-ray magnetic linear dichroism measurements, we investigated the antiferromagnetic (AFM) domain switching process in single crystalline Fe/CoO bilayers on MgO(001). We demonstrate that the CoO AFM switching is a Kolmogorov-Avrami process in which the thermal activation energy creates AFM domain nucleation centers which further expand by domain wall propagation. From the temperature- and thickness-dependent measurements, we are able to retrieve quantitatively the important parameter of the CoO AFM activation energy, which is shown to increase linearly with CoO thickness.
NASA Astrophysics Data System (ADS)
Wu, R.; Yun, C.; Ding, S. L.; Wen, X.; Liu, S. Q.; Wang, C. S.; Han, J. Z.; Du, H. L.; Yang, J. B.
2016-08-01
The motion of antiferromagnetic interfacial spins is investigated through the temperature evolution of training effect in a Co/CoO film with in-plane biaxial anisotropy. Significant differences in the training effect and its temperature dependence are observed in the magnetic easy axis and hard axis (HA) and ascribed to the different motion modes of antiferromagnetic interfacial spins, the collective spin cluster rotation (CSR) and the single spin reversal (SSR), caused by different magnetization reversal modes of ferromagnetic layer. These motion modes of antiferromagnetic spins are successfully separated using a combination of an exponential function and a classic n-1/2 function. A larger CSR to SSR ratio and a shorter lifetime of CSR found in the HA indicates that the domain rotation in the ferromagnetic layer tends to activate and accelerate a CSR mode in the antiferromagnetic spins.
Fragile antiferromagnetism in the heavy-fermion compound YbBiPt
Ueland, Benjamin G.; Kreyssig, Andreas; Prokes, K.; Lynn, J. W.; Harriger, L. W.; Pratt, D. K.; Singh, D. K.; Heitmann, T. W.; Sauerbrei, Samantha; Saunders, Scott M.; Mun, E. D.; Budko, Serguei L.; McQueeney, Robert J.; Canfield, Paul C.; Goldman, Alan I.
2014-05-08
We report results from neutron scattering experiments on single crystals of YbBiPt that demonstrate antiferromagnetic order characterized by a propagation vector, τAFM = (121212), and ordered moments that align along the [1 1 1] direction of the cubic unit cell. We describe the scattering in terms of a two-Gaussian peak fit, which consists of a narrower component that appears below TN≈0.4 K and corresponds to a magnetic correlation length of ξn≈ 80 Å, and a broad component that persists up to T*≈ 0.7 K and corresponds to antiferromagnetic correlations extending over ξb≈ 20 Å. Our results illustrate the fragile magnetic order present in YbBiPt and provide a path forward for microscopic investigations of the ground states and fluctuations associated with the purported quantum critical point in this heavy-fermion compound.
Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet
Fu, Mingxuan; Imai, Takahashi; Han, Tian -Heng; Lee, Young S.
2015-11-06
Here, the kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χkagome, deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with themore » magnetic field dependence of χkagome that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.« less
β-NMR Investigation of the Depth-Dependent Magnetic Properties of an Antiferromagnetic Surface.
Cortie, D L; Buck, T; Dehn, M H; Karner, V L; Kiefl, R F; Levy, C D P; McFadden, R M L; Morris, G D; McKenzie, I; Pearson, M R; Wang, X L; MacFarlane, W A
2016-03-11
By measuring the prototypical antiferromagnet α-Fe_{2}O_{3}, we show that it is possible to determine the static spin orientation and dynamic spin correlations within nanometers from an antiferromagnetic surface using the nuclear spin polarization of implanted ^{8}Li^{+} ions detected with β-NMR. Remarkably, the first-order Morin spin reorientation in single crystal α-Fe_{2}O_{3} occurs at the same temperature at all depths between 1 and 100 nm from the (110) surface; however, the implanted nuclear spin experiences an increased 1/T_{1} relaxation rate at shallow depths revealing soft-surface magnons. The surface-localized dynamics decay towards the bulk with a characteristic length of ε=11±1 nm, closely matching the finite-size thresholds of hematite nanostructures. PMID:27015494
Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet.
Fu, Mingxuan; Imai, Takashi; Han, Tian-Heng; Lee, Young S
2015-11-01
The kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χ(kagome), deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with the magnetic field dependence of χ(kagome) that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap. PMID:26542565
Strain-modulated antiferromagnetic spin orientation and exchange coupling in Fe/CoO(001)
Zhu, J.; Li, Q.; Li, J. X.; Ding, Z.; Wu, Y. Z.; Hua, C. Y.; Huang, M. J.; Lin, H.-J.; Hu, Z.; Won, C.
2014-05-21
The effect of CoO spin orientation on exchange coupling was investigated in single-crystalline Fe/CoO/MnO/MgO(001) systems. An antiferromagnetic CoO spin reorientation transition from the in-plane direction to the out-of-plane direction was found to be associated with the in-plane strain transition in CoO film from compression to expansion. The induced uniaxial anisotropies by exchange coupling at the Fe/CoO interface are significantly stronger for the in-plane CoO spin orientation than for the out-of-plane CoO spin orientation. Our study provides a way to modify the exchange coupling in the ferromagnetic (FM)/antiferromagnetic (AFM) bilayer by modulating the strain in the AFM film.
Electrically tunable transport in the antiferromagnetic Mott insulator Sr2IrO4
NASA Astrophysics Data System (ADS)
Wang, C.; Seinige, H.; Cao, G.; Zhou, J.-S.; Goodenough, J. B.; Tsoi, M.
2015-09-01
Electronic transport properties of the antiferromagnetic Mott insulator S r2Ir O4 have been investigated under extremely high electric biases. Using nanoscale contacts, we apply electric fields up to a few MV/m to a single crystal of S r2Ir O4 and observe a continuous reduction in the material's resistivity with increasing bias, characterized by a reduction in the transport activation energy by as much as 16 % . Temperature-dependent resistivity measurements provide a means to unambiguously retrieve the bias dependence of the activation energy from the Arrhenius plots at different biases. We further demonstrate the feasibility of reversible resistive switching induced by the electric bias, which is of interest for the emerging field of antiferromagnetic spintronics. Our findings demonstrate the potential of electrical means for tuning electronic properties in 5 d transition-metal oxides and suggest a promising path towards development of next-generation functional devices.
Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet
NASA Astrophysics Data System (ADS)
Fu, Mingxuan; Imai, Takashi; Han, Tian-Heng; Lee, Young S.
2015-11-01
The kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χkagome, deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with the magnetic field dependence of χkagome that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.
Enhanced antiferromagnetic coupling in dual-synthetic antiferromagnet with Co2FeAl electrodes
NASA Astrophysics Data System (ADS)
Zhang, D. L.; Xu, X. G.; Wu, Y.; Li, X. Q.; Miao, J.; Jiang, Y.
2012-05-01
We study dual-synthetic antiferromagnets (DSyAFs) using Co2FeAl (CFA) Heusler electrodes with a stack structure of Ta/CFA/Ru/CFA/Ru/CFA/Ta. When the thicknesses of the two Ru layers are 0.45 nm, 0.65 nm or 0.45 nm, 1.00 nm, the CFA-based DSyAF has a strong antiferromagnetic coupling between adjacent CFA layers at room temperature with a saturation magnetic field of ∼11,000 Oe, a saturation magnetization of ∼710 emu/cm3 and a coercivity of ∼2.0 Oe. Moreover, the DSyAF has a good thermal stability up to 400 °C, at which CFA films show B2-ordered structure. Therefore, the CFA-based DSyAFs are favorable for applications in future spintronic devices.
Anomalous Magnetothermopower in a Metallic Frustrated Antiferromagnet.
Arsenijević, Stevan; Ok, Jong Mok; Robinson, Peter; Ghannadzadeh, Saman; Katsnelson, Mikhail I; Kim, Jun Sung; Hussey, Nigel E
2016-02-26
We report the temperature T and magnetic field H dependence of the thermopower S of an itinerant triangular antiferromagnet PdCrO_{2} in high magnetic fields up to 32 T. In the paramagnetic phase, the zero-field thermopower is positive with a value typical of good metals with a high carrier density. In marked contrast to typical metals, however, S decreases rapidly with increasing magnetic field, approaching zero at the maximum field scale for T>70 K. We argue here that this profound change in the thermoelectric response derives from the strong interaction of the 4d correlated electrons of the Pd ions with the short-range spin correlations of the Cr^{3+} spins that persist beyond the Néel ordering temperature due to the combined effects of geometrical frustration and low dimensionality. PMID:26967440
Anomalous Magnetothermopower in a Metallic Frustrated Antiferromagnet
NASA Astrophysics Data System (ADS)
Arsenijević, Stevan; Ok, Jong Mok; Robinson, Peter; Ghannadzadeh, Saman; Katsnelson, Mikhail I.; Kim, Jun Sung; Hussey, Nigel E.
2016-02-01
We report the temperature T and magnetic field H dependence of the thermopower S of an itinerant triangular antiferromagnet PdCrO2 in high magnetic fields up to 32 T. In the paramagnetic phase, the zero-field thermopower is positive with a value typical of good metals with a high carrier density. In marked contrast to typical metals, however, S decreases rapidly with increasing magnetic field, approaching zero at the maximum field scale for T >70 K . We argue here that this profound change in the thermoelectric response derives from the strong interaction of the 4 d correlated electrons of the Pd ions with the short-range spin correlations of the Cr3 + spins that persist beyond the Néel ordering temperature due to the combined effects of geometrical frustration and low dimensionality.
Classical antiferromagnet on a hyperkagome lattice.
Hopkinson, John M; Isakov, Sergei V; Kee, Hae-Young; Kim, Yong Baek
2007-07-20
Motivated by recent experiments on Na4Ir3O8 [Y. Okamoto, M. Nohara, H. Aruga-Katori, and H. Takagi, arXiv:0705.2821 (unpublished)], we study the classical antiferromagnet on a frustrated three-dimensional lattice obtained by selectively removing one of four sites in each tetrahedron of the pyrochlore lattice. This "hyperkagome" lattice consists of corner-sharing triangles. We present the results of large-N mean field theory and Monte Carlo computations on O(N) classical spin models. It is found that the classical ground states are highly degenerate. Nonetheless a nematic order emerges at low temperatures in the Heisenberg model (N=3) via "order by disorder," representing the dominance of coplanar spin configurations. Implications for ongoing experiments are discussed. PMID:17678320
Phonon assisted IR spectroscopy of quantum antiferromagnets
Lorenzana, J.; Eder, R.; Sawatzky, G.A.
1996-12-31
The authors review resent theoretical results for multimagnon-phonon assisted infrared absorption in antiferromagnetic Heisenberg systems. They show spin wave theory line shapes for 2D spin 1/2 systems (like the parent insulating high-Tc cuprates) 1D spin 1/2 systems and 2D spin 1 systems (like the nickelates) and exact diagonalization results in two-dimensional spin 1/2 systems. The theoretical line shapes are compared with experiments. In the case of the cuprates they explain mid-infrared peaks observed in the insulator. In the case of the nickelates a predicted line shape is also shown to agree with the experiments. They discuss the possibility to observe this excitations in other experiments.
Ising antiferromagnet on the 2-uniform lattices
NASA Astrophysics Data System (ADS)
Yu, Unjong
2016-08-01
The antiferromagnetic Ising model is investigated on the twenty 2-uniform lattices using the Monte Carlo method based on the Wang-Landau algorithm and the Metropolis algorithm to study the geometric frustration effect systematically. Based on the specific heat, the residual entropy, and the Edwards-Anderson freezing order parameter, the ground states of them were determined. In addition to the long-range-ordered phase and the spin ice phase found in the Archimedean lattices, two more phases were found. The partial long-range order is long-range order with exceptional disordered sites, which give extensive residual entropy. In the partial spin ice phase, the partial freezing phenomenon appears: A majority of sites are frozen without long-range order, but the other sites are fluctuating even at zero temperature. The spin liquid ground state was not found in the 2-uniform lattices.
Ising antiferromagnet on the Archimedean lattices
NASA Astrophysics Data System (ADS)
Yu, Unjong
2015-06-01
Geometric frustration effects were studied systematically with the Ising antiferromagnet on the 11 Archimedean lattices using the Monte Carlo methods. The Wang-Landau algorithm for static properties (specific heat and residual entropy) and the Metropolis algorithm for a freezing order parameter were adopted. The exact residual entropy was also found. Based on the degree of frustration and dynamic properties, ground states of them were determined. The Shastry-Sutherland lattice and the trellis lattice are weakly frustrated and have two- and one-dimensional long-range-ordered ground states, respectively. The bounce, maple-leaf, and star lattices have the spin ice phase. The spin liquid phase appears in the triangular and kagome lattices.
Spin Transport in Ferromagnetic and Antiferromagnetic Insulators
NASA Astrophysics Data System (ADS)
Su, Shanshan; Yin, Gen; Liu, Yizhou; Zang, Jiadong; Barlas, Yafis; Lake, Roger
Recently, experiments of spin pumping have been done for system with antiferromagnetic oxides (AFMOs) as a spacer between YIG and Pt. Observation of spin transport through the AFMO and the enhancement of spin pumping signal in the system due to the insertion of AFMO have been reported. In this research, we model the spin transport in Pt/YIG/Pt and Pt/YIG/AFMO/Pt heterostructures using the Landau-Lifshitz-Gilbert equations coupled with the non-equilibrium Green's function equations. We show that a pure spin current generated at the first Rashba SOC electrode is carried by magnon through YIG, which can be converted back to spin pumping signal at the second electrode. The spin dynamical details at the heterostructure can determine the transport efficiency. The effect of different magnetization orientations and finite temperatures will be addressed. This work was supported by the SHINES under Award # SC0012670.
Ising antiferromagnet on the Archimedean lattices.
Yu, Unjong
2015-06-01
Geometric frustration effects were studied systematically with the Ising antiferromagnet on the 11 Archimedean lattices using the Monte Carlo methods. The Wang-Landau algorithm for static properties (specific heat and residual entropy) and the Metropolis algorithm for a freezing order parameter were adopted. The exact residual entropy was also found. Based on the degree of frustration and dynamic properties, ground states of them were determined. The Shastry-Sutherland lattice and the trellis lattice are weakly frustrated and have two- and one-dimensional long-range-ordered ground states, respectively. The bounce, maple-leaf, and star lattices have the spin ice phase. The spin liquid phase appears in the triangular and kagome lattices. PMID:26172675
Probing the evolution of antiferromagnetism in multiferroics
Holcomb, M.; Martin, L.; Scholl, A.; He, Q.; Yu, P.; Yang, C.-H.; Yang, S.; Glans, P.-A.; Valvidares, M.; Huijben, M.; Kortright, J.; Guo,, J.; Chu, Y.-H.; Ramesh, R.
2010-06-09
This study delineates the evolution of magnetic order in epitaxial films of the room-temperature multiferroic BiFeO3 system. Using angle- and temperature-dependent dichroic measurements and spectromicroscopy, we have observed that the antiferromagnetic order in the model multiferroic BiFeO3 evolves systematically as a function of thickness and strain. Lattice-mismatch-induced strain is found to break the easy-plane magnetic symmetry of the bulk and leads to an easy axis of magnetization which can be controlled through strain. Understanding the evolution of magnetic structure and how to manipulate the magnetism in this model multiferroic has significant implications for utilization of such magnetoelectric materials in future applications.
Dynamics of antiferromagnets driven by spin current
NASA Astrophysics Data System (ADS)
Cheng, Ran; Niu, Qian
2014-02-01
When a spin-polarized current flows through a ferromagnetic (FM) metal, angular momentum is transferred to the background magnetization via spin-transfer torques. In antiferromagnetic (AFM) materials, however, the corresponding problem is unsolved. We derive microscopically the dynamics of an AFM system driven by spin current generated by an attached FM polarizer, and find that the spin current exerts a driving force on the local staggered order parameter. The mechanism does not rely on the conservation of spin angular momentum, nor does it depend on the induced FM moments on top the AFM background. Two examples are studied: (i) A domain wall is accelerated to a terminal velocity by purely adiabatic effect where the Walker's breakdown is avoided. (ii) Spin injection modifies the AFM resonance frequency, and spin current injection triggers spin wave instability of local moments above a threshold.
Transformation of spin current by antiferromagnetic insulators
NASA Astrophysics Data System (ADS)
Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasil S.; Slavin, Andrei N.; Ivanov, Boris A.
2016-06-01
It is demonstrated theoretically that a thin layer of an anisotropic antiferromagnetic (AFM) insulator can effectively conduct spin current through the excitation of a pair of evanescent AFM spin wave modes. The spin current flowing through the AFM is not conserved due to the interaction between the excited AFM modes and the AFM lattice and, depending on the excitation conditions, can be either attenuated or enhanced. When the phase difference between the excited evanescent modes is close to π /2 , there is an optimum AFM thickness for which the output spin current reaches a maximum, which can significantly exceed the magnitude of the input spin current. The spin current transfer through the AFM depends on the ambient temperature and increases substantially when temperature approaches the Néel temperature of the AFM layer.
Antiferromagnetically Induced Photoemission Band in the Cuprates
NASA Astrophysics Data System (ADS)
Haas, Stephan; Moreo, Adriana; Dagotto, Elbio
1995-05-01
Strong antiferromagnetic correlations in models of high critical temperature (high- Tc) cuprates produce quasiparticlelike features in photoemission (PES) calculations above the Fermi momentum pF corresponding to weakly interacting electrons. This effect, discussed before by Kampf and Schrieffer [Phys. Rev. B 41, 6399 (1990)], is analyzed here using computational techniques in strong coupling. It is concluded that weight above pF should be observable in PES data for underdoped compounds, while in the overdoped regime it will be hidden in the experimental background. At optimal doping the signal is weak. The order of magnitude of our results is compatible with experimental data by Aebi et al. [Phys. Rev. Lett. 72, 2757 (1994)] for Bi2Sr2CaCu2O8.
Antiferromagnetic coupling across silicon regulated by tunneling currents
NASA Astrophysics Data System (ADS)
Gareev, R. R.; Schmid, M.; Vancea, J.; Back, C. H.; Schreiber, R.; Bürgler, D.; Schneider, C. M.; Stromberg, F.; Wende, H.
2012-01-01
We report on the enhancement of antiferromagnetic coupling in epitaxial Fe/Si/Fe structures by voltage-driven spin-polarized tunneling currents. Using the ballistic electron magnetic microscopy, we established that the hot-electron collector current reflects magnetization alignment and the magnetocurrent exceeds 200% at room temperature. The saturation magnetic field for the collector current corresponding to the parallel alignment of magnetizations rises up with the tunneling current, thus demonstrating stabilization of the antiparallel alignment and increasing antiferromagnetic coupling. We connect the enhancement of antiferromagnetic coupling with local dynamic spin torques mediated by spin-polarized tunneling electrons.
Phenomenology of current-induced skyrmion motion in antiferromagnets
NASA Astrophysics Data System (ADS)
Velkov, H.; Gomonay, O.; Beens, M.; Schwiete, G.; Brataas, A.; Sinova, J.; Duine, R. A.
2016-07-01
We study current-driven skyrmion motion in uniaxial thin film antiferromagnets in the presence of the Dzyaloshinskii–Moriya interactions and in an external magnetic field. We phenomenologically include relaxation and current-induced torques due to both spin–orbit coupling and spatially inhomogeneous magnetic textures in the equation for the Néel vector of the antiferromagnet. Using the collective coordinate approach we apply the theory to a two-dimensional antiferromagnetic skyrmion and estimate the skyrmion velocity under an applied DC electric current.
Kapitza problem for the magnetic moments of synthetic antiferromagnetic systems
Dzhezherya, Yu. I.; Demishev, K. O.; Korenivskii, V. N.
2012-08-15
The dynamics of magnetization in synthetic antiferromagnetic systems with the magnetic dipole coupling in a rapidly oscillating field has been examined. It has been revealed that the system can behave similar to the Kapitza pendulum. It has been shown that an alternating magnetic field can be efficiently used to control the magnetic state of a cell of a synthetic antiferromagnet. Analytical relations have been obtained between the parameters of such an antiferromagnet and an external magnetic field at which certain quasistationary states are implemented.
Localized moments and the stability of antiferromagnetic order in Yb3Pt4
NASA Astrophysics Data System (ADS)
Wu, L. S.; Janssen, Y.; Bennett, M. C.; Aronson, M. C.
2012-08-01
We present here the results of electrical resistivity ρ, magnetization M, ac susceptibility χac', and specific heat CM measurements that have been carried out on single crystals of Yb3Pt4 over a wide range of fields and temperatures. The 2.4-K Néel temperature that is found in zero field collapses under field to a first-order transition TN=0 at BCEP=1.85 T. In the absence of antiferromagnetic order, the specific heat CM(T,B), the magnetization M(T,B), and even the resistivity ρ(T,B) all display B/T scaling, indicating that they are dominated by strong paramagnetic fluctuations, where the only characteristic energy scale results from the Zeeman splitting of an energetically isolated, Yb doublet ground state. This paramagnetic scattering disappears with the onset of antiferromagnetic order, revealing Fermi liquid behavior Δρ=AT2 that persists up to the antiferromagnetic phase line TN(B), but not beyond. The first-order character of TN=0 and the ubiquity of the paramagnetic fluctuations imply that non-Fermi-liquid behaviors are absent in Yb3Pt4. In contrast to heavy fermions such as YbRh2Si2, Yb3Pt4 represents an extremely simple regime of f-electron behavior where the Yb moments and conduction electrons are almost decoupled, and where Kondo physics plays little role.
Resonant Two-Magnon Raman Scattering in Cuprate Antiferromagnetic Insulators and Superconductors.
NASA Astrophysics Data System (ADS)
Blumberg, G.; Abbamonte, P.; Klein, M. V.
1996-03-01
We present results of low-temperature two-magnon resonance Raman excitation profile measurements for single layer Sr_2CuO_2Cl2 and bilayer YBa_2Cu_3O6 + δ antiferromagnets over the excitation region from 1.65 to 3.05 eV. These data reveal composite structure of the B_1g two-magnon line shape peaked at ~ 2.7J and ~ 4J and strong nonmonotonic dependence of the scattering intensity on excitation energy. Resonant magnetic scattering contributes also to A_1g and B_2g channels. We analyze these data using the triple resonance theory of Chubukov and Frenkel(A. Chubukov and D. Frenkel, Phys. Rev. Lett.74), 3057 (1995). and deduce information about magnetic interaction (J and J_⊥) and band parameters (NN hopping t and charge transfer gap 2Δ) in these antiferromagnets.(G. Blumberg et. al.), Preprint cond-mat/9511080. The ~ 3J spin superexchange excitation persists upon hole doping and is present in superconductors, proving the universality of the short wavelength magnetic excitations in the cuprate superconducting metals and the parent antiferromagnetic insulators.(G. Blumberg et. al.), Phys. Rev. B 49, 13 295 (1994).
Temperature dependence of anisotropic magnetoresistance in antiferromagnetic Sr{sub 2}IrO{sub 4}
Wang, C.; Seinige, H.; Tsoi, M.; Cao, G.; Zhou, J.-S.; Goodenough, J. B.
2015-05-07
Temperature-dependent magnetotransport properties of the antiferromagnetic semiconductor Sr{sub 2}IrO{sub 4} are investigated with point-contact devices. The point-contact technique allows to probe very small volumes and, therefore, to look for electronic transport on a microscopic scale. Point-contact measurements with single crystals of Sr{sub 2}IrO{sub 4} were intended to see whether the additional local resistance associated with a small contact area between a sharpened Cu tip and the antiferromagnet shows magnetoresistance (MR) such as that seen in bulk crystals. Point-contact measurements at liquid nitrogen temperature revealed large MRs (up to 28%) for modest magnetic fields (250 mT) applied within an IrO{sub 2} (ab) plane with angular dependence showing a crossover from four-fold to two-fold symmetry with an increasing magnetic field. Point contact measurement exhibits distinctive anisotropic magnetoresistance (AMR) in comparison to a bulk experiment, imposing intriguing questions about the mechanism of AMR in this material. Temperature-dependent MR measurements show that the MR falls to zero at the Neel temperature, but the temperature dependence of the MR ratio differs qualitatively from that of the resistivity. This AMR study helps to unveil the entanglement between electronic transport and magnetism in Sr{sub 2}IrO{sub 4} while the observed magnetoresistive phenomena can be potentially used to sense the antiferromagnetic order parameter in spintronic applications.
Kinetically inhibited order in a diamond-lattice antiferromagnet
MacDougall, Gregory J.; Gout, Delphine; Zarestky, Jerel L.; Ehlers, Georg; Podlesnyak, Andrey; McGuire, Michael A.; Mandrus, David; Nagler, Stephen E.
2011-01-01
Frustrated magnetic systems exhibit highly degenerate ground states and strong fluctuations, often leading to new physics. An intriguing example of current interest is the antiferromagnet on a diamond lattice, realized physically in A-site spinel materials. This is a prototypical system in three dimensions where frustration arises from competing interactions rather than purely geometric constraints, and theory suggests the possibility of unusual magnetic order at low temperature. Here, we present a comprehensive single-crystal neutron scattering study of CoAl2O4, a highly frustrated A-site spinel. We observe strong diffuse scattering that peaks at wavevectors associated with Néel ordering. Below the temperature T∗ = 6.5 K, there is a dramatic change in the elastic scattering lineshape accompanied by the emergence of well-defined spin-wave excitations. T∗ had previously been associated with the onset of glassy behavior. Our new results suggest instead that T∗ signifies a first-order phase transition, but with true long-range order inhibited by the kinetic freezing of domain walls. This scenario might be expected to occur widely in frustrated systems containing first-order phase transitions and is a natural explanation for existing reports of anomalous glassy behavior in other materials. PMID:21896723
Kinetically inhibited order in a diamond-lattice antiferromagnet.
MacDougall, Gregory J; Gout, Delphine; Zarestky, Jerel L; Ehlers, Georg; Podlesnyak, Andrey; McGuire, Michael A; Mandrus, David; Nagler, Stephen E
2011-09-20
Frustrated magnetic systems exhibit highly degenerate ground states and strong fluctuations, often leading to new physics. An intriguing example of current interest is the antiferromagnet on a diamond lattice, realized physically in A-site spinel materials. This is a prototypical system in three dimensions where frustration arises from competing interactions rather than purely geometric constraints, and theory suggests the possibility of unusual magnetic order at low temperature. Here, we present a comprehensive single-crystal neutron scattering study of CoAl(2)O(4), a highly frustrated A-site spinel. We observe strong diffuse scattering that peaks at wavevectors associated with Néel ordering. Below the temperature T(∗) = 6.5 K, there is a dramatic change in the elastic scattering lineshape accompanied by the emergence of well-defined spin-wave excitations. T(∗) had previously been associated with the onset of glassy behavior. Our new results suggest instead that T(∗) signifies a first-order phase transition, but with true long-range order inhibited by the kinetic freezing of domain walls. This scenario might be expected to occur widely in frustrated systems containing first-order phase transitions and is a natural explanation for existing reports of anomalous glassy behavior in other materials. PMID:21896723
Photo-induced Spin Angular Momentum Transfer into Antiferromagnetic Insulator
NASA Astrophysics Data System (ADS)
Fang, Fan; Fan, Yichun; Ma, Xin; Zhu, J.; Li, Q.; Ma, T. P.; Wu, Y. Z.; Chen, Z. H.; Zhao, H. B.; Luepke, Gunter; College of William and Mary Team; Department of Physics, Fudan University Team; Department of Optical Science and Engineering, Fudan University Team
2014-03-01
Spin angular momentum transfer into antiferromagnetic(AFM) insulator is observed in single crystalline Fe/CoO/MgO(001) heterostructure by time-resolved magneto-optical Kerr effect (TR-MOKE). The transfer process is mediated by the Heisenberg exchange coupling between Fe and CoO spins. Below the Neel temperature(TN) of CoO, the fact that effective Gilbert damping parameter α is independent of external magnetic field and it is enhanced with respect to the intrinsic damping in Fe/MgO, indicates that the damping process involves both the intrinsic spin relaxation and the transfer of Fe spin angular momentum to CoO spins via FM-AFM exchange coupling and then into the lattice by spin-orbit coupling. The work at the College of William and Mary was sponsored by the Office of Naval Research. The work at Department of Physics, Fudan, was supported by NSFC. The work at Department of Optical Science and Engineering, Fudan was supported by NSFC and NCET.
Kinetically Inhibited Order in a Diamond-Lattice Antiferromagnet
MacDougall, Gregory J; Gout, Delphine J; Zarestky, Jerel L; Ehlers, Georg; Podlesnyak, Andrey A; McGuire, Michael A; Mandrus, David; Nagler, Stephen E
2011-01-01
Frustrated magnetic systems exhibit highly degenerate ground states and strong fluctuations, often leading to new physics. An intriguing example of current interest is the antiferromagnet on a diamond lattice, realized physically in the A-site spinel materials. This is a prototypical system in three dimensions where frustration arises from competing interactions rather than purely geometric constraints, and theory suggests the possibility of novel order at low temperature. Here we present a comprehensive single crystal neutron scattering study CoAl2O4, a highly frustrated A-site spinel. We observe strong diffuse scattering that peaks at wavevectors associated with Neel ordering. Below the temperature T*=6.5K, there is a dramatic change in elastic scattering lineshape accompanied by the emergence of well-defined spin-wave excitations. T* had previously been associated with the onset of glassy behavior. Our new results suggest instead that in fact T* signifies a first-order phase transition, but with true long-range order inhibited by the kinetic freezing of domain walls. This scenario might be expected to occur widely in frustrated systems containing first-order phase transitions and is a natural explanation for existing reports of anomalous glassy behavior in other materials.
Experimental investigation of two-dimensional antiferromagnetic systems
NASA Astrophysics Data System (ADS)
Woodward, Frank Matthew
Quantum fluctuations have a profound effect on the bulk properties of magnetic systems, particularly in low spatial dimension. For example, 1D chains with half integral spins have a gapless excitation spectrum while whole integer spin chains have a (Haldane) gap. The quantum critical behavior of the S = 1/2 2D system is thought to be the origin of high TC superconductivity. Molecular magnets are engineered materials where spin, interaction strength, or dimensionality can be tuned for experimental exploration of magnetism. A conscious effort was made to pick chemical motifs known to generate a quasi two dimensional Heisenberg system and attempt to exploit these motifs by designing classes of compounds based upon them. Creating many similar systems and observing changes in magnetism as a result in changes of chemical structure provides for the development of a phenomenological model of magnetostructural correlations which can then be verified by calculation. This dissertation discusses two distinct classes of antiferromagnetic systems, each based upon entirely different chemical motifs, both exhibiting the desired two dimensional Heisenberg antiferromagnetic behavior. One class is based upon copper tetrabromide: (5gammaAP)2CuBr4 where 5gammaAP = 2-amino-5-gamma-pyridinium with gamma = chloro, bromo, or methyl substituents. These materials are shown, by bulk magnetization and calorimetry studies to possess an exchange strength on the order of J ≈ -7 to -9 K and ordering temperatures in the range of TN ≈ 3.5 to 5 K. In the ordered state, these materials are shown to possesses a weak 3D exchange interaction, and exhibit a spin-flop transition to long range order in the magnetism. The other class under investigation is based upon copper pyrazine: Cu(pz) 2(ClO4)2, Cu(pz)2(BF6) 2, and [Cu(pz)2(NO3)](PF6). By bulk magnetic measurements of powder and single crystal samples they are shown to be a very good approximation of the 2D QHAF model. The two dimensional magnetic
Lifetime of gapped excitations in a collinear quantum antiferromagnet.
Chernyshev, A L; Zhitomirsky, M E; Martin, N; Regnault, L-P
2012-08-31
We demonstrate that local modulations of magnetic couplings have a profound effect on the temperature dependence of the relaxation rate of optical magnons in a wide class of antiferromagnets in which gapped excitations coexist with acoustic spin waves. In a two-dimensional collinear antiferromagnet with an easy-plane anisotropy, the disorder-induced relaxation rate of the gapped mode, Γ(imp)≈Γ(0)+A(TlnT)2, greatly exceeds the magnon-magnon damping, Γ(m-m)≈BT5, negligible at low temperatures. We measure the lifetime of gapped magnons in a prototype XY antiferromagnet BaNi2(PO4)2 using a high-resolution neutron-resonance spin-echo technique and find experimental data in close accord with the theoretical prediction. Similarly strong effects of disorder in the three-dimensional case and in noncollinear antiferromagnets are discussed. PMID:23002874
Giant magnetic effects and oscillations in antiferromagnetic Josephson weak links
Gorkov, L.; Kresin, Vladimir
2001-04-01
Josephson junctions with an antiferromagnetic metal as a link are described. The junction can be switched off by a relatively small magnetic field. The amplitude of the current oscillates as a function of the field.
Antiferromagnetic Skyrmion: Stability, Creation and Manipulation
Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko
2016-01-01
Magnetic skyrmions are particle-like topological excitations in ferromagnets, which have the topo-logical number Q = ± 1, and hence show the skyrmion Hall effect (SkHE) due to the Magnus force effect originating from the topology. Here, we propose the counterpart of the magnetic skyrmion in the antiferromagnetic (AFM) system, that is, the AFM skyrmion, which is topologically protected but without showing the SkHE. Two approaches for creating the AFM skyrmion have been described based on micromagnetic lattice simulations: (i) by injecting a vertical spin-polarized current to a nanodisk with the AFM ground state; (ii) by converting an AFM domain-wall pair in a nanowire junction. It is demonstrated that the AFM skyrmion, driven by the spin-polarized current, can move straightly over long distance, benefiting from the absence of the SkHE. Our results will open a new strategy on designing the novel spintronic devices based on AFM materials. PMID:27099125
Antiferromagnetic Skyrmion: Stability, Creation and Manipulation.
Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko
2016-01-01
Magnetic skyrmions are particle-like topological excitations in ferromagnets, which have the topo-logical number Q = ± 1, and hence show the skyrmion Hall effect (SkHE) due to the Magnus force effect originating from the topology. Here, we propose the counterpart of the magnetic skyrmion in the antiferromagnetic (AFM) system, that is, the AFM skyrmion, which is topologically protected but without showing the SkHE. Two approaches for creating the AFM skyrmion have been described based on micromagnetic lattice simulations: (i) by injecting a vertical spin-polarized current to a nanodisk with the AFM ground state; (ii) by converting an AFM domain-wall pair in a nanowire junction. It is demonstrated that the AFM skyrmion, driven by the spin-polarized current, can move straightly over long distance, benefiting from the absence of the SkHE. Our results will open a new strategy on designing the novel spintronic devices based on AFM materials. PMID:27099125
Antiferromagnetic Skyrmion: Stability, Creation and Manipulation
NASA Astrophysics Data System (ADS)
Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko
2016-04-01
Magnetic skyrmions are particle-like topological excitations in ferromagnets, which have the topo-logical number Q = ± 1, and hence show the skyrmion Hall effect (SkHE) due to the Magnus force effect originating from the topology. Here, we propose the counterpart of the magnetic skyrmion in the antiferromagnetic (AFM) system, that is, the AFM skyrmion, which is topologically protected but without showing the SkHE. Two approaches for creating the AFM skyrmion have been described based on micromagnetic lattice simulations: (i) by injecting a vertical spin-polarized current to a nanodisk with the AFM ground state; (ii) by converting an AFM domain-wall pair in a nanowire junction. It is demonstrated that the AFM skyrmion, driven by the spin-polarized current, can move straightly over long distance, benefiting from the absence of the SkHE. Our results will open a new strategy on designing the novel spintronic devices based on AFM materials.
Room-temperature antiferromagnetic memory resistor.
Marti, X; Fina, I; Frontera, C; Liu, Jian; Wadley, P; He, Q; Paull, R J; Clarkson, J D; Kudrnovský, J; Turek, I; Kuneš, J; Yi, D; Chu, J-H; Nelson, C T; You, L; Arenholz, E; Salahuddin, S; Fontcuberta, J; Jungwirth, T; Ramesh, R
2014-04-01
The bistability of ordered spin states in ferromagnets provides the basis for magnetic memory functionality. The latest generation of magnetic random access memories rely on an efficient approach in which magnetic fields are replaced by electrical means for writing and reading the information in ferromagnets. This concept may eventually reduce the sensitivity of ferromagnets to magnetic field perturbations to being a weakness for data retention and the ferromagnetic stray fields to an obstacle for high-density memory integration. Here we report a room-temperature bistable antiferromagnetic (AFM) memory that produces negligible stray fields and is insensitive to strong magnetic fields. We use a resistor made of a FeRh AFM, which orders ferromagnetically roughly 100 K above room temperature, and therefore allows us to set different collective directions for the Fe moments by applied magnetic field. On cooling to room temperature, AFM order sets in with the direction of the AFM moments predetermined by the field and moment direction in the high-temperature ferromagnetic state. For electrical reading, we use an AFM analogue of the anisotropic magnetoresistance. Our microscopic theory modelling confirms that this archetypical spintronic effect, discovered more than 150 years ago in ferromagnets, is also present in AFMs. Our work demonstrates the feasibility of fabricating room-temperature spintronic memories with AFMs, which in turn expands the base of available magnetic materials for devices with properties that cannot be achieved with ferromagnets. PMID:24464243
Quantum Phase Transitions in Antiferromagnets and Superfluids
NASA Astrophysics Data System (ADS)
Sachdev, Subir
2000-03-01
A general introduction to the non-zero temperature dynamic and transport properties of low-dimensional systems near a quantum phase transition shall be presented. Basic results will be reviewed in the context of experiments on the spin-ladder compounds. Recent large N computations (M. Vojta and S. Sachdev, Phys. Rev. Lett. 83), 3916 (1999) on an extended t-J model motivate a global scenario of the quantum phases and transitions in the high temperature superconductors, and connections will be made to numerous experiments. A universal theory (S. Sachdev, C. Buragohain, and M. Vojta, Science, in press M. Vojta, C. Buragohain, and S. Sachdev, cond- mat/9912020) of quantum impurities in spin-gap antiferromagnets near a magnetic ordering transition will be compared quantitatively to experiments on Zn doped Y Ba2 Cu3 O7 (Fong et al.), Phys. Rev. Lett. 82, 1939 (1999)
Room-temperature antiferromagnetic memory resistor
NASA Astrophysics Data System (ADS)
Marti, X.; Fina, I.; Frontera, C.; Liu, Jian; Wadley, P.; He, Q.; Paull, R. J.; Clarkson, J. D.; Kudrnovský, J.; Turek, I.; Kuneš, J.; Yi, D.; Chu, J.-H.; Nelson, C. T.; You, L.; Arenholz, E.; Salahuddin, S.; Fontcuberta, J.; Jungwirth, T.; Ramesh, R.
2014-04-01
The bistability of ordered spin states in ferromagnets provides the basis for magnetic memory functionality. The latest generation of magnetic random access memories rely on an efficient approach in which magnetic fields are replaced by electrical means for writing and reading the information in ferromagnets. This concept may eventually reduce the sensitivity of ferromagnets to magnetic field perturbations to being a weakness for data retention and the ferromagnetic stray fields to an obstacle for high-density memory integration. Here we report a room-temperature bistable antiferromagnetic (AFM) memory that produces negligible stray fields and is insensitive to strong magnetic fields. We use a resistor made of a FeRh AFM, which orders ferromagnetically roughly 100 K above room temperature, and therefore allows us to set different collective directions for the Fe moments by applied magnetic field. On cooling to room temperature, AFM order sets in with the direction of the AFM moments predetermined by the field and moment direction in the high-temperature ferromagnetic state. For electrical reading, we use an AFM analogue of the anisotropic magnetoresistance. Our microscopic theory modelling confirms that this archetypical spintronic effect, discovered more than 150 years ago in ferromagnets, is also present in AFMs. Our work demonstrates the feasibility of fabricating room-temperature spintronic memories with AFMs, which in turn expands the base of available magnetic materials for devices with properties that cannot be achieved with ferromagnets.
NASA Astrophysics Data System (ADS)
Wang, Bo-Yao; Lin, Po-Han; Tsai, Ming-Shian; Shih, Chun-Wei; Lee, Meng-Ju; Huang, Chun-Wei; Jih, Nae-Yeou; Wei, Der-Hsin
2016-08-01
This study demonstrates the effect of antiferromagnet-induced perpendicular magnetic anisotropy (PMA) on ferromagnetic/antiferromagnetic/ferromagnetic (FM/AFM/FM) trilayers and reveals its interplay with a long-range interlayer coupling between separated FM layers. In epitaxially grown 12 monolayer (ML) Ni/Co/Mn/5 ML Co/Cu(001) films, magnetic hysteresis loops and element-resolved magnetic domain imaging showed that the magnetization direction of the top layers of 12 ML Ni/Co films could be changed from the in-plane direction to the perpendicular direction, when the thickness of the Mn films (tMn) was greater than a critical value close to the thickness threshold associated with the onset of AFM ordering (tMn=3.5 ML). The top FM layers exhibited a significantly enhanced PMA when tMn increased further, and this enhancement can be attributed to a strengthened AFM ordering of the volume moments of the Mn films, as evidenced by the presence of induced domain frustration. By contrast, the long-range interlayer coupling presented clear effects only when tMn was at a lower coverage.
Horio, M; Adachi, T; Mori, Y; Takahashi, A; Yoshida, T; Suzuki, H; Ambolode, L C C; Okazaki, K; Ono, K; Kumigashira, H; Anzai, H; Arita, M; Namatame, H; Taniguchi, M; Ootsuki, D; Sawada, K; Takahashi, M; Mizokawa, T; Koike, Y; Fujimori, A
2016-01-01
In the hole-doped cuprates, a small number of carriers suppresses antiferromagnetism and induces superconductivity. In the electron-doped cuprates, on the other hand, superconductivity appears only in a narrow window of high-doped Ce concentration after reduction annealing, and strong antiferromagnetic correlation persists in the superconducting phase. Recently, Pr1.3-xLa0.7CexCuO4 (PLCCO) bulk single crystals annealed by a protect annealing method showed a high critical temperature of around 27 K for small Ce content down to 0.05. Here, by angle-resolved photoemission spectroscopy measurements of PLCCO crystals, we observed a sharp quasi-particle peak on the entire Fermi surface without signature of an antiferromagnetic pseudogap unlike all the previous work, indicating a dramatic reduction of antiferromagnetic correlation length and/or of magnetic moments. The superconducting state was found to extend over a wide electron concentration range. The present results fundamentally challenge the long-standing picture on the electronic structure in the electron-doped regime. PMID:26843063
Horio, M.; Adachi, T.; Mori, Y.; Takahashi, A.; Yoshida, T.; Suzuki, H.; Ambolode, L. C. C.; Okazaki, K.; Ono, K.; Kumigashira, H.; Anzai, H.; Arita, M.; Namatame, H.; Taniguchi, M.; Ootsuki, D.; Sawada, K.; Takahashi, M.; Mizokawa, T.; Koike, Y.; Fujimori, A.
2016-01-01
In the hole-doped cuprates, a small number of carriers suppresses antiferromagnetism and induces superconductivity. In the electron-doped cuprates, on the other hand, superconductivity appears only in a narrow window of high-doped Ce concentration after reduction annealing, and strong antiferromagnetic correlation persists in the superconducting phase. Recently, Pr1.3−xLa0.7CexCuO4 (PLCCO) bulk single crystals annealed by a protect annealing method showed a high critical temperature of around 27 K for small Ce content down to 0.05. Here, by angle-resolved photoemission spectroscopy measurements of PLCCO crystals, we observed a sharp quasi-particle peak on the entire Fermi surface without signature of an antiferromagnetic pseudogap unlike all the previous work, indicating a dramatic reduction of antiferromagnetic correlation length and/or of magnetic moments. The superconducting state was found to extend over a wide electron concentration range. The present results fundamentally challenge the long-standing picture on the electronic structure in the electron-doped regime. PMID:26843063
Superconducting phase diagram of itinerant antiferromagnets
NASA Astrophysics Data System (ADS)
Rømer, A. T.; Eremin, I.; Hirschfeld, P. J.; Andersen, B. M.
2016-05-01
We study the phase diagram of the Hubbard model in the weak-coupling limit for coexisting spin-density-wave order and spin-fluctuation-mediated superconductivity. Both longitudinal and transverse spin fluctuations contribute significantly to the effective interaction potential, which creates Cooper pairs of the quasiparticles of the antiferromagnetic metallic state. We find a dominant dx2-y2-wave solution in both electron- and hole-doped cases. In the quasi-spin-triplet channel, the longitudinal fluctuations give rise to an effective attraction supporting a p -wave gap, but are overcome by repulsive contributions from the transverse fluctuations which disfavor p -wave pairing compared to dx2-y2. The subleading pair instability is found to be in the g -wave channel, but complex admixtures of d and g are not energetically favored since their nodal structures coincide. Inclusion of interband pairing, in which each fermion in the Cooper pair belongs to a different spin-density-wave band, is considered for a range of electron dopings in the regime of well-developed magnetic order. We demonstrate that these interband pairing gaps, which are nonzero in the magnetic state, must have the same parity under inversion as the normal intraband gaps. The self-consistent solution to the full system of five coupled gap equations gives intraband and interband pairing gaps of dx2-y2 structure and similar gap magnitude. In conclusion, the dx2-y2 gap dominates for both hole and electron doping inside the spin-density-wave phase.
Fishman, Randy Scott; Haraldsen, Jason T
2011-01-01
While a magnetic phase may be both locally stable and globally unstable, global stability always implies local stability. The distinction between local and global stability is studied on a geometrically-frustrated triangular lattice antiferromagnet with easy axis, single-ion anisotropy D along the z axis. Whereas the critical value Dloc c for local stability may be discontinuous across a phase boundary, the critical value Dglo c Dloc c for global stability must be continuous. We demonstrate this behavior across the phase boundary between collinear 3 and 4 sublattice phases that are stable for large D.
Antiferromagnetic Heisenberg Spin Chain of a Few Cold Atoms in a One-Dimensional Trap
NASA Astrophysics Data System (ADS)
Murmann, S.; Deuretzbacher, F.; Zürn, G.; Bjerlin, J.; Reimann, S. M.; Santos, L.; Lompe, T.; Jochim, S.
2015-11-01
We report on the deterministic preparation of antiferromagnetic Heisenberg spin chains consisting of up to four fermionic atoms in a one-dimensional trap. These chains are stabilized by strong repulsive interactions between the two spin components without the need for an external periodic potential. We independently characterize the spin configuration of the chains by measuring the spin orientation of the outermost particle in the trap and by projecting the spatial wave function of one spin component on single-particle trap levels. Our results are in good agreement with a spin-chain model for fermionized particles and with numerically exact diagonalizations of the full few-fermion system.
Phase diagram of a three-dimensional antiferromagnet with random magnetic anisotropy.
Perez, Felio A; Borisov, Pavel; Johnson, Trent A; Stanescu, Tudor D; Trappen, Robbyn; Holcomb, Mikel B; Lederman, David; Fitzsimmons, M R; Aczel, Adam A; Hong, Tao
2015-03-01
Three-dimensional antiferromagnets with random magnetic anisotropy (RMA) that have been experimentally studied to date have competing two-dimensional and three-dimensional exchange interactions which can obscure the authentic effects of RMA. The magnetic phase diagram of Fe_{x}Ni_{1-x}F_{2} epitaxial thin films with true random single-ion anisotropy was deduced from magnetometry and neutron scattering measurements and analyzed using mean-field theory. Regions with uniaxial, oblique, and easy-plane anisotropies were identified. A RMA-induced glass region was discovered where a Griffiths-like breakdown of long-range spin order occurs. PMID:25793845
Phase Diagram of a Three-Dimensional Antiferromagnet with Random Magnetic Anisotropy
Perez, Felio A.; Borisov, Pavel; Johnson, Trent A.; Stanescu, Tudor D.; Trappen, Robbyn; Holcomb, Mikel B.; Lederman, David; Fitzsimmons, M. R.; Aczel, Adam A.; Hong, Tao
2015-03-04
Three-dimensional (3D) antiferromagnets with random magnetic anisotropy (RMA) that were experimentally studied to date have competing two-dimensional and three-dimensional exchange interactions which can obscure the authentic effects of RMA. The magnetic phase diagram of Fe_{x}Ni_{1-x}F_{2} epitaxial thin films with true random single-ion anisotropy was deduced from magnetometry and neutron scattering measurements and analyzed using mean field theory. Regions with uniaxial, oblique and easy plane anisotropies were identified. A RMA-induced glass region was discovered where a Griffiths-like breakdown of long-range spin order occurs.
Phase Diagram of a Three-Dimensional Antiferromagnet with Random Magnetic Anisotropy
Perez, Felio A.; Borisov, Pavel; Johnson, Trent A.; Stanescu, Tudor D.; Trappen, Robbyn; Holcomb, Mikel B.; Lederman, David; Fitzsimmons, M. R.; Aczel, Adam A.; Hong, Tao
2015-03-04
Three-dimensional (3D) antiferromagnets with random magnetic anisotropy (RMA) that were experimentally studied to date have competing two-dimensional and three-dimensional exchange interactions which can obscure the authentic effects of RMA. The magnetic phase diagram of FexNi1-xF2 epitaxial thin films with true random single-ion anisotropy was deduced from magnetometry and neutron scattering measurements and analyzed using mean field theory. Regions with uniaxial, oblique and easy plane anisotropies were identified. A RMA-induced glass region was discovered where a Griffiths-like breakdown of long-range spin order occurs.
Itinerant Antiferromagnetism in FeMnP0.8Si0.2
Sales, Brian C.; Susner, Michael A.; Conner, Benjamin S.; Yan, Jiaqiang Q.; May, Andrew F.
2015-09-25
Compounds based on the Fe2P structure have continued to attract interest because of the interplay between itinerant and localized magnetism in a noncentrosymmetric crystal structure, and because of the recent developments of these materials for magnetocaloric applications. We report the growth and characterization of millimeter-sized single crystals of FeMnP0.8Si0.2 with the Fe2P structure. Single-crystal x-ray diffraction, magnetization, resistivity, and Hall and heat capacity data are reported. The crystals exhibit itinerant antiferromagnetic order below 158 K with no hint of ferromagnetic behavior in the magnetization curves and with the spins ordered primarily in the ab plane. The room-temperature resistivity is closemore » to the Ioffe-Regel limit for a metal. Single-crystal x-ray diffraction indicates a strong preference for Mn to occupy the larger pyramidal 3g site. The cation site preference in the as-grown crystals and the antiferromagnetism were not changed after high-temperature anneals and a rapid quench to room temperature« less
Nematic antiferromagnetic states in bulk FeSe
NASA Astrophysics Data System (ADS)
Liu, Kai; Lu, Zhong-Yi; Xiang, Tao
2016-05-01
The existence of nematic order, which breaks the lattice rotational symmetry with nonequivalent a and b axes in iron-based superconductors, is a well-established experimental fact. An antiferromagnetic (AFM) transition is accompanying this order, observed in nearly all parent compounds, except bulk FeSe. The absence of the AFM order in FeSe casts doubt on the magnetic mechanism of iron-based superconductivity, since the nematic order is believed to be driven by the same interaction that is responsible for the superconducting pairing in these materials. Here we show, through systematic first-principles electronic structure calculations, that the ground state of FeSe is in fact strongly AFM correlated but without developing a magnetic long-range order. Actually, there are a series of staggered n -mer AFM states with corresponding energies below that of the single stripe AFM state, which is the ground state for the parent compounds of most iron-based superconductors. Here, the staggered n -mer (n any integer >1 ) means a set of n adjacent parallel spins on a line along the b axis with antiparallel spins between n -mers along both a and b axes. Moreover, different n -mers can antiparallelly mix with each other to coexist. Among all the states, we find that the lowest energy states formed by the staggered dimer, staggered trimer, and their random antiparallel aligned spin states along the b axis are quasidegenerate. The thermal average of these states does not show any magnetic long-range order, but it does possess a hidden one-dimensional AFM order along the a axis, which can be detected by elastic neutron scattering measurements. Our finding gives a natural account for the absence of long-range magnetic order and suggests that the nematicity is driven predominantly by spin fluctuations even in bulk FeSe, providing a unified description on the phase diagram of iron-based superconductors.
Vertex functions at finite momentum: Application to antiferromagnetic quantum criticality
NASA Astrophysics Data System (ADS)
Wölfle, Peter; Abrahams, Elihu
2016-02-01
We analyze the three-point vertex function that describes the coupling of fermionic particle-hole pairs in a metal to spin or charge fluctuations at nonzero momentum. We consider Ward identities, which connect two-particle vertex functions to the self-energy, in the framework of a Hubbard model. These are derived using conservation laws following from local symmetries. The generators considered are the spin density and particle density. It is shown that at certain antiferromagnetic critical points, where the quasiparticle effective mass is diverging, the vertex function describing the coupling of particle-hole pairs to the spin density Fourier component at the antiferromagnetic wave vector is also divergent. Then we give an explicit calculation of the irreducible vertex function for the case of three-dimensional antiferromagnetic fluctuations, and show that it is proportional to the diverging quasiparticle effective mass.
Antiferromagnetic coupling across silicon regulated by tunneling currents
NASA Astrophysics Data System (ADS)
Gareev, Rashid; Schmid, Maximilian; Vancea, Johann; Back, Christian; Schreiber, Reinert; Buergler, Daniel; Stromberg, Frank; Wende, Heiko
2012-02-01
We present the room temperature enhancement of antiferromagnetic coupling in epitaxial Fe(3 nm)/Si(2.4 nm)/Fe(3 nm) structures by voltage-driven spin-polarized tunneling currents. Using the ballistic electron magnetic microscopy we established that the saturation field for the collector current corresponding to parallel alignment of magnetizations rises up with the tunneling current, thus demonstrating stabilization of the antiparallel alignment and increase of antiferromagnetic coupling. We connect the enhancement of antiferromagnetic coupling with local dynamic spin torques mediated by spin-polarized tunneling electrons. Finally, in the antiparallel state the spin-polarized majority (minority) electrons exert dynamic torques in the bottom (upper) iron layer and, thus, additionally stabilize magnetization alignment.
Antiferromagnetic phase of the gapless semiconductor V3Al
NASA Astrophysics Data System (ADS)
Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; Arena, D.; Lewis, L. H.; Saúl, A. A.; Radtke, G.; Heiman, D.
2015-03-01
Discovering new antiferromagnetic (AF) compounds is at the forefront of developing future spintronic devices without fringing magnetic fields. The AF gapless semiconducting D 03 phase of V3Al was successfully synthesized via arc-melting and annealing. The AF properties were established through synchrotron measurements of the atom-specific magnetic moments, where the magnetic dichroism reveals large and oppositely oriented moments on individual V atoms. Density functional theory calculations confirmed the stability of a type G antiferromagnetism involving only two-thirds of the V atoms, while the remaining V atoms are nonmagnetic. Magnetization, x-ray diffraction, and transport measurements also support the antiferromagnetism. This archetypal gapless semiconductor may be considered as a cornerstone for future spintronic devices containing AF elements.
Exchange-bias-like effect of an uncompensated antiferromagnet
NASA Astrophysics Data System (ADS)
Henne, Bastian; Ney, Verena; de Souza, Mariano; Ney, Andreas
2016-04-01
The exchange bias effect is usually defined as horizontal shift of the field-cooled magnetization loop when an antiferromagnet is directly coupled to a ferromagnet. Uncompensated spins at the interface between the two layers are believed to cause this phenomenon. The presence of such, on the other hand, would infer a vertical, i.e., a magnetization-like shift stemming from the antiferromagnet. Observations of this effect are sparse, especially in the absence of a ferromagnet. We present a model system based on extremely Co doped ZnO in which the uncompensated spins of antiferromagnetic Co-O-Co… configurations lead to this vertical shift and therefore to a field-resistant magnetization. A simple Stoner-Wohlfarth-like model based on configurations of different sizes is used to explain the occurrence of this exchange-bias-like shift and a narrow opening of the magnetization curves.
Ferro- and antiferro-magnetism in (Np, Pu)BC
NASA Astrophysics Data System (ADS)
Klimczuk, T.; Shick, A. B.; Kozub, A. L.; Griveau, J.-C.; Colineau, E.; Falmbigl, M.; Wastin, F.; Rogl, P.
2015-04-01
Two new transuranium metal boron carbides, NpBC and PuBC, have been synthesized. Rietveld refinements of powder XRD patterns of {Np,Pu}BC confirmed in both cases isotypism with the structure type of UBC. Temperature dependent magnetic susceptibility data reveal antiferromagnetic ordering for PuBC below TN = 44 K, whereas ferromagnetic ordering was found for NpBC below TC = 61 K. Heat capacity measurements prove the bulk character of the observed magnetic transition for both compounds. The total energy electronic band structure calculations support formation of the ferromagnetic ground state for NpBC and the antiferromagnetic ground state for PuBC.
Antiferromagnetic majority voter model on square and honeycomb lattices
NASA Astrophysics Data System (ADS)
Sastre, Francisco; Henkel, Malte
2016-02-01
An antiferromagnetic version of the well-known majority voter model on square and honeycomb lattices is proposed. Monte Carlo simulations give evidence for a continuous order-disorder phase transition in the stationary state in both cases. Precise estimates of the critical point are found from the combination of three cumulants, and our results are in good agreement with the reported values of the equivalent ferromagnetic systems. The critical exponents 1 / ν, γ / ν and β / ν were found. Their values indicate that the stationary state of the antiferromagnetic majority voter model belongs to the Ising model universality class.
Thermal Generation of Spin Current in an Antiferromagnet.
Seki, S; Ideue, T; Kubota, M; Kozuka, Y; Takagi, R; Nakamura, M; Kaneko, Y; Kawasaki, M; Tokura, Y
2015-12-31
The longitudinal spin Seebeck effect has been investigated for a uniaxial antiferromagnetic insulator Cr(2)O(3), characterized by a spin-flop transition under magnetic field along the c axis. We have found that a temperature gradient applied normal to the Cr(2)O(3)/Pt interface induces inverse spin Hall voltage of spin-current origin in Pt, whose magnitude turns out to be always proportional to magnetization in Cr(2)O(3). The possible contribution of the anomalous Nernst effect is confirmed to be negligibly small. The above results establish that an antiferromagnetic spin wave can be an effective carrier of spin current. PMID:26765011
Magnetization damping in noncollinear spin valves with antiferromagnetic interlayer couplings
NASA Astrophysics Data System (ADS)
Chiba, Takahiro; Bauer, Gerrit E. W.; Takahashi, Saburo
2015-08-01
We study the magnetic damping in the simplest of synthetic antiferromagnets, i.e., antiferromagnetically exchange-coupled spin valves, in the presence of applied magnetic fields that enforce noncolliear magnetic configurations. We formulate the dynamic exchange of spin currents in a noncollinear texture based on the spin-diffusion theory with quantum mechanical boundary conditions at the ferrromagnet/normal-metal interfaces and derive the Landau-Lifshitz-Gilbert equations coupled by the interlayer static and dynamic exchange interactions. We predict noncollinearity-induced additional damping that is modulated by an applied magnetic field. We compare theoretical results with published experiments.
Antiferromagnetism in Bulk Rutile RuO2
NASA Astrophysics Data System (ADS)
Berlijn, T.; Snijders, P. C.; Kent, P. R. C.; Maier, T. A.; Zhou, H.-D.; Cao, H.-B.; Delaire, O.; Wang, Y.; Koehler, M.; Weitering, H. H.
While bulk rutile RuO2 has long been considered to be a Pauli paramagnet, we conclude it to host antiferromagnetism based on our combined theoretical and experimental study. This constitutes an important finding given the large amount of applications of RuO2 in the electrochemical and electronics industry. Furthermore the high onset temperature of the antiferromagnetism around 1000K together with the high electrical conductivity makes RuO2 unique among the ruthenates and among oxide materials in general. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.
Li, Yuesheng; Adroja, Devashibhai; Biswas, Pabitra K; Baker, Peter J; Zhang, Qian; Liu, Juanjuan; Tsirlin, Alexander A; Gegenwart, Philipp; Zhang, Qingming
2016-08-26
Muon spin relaxation (μSR) experiments on single crystals of the structurally perfect triangular antiferromagnet YbMgGaO_{4} indicate the absence of both static long-range magnetic order and spin freezing down to 0.048 K in a zero field. Below 0.4 K, the μ^{+} spin relaxation rates, which are proportional to the dynamic correlation function of the Yb^{3+} spins, exhibit temperature-independent plateaus. All these μSR results unequivocally support the formation of a gapless U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO_{4}. PMID:27610879
NASA Astrophysics Data System (ADS)
Pires, Antonio; Sousa, Griffith
2014-03-01
The square lattice antiferromagnet with next and next nearest neighbor exchange interaction has been the subject of intense research in the last years. It can present the behavior of a frustrated system and can otherwise describe real materials. However, a large part of the work has been dedicated to spin 1/2 and done at zero temperature. A system with spin 1 is of interest because it can have a single ion anisotropy. To study these models simple approaches which yield an analytical description are very useful for practical purposes. Here we use a Modified Spin Wave theory, where corrections owing to spin wave interactions are taken into account self-consistently, to study the easy axis two dimensional spin 1 antiferromagnet with competing interaction and single ion anisotropy. We calculate the phase diagram at zero temperature, and several thermodynamic quantities such as the magnetization, the gap and the specific heat. Their relations with the temperature and anisotropy parameter are analyzed over the entire range of temperature. We have found a Neel and a collinear phase separated by a disordered phase. This disordered phase could be a candidate for a spin liquid. This work was partially supported by CNPQ, FAPEMIG and FAPEAM.
Magnetoelectric coupling in the honeycomb antiferromagnet Co4Nb2O9
NASA Astrophysics Data System (ADS)
Khanh, N. D.; Abe, N.; Sagayama, H.; Nakao, A.; Hanashima, T.; Kiyanagi, R.; Tokunaga, Y.; Arima, T.
2016-02-01
The magnetic structure and magnetoelectric effect have been investigated for single crystals of the antiferromagnet Co4Nb2O9 . Single-crystal neutron diffraction and magnetic susceptibility measurement have revealed that the magnetic structure is different from a collinear arrangement with spin parallel to the trigonal axis as proposed previously. Co2 + magnetic moments are found to be almost lying in the basal plane, which lowers the magnetic symmetry to C 2 /c' with the propagation vector k =0 . Associated with the magnetic phase transition, a sharp anomaly in the dielectric constant and displacement current indicate the appearance of the magnetoelectric below Néel temperature TN with a large coupling constant up to 30 ps/m. The existence of off-diagonal components in a magnetoelectric tensor indicate the formation of ferrotoroidic order in Co4Nb2O9 . Such a magnetoelectric effect can be ascribed to the reduction of symmetry caused by simple antiferromagnetic order in a honeycomb network.
Thermal behavior in the magnetic phase diagram of the easy axis antiferromagnet Cs2FeCl5·H2O
NASA Astrophysics Data System (ADS)
Freitas, R. S.; Paduan-Filho, A.; Becerra, C. C.
2016-03-01
The specific heat at a constant applied field C H(T) and at fixed temperatures C T(H) of single crystals of the low anisotropy antiferromagnet Cs2FeCl5·H2O was measured across the different boundaries of its magnetic phase diagram, in magnetic fields up to 9 T applied parallel and perpendicular to the easy axis direction and to temperatures down to 0.3 K. The specific heat data indicate that the critical behavior along the antiferromagnetic to paramagnetic phase boundary and the spin-flop to paramagnetic phase boundary, are basically the same. We also measured the specific heat when the first order antiferromagnetic to spin-flop phase boundary is crossed at a fixed temperature. The entropy of the different magnetic phases is discussed.
Birefringence of the antiferromagnetic crystals linear in a magnetic field
NASA Astrophysics Data System (ADS)
Eremenko, V. V.; Kharchenko, N. F.; Beliy, L. I.; Tutakina, O. P.
1980-01-01
The new linear magneto-optical effect-birefringence-of a linear polarized light which is directly proportional to the magnetic field strength has been observed. This effect is permitted in crystals which allow piezo-magnetic properties. One was studied in antiferromagnet CoF 2 and CoCO 3 for the longitudinal geometry of an experiment.
On the ground state of antiferromagnets at zero temperature
NASA Astrophysics Data System (ADS)
Mayer, I.; Angelov, S. A.
1984-02-01
The wave function describing a perfect antiferromagnetic ordering of spins at 0 K (the singlet projection of the Néel function) was proved to be not an eigenfunction of the exchange Hamiltonian: the long-range order is reduced as to permit a higher correlation between the nearest-neighbour spins.
An antiferromagnetic transverse Ising nanoisland; unconventional surface effects
NASA Astrophysics Data System (ADS)
Kaneyoshi, T.
2015-12-01
The phase diagrams and temperature dependences of magnetizations in a transverse Ising nanosisland with an antiferromagnetic spin configuration are studied by the use of the effective-field theory with correlations (EFT). Some novel features, such as the re-entrant phenomena with two compensation points being free from disorder induced frustration, are obtained for the magnetic properties in the system.
Antiferromagnetic order in a semiconductor quantum well with spin-orbit coupling
NASA Astrophysics Data System (ADS)
Marinescu, D. C.
2015-05-01
An argument is made on the existence of a low-temperature itinerant antiferromagnetic (AF) spin alignment, rather than persistent helical (PH), in the ground state of a two dimensional electron gas in a semiconductor quantum well with linear spin-orbit Rashba-Dresselhaus interaction at equal coupling strengths, α. This result is obtained on account of the opposite-spin single-particle state degeneracy at k = 0 that makes the spin instability possible. A theory of the resulting magnetic phase is formulated within the Hartree-Fock approximation of the Coulomb interaction. In the AF state the direction of the fractional polarization is obtained to be aligned along the displacement vector of the single-particle states.
Sequential write-read operations in FeRh antiferromagnetic memory
NASA Astrophysics Data System (ADS)
Moriyama, Takahiro; Matsuzaki, Noriko; Kim, Kab-Jin; Suzuki, Ippei; Taniyama, Tomoyasu; Ono, Teruo
2015-09-01
B2-ordered FeRh has been known to exhibit antiferromagnetic-ferromagnetic (AF-F) phase transitions in the vicinity of room temperature. Manipulation of the Néel order via AF-F phase transition and recent experimental observation of the anisotropic magnetoresistance in antiferromagnetic FeRh has proven that FeRh is a promising candidate for antiferromagnetic memory material. In this work, we demonstrate sequential write and read operations in antiferromagnetic memory resistors made of B2-orderd FeRh thin films by a magnetic field and electric current only, which open a realistic pathway towards operational antiferromagnetic memory devices.
Heisenberg antiferromagnet on Cayley trees: Low-energy spectrum and even/odd site imbalance
NASA Astrophysics Data System (ADS)
Changlani, Hitesh J.; Ghosh, Shivam; Henley, Christopher L.; Läuchli, Andreas M.
2013-02-01
To understand the role of local sublattice imbalance in low-energy spectra of s=(1)/(2) quantum antiferromagnets, we study the s=(1)/(2) quantum nearest neighbor Heisenberg antiferromagnet on the coordination 3 Cayley tree. We perform many-body calculations using an implementation of the density matrix renormalization group (DMRG) technique for generic tree graphs. We discover that the bond-centered Cayley tree has a quasidegenerate set of a low-lying tower of states and an “anomalous” singlet-triplet finite-size gap scaling. For understanding the construction of the first excited state from the many-body ground state, we consider a wave function ansatz given by the single-mode approximation, which yields a high overlap with the DMRG wave function. Observing the ground-state entanglement spectrum leads us to a picture of the low-energy degrees of freedom being “giant spins” arising out of sublattice imbalance, which helps us analytically understand the scaling of the finite-size spin gap. The Schwinger-boson mean-field theory has been generalized to nonuniform lattices, and ground states have been found which are spatially inhomogeneous in the mean-field parameters.
Mechanism of spin and charge separation in one-dimensional quantum antiferromagnets
Mudry, C.; Fradkin, E. )
1994-10-15
We reconsider the problem of separation of spin and charge in one-dimensional quantum antiferromagnets. We show that spin and charge separation in one-dimensional strongly correlated systems cannot be described by the slave-boson or fermion representation within any perturbative treatment of the interactions between the slave holons and slave spinons. The constraint of single occupancy must be implemented exactly. As a result the slave fermions and bosons are not part of the physical spectrum. Instead, the excitations that carry the separate spin and charge quantum numbers are solitons. To prove this result, it is sufficient to study the pure spinon sector in the slave-boson representation. We start with a short-range resonating-valence-bond state spin liquid mean-field theory for the frustrated antiferromagnetic spin-1/2 chain. We derive an effective theory for the fluctuations of the Affleck-Marston and Anderson order parameters. We show how to recover the phase diagram as a function of the frustration by treating the fluctuations nonperturbatively.
Antiferromagnetism and Hidden Order in Isoelectronic Doping of URu2Si2
NASA Astrophysics Data System (ADS)
Wilson, Murray; Williams, Travis; Cai, Yipeng; Hallas, Alannah; Medina, Teresa; Munsie, Timothy; Cheung, Sky; Liu, Lian; Frandsen, Benjamen; Uemura, Yasutomo; Luke, Graeme
URu2Si2 has been studied for three decades to understand its unusual hidden order state. Doping of this compound on the Ru site usually causes the transition temperature to decrease and hidden order to transition to magnetic order. In contrast, the isoelectronic dopings Fe and Os cause a substantial increase in the transition temperature over a wide range of dopings, with Fe in particular mimicking applied hydrostatic pressure. However, until recently, the magnetic states of these dopings have not been well characterized. In the past year, neutron scattering results have been reported on Fe doping that show antiferromagnetism with moments that are twice as large as those measured for pure URu2Si2 under pressure. In this talk we present an investigation of the magnetic properties of single crystal samples of URu-xFexSi2 and URu2-xOsxSi2 by muon spin rotation (μSR) and susceptibility. Our μSR results demonstrate that both of these dopings show an antiferromagnetic ground state with internal fields comparable to pure URu2Si2 under pressure. Interpretation of our data indicates that the evolution of magnetism with doping for both Fe and Os is driven by changes in hybridization.
Magnetic ordering of the buckled honeycomb lattice antiferromagnet Ba2NiTeO6
NASA Astrophysics Data System (ADS)
Asai, Shinichiro; Soda, Minoru; Kasatani, Kazuhiro; Ono, Toshio; Avdeev, Maxim; Masuda, Takatsugu
2016-01-01
We investigate the magnetic order of the buckled honeycomb lattice antiferromagnet Ba2NiTeO6 and its related antiferromagnet Ba3NiTa2O9 by neutron diffraction measurements. We observe magnetic Bragg peaks below the transition temperatures, and identify propagation vectors for these oxides. A combination of representation analysis and Rietveld refinement leads to a collinear magnetic order for Ba2NiTeO6 and a 120∘ structure for Ba3NiTa2O9 . We find that the spin model of the bilayer triangular lattice is equivalent to that of the two-dimensional buckled honeycomb lattice having magnetic frustration. We discuss the magnetic interactions and single-ion anisotropy of Ni+2 ions for Ba2NiTeO6 in order to clarify the origin of the collinear magnetic structures. Our calculation suggests that the collinear magnetic order of Ba2NiTeO6 is induced by the magnetic frustration and easy-axis anisotropy.
Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet
Fu, Mingxuan; Imai, Takahashi; Han, Tian -Heng; Lee, Young S.
2015-11-06
Here, the kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu_{3}(OH)_{6}Cl_{2}], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χkagome, deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with the magnetic field dependence of χ_{kagome} that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.
Magnetoelectric effect in antiferromagnetic LiCoPO4 in pulsed magnetic fields
NASA Astrophysics Data System (ADS)
Khrustalyov, V. M.; Savytsky, V. M.; Kharchenko, M. F.
2016-04-01
The magnetoelectric effect in single-crystal LiCoPO4 (TN = 21.8 K) is studied in strong pulsed magnetic fields which destroy the antiferromagnetic structure of the crystal spin ordering. The electric polarization along the crystallographic a axis induced by a magnetic field H||b is measured. New features of the electric polarization in a magnetic field are found, including a spike in the polarization near the field for the first magnetic transition at H1 = 123 kOe, a recovery of the electric polarization at the second magnetic transition H2 = 210 kOe, and a gradual reduction to zero on approaching the third transition at H3 = 263 kOe. Various possible magnetic structures in the high field phases are examined which are consistent with their magnetization and electric polarization. The observed linear dependence of the polarization on field strength in the initial antiferromagnetic phase and the vanishing of the polarization in the first high-field phase are in good agreement with previous studies of the magnetoelectric effect in LiCoPO4 [Wiegelmann et al., Ferroelectrics 161, 147 (1994); H. Wiegelman, Ph.D. thesis (University of Konstanz, Konstanz, 1995)].
Anomalous net magnetization in collinear antiferromagnets with uncompensated surfaces
NASA Astrophysics Data System (ADS)
Hellman, Frances
2015-03-01
Like ferromagnets (FM), antiferromagnets (AFM) exhibit spontaneous long-range spin order below a transition temperature. The traditional FM order parameter is the spontaneous magnetization, while that of a simple AFM is the staggered magnetization, sometimes called the Neel vector N. The net magnetization M of a perfect AFM is (seemingly) zero at all temperatures T; however, defects such as vacancies, grain boundaries, and even surfaces create an M(T) which has a non-trivial relationship to the staggered magnetization N(T), even in ideal systems. As a specific example, we consider AFM CoO, which consists of AFM-coupled FM (111) planes; (111)-oriented epitaxial films with an odd number of planes will exhibit non-zero M due to uncompensated surfaces. These uncompensated surfaces were used to produce an artificially-structured FM semiconductor using epitaxial layers of AFM CoO with a doped semiconductor Al:ZnO (AZO). Both M(T) and the anomalous Hall effect show oscillatory behavior with thickness of either CoO (odd vs even numbers of planes) or AZO (~1 nm RKKY-like oscillations related to the AZO Fermi wavevector due to electron-induced coupling between Co moments at its two CoO surfaces). Mean field theory and Monte Carlo simulations show that M(T) of collinear AFM such as CoO with uncompensated surfaces exhibits T-dependence unlike that of N(T), of the absolute value of its individual layers, or m(T) of any single atomic plane including the uncompensated surface, due to incomplete cancellations of different planes. This phenomenon is valid even in the limit of semi-infinite systems; it is a topological state due to the presence of a free surface. Modifications of surface exchange coupling (leading to ordinary or extraordinary transitions), due to electron correlations in these Mott insulators, changes in crystal fields, spin-orbit coupling, or an incomplete (rough) surface, result in compensation points and highly non-Brillouin-like M(T). Work supported by the U
Frustration and multicriticality in the antiferromagnetic spin-1 chain
NASA Astrophysics Data System (ADS)
Pixley, J. H.; Shashi, Aditya; Nevidomskyy, Andriy H.
2014-12-01
The antiferromagnetic spin-1 chain has a venerable history and has been thought to be well understood. Here, we show that inclusion of both next-nearest-neighbor (α ) and biquadratic (β ) interactions results in a rich phase diagram with a multicritical point that has not been observed before. We study the problem using a combination of the density matrix renormalization group (DMRG), an analytic variational matrix product state wave function, and conformal field theory. For negative β <β* , we establish the existence of a spontaneously dimerized phase, separated from the Haldane phase by the critical line αc(β ) of second-order phase transitions. In the opposite regime, β >β* , the transition from the Haldane phase becomes first order into the next-nearest-neighbor (NNN) AKLT phase. Based on the field theoretical arguments and DMRG calculations, we find that these two regimes are separated by a multicritical point (β*,α*) of a different universality class, described by the level-4 SU(2) Wess-Zumino-Witten conformal theory. From the DMRG calculations, we estimate this multicritical point to lie in the range -0.2 <β*<-0.15 and 0.47 <α*<0.53 . We further find that the dimerized and NNN-AKLT phases are separated from each other by a line of first-order phase transitions that terminates at the multicritical point. We establish that transitions out of the Haldane phase into the dimer or NNN-AKLT phases are topological in nature and occur either with or without closing of the bulk gap, respectively. We also study short-range incommensurate-to-commensurate transitions in the resulting phase diagram. Inside the Haldane phase, we show the existence of two incommensurate crossovers: the Lifshitz transition and the disorder transition of the first kind, marking incommensurate correlations in momentum and real space, respectively. Notably, these crossover lines stretch across the entire (β ,α ) phase diagram, merging into a single incommensurate
Control of antiferromagnetic domain distribution via polarization-dependent optical annealing.
Higuchi, Takuya; Kuwata-Gonokami, Makoto
2016-01-01
The absence of net magnetization inside antiferromagnetic domains has made the control of their spatial distribution quite challenging. Here we experimentally demonstrate an optical method for controlling antiferromagnetic domain distributions in MnF2. Reduced crystalline symmetry can couple an order parameter with non-conjugate external stimuli. In the case of MnF2, time-reversal symmetry is macroscopically broken reflecting the different orientations of the two magnetic sublattices. Thus, it exhibits different absorption coefficients between two orthogonal linear polarizations below its antiferromagnetic transition temperature under an external magnetic field. Illumination with linearly polarized laser light under this condition selectively destructs the formation of a particular antiferromagnetic order via heating. As a result, the other antiferromagnetic order is favoured inside the laser spot, achieving spatially localized selection of an antiferromagnetic order. Applications to control of interface states at antiferromagnetic domain boundaries, exchange bias and control of spin currents are expected. PMID:26911337
Control of antiferromagnetic domain distribution via polarization-dependent optical annealing
Higuchi, Takuya; Kuwata-Gonokami, Makoto
2016-01-01
The absence of net magnetization inside antiferromagnetic domains has made the control of their spatial distribution quite challenging. Here we experimentally demonstrate an optical method for controlling antiferromagnetic domain distributions in MnF2. Reduced crystalline symmetry can couple an order parameter with non-conjugate external stimuli. In the case of MnF2, time-reversal symmetry is macroscopically broken reflecting the different orientations of the two magnetic sublattices. Thus, it exhibits different absorption coefficients between two orthogonal linear polarizations below its antiferromagnetic transition temperature under an external magnetic field. Illumination with linearly polarized laser light under this condition selectively destructs the formation of a particular antiferromagnetic order via heating. As a result, the other antiferromagnetic order is favoured inside the laser spot, achieving spatially localized selection of an antiferromagnetic order. Applications to control of interface states at antiferromagnetic domain boundaries, exchange bias and control of spin currents are expected. PMID:26911337
NASA Astrophysics Data System (ADS)
Sun, Wei; Huang, Ya-Xi; Pan, Yuanming; Mi, Jin-Xiao
2016-02-01
Minerals of the atacamite group such as herbertsmithite and kapellasite have recently attracted enormous attention as the S = ½ Kagomé antiferromagnets for achieving the quantum spin liquid (QSL) state with diverse technological applications. Herein we report on the synthesis of the newly discovered mineral centennialite by using an unconventional "solid-state" reaction method at 463 K. Synthetic centennialite, Ca1.06Cu2.94Cl2.01(OH)5.99·0.73H2O, has been characterized by scanning electron microscopy, electron microprobe analyses, Fourier-transform infrared spectroscopy, thermogravimetric and differential scanning calorimetric analyses, single-crystal X-ray diffraction structure refinements, and magnetic susceptibility measurements. The crystal structure of centennialite is characterized by a perfect (threefold symmetry) Kagomé layer with <5 % substitution between Ca and Cu and therefore differs from those of herbertsmithite and kapellasite, in which 15-25 % mixing between similar Zn and Cu atoms dramatically affects the QSL state. Centennialite remains antiferromagnetic down to ~7 K with a moderate spin frustration (i.e., a Weiss temperature θ = -56 K and a spin frustration parameter f = 8), but exhibits a canted antiferromagnetic ordering with a ferromagnetic component at lower temperatures.
Segregation of antiferromagnetism and high-temperature superconductivity in Ca1-xLaxFe2As2
NASA Astrophysics Data System (ADS)
Saha, Shanta R.; Drye, T.; Goh, S. K.; Klintberg, L. E.; Silver, J. M.; Grosche, F. M.; Sutherland, M.; Munsie, T. J. S.; Luke, G. M.; Pratt, D. K.; Lynn, J. W.; Paglione, J.
2014-04-01
We report the effect of applied pressures on magnetic and superconducting order in single crystals of the aliovalent La-doped iron pnictide material Ca1-xLaxFe2As2. Using electrical transport, elastic neutron scattering, and resonant tunnel diode oscillator measurements on samples under both quasihydrostatic and hydrostatic pressure conditions, we report a series of phase diagrams spanning the range of substitution concentrations for both antiferromagnetic and superconducting ground states that include pressure-tuning through the antiferromagnetic (AFM) superconducting critical point. Our results indicate that the observed superconducting phase with a maximum transition temperature of Tc=47 K is intrinsic to these materials, appearing only upon suppression of magnetic order by pressure-tuning through the AFM critical point. Thus, the superconducting phase appears to exist exclusively in juxtaposition to the antiferromagnetic phase in a manner similar to the oxygen- and fluorine-based iron-pnictide superconductors with the highest transition temperatures reported to date. Unlike the lower-Tc systems, in which superconductivity and magnetism usually coexist, the tendency for the highest-Tc systems to show noncoexistence provides an important insight into the distinct transition temperature limits in different members of the iron-based superconductor family.
EuCo2P2 : A model molecular-field helical Heisenberg antiferromagnet
NASA Astrophysics Data System (ADS)
Sangeetha, N. S.; Cuervo-Reyes, Eduardo; Pandey, Abhishek; Johnston, D. C.
2016-07-01
The metallic compound EuCo2P2 with the body-centered tetragonal ThCr2Si2 structure containing Eu spins-7/2 was previously shown from single-crystal neutron diffraction measurements to exhibit a helical antiferromagnetic (AFM) structure below TN=66.5 K with the helix axis along the c axis and with the ordered moments aligned within the a b plane. Here we report crystallography, electrical resistivity, heat capacity, magnetization, and magnetic susceptibility measurements on single crystals of this compound. We demonstrate that EuCo2P2 is a model molecular-field helical Heisenberg antiferromagnet from comparisons of the anisotropic magnetic susceptibility χ , high-field magnetization, and magnetic heat capacity of EuCo2P2 single crystals at temperature T ≤TN with the predictions of our recent formulation of molecular-field theory. Values of the Heisenberg exchange interactions between the Eu spins are derived from the data. The low-T magnetic heat capacity ˜T3 arising from spin-wave excitations with no anisotropy gap is calculated and found to be comparable to the lattice heat capacity. The density of states at the Fermi energy of EuCo2P2 and the related compound BaCo2P2 are found from the heat capacity data to be large, 10 and 16 states/eV per formula unit for EuCo2P2 and BaCo2P2 , respectively. These values are enhanced by a factor of ˜2.5 above those found from DFT electronic structure calculations for the two compounds. The calculations also find ferromagnetic Eu-Eu exchange interactions within the a b plane and AFM interactions between Eu spins in nearest- and next-nearest planes, in agreement with the MFT analysis of χa b(T ≤TN) .
EuCo2P2: A model molecular-field helical Heisenberg antiferromagnet
Sangeetha, N. S.; Cuervo-Reyes, Eduardo; Pandey, Abhishek; Johnston, D. C.
2016-07-19
Here, the metallic compound EuCo2P2 with the body-centered tetragonal ThCr2Si2 structure containing Eu spins-7/2 was previously shown from single-crystal neutron diffraction measurements to exhibit a helical antiferromagnetic (AFM) structure below TN=66.5 K with the helix axis along the c axis and with the ordered moments aligned within the ab plane. Here we report crystallography, electrical resistivity, heat capacity, magnetization, and magnetic susceptibility measurements on single crystals of this compound. We demonstrate that EuCo2P2 is a model molecular-field helical Heisenberg antiferromagnet from comparisons of the anisotropic magnetic susceptibility χ, high-field magnetization, and magnetic heat capacity of EuCo2P2 single crystals at temperaturemore » T ≤ TN with the predictions of our recent formulation of molecular-field theory. Values of the Heisenberg exchange interactions between the Eu spins are derived from the data. The low-T magnetic heat capacity ~T3 arising from spin-wave excitations with no anisotropy gap is calculated and found to be comparable to the lattice heat capacity. The density of states at the Fermi energy of EuCo2P2 and the related compound BaCo2P2 are found from the heat capacity data to be large, 10 and 16 states/eV per formula unit for EuCo2P2 and BaCo2P2, respectively. These values are enhanced by a factor of ~2.5 above those found from DFT electronic structure calculations for the two compounds. The calculations also find ferromagnetic Eu–Eu exchange interactions within the ab plane and AFM interactions between Eu spins in nearest- and next-nearest planes, in agreement with the MFT analysis of χab(T ≤ TN).« less
Interaction-induced adiabatic cooling for antiferromagnetism in optical lattices
Dare, A.-M.; Raymond, L.; Albinet, G.; Tremblay, A.-M. S.
2007-08-01
In the experimental context of cold-fermion optical lattices, we discuss the possibilities to approach the pseudogap or ordered phases by manipulating the scattering length or the strength of the laser-induced lattice potential. Using the two-particle self-consistent approach, as well as quantum Monte Carlo simulations, we provide isentropic curves for the two- and three-dimensional Hubbard models at half-filling. These quantitative results are important for practical attempts to reach the ordered antiferromagnetic phase in experiments on optical lattices of two-component fermions. We find that adiabatically turning on the interaction in two dimensions to cool the system is not very effective. In three dimensions, adiabatic cooling to the antiferromagnetic phase can be achieved in such a manner, although the cooling efficiency is not as high as initially suggested by dynamical mean-field theory. Adiabatic cooling by turning off the repulsion beginning at strong coupling is possible in certain cases.
Resonating Valence Bond states for low dimensional S=1 antiferromagnets
NASA Astrophysics Data System (ADS)
Liu, Zheng-Xin; Zhou, Yi; Ng, Tai-Kai
2014-03-01
We study S = 1 spin liquid states in low dimensions. We show that the resonating-valence-bond (RVB) picture of S = 1 / 2 spin liquid state can be generalized to S = 1 case. For S = 1 system, a many-body singlet (with even site number) can be decomposed into superposition of products of two-body singlets. In other words, the product states of two-body singlets, called the singlet pair states (SPSs), are over complete to span the Hilbert space of many-body singlets. Furthermore, we generalized fermionic representation and the corresponding mean field theory and Gutzwiller projected stats to S = 1 models. We applied our theory to study 1D anti-ferromagnetic bilinear-biquadratic model and show that both the ground states (including the phase transition point) and the excited states can be understood excellently well within the framework. Our method can be applied to 2D S = 1 antiferromagnets.
Layer Anti-Ferromagnetism on Bilayer Honeycomb Lattice
Tao, Hong-Shuai; Chen, Yao-Hua; Lin, Heng-Fu; Liu, Hai-Di; Liu, Wu-Ming
2014-01-01
Bilayer honeycomb lattice, with inter-layer tunneling energy, has a parabolic dispersion relation, and the inter-layer hopping can cause the charge imbalance between two sublattices. Here, we investigate the metal-insulator and magnetic phase transitions on the strongly correlated bilayer honeycomb lattice by cellular dynamical mean-field theory combined with continuous time quantum Monte Carlo method. The procedures of magnetic spontaneous symmetry breaking on dimer and non-dimer sites are different, causing a novel phase transition between normal anti-ferromagnet and layer anti-ferromagnet. The whole phase diagrams about the magnetism, temperature, interaction and inter-layer hopping are obtained. Finally, we propose an experimental protocol to observe these phenomena in future optical lattice experiments. PMID:24947369
Ferro- and antiferro-magnetism in (Np, Pu)BC
Klimczuk, T.; Kozub, A. L.; Griveau, J.-C.; Colineau, E.; Wastin, F.; Falmbigl, M.; Rogl, P.
2015-04-01
Two new transuranium metal boron carbides, NpBC and PuBC, have been synthesized. Rietveld refinements of powder XRD patterns of (Np,Pu)BC confirmed in both cases isotypism with the structure type of UBC. Temperature dependent magnetic susceptibility data reveal antiferromagnetic ordering for PuBC below T{sub N} = 44 K, whereas ferromagnetic ordering was found for NpBC below T{sub C} = 61 K. Heat capacity measurements prove the bulk character of the observed magnetic transition for both compounds. The total energy electronic band structure calculations support formation of the ferromagnetic ground state for NpBC and the antiferromagnetic ground state for PuBC.
Room-temperature antiferromagnetism in CuMnAs
NASA Astrophysics Data System (ADS)
Máca, F.; Mašek, J.; Stelmakhovych, O.; Martí, X.; Reichlová, H.; Uhlířová, K.; Beran, P.; Wadley, P.; Novák, V.; Jungwirth, T.
2012-04-01
We report on an experimental and theoretical study of CuMn-V compounds. In agreement with previous works we find low-temperature antiferromagnetism with Néel temperature of 50 K in the cubic half-Heusler CuMnSb. We demonstrate that the orthorhombic CuMnAs is a room-temperature antiferromagnet. Our results are based on X-ray diffraction, magnetization, transport, and differential thermal analysis measurements, and on density-functional theory calculations of the magnetic structure of CuMn-V compounds. In the discussion part of the paper we make a prediction, based on our density-functional theory calculations, that the electronic structure of CuMn-V compounds makes a transition from a semimetal to a semiconductor upon introducing the lighter group-V elements.
Observation of superficial antiferromagnetism in Co3O4 polycrystals
NASA Astrophysics Data System (ADS)
von Dreifus, Driele; Chaves Pereira, Ernesto; Aparecido de Oliveira, Adilson Jesus
2015-11-01
We report on a systematic study about the magnetic properties of Co3O4 polycrystals with large size distribution (100-1200 nm) and the crystallite size of 68(4) nm on average. An antiferromagnetic transition at T N = 32 K, extensively reported in the literature for Co3O4, was observed. Furthermore, another transition at T t = 14 K, which is suppressed for H ≥ 35 kOe, was also identified. An increase in the magnetic susceptibility, as well as irreversibility between zero field cooled and field cooled data below T t were observed. The non-detection of a coercive field below T t, and the fact that T t and T N are independent from the driven frequencies in ac magnetic measurements as a function of temperature, confirm that both peaks are associated to antiferromagnetic transitions.
Drone-fermions in the two-dimensional antiferromagnet
NASA Astrophysics Data System (ADS)
Krivenko, S.; Khaliullin, G.
1995-02-01
Two different representations of spins - via the conventional fermions, or via the Mattis drone-fermions - are compared considering the planar antiferromagnetic Heisenberg model as an example. Mean-field spin correlation functions calculated for the uniform and flux RVB states show that the drone-fermion approach has an advantage in giving the lower energy and the enhanced AF correlations, because of the absence of unphysical spinless states in this representation.
Singular field response and singular screening of vacancies in antiferromagnets.
Wollny, Alexander; Andrade, Eric C; Vojta, Matthias
2012-10-26
For isolated vacancies in ordered local-moment antiferromagnets we show that the magnetic-field linear-response limit is generically singular: The magnetic moment associated with a vacancy in zero field is different from that in a finite field h in the limit h→0(+). The origin is a universal and singular screening cloud, which moreover leads to perfect screening as h→0(+) for magnets which display spin-flop bulk states in the weak-field limit. PMID:23215218
Entanglement Perturbation Theory for Antiferromagnetic Heisenberg Spin Chains
NASA Astrophysics Data System (ADS)
Wang, Lihua; Chung, Sung Gong
2012-11-01
A recently developed numerical method, entanglement perturbation theory (EPT), is used to study the antiferromagnetic Heisenberg spin chains with z-axis anisotropy λ and magnetic field B. To demonstrate its accuracy, we first apply EPT to the isotropic spin-1/2 antiferromagnetic Heisenberg model, and find that EPT successfully reproduces the exact Bethe ansatz results for the ground state energy, the local magnetization, and the spin correlation functions (Bethe ansatz result is available for the first seven lattice separations). In particular, EPT confirms for the first time the asymptotic behavior of the spin correlation functions predicted by the conformal field theory, which realizes only for lattice separations larger than 1000. Next, turning on the z-axis anisotropy and the magnetic field, the 2- and 4-spin correlation functions are calculated, and the results are compared with those obtained by bosonization and density matrix renormalization group methods. Finally, for the spin-1 antiferromagnetic Heisenberg model, the ground state phase diagram in λ space is determined by Roomany--Wyld renormalization group (RG) finite size scaling. The results are in good agreement with those obtained by the level-spectroscopy method.
Electric-field induced ferromagnetic phase in paraelectric antiferromagnets
NASA Astrophysics Data System (ADS)
Glinchuk, Maya D.; Eliseev, Eugene A.; Gu, Yijia; Chen, Long-Qing; Gopalan, Venkatraman; Morozovska, Anna N.
2014-01-01
The phase diagram of a quantum paraelectric antiferromagnet EuTiO3 under an external electric field is calculated using Landau-Ginzburg-Devonshire theory. The application of an electric field E in the absence of strain leads to the appearance of a ferromagnetic (FM) phase due to the magnetoelectric (ME) coupling. At an electric field greater than a critical field, Ecr, the antiferromagnetic (AFM) phase disappears for all considered temperatures, and FM becomes the only stable magnetic phase. The calculated value of the critical field is close to the values reported recently by Ryan et al. [Nat. Commun. 4, 1334 (2013), 10.1038/ncomms2329] for EuTiO3 film under a compressive strain. The FM phase can also be induced by an E-field in other paraelectric antiferromagnetic oxides with a positive AFM-type ME coupling coefficient and a negative FM-type ME coupling coefficient. The results show the possibility of controlling multiferroicity, including the FM and AFM phases, with help of an electric field application.
Electrical manipulation of a ferromagnet by an antiferromagnet
NASA Astrophysics Data System (ADS)
Tshitoyan, V.; Ciccarelli, C.; Mihai, A. P.; Ali, M.; Irvine, A. C.; Moore, T. A.; Jungwirth, T.; Ferguson, A. J.
Several recent studies of antiferromagnetic (AFM) spintronics have focused on transmission and detection of spin-currents in AFMs. Efficient spin transmission through AFMs was inferred from experiments in FM/AFM/NM (normal metal) structures. Measurements in FM/AFM bilayers have demonstrated that a metallic AFM can also act as an efficient ISHE detector of the spin-current, with spin-Hall angles comparable to heavy NMs. Here we demonstrate that an antiferromagnet can be employed for a highly efficient electrical manipulation of a ferromagnet. We use an all-electrical excitation and detection technique of ferromagnetic resonance in a NiFe/IrMn bilayer. We observe antidamping-like spin torque acting on the NiFe generated by the in-plane current driven through the IrMn antiferromagnet. A large enhancement of the torque, characterized by an effective spin-Hall angle exceeding most heavy transition metals, correlates with the presence of the exchange-bias field at the NiFe/IrMn interface. It highlights that, in addition to strong spin-orbit coupling, the AFM order in IrMn governs the observed phenomenon.
Novel current driven domain wall dynamics in synthetic antiferromagnets
NASA Astrophysics Data System (ADS)
Yang, See-Hun
It was reported that the domain walls in nanowires can be moved efficiently by electrical currents by a new type of torque, chiral spin torque (CST), the combination of spin Hall effect and Dzyaloshinskii-Moriya interaction. Recently we domonstrated that ns-long current pulses can move domain walls at extraordinarily high speeds (up to ~750 m s -1) in synthetic antiferromagnetic (SAF) nanowires that have almost zero net magnetization, which is much more efficient compared with similar nanowires in which the sub-layers are coupled ferromagnetically (SF). This high speed is found to be due to a new type of powerful torque, exchange coupling torque (ECT) that is directly proportional to the strength of the antiferromagnetic exchange coupling between the two sub-layers, showing that the ECT is effective only in SAF not in SF. Moreover, it is found that the dependence of the wall velocity on the magnetic field applied along the nanowire is non-monotonic. Most recently we predict an Walker-breakdown-like domain wall precession in SAF nanowires in the presence of in-plane field based on the model we develop, and this extraordinary precession has been observed. In this talk I will discuss this in details by showing a unique characteristics of SAF sublayers' DW boost-and-drag mechanism along with CST and ECT. Novel current driven domain wall dynamics in synthetic antiferromagnets.
Revealing the properties of Mn2Au for antiferromagnetic spintronics
NASA Astrophysics Data System (ADS)
Barthem, V. M. T. S.; Colin, C. V.; Mayaffre, H.; Julien, M.-H.; Givord, D.
2013-12-01
The continuous reduction in size of spintronic devices requires the development of structures, which are insensitive to parasitic external magnetic fields, while preserving the magnetoresistive signals of existing systems based on giant or tunnel magnetoresistance. This could be obtained in tunnel anisotropic magnetoresistance structures incorporating an antiferromagnetic, instead of a ferromagnetic, material. To turn this promising concept into real devices, new magnetic materials with large spin-orbit effects must be identified. Here we demonstrate that Mn2Au is not a Pauli paramagnet as hitherto believed but an antiferromagnet with Mn moments of ~4 μB. The particularly large strength of the exchange interactions leads to an extrapolated Néel temperature well above 1,000 K, so that ground-state magnetic properties are essentially preserved up to room temperature and above. Combined with the existence of a significant in-plane anisotropy, this makes Mn2Au the most promising material for antiferromagnetic spintronics identified so far.
Revealing the properties of Mn2Au for antiferromagnetic spintronics.
Barthem, V M T S; Colin, C V; Mayaffre, H; Julien, M-H; Givord, D
2013-01-01
The continuous reduction in size of spintronic devices requires the development of structures, which are insensitive to parasitic external magnetic fields, while preserving the magnetoresistive signals of existing systems based on giant or tunnel magnetoresistance. This could be obtained in tunnel anisotropic magnetoresistance structures incorporating an antiferromagnetic, instead of a ferromagnetic, material. To turn this promising concept into real devices, new magnetic materials with large spin-orbit effects must be identified. Here we demonstrate that Mn2Au is not a Pauli paramagnet as hitherto believed but an antiferromagnet with Mn moments of ~4 μB. The particularly large strength of the exchange interactions leads to an extrapolated Néel temperature well above 1,000 K, so that ground-state magnetic properties are essentially preserved up to room temperature and above. Combined with the existence of a significant in-plane anisotropy, this makes Mn2Au the most promising material for antiferromagnetic spintronics identified so far. PMID:24327004
Coexistence of superconductivity, ferromagnetism and antiferromagnetism in iron pnictides
NASA Astrophysics Data System (ADS)
Gill, Raminder
2016-05-01
Coexistence of Superconductivity and magnetism have always been the fascinating area of interest for condensed-matter physicists. A variety of systems, such as cuprates, heavy fermions, and iron pnictides showed superconductivity in a narrow region near the border to antiferromagnetism (AFM)as a function of pressure or doping. However, the coexistence of superconductivity and ferromagnetism (FM) has seen in URhGe, UGe2, ErRh4B4 and many compounds. Here, we present a third situation where superconductivity coexists with FM and AFM. The recent experimental finding of interplay of ferromagnetism,antiferromagnetism and superconductivity in EuFe2(As1-xPx)2 impressed us to discuss this problem in detail. Ironpnictides are high Tc magnetic superconductors and could be very useful in finding many new superconductorswith high Tc probably near to room temperature. In this paper, we have theoretically calculated the superconducting order parameter of EuFe2(As1-xPx)2 where magnetic ordering is due to Eu+ moments and superconductivity is due to Fe3+ moments. The Eu ions order antiferromagnetically for x≤0.13, while a crossover is observed for x≥0.22 whereupon the Eu ions order ferromagnetically.
Spin pumping and spin-transfer torques in antiferromagnet
NASA Astrophysics Data System (ADS)
Niu, Qian
2015-03-01
Spin pumping and spin-transfer torques are key elements of coupled dynamics of magnetization and conduction electron spin, which have been widely studied in various ferromagnetic materials. Recent progress in spintronics suggests that a spin current can significantly affects the behavior of an antiferromagnetic material, and the electron motion become adiabatic when the staggered field varies sufficiently slowly. However, pumping from antiferromagnets and its relation to current-induced torques is yet unclear. In a recent study, we have solved this puzzle analytically by calculating how electrons scatter off a normal metal-antiferromagnetic interface. The pumped spin and staggered spin currents are derived in terms of the staggered field, the magnetization, and their rates of change. We find that for both compensated and uncompensated interfaces, spin pumping is of a similar magnitude as in ferromagnets; the direction of spin pumping is controlled by the polarization of the driving microwave. Via the Onsager reciprocity relations, the current-induced torques are also derived, the salient feature of which is illustrated by a terahertz nano-oscillator. In collaboration with Ran Cheng, Jiang Xiao, and A. Brataas.
Magnetic soft modes in the distorted triangular antiferromagnet -CaCr2O4
Toth, Sandor; Lake, Bella; Hradil, Klaudia; Rule, K; Stone, Matthew B; Islam, A. T. M. N.
2012-01-01
-CaCr2O4 is a spin-3/2, distorted triangular lattice antiferromagnet with a simple 120 spin structure that masks the complex pattern of exchange interactions. The magnetic excitation spectrum has been measured using inelastic neutron scattering on powder and single crystal samples. It reveals unusual low energy modes which can be explained by linear spin-wave theory assuming nearest and next-nearest neighbor interactions. The mode softening is due to the next-nearest neighbor interactions and indicates a new magnetic phase nearby as revealed by the phase diagram constructed for this system. The extracted direct exchange interactions correlate well with the Cr3+{Cr3+ distances and are in agreement with other chromium oxide delafossite compounds.
First-principles DFT+U modeling of defect behaviors in anti-ferromagnetic uranium mononitride
Lan, Jian-Hui; Zhao, Zi-Chen; Wu, Qiong; Zhao, Yu-Liang; Shi, Wei-Qun; Chai, Zhi-Fang
2013-12-14
A series of point defects in uranium mononitride (UN) have been studied by first-principles DFT+U calculations. The influence of intrinsic defects on the properties of UN was explored by considering the anti-ferromagnetic (AFM) order along the [001] direction. Our results show that all the point defects lead to obvious volume swelling of UN crystal. Energetically, the interstitial nitrogen defect is the most favorable one among single-point defects in UN crystal with the formation energy of 4.539 eV, while the N-Frenkel pair becomes the most preferable one among double-point defects. The AFM order induces obvious electron spin polarization of uranium towards neighboring uranium atoms with opposite spin orientations in UN crystal.
On the influence of nanometer-thin antiferromagnetic surface layer on ferromagnetic CrO2
NASA Astrophysics Data System (ADS)
Das, P.; Bajpai, A.; Ohno, Y.; Ohno, H.; Müller, J.
2012-09-01
We investigate the influence of naturally grown 2-5 nm thin surface layer of antiferromagnetic (AFM) Cr2O3 on the half metallic ferromagnet CrO2 by measuring the magnetic behavior of a single micro-crystal. The temperature variation of the magnetic stray fields of the micro-crystal measured by micro-Hall magnetometry shows an anomalous increase below ˜60 K. We find clear evidence that this behavior is due to the influence of the AFM surface layer. The average amplitude of the Barkahausen jumps exhibits a similar temperature dependence indicating that the AFM surface layer plays a role in defining the potential landscape seen by the domain configuration in the ferromagnetic grain.
Magnetization of the canted antiferromagnetic CoCO 3 in Abragam-Pryce approximation
NASA Astrophysics Data System (ADS)
Meshcheryakov, V. F.
2006-05-01
Weiss molecular field theory was used to calculate the magnetization of the canted antiferromagnetic CoCO 3 ( T=18.1 K). Wave functions of magnetic doublets near Co 2+ ground state in Abragam-Pryce approximation were determined. One of the crystal field variables, free Co 2+ ion isotropic exchange interaction inside, and between magnetic sublatticies, and rotation angle ϕ, characterizing nonequivalence ion Co 2+ positions, were used as parameters. From comparison with the experimental data exchange interaction anisotropy and g-factors g, g were obtained. At low temperatures T<40 K the coincidence of calculated and experimental results are good and g-factor values are almost the same as have been obtained from EPR data in Co(1%)+CdCO single crystals. At high temperatures in the paramagnetic region, experimental data differs from calculated ones by more than two times. It is shown that this discrepancy cannot be described within the frames of used approximations.