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Antiferromagnetic materials, which have drawn considerable attention recently, have fascinating features: they are robust against perturbation, produce no stray fields, and exhibit ultrafast dynamics. Discerning how to efficiently...
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Antiferromagnetic materials, which have drawn considerable attention recently, have fascinating features: they are robust against perturbation, produce no stray fields, and exhibit ultrafast dynamics. Discerning how to efficiently manipulate the magnetic state of an antiferromagnet is key to the development of antiferromagnetic spintronics. In this review, we introduce four main methods (magnetic, strain, electrical, and optical) to mediate the magnetic states and elaborate on intrinsic origins of different antiferromagnetic materials. Magnetic control includes a strong magnetic field, exchange bias, and field cooling, which are traditional and basic. Strain control involves the magnetic anisotropy effect or metamagnetic transition. Electrical control can be divided into two parts, electric field and electric current, both of which are convenient for practical applications. Optical control includes thermal and electronic excitation, an inertiadriven mechanism, and terahertz laser control, with the potential for ultrafast antiferromagnetic manipulation. This review sheds light on effective usage of antiferromagnets and provides a new perspective on antiferromagnetic spintronics.
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We perform highly accurate density matrix renormalization group (DMRG) simulations to investigate the ground-state properties of the spin-1/2 antiferromagnetic square lattice Heisenberg J_1-J_2 model. Based on studies of numerous ...
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We perform highly accurate density matrix renormalization group (DMRG) simulations to investigate the ground-state properties of the spin-1/2 antiferromagnetic square lattice Heisenberg J_1-J_2 model. Based on studies of numerous long cylinders with circumferences of up to 14 lattice spacings, we obtain strong evidence for a topological quantum spin liquid state in the region 0.41 ^ J2I J\ ^ 0.62, separating conventional Neel and striped antiferromagnetic states for smaller and larger J2/J], respectively. The quantum spin liquid is characterized numerically by the absence of magnetic or valence bond solid order, and nonzero singlet and triplet energy gaps. Furthermore, we positively identify its topological nature by measuring a nonzero topological entanglement entropy y - 0.70 ± 0.02, extremely close to y = ln(2) =a 0.69 (expected for a Z_2 quantum spin liquid) and a nontrivial finite size dimerization effect depending upon the parity of the circumference of the cylinder. We also point out that a valence bond solid, and indeed any discrete symmetry breaking state, would be expected to show a constant correction to the entanglement entropy of opposite sign to the topological entanglement entropy.
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In ACrF_5 (A = Cs, Rb, K), Cr(IV) ions are coordinated by six fluoride ligands where the resulting CrF_6 octahedra share cis vertexes to form infinite chains of ([Cr~(IV)F_5]~−)_n. The geometry of the latter in Cs compound diff...
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In ACrF_5 (A = Cs, Rb, K), Cr(IV) ions are coordinated by six fluoride ligands where the resulting CrF_6 octahedra share cis vertexes to form infinite chains of ([Cr~(IV)F_5]~−)_n. The geometry of the latter in Cs compound differs from that in K and Rb compounds. The results of investigations of the magnetic behaviour of these compounds have shown that an antiferromagnetic superexchange interaction is present within the chains with J_(Cs) = −10.2 cm~(−1), J_(Rb) = −13.3 cm~(−1), and J_K = −13.1 cm~(−1). Additional ferromagnetic-like long-range ordering has been observed in KCrF_5 and RbCrF_5 below 6 K which can be explained, in a correlation with their crystal structures, as canted antiferromagnetism.
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Magnons (the quanta of spin waves) could be used to encode information in beyond Moore computing applications. In this study, the magnon coupling between acoustic mode and optic mode in synthetic antiferromagnets (SAFs) is investi...
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Magnons (the quanta of spin waves) could be used to encode information in beyond Moore computing applications. In this study, the magnon coupling between acoustic mode and optic mode in synthetic antiferromagnets (SAFs) is investigated by micromagnetic simulations. For a symmetrical SAF system, the time-evolution magnetizations of the two ferromagnetic layers oscillate in-phase at the acoustic mode and out-of-phase at the optic mode, showing an obvious crossing point in their antiferromagnetic resonance spectra. However, the symmetry breaking in an asymmetrical SAF system by the thickness difference, can induce an anti-crossing gap between the two frequency branches of resonance modes and thereby a strong magnon-magnon coupling appears between the resonance modes. The magnon coupling induced a hybridized resonance mode and its phase difference varies with the coupling strength. The maximum coupling occurs at the bias magnetic field at which the two ferromagnetic layers oscillate with a 90° phase difference. Besides, we show how the resonance modes in SAFs change from the in-phase state to the out-of-phase state by slightly tuning the magnon-magnon coupling strength. Our work provides a clear physical picture for the understanding of magnon-magnon coupling in a SAF system and may provide an opportunity to handle the magnon interaction in synthetic antiferromagnetic spintronics.
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We perform a stability analysis of an isolated atomic-sized antiferromagnetic skyrmion (AFM-Sk), formed on the superior layer of a magnetic bilayer. The coupling between both square lattices acts as an effective staggered magnetic...
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We perform a stability analysis of an isolated atomic-sized antiferromagnetic skyrmion (AFM-Sk), formed on the superior layer of a magnetic bilayer. The coupling between both square lattices acts as an effective staggered magnetic field that stabilizes the AFM-Sk and reduces its radius. A suitable anisotropy constant of the bottom layer material keeps it close to the homogeneous AFM state. We compare the energy of the AFM-Sk with the energy of the AFM ground state. In addition, an estimation of the energy barrier that protects the skyrmion from being destabilized is provided and its value determined to be in the order of similar to 300 K. The remarkable reduction in the skyrmion radius towards atomic size and avoiding an external magnetic field are key points in order to increase our ability to manipulate AFM-Sk on skyrmionic devices. Our calculations provide an insight into novel ways to create and manipulate AFM-Sk at the atomic scale. (C) 2019 Elsevier Inc. All rights reserved.
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The dependence for the frequencies of the internal modes on the external field in spiral structures in easy-plane antiferromagnets with a small in-plane anisotropy are studied theoretically in a wide region of the fields including...
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The dependence for the frequencies of the internal modes on the external field in spiral structures in easy-plane antiferromagnets with a small in-plane anisotropy are studied theoretically in a wide region of the fields including the spin-flop transition field. The theoretical results are compared with the known experimental data for the antiferromagnetic resonance in NdFe3(BO3)(4). This comparison enabled to reconstruct the dependence for the spiral period of the magnetic structure on the external field.
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We have investigated the crystallographic and magnetic properties of (Mn,Fe)_(3-δ)Ga alloys. The hexagonal phase is stable between 600 and 700 °C and can be stabilized by quenching to room temperature. Mn_3Ga is reported to be o...
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We have investigated the crystallographic and magnetic properties of (Mn,Fe)_(3-δ)Ga alloys. The hexagonal phase is stable between 600 and 700 °C and can be stabilized by quenching to room temperature. Mn_3Ga is reported to be off-stoichiometric, but we show that using melt-spinning the stoichiometric compound is attainable. Below the antiferromagnetic transition temperature T_N, the crystal undergoes a hexagonal to monoclinic transition at the distortion temperature T_d. This gives rise to an in-plane rotation of the magnetic moments that is accompanied by a simultaneous increase in magnetization in a magnetic field of 1 T. Fe substitution for Mn removes the monoclinic distortion. Substitutional Fe weakens the antiferromagnetism and a paramagnetic to ferromagnetic transition is observed. The Mn sublattice couples antiparallel throughout the series. Substitution of Ga with Si preserves the monoclinic distortion.
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Antiferromagnetic (AF) nanostructures from Co_3O_4, CoO, and Cr_2O_3 were prepared by the nanocasting method and were characterized magnetometrically. The field- and temperature-dependent magnetization data suggests that the nanos...
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Antiferromagnetic (AF) nanostructures from Co_3O_4, CoO, and Cr_2O_3 were prepared by the nanocasting method and were characterized magnetometrically. The field- and temperature-dependent magnetization data suggests that the nanostructures consist of a core-shell structure. The core behaves as a regular antiferromagnet and the shell as a two-dimensional diluted antiferromagnet in a field (2D DAFF) as previously shown on CO_3O_4 nanowires [M. J. Benitez et ah, Phys. Rev. Lett. 101, 097206 (2008)]. Here we present a more general picture on three different material systems, i.e., CO_3O_4, CoO, and Cr_2O_3. In particular, we consider the thermoremanent (TRM) and the isothermoremanent (IRM) magnetization curves as "fingerprints" in order to identify the irreversible magnetization contribution originating from the shells. The TRM/IRM fingerprints are compared to those of superparamagnetic systems, superspin glasses, and 3D DAFFs. We demonstrate that TRM/IRM vs H plots are generally useful fingerprints to identify irreversible magnetization contributions encountered in particular in nanomagnets.
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In this paper, I analyze the symmetries and degeneracies of electron eigenstates in a commensurate collinear antiferromagnet. In a magnetic field transverse to the staggered magnetization, a hidden antiunitary symmetry protects do...
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In this paper, I analyze the symmetries and degeneracies of electron eigenstates in a commensurate collinear antiferromagnet. In a magnetic field transverse to the staggered magnetization, a hidden antiunitary symmetry protects double degeneracy of the Bloch eigenstates at a special set of momenta. In addition to this "Kramers degeneracy" subset, the manifold of momenta, labeling the doubly degenerate Bloch states in the Brillouin zone, may also contain an "accidental degeneracy" subset that is not protected by symmetry and that may change shape under perturbation. These degeneracies give rise to a substantial momentum dependence of the transverse g-factor in the Zeeman coupling, turning the latter into a spin-orbit interaction. I discuss a number of materials, where Zeeman spin-orbit coupling is likely to be present, and outline the simplest properties and experimental consequences of this interaction, that may be relevant to systems from chromium to borocarbides, cuprates, hexaborides, iron pnictides, as well as organic and heavy fermion conductors.
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