Spin Reorientation Research Articles

Multiple magnetic transitions and anomalous magnetocaloric effect in an arc melting TbMn2 compound

Magnetic properties of Mn-base alloys are obviously influenced by Mn-content. In this work, multiple magnetic transitions and anomalous magnetocaloric effect of an arc melting TbMn2 intermetallic compound were measured and discussed. TbMn2 shows paramagnetic properties at room temperature. The small bulge at ∼ 230.3 K suggests the rise of a Griffiths phase. The long-range ferromagnetic ordering is established at TC ∼ 60.0 K. The observed antiferromagnetic transition at TN ∼ 45.0 K is caused by the collapse of Mn moments. At ∼ 20.2 K, an unexpected spin reorientation transition is probably due to the arrangement of the sublattice of rare earth. The field induced metamagnetic transition below TN results in an anomalous magnetocaloric effect.

Spin-fluctuation theory of temperature-driven spin reorientations in ferromagnetic transition metal thin films

Spin-fluctuation theory of temperature-driven spin reorientations in ferromagnetic transition metal thin films

Effect of sintering temperature on microstructure and magnetic properties of ErFeO3 ceramics

ErFeO3 ceramics had been synthesized by the solid-state reaction method at a variety of sintering temperatures (1250, 1300, 1350, 1400, 1450, and 1500 °C). The microstructure, surface morphology, and elemental valence state of ErFeO3 polycrystalline ceramics were investigated using X-ray diffraction (XRD), Raman spectroscopy (Raman), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The study discovered that Fe3+ ions keep their valence, and all samples at temperatures ranging from 1300 to 1450 °C are in a pure phase. Within this range, increasing temperature widens the Fe-O-Fe bond angle, lengthens the Er-O bond, suppresses the super-exchange contact between the two ions via O2−, and diminishes the electromagnetic coupling effect. A Physical Property Measurement System (PPMS) was utilized to assess the magnetic properties of ErFeO3 polycrystalline ceramics. Ceramic samples sintered at 1300 °C showed spontaneous spin reorientation and a shift from ionic magnetic disorder to magnetic order. The magnetic hysteresis loops at temperatures before and after spin reorientation were examined. It was noted that the polycrystalline ceramic ErFeO3 underwent a transition in its magnetic configuration from Γ4 (Gx, Ay, Fz) to Γ2 (Fx, Cy, and Gz). As the sintering temperature increases, ErFeO3 polycrystalline ceramics lose their temperature adjustment point. This disrupts the spin reorientation of Er3+ and Fe3+ magnetic moments in the 89–102 K region. The secondary phase transition of ErFeO3 polycrystalline ceramics causes disorder, and the Néel temperature of Er3+ rises. This suggests that the sublattice field and magnetic ordering of Er3+ and Fe3+ are disturbed when the sintering temperature is raised. Consequently, 1300 °C is the optimal sintering temperature for ErFeO3 polycrystalline ceramics.

Néel Vector Auto-Oscillations and Reorientations Induced by Spin-Polarized Electric Currents in Antiferromagnetic Mn2Au Nanolayer

The electrical excitation of spin dynamics in antiferromagnets is important for the development of high-speed spintronic devices with a low power consumption. Here, we present a theoretical study of the spin dynamics generated in the Ni/Cu/Mn2Au/Cu/Ni nanostructure by a perpendicular-to-plane electric current. Our investigation includes atomistic simulations of spin reorientations in a few monolayer antiferromagnetic Mn2Au film and numerical calculations of nonequilibrium spin accumulation in the nanostructure comprising ferromagnetic Ni polarizers with antiparallel magnetizations. This combined approach enables us to quantify the dynamics of Mn magnetic moments induced by the spin-transfer torque created by the spin-polarized charge flow. The calculations show that the direct electric current with the density exceeding some temperature-dependent threshold value gives rise to steady-state auto-oscillations of the Néel vector in the [Formula: see text]-oriented Mn2Au nanolayer. As the precession of Mn magnetic moments occurs around an out-of-plane direction strongly deflected from their initial in-plane orientations, the emergence of auto-oscillations should be regarded as the realization of a dynamic spin reorientation transition in the antiferromagnetic crystal. Remarkably, the precession frequency rises with increasing current density J and exceeds 1[Formula: see text]THz at [Formula: see text][Formula: see text]A[Formula: see text]m[Formula: see text], which makes the described antiferromagnetic spin transfer nano-oscillator attractive for device applications. Furthermore, our simulations demonstrate that a picosecond current pulse injected into the Ni/Cu/Mn2Au/Cu/Ni nanostructure can induce a precessional switching of the Néel vector. Depending on the current density and pulse duration, the Néel vector rotates by either 90° or 180° and attains stable orientation along the corresponding [Formula: see text] easy axis in the plane of the Mn2Au nanolayer. This feature shows that the Ni/Cu/Mn2Au/Cu/Ni nanostructure could be used as a nonvolatile memory cell with the electrical writing and readout.

Spin reorientation and the interplay of magnetic sublattices in Er2CuMnMn4O12.

Through a combination of magnetic susceptibility, specific heat, and neutron powder diffraction measurements we have revealed a sequence of four magnetic phase transitions in the columnar quadruple perovskite Er2CuMnMn4O12. A key feature of the quadruple perovskite structural framework is the complex interplay of multiple magnetic sublattices via frustrated exchange topologies and competing magnetic anisotropies. It is shown that in Er2CuMnMn4O12, this phenomenology gives rise to multiple spin-reorientation transitions driven by the competition of easy-axis single ion anisotropy and the Dzyaloshinskii-Moriya interaction; both within the manganese B-site sublattice. At low temperature, one Er sublattice orders due to a finite f-d exchange field aligned parallel to its Ising axis, while the other Er sublattice remains non-magnetic until a final, symmetry-breaking phase transition into the ground state. This non-trivial low-temperature interplay of transition metal and rare-earth sublattices, as well as an observed k = (0, 0, ½) periodicity in both manganese spin canting and Er ordering, raises future challenges to develop a complete understanding of the R2CuMnMn4O12 family.

Structure and magnetostriction in Nd0.25Tb0.3Dy0.45 (Fe0.9B0.1)1.93 compound

We investigate the structural, magnetic, and magnetostrictive properties of a Nd-containing Nd0.25Tb0.3Dy0.45(Fe0.9B0.1)1.93 (NTDFB) alloy. X-ray diffraction and electron backscatter diffraction analyses reveal that NTDFB exhibits a homogeneous Laves phase, contrasting with the multiphase nature of the boron-free counterpart. At room temperature, the spontaneous and saturation magnetostrictions of NTDFB are 2094 ppm and 1447 ppm, respectively, representing enhancements of 15.9 % and 29.5 % compared to boron-free samples. Another intriguing finding is that the introduction of Nd effectively alters the spin reorientation temperature of Terfenol-D (Tb0.3Dy0.7Fe1.93) and narrows the temperature span of easy magnetic direction (EMD) along < 100 > . NTDFB undergoes two spin reorientations, with the EMD transitioning from < 111 > to < 100 > at TSR1 173 K and from < 100 > to < 110 > at TSR2 92 K, contrasting with TSR1 245 K and TSR2 25 K of Terfenol-D. Additionally, the introduction of Nd into Terfenol-D effectively increases its magnetostriction coefficient,λ110 and λ100. As a result, NTDFB, with a raw material cost 80 % that of Terfenol-D, exhibits magnetostriction values exceeding 1000 ppm from 300 to 20 K, indicating its cost-effectiveness and promising potential as a magnetostrictive alloy.

Tailoring the Spin Reorientation Transition of Co Films by Pd Monolayer Capping.

We have characterized the magnetization easy-axis of ultra-thin Co films (2-5 atomic layers, AL) grown on Ru(0001) when they are capped with a monolayer of Pd. The addition of a Pd monolayer turns the magnetization of 3 and 4 AL-thick Co films from an in-plane to an out-of-plane alignment, but not that of a 5 AL-thick film. These observations are explained in terms of an enhancement of the surface anisotropy. The exposure of the sample to hydrogen, CO or a combination of both gases does not overcome this effect.

Evidence of Spin Reorientation from Γ4 to Γ2 and Sign Reversal Exchange Bias in CeCrO3 Nanoparticles

Herein, the temperature‐dependent magnetic structure and sign reversal exchange bias in CeCrO3 using magnetization data and time‐of‐flight neutron diffraction data which is given less attention among RCrO3 are investigated. While nuclear structural analysis using Rietveld refinement exhibits distorted orthorhombic structure within Pnma space group, temperature dependence of the magnetic structure using neutron diffraction reveals possible spin configurations, namely, Γ4, Γ2, and Γ1, within the temperature range of 6–300 K. Temperature‐dependent magnetization shows compensation temperature, Tcomp, at 58 K, spin reorientation temperature, TSR, at 15 K along with a Neel temperature, TN, at 260 K which is the outcome of the competition between canted antiferromagnetic ordering of Cr3+ ions and Ce3+ ions in CeCrO3. Furthermore, the magnetization versus magnetic field (M vs H) measurements indicate transition of the Γ4 spin structure to Γ2 spin structure around TSR which is further supported by reversible‐to‐irreversible changes observed in temperature‐dependent MFCC and MFCW. Moreover, a temperature‐driven sign reversal of exchange bias in CeCrO3 is observed, resulting from the competition between antiferromagnetic coupling between chromium moment (MCr) and cerium moment (MCe) in these nanoparticles. This intriguing behavior holds significant potential for the development of thermally assisted magnetic random access memory.

Mn doping-induced twofold spin reorientation and multi-step spin switching in NdFeO3 single crystal

Magnetization reversal and magnetic state regulation are the basis of application for magnetic materials in information processing. Here, twofold spin reorientation transitions (SRT) and field-induced multi-step spin switching phenomena were observed in NdMn0.2Fe0.8O3 (NMFO) single crystals grown via the optical floating zone method. Magnetic anisotropy was systematically investigated in both Zero-Field-Cooled (ZFC) and Field-Cooled (FC) modes. The NMFO single crystal exhibited twofold SRTs: from Γ4 (Gx, Ay, Fz) to Γ1 (Ax, Gy, Cz) and from Γ1 (Ax, Gy, Cz) to Γ2 (Fx, Cy, Gz). Furthermore, a magnetic field-induced spin reorientation transition was identified along the c-axis. Additionally, closer proximity to the SRT temperature corresponded to a reduced magnetic field requirement for inducing the spin reorientation transition. These findings contribute to our comprehension of spin dynamics in NMFO, presenting possibilities for future device applications.

Disclosing the magnetic ground state of PrBaMn2O6

In this work, we report a neutron diffraction study on a single crystal of the layered PrBaMn2O6 perovskite. This compound undergoes two consecutive magnetic transitions with decreasing temperature. At TC ≈ 309 K, a long-range ferromagnetic ordering is established with the Mn magnetic moments oriented along the c axis. Below TN ≈ 240 K, a spin reorientation gives rise to a sudden decrease of the magnetization and the formation of an antiferromagnetic order. This magnetic transition is also accompanied by an electronic localization caused by a structural phase transition from a high-temperature tetragonal phase (P4/mmm) into a low-temperature orthorhombic one (P21am). Our neutron diffraction study at 12 K has unambiguously identified that the ground magnetic structure for this compound is a layered antiferromagnetic structure along the c axis with the Mn moments oriented in the ab plane along one diagonal of the primitive tetragonal cell. No sign of magnetic scattering associated to a CE-type magnetic structure was found in our study, discarding its occurrence in this compound. This result excludes the occurrence of a charge order transition to account for the electronic localization and it is fully consistent with previous structural studies showing a unique crystallographic site for Mn atom in the low-temperature phase. A symmetry analysis was carried out to identify the magnetic space group of the ferromagnetic order above TN and the two possible groups for the antiferromagnetic ordering below TN.

Controllable magnetic anisotropy in two-dimensional 1T-CrTe2 with electrides sublayer

Exploring the controlled magnetic anisotropy energy (MAE) in two-dimensional (2D) ferromagnets is an essential step towards the emergent magnetic tunnel junctions (MTJs) with robust storage stability and low-power consumption. In addition to the transitional charge doping method, we propose that stacking 2D ferromagnet 1T-CrTe2 with electrides substrate can achieve not only the high interfacial charge transfer up to 5.24×1014 cm−2 and but also efficient modification of magnetic behaviors via interfacial engineering. Employing first-principles calculations, we show that the 1T-CrTe2/Ca2N(Y2C) heterostructures exhibit a significant reduction in MAE with a spin reorientation. Notably, the synergistic effect of internal charge transfer, external strain and charge doping shows a significant influence on the magnetic behaviors of the bilayer structures, enabling an efficient modulating of their MAE with distinct dependences. We elucidate that the underlying mechanism is the synergistic effect induced alteration of the spin-polarized px and py states on the Te atom located at the interfaces, which in turn changes the competitive spin-orbit coupling (SOC) contributions to the MAE. These findings provide a practical path toward the controllable MAE in 2D ferromagnets, and make the proposed heterostructures promising candidates for emergent spintronic devices.

Thermal expansion, quasi-metamagnetism and spin-reorientation in Fe7Se8 substituted with chromium

The properties of the selenide compound Fe7Se8 with a layered crystal structure of the NiAs type are strongly influenced by substitutions and the distribution of vacancies. The Cr-substituted compound Fe6.5Cr0.5Se8 was obtained in single-crystalline form and studied by x-ray diffraction, energy-dispersive x-ray spectroscopy, thermal expansion and magnetization measurements. It was observed that the partial replacement of iron with chromium led to a twofold decrease in spontaneous volume magnetostriction due to changes in competing magnetoelastic contributions to thermal expansion along and perpendicular to the c axis of the crystal. The replacement of iron with chromium slightly decreases the Néel temperature (from 440 to 435 K) and significantly enhances the critical temperature of spin reorientation transition Tsr (from 115 to 160 K), apparently due to a change in the crystal electric field. Below 160 K, the Fe6.5Cr0.5Se crystal is found to exhibit metamagnetic-like behavior of the magnetization when the magnetic field is applied along the c axis. A jump-like change of the magnetization at a critical field up to ∼10 kOe is attributed to the presence of pinning centers of domain walls presumably due the ordering of chromium atoms substituting iron in cationic layers.

Magnetism Measurements of Two-Dimensional van der Waals Antiferromagnet CrPS4 Using Dynamic Cantilever Magnetometry

Abstract Recent experimental and theoretical work has focused on two-dimensional van der Waals (2D vdW) magnets due to their potential applications in sensing and spintronics devises. In measurements of these emerging materials, conventional magnetometry often encounters challenges in characterizing the magnetic properties of small-sized vdW materials, especially for antiferromagnets with nearly compensated magnetic moments. Here, we investigate the magnetism of 2D antiferromagnet CrPS4 with a thickness of 8 nm by using dynamic cantilever magnetometry (DCM). Through a combination of DCM experiment and the calculation based on a Stoner–Wohlfarth-type model, we unravel the magnetization states in 2D CrPS4 antiferromagnet. In the case of H ∥ c, a two-stage phase transition is observed. For H ⊥ c, a hump in the effective magnetic restoring force is noted, which implies the presence of spin reorientation as temperature increases. These results demonstrate the benefits of DCM for studying magnetism of 2D magnets.

Incommensurate magnetic order in an axion insulator candidate EuIn2As2 investigated by NMR measurement

Magnetic topological insulators exhibit unique electronic states due to the interplay between the electronic topology and the spin structure. The antiferromagnetic metal EuIn2As2 is a prominent candidate material in which exotic topological phases, including an axion insulating state, are theoretically predicted depending on the magnetic structure of the Eu2+ moments. Here, we report experimental results of the nuclear magnetic resonance (NMR) measurements of all the nuclei in EuIn2As2 to investigate the coupling between the magnetic moments in the Eu ions and the conduction electrons in In2As2 layers and the magnetic structure. The 75As and 115In NMR spectra observed at zero external magnetic fields reveal the appearance of internal fields of 4.9 and 3.6 T, respectively, at the lowest temperature, suggesting a strong coupling between the conduction electrons in the In2As2 layer and the ordered magnetic moments in the Eu ions. The 75As NMR spectra under in-plane external magnetic fields show broad distributions of the internal fields produced by an incommensurate fan-like spin structure which turns into a forced ferromagnetic state above 0.7 T. We propose a spin reorientation process that an incommensurate helical state at zero external magnetic field quickly changes into a fan state by applying a slight magnetic field.

Manipulation of anisotropic Zhang-Rice exciton in NiPS3 by magnetic field

The effect of external magnetic fields on the behavior of the Zhang-Rice exciton in NiPS3, which captures the physics of spin-orbital entanglement in 2D XY-type antiferromagnets, remains unclear. This study presents systematic study of angle-resolved and polarization-resolved magneto-optical photoluminescence spectra of NiPS3 in the Voigt geometry. We observed highly anisotropic, non-linear Zeeman splitting and polarization rotation of the Zhang-Rice exciton, which depends on the direction and intensity of the magnetic field and can be attributed to the spin-orbital coupling and field-induced spin reorientation. Furthermore, above the critical magnetic field, we detected additional splitting of the exciton peaks, indicating the coexistence of various orientations of Néel vector. This study characterizes orbital change of Zhang-Rice exciton and field-induced spin-reorientation phase transitions in a 2D hexagonal XY-type antiferromagnet, and it further demonstrates the continuous manipulation of the spin and polarization of the Zhang-Rice exciton.

Unusual Magnetocaloric Effect Triggered by Spin Reorientation

AbstractAdvancements and utilization of magnetic refrigeration technology hinge on the ongoing enhancement and optimization of magnetic refrigeration material properties. Nevertheless, the intricacy of the magnetocaloric effect (MCE) mechanism has emerged as a bottleneck, constraining the progress and refinement of magnetic refrigeration materials. In this study, a classic magnetic system is chosen to investigate the mechanism of MCE across four different scales–macroscopic magnetism, micrometer‐scale magnetic domains, atomic magnetic moments, and electronic structure. It simultaneously exhibits two inverse MCEs and one direct MCE, with a working temperature span as wide as 125 K (most are &lt;50 K) for the direct MCE. The measurements of the vibrating sample magnetometer, in situ Lorentz electron microscopy and variable‐temperature neutron powder diffraction directly reveal that the complex magnetic entropy changes arise from the magnetic domain wall pinning, the instability of Ho magnetic moments, and the spin rotation. First‐principles calculations elucidate the crucial role of strong hybridization between localized Ho and itinerant Co electrons in the spin reorientation of HoCo4Al. This study contributes significantly to comprehending the induction mechanism of the MCE and holds vital reference value for exploring new magnetic refrigeration materials and enhancing MCE performance.

Study of the Structure, Multiferroic, and Magnetic Order of Er0.9La0.1Cr0.8Fe0.2O3

Herein, the multiferroic perovskite Er0.9La0.1Cr0.8Fe0.2O3 was synthesized using the sol–gel method, and its structure and multiferroic properties were investigated. The magnetic order of Er0.9La0.1Cr0.8Fe0.2O3 was analyzed through magnetic entropy change curves. Furthermore, a four‐sublattice molecular field model was constructed to study the spin reorientation phenomena and explain the differences between various spin redirections through magnetic order correction. This work will provide a new perspective for studying the properties of type II multiferroic materials.

Evolution of static and dynamic magnetic properties of Re/Co/Pt and Pt/Co/Re trilayers with enhanced Dzyaloshinskii-Moriya interaction

The influence of Re layer insertion either at the bottom or top interface of epitaxially grown Pt/Co/Pt heterostructures on their static and dynamic magnetic properties is discussed in terms of their crystalline structure. Magnetic properties were studied as a function of both Re and Co layer thicknesses (dRe and dCo, respectively) in the matrix-like samples with a double-wedge structure, in which the layer thickness gradients were oriented orthogonally. The comprehensive investigations of the changes in coercivity, perpendicular magnetic anisotropy, spin reorientation transition, interfacial Dzyaloshinskii-Moriya interaction (iDMI) and spin wave damping are reported. Two different magnetic phases depending on the Co layer thickness with volume anisotropies (determined without demagnetization term) of KV∼0.25 (low) and KV∼0.75 MJ/m3 (high) were observed. The relation between these phases depends on the stack sequence and thickness of Re inserted layer. For dRe = 0.2 ÷ 0.7 nm deposited as the bottom interface, dCo induced transition at dtr ∼ 2 nm from low to high volume anisotropy phases was observed. Low and high volume anisotropy phases are associated to Co fcc and hcp structural phases. The insertion of half atomic layer of Re had no influence on surface anisotropy but significantly enhanced iDMI above 1 pJ/m and reduced spin wave damping.

Multiple magnetic orders discovered in the superconducting state of EuFe2(As1−xPx)2

Abstract The interplay between superconductivity and magnetism is an important subject in condensed matter physics. EuFe2As2-based iron pnictides could offer an interesting plateau to study their relationship that has attracted considerable attention. So far, two magnetic phase transitions were observed in EuFe2As2-based crystal, which were deemed to originate from the itinerant Fe moments ( 190 K) and the localized Eu2+ moments ( 19 K), respectively. Here, we systematically studied the heat capacity for the EuFe2(As1−xPx)2 crystals with x = 0.21 (optimally doped) and x = 0.29 (overdoped). We have found two new magnetic orders in the superconducting state (ranging from 0.4 to 1.2 K) in the optimally doped crystal. As more P was introduced into the As site, one of the magnetic orders becomes absent in the overdoped crystal. Additionally, we observed strong field and orientation dependence in heat capacity. The present findings in EuFe2(As1−xPx)2 have detected the new low-temperature magnetic orders, which may originate from the localized Eu2+ spins order or the spin reorientation.&amp;#xD;

Anomalous Hall effect and electronic correlation in a spin-reoriented kagome antiferromagnet LuFe6Sn6

Abstract The kagome lattice system has been identified as a fertile ground for the emergence of a number of new quantum states, including superconductivity, quantum spin liquids, and topological electronic states. This has attracted significant interest within the field of condensed matter physics. Here, we present the observation of an anomalous Hall effect in an iron-based kagome antiferromagnet LuFe6Sn6, which implies a non-zero Berry curvature in this compound. By means of extensive magnetic measurements, a high Neel temperature, T N = 552 K, and a spin reorientation behavior were identified and a simple temperature-field phase diagram was constructed. Furthermore, this compound was found to exhibit a large Sommerfeld coefficient of γ = 87 mJ⋅mol−1⋅K−2, suggesting the presence of a strong electronic correlation effect. Our research indicates that LuFe6Sn6 is an intriguing compound that may exhibit magnetism, strong correlation, and topological states.