Noncollinear Antiferromagnetic Structure Research Articles

Voltage control of multiferroic magnon torque for reconfigurable logic-in-memory

Magnons, bosonic quasiparticles carrying angular momentum, can flow through insulators for information transmission with minimal power dissipation. However, it remains challenging to develop a magnon-based logic due to the lack of efficient electrical manipulation of magnon transport. Here we show the electric excitation and control of multiferroic magnon modes in a spin-source/multiferroic/ferromagnet structure. We demonstrate that the ferroelectric polarization can electrically modulate the magnon-mediated spin-orbit torque by controlling the non-collinear antiferromagnetic structure in multiferroic bismuth ferrite thin films with coupled antiferromagnetic and ferroelectric orders. In this multiferroic magnon torque device, magnon information is encoded to ferromagnetic bits by the magnon-mediated spin torque. By manipulating the two coupled non-volatile state variables—ferroelectric polarization and magnetization—we further present reconfigurable logic operations in a single device. Our findings highlight the potential of multiferroics for controlling magnon information transport and offer a pathway towards room-temperature voltage-controlled, low-power, scalable magnonics for in-memory computing.

Cubic Mn3Ge thin films stabilized through epitaxial growth as a candidate noncollinear antiferromagnet

Metallic antiferromagnets with chiral spin textures induce Berry curvature-driven anomalous and spin Hall effects that arise from the topological structure of their electronic bands. Here, we use epitaxial engineering to stabilize (111)-oriented thin films of Mn3Ge with a cubic phase. This cubic phase is distinct from tetragonal ferrimagnetic and hexagonal noncollinear antiferromagnetic structures with the same chemical composition. First-principles calculations indicate that cubic Mn3Ge will preferentially form an all-in/all-out triangular spin texture. We present evidence for this noncollinear antiferromagnetism through magnetization measurements with a Néel temperature of 490 K. First-principles calculations of the corresponding band structure indicate the presence of Weyl points. These highlight cubic Mn3Ge as a candidate material for topological antiferromagnetic spintronics.

Magnetic properties of Dy[formula omitted](Co,Ni) compounds at ambient and high pressures

Dy3Co, in addition to two antiferromagnetic (AFM) transitions (35 K and TN∼ 44 K), exhibits a Griffiths-like phase around 65 K and it persists up to ∼1 GPa pressure. External pressure alters the magnetic state significantly and results in increase (decrease) of TN (TAF) by 6.5% (∼13%) with dTN/dP ∼ 3 K/GPa (dTAF/dP ∼ −4.5 K/GPa). Increase in metamagnetic critical field and other changes with pressure indicate the strengthening of AFM interactions in Dy3Co. On the other hand, Dy3Ni shows three magnetic transitions at To∼ 55 K, T1∼ 39 K (AFM) and T2∼ 24 K (AFM). Experimental evidence points to the magnetic ordering temperature to be at To∼55 K instead of 39 K as claimed by certain reports. External pressure reduces (increases) the transition temperature To (T1) by ∼7.9% (7.6%) at a rate of −3.5 K/GPa (2.5 K/GPa). Pressure has only marginal effect on the other low temperature transition at T2. Additionally, ac-susceptibility data exhibit spin-glass like features, which seem to arise from domain wall movements and probably random freezing of small components of spins, coexisting with dominant long-ranged non-collinear AFM structure in these compounds.

Noncollinear commensurate antiferromagnetic structure in metallic Pr2PdAl7Ge4

We report the crystal structure, magnetic structure, magnetic properties, electrical- and magnetotransport properties, and heat capacity of the rare-earth transition-metal compound ${\mathrm{Pr}}_{2}{\mathrm{PdAl}}_{7}{\mathrm{Ge}}_{4}$. ${\mathrm{Pr}}_{2}{\mathrm{PdAl}}_{7}{\mathrm{Ge}}_{4}$ crystallizes in the noncentrosymmetric tetragonal structure $P\overline{4}{2}_{1}m$ (No. 113) with unit cell parameters $a=6.0059(3)\phantom{\rule{4pt}{0ex}}\AA{}$ and $c=15.2278(13)\phantom{\rule{4pt}{0ex}}\AA{}$. The N\'eel temperature ${T}_{\mathit{N}}$ of ${\mathrm{Pr}}_{2}{\mathrm{PdAl}}_{7}{\mathrm{Ge}}_{4}$ was determined to be 6 K by the temperature dependences of magnetization, heat capacity, and electrical resistivity. The magnetic-field-induced antiferromagnetic to ferromagnetic transition occurs for magnetic fields $H$ along both the $ab$ plane and the $c$ axis. The electrical resistivity shows a metallic behavior with an upturn at the ordering temperature due to a superzone gap. Negative linear magnetoresistance is observed since the magnetic field increases the order degree of the antiferromagnetic state, reducing the magnetic correlation scattering. Neutron powder diffraction experiments reveal that metallic ${\mathrm{Pr}}_{2}{\mathrm{PdAl}}_{7}{\mathrm{Ge}}_{4}$ has an unusual noncollinear commensurate antiferromagnetic structure with the propagation vector $\mathbit{k}=(0,\phantom{\rule{0.28em}{0ex}}0,\phantom{\rule{0.28em}{0ex}}0.5)$. Magnetic Pr atom layers stack with the ABBA sequence along the $c$ axis. Within the layers, the Pr moments lie in the $ab$ plane, and the angle between the nearest-neighbor spins is $67.{1}^{\ensuremath{\circ}}$. This magnetic structure can well explain the magnetic properties of ${\mathrm{Pr}}_{2}{\mathrm{PdAl}}_{7}{\mathrm{Ge}}_{4}$.

Multiple magnetic transitions and complex magnetic structures in Fe2SiSe4 with the sawtooth lattice

The sawtooth lattice shares some structural similarities with the kagome lattice and may attract renewed research interest. Here we report a comprehensive study on the physical properties of ${\mathrm{Fe}}_{2}{\mathrm{SiSe}}_{4}$, an unexplored member in the olivine chalcogenides with the sawtooth lattice of Fe. Our results show that ${\mathrm{Fe}}_{2}{\mathrm{SiSe}}_{4}$ is a magnetic semiconductor with band gap of 0.66 eV. It first undergoes an antiferromagnetic transition at ${\mathrm{T}}_{m1}=110$ K, then an ferrimagneticlike one at ${\mathrm{T}}_{m2}=50$ K, and finally a magnetic transition at ${\mathrm{T}}_{m3}=25$ K, which is likely driven by the thermal populations of spin-orbit manifold on the Fe sites. Neutron diffraction analysis reveals a noncollinear antiferromagnetic structure with propagation vector ${\mathbf{q}}_{\mathbf{1}}=(0,0,0)$ at ${\mathrm{T}}_{m2}<\mathrm{T}<{\mathrm{T}}_{m1}$. Interestingly, below ${\mathrm{T}}_{m2}$, an additional antiferromagnetic structure with ${\mathbf{q}}_{\mathbf{2}}=(0,0.5,0)$ appears, and ${\mathrm{Fe}}_{2}{\mathrm{SiSe}}_{4}$ exhibits a complex double-$\mathbf{q}$ magnetic structure which has never been observed in sawtooth olivines. Density functional theory calculations suggest this complex noncollinear magnetic structure may originate from the competing antiferromagnetic interactions for both intra- and interchain in the sawtooth lattice. Furthermore, band-structural calculations show that ${\mathrm{Fe}}_{2}{\mathrm{SiSe}}_{4}$ has quasi-flat-band features near the valence and conduction band structure. Our results have shown that ${\mathrm{Fe}}_{2}{\mathrm{SiSe}}_{4}$ could serve as a new material playground for further research on magnetic devices and the flat-band effect through chemical doping.

Features of the magnetization in ceramics Bi0.86Sm0.14Fe1-xMnxO3 in the rhombohedral - orthorhombic morphotropic phase boundary

Crystal structure of the ceramic compounds Bi0.86Sm0.14Fe1-xMnxO3 prepared by solid state reaction method was studied using X-ray diffraction, scanning electron microscopy and Raman spectroscopy; magnetometry measurements were performed to study magnetic properties and to investigate a correlation between the magnetic and crystal structures of the compounds. The compounds with 0 = x ≤ 0.1 are characterized by the coexistence of the polar rhombohedral and the antipolar orthorhombic phases, an increase of Mn doping causes a stabilization of the orthorhombic phase. Room temperature magnetization data show a gradual reduction of the remanent magnetization with an increase of Mn concentration, while a decrease of temperature causes a nontrivial reduction of remanent magnetization which is determined by a transformation of the non-collinear antiferromagnetic structure towards the collinear antiferromagnetic structure. The magnetic state of the compounds notably depends on the phase ratio of the coexisting structural phases and consists of the antiferromagnetic phases associated with the respective rhombohedral and the orthorhombic phases as well as the ferromagnetic component associated with the phase boundary spins. An evolution of the mentioned magnetic subsystems is discussed as a function of the chemical composition and temperature.

Spin-dependent transport in a driven non-collinear antiferromagnetic fractal network

Non-collinear magnetic texture breaks the spin-sublattice symmetry which gives rise to a spin-splitting effect. Inspired by this, we study the spin-dependent transport properties in a non-collinear antiferromagnetic fractal structure, namely, the Sierpinski Gasket (SPG) triangle. We find that though the spin-up and spin-down currents are different, the degree of spin polarization is too weak. Finally, we come up with a proposal, where the degree of spin polarization can be enhanced significantly in the presence of a time-periodic driving field. Such a prescription of getting spin-filtering effect from an unpolarized source in a fractal network is completely new to the best of our knowledge. Starting from a higher generation of SPG to smaller ones, the precise dependencies of driving field parameters, spin-dependent scattering strength, interface sensitivity on spin polarization are critically investigated. The spatial distribution of spin-resolved bond current density is also explored. Interestingly, our proposed setup exhibits finite spin polarization for different spin-quantization axes. Arbitrarily polarized light is considered and its effect is incorporated through Floquet–Bloch ansatz. All the spin-resolved transport quantities are computed using Green’s function formalism following the Landauer–Büttiker prescription. In light of the experimental feasibility of such fractal structures and manipulation of magnetic textures, the present work brings forth new insights into spintronic properties of non-collinear antiferromagnetic SPG. This should also entice the AFM spintronic community to explore other fractal structures with the possibility of unconventional features.

Magnetic particles and strings in iron langasite

Magnetic topological defects can store and carry information. Replacement of extended defects, such as domain walls and Skyrmion tubes, by compact magnetic particles that can propagate in all three spatial directions may open an extra dimension in the design of magnetic memory and data processing devices. We show that such objects can be found in iron langasite, which exhibits a hierarchy of non-collinear antiferromagnetic spin structures at very different length scales. We derive an effective model describing long-distance magnetic modulations in this chiral magnet and find unusual two- and three-dimensional topological defects. The order parameter space of our model is similar to that of superfluid 3He-A, and the particle-like magnetic defect is closely related to the Shankar monopole and hedgehog soliton in the Skyrme model of baryons. Mobile magnetic particles stabilized in non-collinear antiferromagnets can play an important role in antiferromagnetic spintronics.

Magnetization spin reversal and neutron diffraction study of polycrystalline Tb0.55Sr0.45MnO3

We have investigated the structural and magnetic phase transitions in Sr doped polycrystalline Tb0.55Sr0.45MnO3, using temperature-dependent high-resolution neutron powder diffraction in the HRPT diffractometer at PSI to address the origin of magnetization reversal at low temperature. The solid solution Tb0.55Sr0.45MnO3 crystallizes in O′ type orthorhombic structure having the Pnma symmetry. The substitution of the divalent cation of Sr2+ at the site of Tb3+ dilutes the Mn–Tb interaction and affects the magnetic structure, which was observed by the field and temperature-dependent dc magnetization and neutron diffraction study. The temperature-dependent zero field-cooled and field cooled dc magnetization study reveals the indication of spin reversal phenomena, which is the nature of canted antiferromagnetic or ferrimagnetic transition at 100 Oe because of Mn–Mn sub-lattices interaction below 65 K. By increasing the applied magnetic field up to 20 kOe, a weak ferromagnetic type of behaviour is observed. The field-dependent magnetization shows weak coercivity due to the canted spin structure at low temperatures. The low-temperature neutron diffraction study of polycrystalline Tb0.55Sr0.45MnO3 reveals the non-collinear canted antiferromagnetic structure due to Tb ordering at 1.5 K, which turns into a non-collinear ferromagnetic structure along with spin canting followed by the spin reversal phenomena at 25 K.

Original Network of Zigzag Chains in the β Polymorph of Fe2WO6: Crystal Structure and Magnetic Ordering.

The structural and physical properties of the β polymorph of iron tungstate Fe2WO6 have been investigated by synchrotron and neutron diffraction vs temperature, combined with magnetization and dielectric properties measurements. The monoclinic P21/a crystal structure of β-Fe2WO6 has been determined and consists of an original network of zigzag chains of FeO6 and WO6 octahedra sharing trans and skew edges, connected through corners into a 3D structure. Magnetization measurements indicate an antiferromagnetic transition at TN = 264 K, which corresponds to a ↑↑↓↓ nearly collinear ordering of iron moments inside sequences of four edge-sharing FeO6 octahedra, as determined by neutron diffraction. A canting of the moments out of the ac plane is observed below 150 K, leading to a noncollinear antiferromagnetic structure, the P21/a' magnetic space group remaining unchanged. These results are discussed in comparison with the crystal and magnetic structures of γ-Fe2WO6 and with the magnetic couplings in other iron tungstates and trirutile Fe2TeO6.

Magnetic properties and magnetic structures of R2PdGe6 (R = Pr, Nd, Gd-Er) and R2PtGe6 (R = Tb, Ho, Er)

Polycrystalline samples of the intermetallic compounds R2PdGe6 (R = Pr, Nd, Gd-Er) and R2PtGe6 (R = Tb, Ho, Er) have been studied using X-ray diffraction as well as magnetometric and neutron diffraction measurements. All compounds have an orthorhombic crystal structure of the Yb2PdGe6-type (space group Cmca) and are antiferromagnetic with the Néel temperatures ranging from 4.9 K for Er2PtGe6 up to 48 K for Tb2PdGe6. The magnetic properties and specific heat data collected for Nd2PdGe6 show the presence of an additional phase transition below TN at T = 4 K. Based on the neutron diffraction data, the magnetic structures have been determined for R2PdGe6 (R = Pr, Nd, Tb, Dy, Ho) and R2PtGe6 (R = Tb and Er). Both the magnetic properties and neutron diffraction data indicate that the magnetic moment is localized on rare earth atoms. The magnetic unit cell is equal to the crystal one, however, individual compounds show different types of magnetic orderings. Magnetic moments in Pr2PdGe6 form a non-collinear antiferromagnetic structure at low temperatures with magnetic moments confined to the (001) plane. The low temperature magnetic structure in Nd2PdGe6 is a collinear antiferromagnetic one with moments parallel to the b-axis and coupled ferromagnetically within the (001) plane, while along the c-axis the moments follow the +−−+ sequence. With increasing temperature, atransition to a modulated magnetic structure is observed in Nd2PdGe6 at T = 4 K. The magnetic moments in R2PdGe6 (R = Tb, Dy, Ho) and Tb2PtGe6 assume a non-collinear antiferromagnetic order within the (001) plane with the +−+− sequence of signs of the moments in the neighboring planes along the c-axis. The Er moments in Er2PtGe6 form a collinear magnetic structure with magnetic moments oriented along the a-axis and coupled ferromagnetically within the (001) plane. Along the c-axis the moments follow the +−+− sequence. The magnetic structures determined here are discussed on the basis of the competition between the RKKY-type interactions and influence of Crystalline Electric Field.

Anomalous Hall effect in noncollinear antiferromagnetic Mn3NiN thin films

We have studied the anomalous Hall effect (AHE) in strained thin films of the frustrated antiferromagnet Mn$_{3}$NiN. The AHE does not follow the conventional relationships with magnetization or longitudinal conductivity and is enhanced relative to that expected from the magnetization in the antiferromagnetic state below $T_{\mathrm{N}} = 260$\,K. This enhancement is consistent with origins from the non-collinear antiferromagnetic structure, as the latter is closely related to that found in Mn$_{3}$Ir and Mn$_{3}$Pt where a large AHE is induced by the Berry curvature. As the Berry phase induced AHE should scale with spin-orbit coupling, yet larger AHE may be found in other members of the chemically flexible Mn$_{3}A$N structure.

Topology analysis for anomalous Hall effect in the noncollinear antiferromagnetic states of Mn3AN (A=Ni, Cu, Zn, Ga, Ge, Pd, In, Sn, Ir, Pt)

We investigate topological features of electronic structures which produce large anomalous Hall effect in the non-collinear antiferromagnetic metallic states of anti-perovskite manganese nitrides by first-principles calculations. We first predict the stable magnetic structures of these compounds to be non-collinear antiferromagnetic structures characterized by either $T_{1g}$ or $T_{2g}$ irreducible representation by evaluating the total energy for all of the magnetic structures classified according to the symmetry and multipole moments. The topology analysis is next performed for the Wannier tight-binding models obtained from the first-principles band structures. Our results reveal the small Berry curvature induced through the coupling between occupied and unoccupied states with the spin-orbit coupling, which is widely spread around the Fermi surface in the Brillouin zone, dominantly contributes after the $k$-space integration to the anomalous Hall conductivity, while the local divergent Berry curvature around Weyl points has a rather small contribution to the anomalous Hall conductivity.

The Biaxial Strain Dependence of Magnetic Order in Spin Frustrated Mn3NiN Thin Films

AbstractMulticomponent magnetic phase diagrams are a key property of functional materials for a variety of uses, such as manipulation of magnetization for energy efficient memory, data storage, and cooling applications. Strong spin‐lattice coupling extends this functionality further by allowing electric‐field‐control of magnetization via strain coupling with a piezoelectric. Here this work explores the magnetic phase diagram of piezomagnetic Mn3NiN thin films, with a frustrated noncollinear antiferromagnetic (AFM) structure, as a function of the growth induced biaxial strain. Under compressive strain, the films support a canted AFM state with large coercivity of the transverse anomalous Hall resistivity, ρxy, at low temperature, that transforms at a well‐defined Néel transition temperature (TN) into a soft ferrimagnetic‐like (FIM) state at high temperatures. In stark contrast, under tensile strain, the low temperature canted AFM phase transitions to a state where ρxy is an order of magnitude smaller and therefore consistent with a low magnetization phase. Neutron scattering confirms that the high temperature FIM‐like phase of compressively strained films is magnetically ordered and the transition at TN is first‐order. The results open the field toward future exploration of electric‐field‐driven piezospintronic and thin film caloric cooling applications in both Mn3NiN itself and the broader Mn3AN family.

Antiferromagnetic ordering and dipolar interactions of YbAlO3

In this paper we report low-temperature magnetic properties of the rare-earth perovskite material YbAlO$_3$. Results of elastic and inelastic neutron scattering experiment, magnetization measurements along with the crystalline electrical field (CEF) calculations suggest that the ground state of Yb moments is a strongly anisotropic Kramers doublet, and the moments are confined in the $ab$-plane, pointing at an angle of $\varphi = \pm 23.5^{\circ}$ to the $a$-axis. With temperature decreasing below $T_{\rm N}=0.88$ K, Yb moments order into the coplanar, but non-collinear antiferromagnetic (AFM) structure $AxGy$, where the moments are pointed along their easy-axes. In addition, we highlight the importance of the dipole-dipole interaction, which selects the type of magnetic ordering and may be crucial for understanding magnetic properties of other rare-earth orthorhombic perovskites. Further analysis of the broad diffuse neutron scattering shows that one-dimensional interaction along the $c$-axis is dominant, and suggests YbAlO$_3$ as a new member of one dimensional quantum magnets.

Local magnetism, magnetic order and spin freezing in the ‘nonmetallic metal’ FeCrAs

We present the results of x-ray scattering and muon-spin relaxation (SR) measurements on the iron-pnictide compound FeCrAs. Polarized non-resonant magnetic x-ray scattering results reveal the 120° periodicity expected from the suggested three-fold symmetric, non-collinear antiferromagnetic structure. SR measurements indicate a magnetically ordered phase throughout the bulk of the material below K. There are signs of fluctuating magnetism in a narrow range of temperatures above involving low-energy excitations, while at temperatures well below behaviour characteristic of freezing of dynamics is observed, likely reflecting the effect of disorder in our polycrystalline sample. Using density functional theory we propose a distinct muon stopping site in this compound and assess the degree of distortion induced by the implanted muon.

Insight into electronic, magnetic and optical properties of magnetically ordered Bi2Fe4O9

Abstract Non-collinear antiferromagnetic (AFM) spin structure is imposed in Bi2Fe4O9 to study the electronic and magnetic properties of magnetically ordered Bi2Fe4O9 using first principles. Electronic properties carried out for both ferromagnetic (FM) and antiferromagnetic (AFM) orderings in Bi2Fe4O9 suggest that FM Bi2Fe4O9 is a semiconductor with an indirect optical bandgap of 1.732 eV, whereas, AFM Bi2Fe4O9 is a multiband semiconductor. The influence of different magnetic orderings on the electronic properties of Bi2Fe4O9 are studied in detail. The linear optical response of FM Bi2Fe4O9 is also investigated.

Magnetic and Structural Transitions Tuned through Valence Electron Concentration in Magnetocaloric Mn(Co1–xNix)Ge

The structural and magnetic properties of magnetocaloric Mn(Co1–xNix)Ge compounds have been studied. Two responses to the increase of valence electron concentration on substitution of Ni (3d84s2) for Co (3d74s2) in the orthorhombic phase (Pnma) are proposed: expansion of unit-cell volume and redistribution of valence electrons. We present experimental evidence for electronic redistribution associated with the competition between magnetism and bonding. This competition in turn leads to complex dependences of the reverse martensitic transformation temperature TM (orthorhombic to hexagonal (P63/mmc)) and the magnetic structures on the Ni concentration. Magnetic transitions from ferromagnetic structures below x = 0.50 to noncollinear spiral antiferromagnetic structures above x = 0.55 at low temperature (e.g., 5 K) are induced by modification of the density of states at the Fermi surface due to the redistribution of valence electrons. TM is found to decrease initially with increasing Ni content and then increa...

First-principles Theory of Magnetic Multipoles in Condensed Matter Systems

The multipole concept, which characterizes the spacial distribution of scalar and vector objects by their angular dependence, has already become widely used in various areas of physics. In recent years it has become employed to systematically classify the anisotropic distribution of electrons and magnetization around atoms in solid state materials. This has been fuelled by the discovery of several physical phenomena that exhibit unusual higher rank multipole moments, beyond that of the conventional degrees of freedom as charge and magnetic dipole moment. Moreover, the higher rank electric/magnetic multipole moments have been suggested as promising order parameters in exotic hidden order phases. While the experimental investigations of such anomalous phases have provided encouraging observations of multipolar order, theoretical approaches have developed at a slower pace. In particular, a materials' specific theory has been missing. The multipole concept has furthermore been recognized as the key quantity which characterizes the resultant configuration of magnetic moments in a cluster of atomic moments. This cluster multipole moment has then been introduced as macroscopic order parameter for a noncollinear antiferromagnetic structure in crystals that can explain unusual physical phenomena whose appearance is determined by the magnetic point group symmetry. It is the purpose of this review to discuss the recent developments in the first-principles theory investigating multipolar degrees of freedom in condensed matter systems. These recent developments exemplify that ab initio electronic structure calculations can unveil detailed insight in the mechanism of physical phenomena caused by the unconventional, multipole degree of freedom.

Microscopic Insights on the Multiferroic Perovskite-Like [CH3 NH3 ][Co(COOH)3 ] Compound.

The characterization of the crystal structure, phase transitions, magnetic structure and dielectric properties has been carried out on [CH3 NH3 ][Co(COOH)3 ] (1) perovskite-like metal-organic compound through variable-temperature single-crystal and powder neutron and X-ray diffraction and relative permittivity measurements. The paraelectric to antiferroelectric-like phase transition observed at around 90 K is triggered by a structural phase transition; the structural studies show a change from Pnma space group at RT (1A) to P21 /n space group at low temperature (1B). This phase transition involves the occurrence of small distortions in the framework and counterions. Neutron diffraction studies have shown a magnetic order showing spontaneous magnetization below 15 K, due to the occurrence of a non-collinear antiferromagnetic structure with a weak ferromagnetic component, mainly due to the single-ion anisotropy of the CoII ions.