Weak Magnetic Anisotropy Research Articles

Observation of Néel-type magnetic skyrmion in a layered non-centrosymmetric itinerant ferromagnet CrTe1.38

Magnetic skyrmions are nanoscale vortex-like magnetization textures that hold great promise for next-generation memory and spintronic devices. While extensive research has focused on discovering such localized spin textures in bulk magnets and multilayers with heavy metals, there is a growing interest in finding them in two-dimensional (2D) magnetic materials. In this research work, we report two distinct phases of the 2D CrxTey family: non-centrosymmetric CrTe1.38 and centrosymmetric CrTe0.96, with a Curie temperature of around 200 and 300 K, respectively. Detailed magnetic study indicates a prominent out-of-plane magnetic anisotropy in CrTe1.38. In contrast, CrTe0.96 exhibits a weak uniaxial magnetic anisotropy. Lorentz transmission electron microscopy shows that the spontaneous ferromagnetic ground state of CrTe1.38 consists of Néel skyrmions, whereas CrTe0.96 exhibits Bloch domain walls, consistent with their crystalline symmetries. This research expands the quasi-2D CrxTey family and opens up new avenues for exploring non-trivial spin structures and their potential applications in spintronic devices.

Microstructural contribution to the magnetic anisotropy in Fe 1−x Ga x thin films: correlation between crystallographic texture and magnetic response

In this study, we present a systematic analysis of the relation between the structural properties and magnetic anisotropies of as-grown and heat-treated polycrystalline Fe 1−x Ga x (0.11 <x< 0.19) thin films deposited on glass and Si(100) substrates. The results show that the crystallographic texture of the films has a significant impact on the evolution of the magnetic anisotropies. The samples grown on glass do not exhibit a preferred texture while, for samples grown on Si(100), the appearance of a weak in-plane fourfold magnetic anisotropy is reported. Such anisotropy is enhanced and better defined in the heat treated samples. Via a phenomenological model we show that this anisotropy has a microstructural origin. These findings demonstrate the possibility of tuning magnetic anisotropies by growing on different substrates and/or performing thermal treatments, which in turn reinforces the possibility of developing smart magnetic switching materials for electronic applications.

Lattice-commensurate skyrmion texture in a centrosymmetric breathing kagome magnet

Skyrmion lattices (SkL) in centrosymmetric materials typically have a magnetic period on the nanometer-scale, so that the coupling between magnetic superstructures and the underlying crystal lattice cannot be neglected. We reveal the commensurate locking of a SkL to the atomic lattice in Gd3Ru4Al12 via high-resolution resonant elastic x-ray scattering (REXS). Weak easy-plane magnetic anisotropy, demonstrated here by a combination of ferromagnetic resonance and REXS, penalizes placing a skyrmion core on a site of the atomic lattice. Under these conditions, a commensurate SkL, locked to the crystal lattice, is stable at finite temperatures – but gives way to a competing incommensurate ground state upon cooling. We discuss the role of Umklapp-terms in the Hamiltonian for the formation of this lattice-locked state, its magnetic space group, and the role of slight discommensurations, or (line) defects in the magnetic texture. We also contrast our findings with the case of SkLs in noncentrosymmetric material platforms.

Tailoring Magnetic Anisotropy in Ultrathin Cobalt by Surface Carbon Chemistry

AbstractThe ability to manipulate magnetic anisotropy is essential for magnetic sensing and storage tools. Surface carbon species offer cost‐effective alternatives to metal‐oxide and noble metal capping layers, inducing perpendicular magnetic anisotropy in ultrathin ferromagnetic films. Here, the different mechanisms by which the magnetism in a few‐layer‐thick Co thin film is modified upon adsorption of carbon monoxide (CO), dispersed carbon, and graphene are elucidated. Using X‐ray microscopy with chemical and magnetic sensitivity, the in‐plane to out‐of‐plane spin reorientation transition in cobalt is monitored during the accumulation of surface carbon up to the formation of graphene. Complementary magneto‐optical measurements show weak perpendicular magnetic anisotropy (PMA) at room temperature for dispersed carbon on Co, while graphene‐covered cobalt exhibits a significant out‐of‐plane coercive field. Density‐functional theory (DFT) calculations show that going from CO/Co to C/Co and to graphene/Co, the magnetocrystalline and magnetostatic anisotropies combined promote out‐of‐plane magnetization. Anisotropy energies weakly depend on carbidic species coverage. Instead, the evolution of the carbon chemical state from carbidic to graphitic is accompanied by an exponential increase in the characteristic domain size, controlled by the magnetic anisotropy energy. Beyond providing a basic understanding of the carbon‐ferromagnet interfaces, this study presents a sustainable approach to tailor magnetic anisotropy in ultrathin ferromagnetic films.

Evolution of Microscopic Magnetic Domains in Quasi‐2D Cr0.92Te at Room Temperature

Abstract2D materials with long‐range ferromagnetic order hold promises for the development of compact spintronic devices with unprecedented multifunctionality and tunability. Among various 2D magnets, self‐intercalated transition metal chalcogenides Cr1+δTe2 exhibit unique features, especially excellent ambient stability and intrinsic ferromagnetic ordering above room temperature, which are critical requirements for real‐life device applications. Despite the many investigations of the magnetic properties of the Cr1+δTe2 family on the averaging macroscopic level, the domain evolution on the microscale, which is vital to nanoscale spintronics, is yet to be fully understood. Here, the evolution of magnetic behaviors of Cr0.92Te crystals is presented on both macro‐ and micro‐scales under magnetic field and thermal excitation. The crystal exhibits a high Curie temperature (Tc ≈ 343 K) among the Cr1+δTe2 family with weak magnetic anisotropy and in‐plane magnetic easy axis. Utilizing magnetic force microscopy, a pristine multidomain state and typical domain‐switching behavior are observed. Moreover, the evolution of domain texture under thermal excitation shows statistical power‐law scaling as approaching Tc. The results provide microscopic insight into the ferromagnetic behavior of a room‐temperature quasi‐2D crystal, which can be useful for further engineering of domain texture in low‐dimensional magnetic materials.

Spin Qubit in a 2D GdIII NaI -Based Oxamato Supramolecular Coordination Framework.

Qubits are the basic unit of quantum information and computation. To realize quantum computing and information processing, the decoherence times of qubits must be long enough. Among the studies of molecule-based electron spin qubits, most of the work focused on the ions with the spin S=1/2, where only single-bit gates can be constructed. However, quantum operations require the qubits to interact with each other, so people gradually carry out relevant research in ions or systems with S>1/2 and multilevel states. In this work, a two-dimensional (2D) oxygen-coordinated GdIII NaI -based oxamato supramolecular coordination framework, Na[Gd(4-HOpa)4 (H2 O)] ⋅ 2H2 O (1, 4-HOpa=N-4-hydroxyphenyloxamate), was selected as a possible carrier of qubit. The field-induced slow magnetic relaxation shows this system has phonon bottleneck (PB) effect at low temperatures with a very weak magnetic anisotropy. The pulse electron paramagnetic resonance studies show the spin-lattice and spin-spin relaxation times are T1 =1.66 ms at 4 K and Tm =4.25 μs at 8 K for its diamagnetically diluted sample (1Gd0.12 %). It suggested that the relatively long decoherence time is mainly ascribed to its near isotropic and the PB effect from resonance phonon trapped for pure sample, while the dilution further improves its qubit performance.

THE INFLUENCE OF STRUCTURAL AND COMPOSITIONAL FACTORS ON THE REALIZATION OF THE EXCHANGE BIAS EFFECT IN (Cr-Mn)/Fe20Ni80

The influence of a number of physical factors on the structural and hysteresis properties of multilayer films (Cr-Mn)/Fe Ni has been studied. By indirect signs, the presence of antiferromagnetism in Cr-Mn layers with a Mn content in the range of 20-40 at.% has been established. It is shown that in such structures, the exchange bias effect can be observed, but only when the thickness of the antiferromagnetic layer is greater than 40 nm. The initial reason for the low "fixing" properties of the Cr-Mn layer is its weak magnetic anisotropy, which is superimposed with instability in the reproduction of the micro-structure. The use of substrate heating during film deposition increased the reproducibility of microstructure parameters and hysteresis characteristics but led to a weakening of the exchange bias effect, apparently due to changes in the structure and composition of the interlayer interface.

Highly Tunable Perpendicular Magnetic Anisotropy and Anisotropic Magnetoresistance in Ru-doped La0.67Sr0.33MnO3 Epitaxial Films

Abstract As a prototypical half-metallic ferromagnet, La 0.67 Sr 0.33 MnO 3 (LSMO) has been extensively studied due to its versatile physical properties and great potential in spintronic applications. However, the weak perpendicular magnetic anisotropy (PMA) limits the controllability and detection of magnetism in LSMO, thus hindering the realization of oxide-based spintronic devices with low energy consumption and high integration level. Motivated by this challenge, we developed an experimental approach to enhance the PMA of LSMO epitaxial films. By cooperatively introducing 4 d Ru doping and a moderate compressive strain, the maximum uniaxial magnetic anisotropy in Ru-doped LSMO can reach 3.0×10 5 J/m 3 at 10 K. Furthermore, we also found a significant anisotropic magnetoresistance effect in these Ru-doped LSMO films, which is dominated by the strong PMA. Our findings offer an effective pathway to harness and detect the orientations of magnetic moments in LSMO films, thus promoting the feasibility of oxide-based spintronic devices, such as in spin valves and magnetic tunnel junctions.

Highly Tunable Perpendicular Magnetic Anisotropy and Anisotropic Magnetoresistance in Ru-Doped La0.67Sr0.33MnO3 Epitaxial Films

As a prototypical half-metallic ferromagnet, La0.67Sr0.33MnO3 (LSMO) has been extensively studied due to its versatile physical properties and great potential in spintronic applications. However, the weak perpendicular magnetic anisotropy (PMA) limits the controllability and detection of magnetism in LSMO, thus hindering the realization of oxide-based spintronic devices with low energy consumption and high integration level. Motivated by this challenge, we develop an experimental approach to enhance the PMA of LSMO epitaxial films. By cooperatively introducing 4d Ru doping and a moderate compressive strain, the maximum uniaxial magnetic anisotropy in Ru-doped LSMO can reach 3.0 × 105 J/m3 at 10 K. Furthermore, we find a significant anisotropic magnetoresistance effect in these Ru-doped LSMO films, which is dominated by the strong PMA. Our findings offer an effective pathway to harness and detect the orientations of magnetic moments in LSMO films, thus promoting the feasibility of oxide-based spintronic devices, such as spin valves and magnetic tunnel junctions.

Charge invertible nanowires [Ni5Bi5.6]x (x = 1+, 0, 1−): Infinite columns [Ni5Bi5.6]− in a novel quasi-one-dimensional compound KNi5Bi5.6

A novel quasi-one-dimensional (Q1D) compound KNi5Bi5.6 has been synthesized and its crystal structure has been determined by X-ray crystallography. The structure contains double-walled anionic nanowires [Ni5Bi5.6]− separated by potassium cations. KNi5Bi5.6 forms a new series of compounds together with previously reported Bi5.6Ni5I and Bi28Ni25 featuring [Ni5Bi5.6]x (x = 1+, 0, 1−) nanowires for which the charge can be cationic, neutral or anionic without appreciably affecting the structure and composition. This unique characteristic provides a new platform to investigate charge invertible Q1D transition metal systems. Resistivity measurement of KNi5Bi5.6 reveals a metallic type of conductivity. Magnetic susceptibility obeys a modified Curie-Weiss behavior with a small average effective magnetic moment of Ni and shows a weak magnetic anisotropy.

A puzzling insensitivity of magnon spin diffusion to the presence of 180-degree domain walls

We present room-temperature measurements of magnon spin diffusion in epitaxial ferrimagnetic insulator MgAl0.5Fe1.5O4 (MAFO) thin films near zero applied magnetic field where the sample forms a multi-domain state. Due to a weak uniaxial magnetic anisotropy, the domains are separated primarily by 180° domain walls. We find, surprisingly, that the presence of the domain walls has very little effect on the spin diffusion – nonlocal spin transport signals in the multi-domain state retain at least 95% of the maximum signal strength measured for the spatially-uniform magnetic state, over distances at least five times the typical domain size. This result is in conflict with simple models of interactions between magnons and static domain walls, which predict that the spin polarization carried by the magnons reverses upon passage through a 180° domain wall.

Ab initio exploration of short-pitch skyrmion materials: Role of orbital frustration

In recent years, the skyrmion lattice phase with a short lattice constant has attracted attention due to its high skyrmion density, making it a promising option for achieving high-density storage memory and for observing novel phenomena like the quantized topological Hall effect. Unlike conventional non-centrosymmetric systems where the Dzyaloshinsky–Moriya interaction plays a crucial role, the short pitch skyrmion phase requires a quadratic magnetic interaction J(q) with a peak at finite-Q, and weak easy-axis magnetic anisotropy is also critical. Thus, conducting first-principles evaluations is essential for understanding the formation mechanism as well as for promoting the discovery of new skyrmion materials. In this Perspective, we focus on recent developments of the first-principles evaluations of these properties and apply them to the prototype systems GdT2X2 and EuT2X2, where T denotes a transition metal and X represents Si or Ge. In particular, based on the spin density functional theory with the Hubbard correction combined with the Liechtenstein method in the Wannier tight-binding model formalism, we first show that the Hubbard U and Hund’s coupling is essential to stabilize a skyrmion lattice state by enhancing the easy-axis anisotropy. We then discuss mechanisms of finite-Q instability and show that competition among Gd-5d orbitals determines whether ferromagnetism or a finite-Q structure is favored in GdT2Si2 with T= Fe and Ru. Our systematic calculations reveal that GdRu2X2, GdOs2X2, and GdRe2X2 are promising, while GdAg2X2, GdAu2X2, and EuAg2X2 are possible candidates as the skyrmion host materials. Analysis based on a spin spiral calculation for the candidate materials is also presented.

Perpendicular magnetic anisotropy induced by antiferromagnetic Mn-Pd alloy films: Dual effects of exchange and spin-orbit coupling

Ferromagnetic (FM) films with perpendicular magnetic anisotropy (PMA) are crucial building blocks of state-of-the-art perpendicular magnetic devices. This study investigated the effects of triggering PMA in FM thin films by applying ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$-based antiferromagnetic (AFM) thin films with strong AFM exchange coupling from Mn and high spin-orbit coupling from Pd atoms. Our results reveal that ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films can trigger PMA in Co/Ni films with weak in-plane magnetic anisotropy at room temperature through either ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$-facilitated interfacial perpendicular crystalline anisotropy (spin-orbit coupling, $x \ensuremath{\ge}10%$) or incorporation of them with antiferromagnet-induced exchange coupling ($x \ensuremath{\le}10%$). In Co/Fe films with strong in-plane magnetic anisotropy, Mn-rich ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films ($x \ensuremath{\le}10%$) can induce stable PMA at low temperatures through concurrently enhanced spin-orbit coupling and antiferromagnet-induced exchange coupling across the AFM--FM interface. Our research clarifies the dual effects of exchange and spin-orbit coupling in ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films, which trigger the PMA of adjacent FM films. This indicates that ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films are promising candidates for achieving controllable PMA.

Влияние буферных покрытий на структурное состояние и магнитные свойства пленок (Cr-Mn)/Fe

The article presents the results of a systematic study of the crystalline structure, microstructure, and hysteresis properties of (Cr80Mn20)/Fe bilayers, deposited on buffer coatings of various metals (Cr, Fe, W, Ta). It has been established that depending on the composition of the buffer coating and the thickness of the Cr-Mn layer, the latter develops body-centered cubic structure with either the (110) or (200) texture, or none. It is shown that the Cr-Mn layer is a source of increased coercivity in the adjacent Fe layer and when is in a certain structural state and has a relatively large thickness (100 nm) induces exchange bias in the Fe layer. The regularities obtained are interpreted in terms of the antiferromagnetic ordering of Cr-Mn and its relatively weak magnetic anisotropy

Effect of buffer coatings on the structural state and magnetic properties of (Cr-Mn)/Fe films

The article presents the results of a systematic study of the crystalline structure, microstructure, and hysteresis properties of (Cr80Mn20)/Fe bilayers, deposited on buffer coatings of various metals (Cr, Fe, W, Ta). It has been established that depending on the composition of the buffer coating and the thickness of the Cr-Mn layer, the latter develops body-centered cubic structure with either the (110) or (200) texture, or none. It is shown that the Cr-Mn layer is a source of increased coercivity in the adjacent Fe layer and when is in a certain structural state and has a relatively large thickness (100 nm) induces exchange bias in the Fe layer. The regularities obtained are interpreted in terms of the antiferromagnetic ordering of Cr-Mn and its relatively weak magnetic anisotropy Keywords: antiferromagnetics, ferromagnetic, bilayers, thickness, composition, temperature, texture, coercivity, exchange bias.

Topologically reconfigurable magnetic polaritons

Hyperbolic polaritons in extremely anisotropic materials have attracted intensive attention due to their exotic optical features. Recent advances in optical materials reveal unprecedented dispersion engineering of polaritons, resulting in twistronics for photons, canalized phonon polaritons, shear polaritons, and tunable topological polaritons. However, the on-demand reconfigurability of polaritons, especially with magnetic anisotropic dispersions, is restricted by weak natural magnetic anisotropy and hence remains largely unexplored. Here, we show how origami fused with artificial magnetism unveils a versatile pathway to topologically reconfigure magnetic polaritons. We experimentally demonstrate that the three-dimensional origami deformation allows to reconfigure hyperbolic or elliptic topology of polariton dispersion and modulate group velocity. With group velocity transitioning from positive to negative directions, we further report reconfigurable origami polariton circuitry in which the polariton propagation and phase distribution can be tailored. Our findings provide alternative perspectives on on-chip polaritonics, with potential applications in energy transfer, sensing, and information transport.

Room-Temperature Magnetic Skyrmions and Large Topological Hall Effect in Chromium Telluride Engineered by Self-Intercalation.

Room-temperature magnetic skyrmion materials exhibiting robust topological Hall effect (THE) are crucial for novel nano-spintronic devices. However, such skyrmion-hosting materials are rare in nature. In this study, a self-intercalated transition metal dichalcogenide Cr1+ x Te2 with a layered crystal structure that hosts room-temperature skyrmions and exhibits large THE is reported. By tuning the self-intercalate concentration, a monotonic control of Curie temperature from 169 to 333K and a magnetic anisotropy transition from out-of-plane to the in-plane configuration are achieved. Based on the intercalation engineering, room-temperature skyrmions are successfully created in Cr1.53 Te2 with a Curie temperature of 295K and a relatively weak perpendicular magnetic anisotropy. Remarkably, a skyrmion-induced topological Hall resistivity as large as ≈106nΩ cm is observed at 290K. Moreover, a sign reversal of THE is also found at low temperatures, which can be ascribed to other topological spin textures having an opposite topological charge to that of the skyrmions. Therefore, chromium telluride can be a new paradigm of the skyrmion material family with promising prospects for future device applications.

Revealing 2D Magnetism in a Bulk CrSBr Single Crystal by Electron Spin Resonance

Abstract2D magnets represent material systems in which magnetic order and topological phase transitions can be observed. Based on these phenomena, novel types of computing architectures and magnetoelectronic devices can be envisaged. Unlike conventional magnetic films, their magnetism is independent of the substrate and interface qualities, and 2D magnetic properties manifest even in formally bulk single crystals. However, 2D magnetism in layered materials is rarely reported often due to weak exchange interactions and magnetic anisotropy, and low magnetic transition temperatures. Here, the electron spin resonance (ESR) properties of a layered antiferromagnetic CrSBr single crystal are reported. The W‐like shape angular dependence of the ESR linewidth provides a signature for room temperature spin–spin correlations and for the XY spin model. By approaching the Néel temperature the arising of competing intralayer ferromagnetic and interlayer antiferromagnetic interactions might lead to the formation of vortex and antivortex pairs. This argument is inferred by modeling the temperature dependence of the ESR linewidth with the topological Berezinskii‐Kosterlitz‐Thouless phase transition. These findings together with the chemical stability and semiconducting properties, make CrSBr a promising layered magnet for future magneto‐ and topological‐electronics.

Electronic structure and magnetic anisotropy transition in Mn3−xCoxGa Heusler films investigated with soft x-ray spectroscopy

Employing soft x-ray magnetic circular dichroism (XMCD) and soft x-ray absorption spectroscopy (XAS), we have investigated electronic structures and spin configurations of Co-substituted ${\mathrm{Mn}}_{3}\mathrm{Ga}$ (${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$) Heusler films, which are promising spintronic materials exhibiting perpendicular magnetic anisotropy (PMA). Co $2p$ XAS and XMCD measurements, combined with the charge-transfer multiplet analysis, show that the substituted Co ions in ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ consist of mainly ferromagnetic metallic Co clusters and a small amount of divalent Co ions with disordered magnetic moments. Mn $2p$ XAS and XMCD measurements show that Mn ions at both the octahedral and tetrahedral sites in ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ are nearly divalent with weak covalent-bonding nature, reflecting non-Jahn-Teller ions, and that the magnetic moments of Mn ions are polarized along the ordered magnetic moments of the substituted Co ions. Angle-dependent Co $2p$ XMCD data of ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ agree with the weak magnetic anisotropy transition from PMA to in-plane magnetic anisotropy (IMA) with increasing $x$. Spin and orbital magnetic moments of Co ions are estimated by using the sum-rule analysis, which reveal negligible Co-content and polar-angle dependencies of the Co orbital to spin magnetic moment ratio. This work reveals that the PMA-to-IMA magnetic transition in ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ is determined mainly by ferromagnetic metallic Co clusters.

Spin dynamics, critical scattering and magnetoelectric coupling mechanism of Mn4Nb2O9

The spin dynamics of Mn4Nb2O9 were studied using inelastic neutron scattering. A dynamic model is proposed to explain the observed spin-wave excitation spectrum from Mn4Nb2O9. The model indicates that the exchange interactions along the chain direction are weakly ferromagnetic while the exchange interactions between the neighbour chains are strongly antiferromagnetic. The antiferromagnetic interactions on the two MnO6 octahedron networks are dominant in the spin dynamics of this compound. A spin gap of about 1.4 meV was observed at the zone centre, which is attributed to the weak easy-axis magnetic anisotropy of Mn2+ ions. Magnetic critical scattering from Mn4Nb2O9 was studied in the vicinity of its Néel temperature T N as well, indicating homogeneous development of magnetic correlations. According to the symmetry analysis and its magnetic structure, the weak magnetoelectric coupling effect in Mn4Nb2O9 is ascribed to the uncancelled exchange striction on the two non-equivalent Mn2+ sites.