Showing papers on "Antiferromagnetism published in 2013"
TL;DR: In this paper, the authors employ ab-initio electronic structure calculations to study 60 LiMgPdSn-type quaternary Heusler compounds, including half-metals, spin-gapless semiconductors, and 9 semiconductor types.
Abstract: We employ ab-initio electronic structure calculations to study 60 LiMgPdSn-type (also known as LiMgPdSb-type) quaternary Heusler compounds. All compounds obey the Slater-Pauling rule with diverse electronic and magnetic properties. 41 compounds are found to be half-metals, 8 spin-gapless semiconductors, and 9 semiconductors. CoVTiAl and CrVTiAl compounds are identified as ferromagnetic and antiferromagnetic semiconductors, respectively, with large energy gaps in both spin directions. All magnetic compounds are expected to have high Curie temperatures making them suitable for spintronics/magnetoelectronics applications.
329 citations
University of Paris-Sud1, University of Rouen2, University of Arkansas3, Paris Diderot University4, University of New South Wales5, École Centrale Paris6, Russian Academy of Sciences7, Moscow State University8, University of South Florida9, Xi'an Jiaotong University10, Moscow Institute of Physics and Technology11
TL;DR: It is revealed that strain progressively drives the average spin angle from in-plane to out-of-plane, a property used to tune the exchange bias and giant-magnetoresistive response of spin valves.
Abstract: Multiferroics are compounds that show ferroelectricity and magnetism. BiFeO3, by far the most studied, has outstanding ferroelectric properties, a cycloidal magnetic order in the bulk, and many unexpected virtues such as conductive domain walls or a low bandgap of interest for photovoltaics. Although this flurry of properties makes BiFeO3 a paradigmatic multifunctional material, most are related to its ferroelectric character, and its other ferroic property--antiferromagnetism--has not been investigated extensively, especially in thin films. Here we bring insight into the rich spin physics of BiFeO3 in a detailed study of the static and dynamic magnetic response of strain-engineered films. Using Mossbauer and Raman spectroscopies combined with Landau-Ginzburg theory and effective Hamiltonian calculations, we show that the bulk-like cycloidal spin modulation that exists at low compressive strain is driven towards pseudo-collinear antiferromagnetism at high strain, both tensile and compressive. For moderate tensile strain we also predict and observe indications of a new cycloid. Accordingly, we find that the magnonic response is entirely modified, with low-energy magnon modes being suppressed as strain increases. Finally, we reveal that strain progressively drives the average spin angle from in-plane to out-of-plane, a property we use to tune the exchange bias and giant-magnetoresistive response of spin valves.
305 citations
TL;DR: Optical manipulation of magnetic order by femtosecond laser pulses has developed into an exciting and still expanding research field that keeps being fueled by a continuous stream of new and sometimes counterintuitive results, which may also potentially revolutionize data storage and information processing technologies.
Abstract: This review discusses the recent studies of magnetization dynamics and the role of angular momentum in thin films of ferrimagnetic rare-earth-transition metal (RE-TM) alloys, e.g. GdFeCo, where both magnetization and angular momenta are temperature dependent. It has been experimentally demonstrated that the magnetization can be manipulated and even reversed by a single 40 fs laser pulse, without any applied magnetic field. This switching is found to follow a novel reversal pathway, that is shown however to depend crucially on the net angular momentum, reflecting the balance of the two opposite sublattices. In particular, optical excitation of ferrimagnetic GdFeCo on a time scale pertinent to the characteristic time of the exchange interaction between the RE and TM spins, i.e. on the time scale of tens of femtoseconds, pushes the spin dynamics into a yet unexplored regime, where the two exchange-coupled magnetic sublattices demonstrate substantially different dynamics. As a result, the reversal of spins appears to proceed via a novel transient state characterized by a ferromagnetic alignment of the Gd and Fe magnetic moments, despite their ground-state antiferromagnetic coupling.Thus, optical manipulation of magnetic order by femtosecond laser pulses has developed into an exciting and still expanding research field that keeps being fueled by a continuous stream of new and sometimes counterintuitive results. Considering the progress in the development of plasmonic antennas and compact ultrafast lasers, optical control of magnetic order may also potentially revolutionize data storage and information processing technologies.
305 citations
TL;DR: A quantum gas trapped in an optical lattice of triangular symmetry can be driven from a paramagnetic to an antiferromagnetic state by a tunable artificial magnetic field as discussed by the authors.
Abstract: A quantum gas trapped in an optical lattice of triangular symmetry can now be driven from a paramagnetic to an antiferromagnetic state by a tunable artificial magnetic field
298 citations
TL;DR: The observation of nearest-neighbor magnetic correlations emerging in the many-body state of a thermalized Fermi gas in an optical lattice facilitates addressing open problems in quantum magnetism through the use of quantum simulation.
Abstract: Quantum magnetism originates from the exchange coupling between quantum mechanical spins. Here, we report on the observation of nearest-neighbor magnetic correlations emerging in the many-body state of a thermalized Fermi gas in an optical lattice. The key to obtaining short-range magnetic order is a local redistribution of entropy, which allows temperatures below the exchange energy for a subset of lattice bonds. When loading a repulsively interacting gas into either dimerized or anisotropic simple cubic configurations of a tunable-geometry lattice, we observe an excess of singlets as compared with triplets consisting of two opposite spins. For the anisotropic lattice, the transverse spin correlator reveals antiferromagnetic correlations along one spatial axis. Our work facilitates addressing open problems in quantum magnetism through the use of quantum simulation.
275 citations
TL;DR: In this article, the long-range ferromagnetism of Mn spins is mediated by an antiferromagnetic (AFM) exchange between the localized Mn $d$ states and the delocalized $p$ states of the S, Se, and Te atoms.
Abstract: We report an investigation of long-range ferromagnetic (FM) ordering in Mn-doped MoS${}_{2}$, MoSe${}_{2}$, MoTe${}_{2}$, and WS${}_{2}$ for Mn concentration less than 5$%$ using density functional theory calculations. The long-range ferromagnetism of Mn spins is mediated by an antiferromagnetic (AFM) exchange between the localized Mn $d$ states and the delocalized $p$ states of the S, Se, and Te atoms. In contrast, transition metals like Fe, Co, and Ni show a FM exchange with the S, Se, and Te atoms, which results in a very weak FM (even slightly AFM) coupling for transition-metal defects with large separations. The Mn substitution at Mo or W sites is energetically favorable, thus making the Mn-doped dichalcogenides promising candidates for two-dimensional dilute magnetic semiconductors.
262 citations
TL;DR: There is an emergent electronic degree of freedom characterized by the product of spin and valley indices, which leads to spin–valley-dependent optical selection rule and Berry curvature–induced topological quantum transport.
Abstract: Conventional electronics are based invariably on the intrinsic degrees of freedom of an electron, namely its charge and spin. The exploration of novel electronic degrees of freedom has important implications in both basic quantum physics and advanced information technology. Valley, as a new electronic degree of freedom, has received considerable attention in recent years. In this paper, we develop the theory of spin and valley physics of an antiferromagnetic honeycomb lattice. We show that by coupling the valley degree of freedom to antiferromagnetic order, there is an emergent electronic degree of freedom characterized by the product of spin and valley indices, which leads to spin–valley-dependent optical selection rule and Berry curvature–induced topological quantum transport. These properties will enable optical polarization in the spin–valley space, and electrical detection/manipulation through the induced spin, valley, and charge fluxes. The domain walls of an antiferromagnetic honeycomb lattice harbors valley-protected edge states that support spin-dependent transport. Finally, we use first-principles calculations to show that the proposed optoelectronic properties may be realized in antiferromagnetic manganese chalcogenophosphates (MnPX3, X = S, Se) in monolayer form.
244 citations
TL;DR: It is shown that ferrimagnetic ordering is essential to isothermally induce the exchange anisotropy needed for the zero-field cooled exchange bias during the virgin magnetization process.
Abstract: We report a large exchange-bias effect after zero-field cooling the new tetragonal Heusler compound ${\mathrm{Mn}}_{2}\mathrm{PtGa}$ from the paramagnetic state. The first-principles calculation and the magnetic measurements reveal that ${\mathrm{Mn}}_{2}\mathrm{PtGa}$ orders ferrimagnetically with some ferromagnetic inclusions. We show that ferrimagnetic ordering is essential to isothermally induce the exchange anisotropy needed for the zero-field cooled exchange bias during the virgin magnetization process. The complex magnetic behavior at low temperatures is characterized by the coexistence of a field-induced irreversible magnetic behavior and a spin-glass-like phase. The field-induced irreversibility originates from an unusual first-order ferrimagnetic to antiferromagnetic transition, whereas the spin-glass-like state forms due to the existence of antisite disorder intrinsic to the material.
193 citations
TL;DR: O(3) films are room-temperature multiferroics; and the switchability of the polar behavior is observed at room temperature, indicating ferroelectricity.
Abstract: The crystal and magnetic structures of single-crystalline hexagonal LuFeO(3) films have been studied using x-ray, electron, and neutron diffraction methods. The polar structure of these films are found to persist up to 1050 K; and the switchability of the polar behavior is observed at room temperature, indicating ferroelectricity. An antiferromagnetic order was shown to occur below 440 K, followed by a spin reorientation resulting in a weak ferromagnetic order below 130 K. This observation of coexisting multiple ferroic orders demonstrates that hexagonal LuFeO(3) films are room-temperature multiferroics.
189 citations
TL;DR: In this article, the singular-mode functional renormalization group theory was used to discover a rich variety of electronic instabilities under short-range interactions on a kagome lattice at van Hove filling.
Abstract: The electronic orders in Hubbard models on a kagome lattice at van Hove filling are of intense current interest and debate. We study this issue using the singular-mode functional renormalization group theory. We discover a rich variety of electronic instabilities under short-range interactions. With increasing on-site repulsion $U$, the system develops successively ferromagnetism, intra-unit-cell antiferromagnetism, and charge bond order. With nearest-neighbor Coulomb interaction $V$ alone ($U=0$), the system develops intra-unit-cell charge density wave order for small $V$, $s$-wave superconductivity for moderate $V$, and the charge density wave order appears again for even larger $V$. With both $U$ and $V$, we also find spin bond order and chiral ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}+i{d}_{xy}$ superconductivity in some particular regimes of the phase diagram. We find that the $s$-wave superconductivity is a result of charge density wave fluctuations and the squared logarithmic divergence in the pairing susceptibility. On the other hand, the $d$-wave superconductivity follows from bond order fluctuations that avoid the matrix element effect. The phase diagram is vastly different from that in honeycomb lattices because of the geometrical frustration in the kagome lattice.
181 citations
TL;DR: An unrestricted Hartree-Fock computation of charge-ordering instabilities of two-dimensional metals with antiferromagnetic exchange interactions is presented, allowing for arbitrary ordering wave vectors and internal wave functions of the particle-hole pair condensate.
Abstract: We present an unrestricted Hartree-Fock computation of charge-ordering instabilities of two-dimensional metals with antiferromagnetic exchange interactions, allowing for arbitrary ordering wavevectors and internal wavefunctions of the particle-hole pair condensate. We find that the ordering has a dominant d symmetry of rotations about lattice points for a range of ordering wavevectors, including those observed in recent experiments at low temperatures on YBa2Cu3Oy. This d symmetry implies the charge ordering is primarily on the bonds of the Cu lattice, and we propose incommensurate bond order parameters for the underdoped cuprates. The field theory for the onset of N´ eel order in a metal has an emergent pseudospin symmetry which ‘rotates’ d-wave Cooper pairs to particle-hole pairs (Metlitski et al., Phys. Rev. B 82, 075128 (2010)): our results show that this symmetry has consequences even when the spin correlations are short-ranged and incommensurate.
TL;DR: On the decay of the antiferromagnetic Mott insulating state into a non-Fermi liquid, this work finds evidence of a quantum metal-to-insulator transition that spans aNon-magnetic insulating phase.
Abstract: Mott physics is characterized by an interaction-driven metal-to-insulator transition in a partially filled band In the resulting insulating state, antiferromagnetic orders of the local moments typically develop, but in rare situations no long-range magnetic order appears, even at zero temperature, rendering the system a quantum spin liquid A fundamental and technologically critical question is whether one can tune the underlying energetic landscape to control both metal-to-insulator and Neel transitions, and even stabilize latent metastable phases, ideally on a platform suitable for applications Here we demonstrate how to achieve this in ultrathin films of NdNiO3 with various degrees of lattice mismatch, and report on the quantum critical behaviours not reported in the bulk by transport measurements and resonant X-ray spectroscopy/scattering In particular, on the decay of the antiferromagnetic Mott insulating state into a non-Fermi liquid, we find evidence of a quantum metal-to-insulator transition that spans a non-magnetic insulating phase
TL;DR: In this paper, the synthesis of undoped and Sc3+-doped BiFeO3 nanoparticles using the sonochemical technique was reported, where the substitution of Sc ions for Bi enhances the ferromagnetic as well as ferroelectric properties of this system.
Abstract: We report the synthesis of undoped and Sc3+-doped BiFeO3 nanoparticles using the sonochemical technique. X-ray diffraction reveals that all samples are single phase with no impurities detected. EDX analysis was done to confirm the extent of Sc3+ doping in the samples. The size and morphology of the nanoparticles have been analyzed using transmission electron microscopy (TEM). XPS studies were done to check the presence of Fe2+ ions in the samples. The BiFeO3 nanoparticles show a weak ferromagnetic behavior at room temperature, which is quite different from the linear M–H relationship reported for bulk BiFeO3. The substitution of Sc ions for Bi enhances the ferromagnetic as well as ferroelectric properties of this system, which is mainly attributed to the antiferromagnetic core and ferromagnetic surface of the nanoparticles, together with the mild structural distortion. Temperature and field dependence of magnetization curves reveal the frustrated magnetic behavior of this system. The leakage current is co...
TL;DR: It is demonstrated that Mn2Au is not a Pauli paramagnet as hitherto believed but an antiferromagnet with Mn moments of ~4 μB, which makes it the most promising material for Antiferromagnetic spintronics identified so far.
Abstract: Few of the known antiferromagnetic materials are suitable for use in spintronic devices Here, the authors show that Mn2Au, which was believed to be paramagnetic, is an antiferromagnet, combining high Neel temperature and in-plane anisotropy, thus demonstrating its potential for antiferromagnetic spintronics
TL;DR: In this article, nonequilibrium dynamics for an ensemble of tilted one-dimensional atomic Bose-Hubbard chains after a sudden quench to the vicinity of the transition point of the Ising paramagnetic to antiferromagnetic quantum phase transition was studied.
Abstract: We study nonequilibrium dynamics for an ensemble of tilted one-dimensional atomic Bose-Hubbard chains after a sudden quench to the vicinity of the transition point of the Ising paramagnetic to antiferromagnetic quantum phase transition. The quench results in coherent oscillations for the orientation of effective Ising spins, detected via oscillations in the number of doubly occupied lattice sites. We characterize the quench by varying the system parameters. We report significant modification of the tunneling rate induced by interactions and show clear evidence for collective effects in the oscillatory response.
TL;DR: In this paper, different bilayers, trilayers and multilayers, such as anisotropic hard-/soft-magnetic multilayer films, ferromagnetic/antiferromagnetic /ferromagnetic trilayer, were designed.
Abstract: Recent advances in the study of exchange couplings in magnetic films are introduced. To provide a comprehensive understanding of exchange coupling, we have designed different bilayers, trilayers and multilayers, such as anisotropic hard-/soft-magnetic multilayer films, ferromagnetic/antiferromagnetic/ferromagnetic trilayers, [Pt/Co]/NiFe/NiO heterostructures, Co/NiO and Co/NiO/Fe trilayers on an anodic aluminum oxide (AAO) template. The exchange-coupling interaction between soft- and hard-magnetic phases, interlayer and interfacial exchange couplings and magnetic and magnetotransport properties in these magnetic films have been investigated in detail by adjusting the magnetic anisotropy of ferromagnetic layers and by changing the thickness of the spacer layer, ferromagnetic layer, and antiferromagnetic layer. Some particular physical phenomena have been observed and explained.
TL;DR: This study characterizes the ferromagnetic properties of individual lattice defects in NiO crystals, discusses the origin of the unexpected ferromagnetism in terms of the physical properties of the atomic-scale core structures of single dislocations, and demonstrates that it is possible to fabricate stable nanoscale magnetic elements inside crystalline environments composed of these microstructures.
Abstract: Magnetic force microscopy imaging reveals that individual dislocations in antiferromagnetic NiO crystals show ferromagnetic behaviour originating from the local atomic-scale structure.
TL;DR: In this article, a quantum phase transition from an antiferromagnetic to a ferromagnetic state is measured in graphene bilayers, which supports the idea that bilayer graphene can sustain counter-propagating spin-polarized edge modes in analogy to the quantum spin Hall effect seen in topological insulators.
Abstract: A quantum phase transition from an antiferromagnetic to a ferromagnetic state is now measured in graphene bilayers. This observation supports the idea that bilayer graphene can sustain counter-propagating spin-polarized edge modes in analogy to the quantum spin Hall effect seen in topological insulators.
TL;DR: A magnetic field is applied and a series of spin-gapped phases appearing at five different fractions of magnetization are discovered by means of a grand canonical density matrix renormalization group, an unbiased state-of-the-art numerical technique.
Abstract: Quantum spin liquids—quantum states in which spins show no order even at very low temperatures—are possibly hosted in a kagome Heisenberg antiferromagnet. Using a powerful numerical method, the authors show that applying a magnetic field leads to various exotic plateau states, including two spin liquids.
TL;DR: The synthesis of a new diluted magnetic semiconductor is reported, which is isostructural to the 122 iron-based superconductors with the tetragonal ThCr( 2)Si(2) (122) structure, which makes them promising for the development of multilayer functional devices.
Abstract: Diluted magnetic semiconductors have received much attention due to their potential applications for spintronics devices. A prototypical system (Ga,Mn)As has been widely studied since the 1990s. The simultaneous spin and charge doping via hetero-valent (Ga(3+),Mn(2+)) substitution, however, resulted in severely limited solubility without availability of bulk specimens. Here we report the synthesis of a new diluted magnetic semiconductor (Ba(1-x)K(x))(Zn(1-y)Mn(y))(2)As(2), which is isostructural to the 122 iron-based superconductors with the tetragonal ThCr(2)Si(2) (122) structure. Holes are doped via (Ba(2+), K(1+)) replacements, while spins via isovalent (Zn(2+),Mn(2+)) substitutions. Bulk samples with x=0.1-0.3 and y=0.05-0.15 exhibit ferromagnetic order with T(C) up to 180 K, which is comparable to the highest T(C) for (Ga,Mn)As and significantly enhanced from T(C) up to 50 K of the '111'-based Li(Zn,Mn)As. Moreover, ferromagnetic (Ba,K)(Zn,Mn)(2)As(2) shares the same 122 crystal structure with semiconducting BaZn(2)As(2), antiferromagnetic BaMn(2)As(2) and superconducting (Ba,K)Fe(2)As(2), which makes them promising for the development of multilayer functional devices.
TL;DR: In this paper, the magnetic properties of manganite bilayers composed of G-type antiferromagnetic (AFM) SrMnO3 and double-exchange ferromagnetic La 0.7Sr0.3
Abstract: The magnetic properties of manganite bilayers composed of G-type antiferromagnetic (AFM) SrMnO3 and double-exchange ferromagnetic (FM) La0.7Sr0.3MnO3 are studied. A spin-glass state is observed as a result of competing magnetic orders and spin frustration at the La0.7Sr0.3MnO3/SrMnO3 interface. The dependence of the irreversible temperature on the cooling magnetic field follows the Almeida-Thouless line. Although an ideal G-type AFM SrMnO3 is featured with a compensated spin configuration, the bilayers exhibit exchange bias
TL;DR: It is predicted that the existence of novel magnetic phases in the steady state of this system, subject to dissipative spin-flip processes associated with optical pumping, will emerge due to the competition between coherent and dissipative processes.
Abstract: We consider strongly interacting systems of effective spins, subject to dissipative spin-flip processes associated with optical pumping. We predict the existence of novel magnetic phases in the steady state of this system, which emerge due to the competition between coherent and dissipative processes. Specifically, for strongly anisotropic spin-spin interactions, we find ferromagnetic, antiferromagnetic, spin-density-wave, and staggered-$XY$ steady states, which are separated by nonequilibrium phase transitions meeting at a Lifshitz point. These transitions are accompanied by quantum correlations, resulting in spin squeezing. Experimental implementations in ultracold atoms and trapped ions are discussed.
TL;DR: In this paper, the authors reported an exchange bias effect up to room temperature in the binary intermetallic bulk compound Mn3.04Ge0.96 with an EB of around 70 mT at 2 K and a non-zero value up to 3 K. The exchange anisotropy is attributed to the exchange interaction between the triangular antiferromagnetic host and the embedded ferrimagnetic like clusters.
Abstract: This work reports an exchange bias (EB) effect up to room temperature in the binary intermetallic bulk compound Mn3.04Ge0.96. The sample annealed at 700 K crystallizes in a tetragonal structure with ferromagnetic ordering, whereas, the sample annealed at 1073 K crystallizes in a hexagonal structure with antiferromagnetic ordering. The hexagonal Mn3.04Ge0.96 sample exhibits an EB of around 70 mT at 2 K that continues with a non-zero value up to room temperature. The exchange anisotropy is proposed to be originating from the exchange interaction between the triangular antiferromagnetic host and the embedded ferrimagnetic like clusters. The ferrimagnetic clusters develop when excess Mn atoms occupy empty Ge sites in the original triangular antiferromagnet structure of Mn3Ge.
TL;DR: Surprisingly, after magnetic saturation, measurements and numerical simulations show that overall ferromagnetic order exists in the present nanoparticle assemblies even when their arrangement is completely disordered.
Abstract: Magnetostatic (dipolar) interactions between nanoparticles promise to open new ways to design nanocrystalline magnetic materials and devices if the collective magnetic properties can be controlled at the nanoparticle level. Magnetic dipolar interactions are sufficiently strong to sustain magnetic order at ambient temperature in assemblies of closely-spaced nanoparticles with magnetic moments of $ 100 mB. Here we use electron holography with sub-particle resolution to reveal the correlation between particle arrangement and magnetic order in self-assembled 1D and quasi-2D arrangements of 15 nm cobalt nanoparticles. In the initial states, we observe dipolar ferromagnetism, antiferromagnetism and local flux closure, depending on the particle arrangement. Surprisingly, after magnetic saturation, measurements and numerical simulations show that overall ferromagnetic order exists in the present nanoparticle assemblies even when their arrangement is completely disordered. Such direct quantification of the correlation between topological and magnetic order is essential for the technological exploitation of magnetic quasi-2D nanoparticle assemblies.
TL;DR: In this paper, measurements of angular momentum transmission in antiferromagnetic NiO and in the non-magnetic light element insulator SiO2 have been carried out for spin current conduction.
Abstract: Spintronics is a eld of electronics based on using the electron spin instead of its charge The recent advance in the manipulation of pure spin currents, ie angular momentum transfer not associated to conventional charge currents, has opened new opportunities to build spin based devices with low energy consumption [1] It has also allowed to integrate ferromagnetic insulators in spintronic devices, either as spin sources [2{6] or spin conductors [2, 7, 8] using their magnetic excitations to propagate a spin signal Antiferromagnetic insulators belong to another class of materials that can also sustain magnetic excitations, even with a higher group velocity [9] Hence, they have potential as angular momentum conductors, possibly making faster spin devices At the opposite end, angular momentum insulators are also required in spintronic circuits The present letter underlines some essential features relevant for spin current conduction, based on measurements of angular momentum transmission in antiferromagnetic NiO and in the non-magnetic light element insulator SiO2
TL;DR: In this article, the spontaneous symmetry breaking and subsequent onset of unidirectional anisotropy driven by superinteraction bias coupling between the ferromagnetic core of Bi(2)Fe(4)O(9) and the canted antiferromagnetic structure of BiFeO(3) via superspin glass moments at the shell were observed.
Abstract: We observe an enormous spontaneous exchange bias (~300-600 Oe)--measured in an unmagnetized state following zero-field cooling--in a nanocomposite of BiFeO(3) (~94%)-Bi(2)Fe(4)O(9) (~6%) over a temperature range 5-300 K. Depending on the path followed in tracing the hysteresis loop--positive (p) or negative (n)--as well as the maximum field applied, the exchange bias (H(E)) varies significantly with | - H(Ep) | > | H(En) |. The temperature dependence of H(E) is nonmonotonic. It increases, initially, till ~150 K and then decreases as the blocking temperature T(B) is approached. All these rich features appear to be originating from the spontaneous symmetry breaking and consequent onset of unidirectional anisotropy driven by "superinteraction bias coupling" between the ferromagnetic core of Bi(2)Fe(4)O(9) (of average size ~19 nm) and the canted antiferromagnetic structure of BiFeO(3) (of average size ~112 nm) via superspin glass moments at the shell.
TL;DR: In this paper, the transport and thermoelectric coefficients of silicene nanoribbons with zigzag edges are investigated by ab initio numerical methods, and the phonon contribution to the heat conductance is calculated numerically by two different methods.
Abstract: Transport and thermoelectric coefficients (including also spin thermopower) of silicene nanoribbons with zigzag edges are investigated by ab initio numerical methods. Local spin density of such nanoribbons reveals edge magnetism. As in graphene, one finds antiferromagnetic and ferromagnetic ordering, with spin polarization at one edge antiparallel or parallel to that at the other edge, respectively. Thermoelectric properties, especially the Seebeck coefficient, significantly depend on the electronic band structure and are enhanced when the Fermi level is in the energy gap. However, the thermoelectric efficiency is significantly reduced when the phonon contribution to the heat conductance is included. This phonon contribution has been calculated numerically by two different methods. Transition from antiferromagnetic to ferromagnetic states leads to a large magnetoresistance as well as to a considerable magnetothermopower. Thermoelectric parameters in the antiparallel configuration, when spin polarization in the left part of the nanoribbon is opposite to that in the right part, are also analyzed.
TL;DR: In this paper, an effective scheme of isostructural alloying was applied to establish a Curie-temperature window in the MnNiGe-CoNiGe system.
Abstract: An effective scheme of isostructural alloying was applied to establish a Curie-temperature window in isostructural MnNiGe-CoNiGe system. With the simultaneous accomplishment of decreasing structural-transition temperature and converting antiferromagnetic martensite to ferromagnetic state, a 200 K Curie-temperature window was established between Curie temperatures of austenite and martensite phases. In the window, a first-order magnetostructural transition between paramagnetic austenite and ferromagnetic martensite occurs with a sharp jump in magnetization, showing a magnetic entropy change as large as −40 J kg−1 K−1 in a 50 kOe field change. This giant magnetocaloric effect enables Mn1−xCoxNiGe to become a potential magnetic refrigerant.
TL;DR: The magnetic structure of the chemically-disordered face-centred-cubic alloy for the first time is determined, which differs from theoretical predictions, with magnetic moments tilted away from the crystal diagonals towards the face-planes.
Abstract: We have determined the magnetic structures of single-crystal thin-films of IrMn3 for the crystallographic phases of chemically-ordered L12, and for chemically-disordered face-centred-cubic, which is the phase typically chosen for information-storage devices. For the chemically-ordered L12 thin-film, we find the same triangular magnetic structure as reported for the bulk material. We determine the magnetic structure of the chemically-disordered face-centred-cubic alloy for the first time, which differs from theoretical predictions, with magnetic moments tilted away from the crystal diagonals towards the face-planes. We study the influence of these two antiferromagnetic structures on the exchange-bias properties of an epitaxial body-centred-cubic Fe layer showing that magnetization reversal mechanism and bias-field in the ferromagnetic layer is altered significantly. We report a change of reversal mechanism from in-plane nucleation of 90° domain-walls when coupled to the newly reported cubic structure towards a rotational process, including an out-of-plane magnetization component when coupled to the L12 triangular structure.
TL;DR: The vanadium oxyfluoride (DQVOF) is a geometrically frustrated magnetic bilayer material as discussed by the authors, whose structure consists of S = 1/2 kagome planes of V(4+) d(1) ions with s = 1 V(3+d+d(2) ions located between the KGome layers.
Abstract: The vanadium oxyfluoride [NH(4)](2)[C(7)H(14)N][V(7)O(6)F(18)] (DQVOF) is a geometrically frustrated magnetic bilayer material. The structure consists of S = 1/2 kagome planes of V(4+) d(1) ions with S = 1 V(3+) d(2) ions located between the kagome layers. Muon spin relaxation measurements demonstrate the absence of spin freezing down to 40 mK despite an energy scale of 60 K for antiferromagnetic exchange interactions. From magnetization and heat capacity measurements we conclude that the S = 1 spins of the interplane V(3+) ions are weakly coupled to the kagome layers, such that DQVOF can be viewed as an experimental model for S = 1/2 kagome physics, and that it displays a gapless spin liquid ground state.