Spin Reorientation Transition Research Articles

Spontaneous Topological Magnetic Transitions in NdCo5 Rare-Earth Magnets.

Particle-like magnetic textures with nanometric sizes, such as skyrmions, are potentially suitable for designing high-efficiency information bits in future spintronics devices. In general, the Dzyaloshinskii-Moriya interactions and dipolar interactions are the dominant factors for generating nonlinear spin configurations. However, to stabilize the topological skyrmions, an external magnetic field is usually required. In this study, the spontaneous emergence of skyrmions is directly observed, together with the unique successive topological domain evolution during the spin reorientation transition in a neodymium-cobalt (NdCo5 ) rare-earth magnet. On decreasing the temperature, nanometric skyrmion lattices evolve into enclosed in-plane domains (EIPDs) similar to mini bar-magnets with size below 120nm. The internal magnetization rotates with magnetic anisotropy, demonstrating the ability to manipulate the mini bar-magnets. The nanoscale EIPD lattices remain robust over the wide temperature range of 241-167 K, indicating the possibility of high-density in-plane magnetic information storage. The generation of spontaneous magnetic skyrmions and the successive domain transformation in the traditional NdCo5 rare-earth magnet may prompt application exploration for topological magnetic spin textures with novel physical mechanisms in versatile magnets.

Magnetic phase diagram of rare-earth orthorhombic perovskite oxides

Spin reorientation and magnetization reversal are two important features of the rare-earth orthorhombic perovskites ($RM{\mathrm{O}}_{3}$) that have attracted a lot of attention, though their exact microscopic origin has eluded researchers. Here, using density functional theory and classical atomistic spin dynamics we build a general Heisenberg magnetic model that allows to explore the whole phase diagram of the chromite and ferrite compounds and to scrutinize the microscopic mechanism responsible for spin reorientations and magnetization reversals. We show that the occurrence of a magnetization reversal transition depends on the relative strength and sign of two interactions between rare-earth and transition-metal atoms: superexchange and Dzyaloshinskii-Moriya. We also conclude that the presence of a smooth spin reorientation transition between the so-called ${\mathrm{\ensuremath{\Gamma}}}_{4}$ and the ${\mathrm{\ensuremath{\Gamma}}}_{2}$ phases through a coexisting region, and the temperature range in which it occurs, depends on subtle balance of metal-metal (superexchange and Dzyaloshinskii-Moriya) and metal--rare-earth (Dzyaloshinsky-Moriya) couplings. In particular, we show that the intermediate coexistence region occurs because the spin sublattices rotate at different rates.

Topological Hall effect in frustrated B2-ordered Mn0.74Co0.57Al0.69 films

Exploring materials with topological magnetic structures has always been the subject of intense research due to fundamental and technological interests. Here we report the topological Hall effect in the frustrated B2-ordered ${\mathrm{Mn}}_{0.74}{\mathrm{Co}}_{0.57}{\mathrm{Al}}_{0.69}$ thin films. A large topological Hall resistivity of $58.3\phantom{\rule{0.28em}{0ex}}\mathrm{n}\mathrm{\ensuremath{\Omega}}$ cm is found at 300 K. It is shown that a spin reorientation transition occurs around 200 K through the temperature-dependent magnetization and angular-dependent ferromagnetic resonance measurements. Using the obtained magnetic anisotropy parameters, we perform the micromagnetic simulations to simulate the formation and evolution of topological magnetic structures with temperature, demonstrating the influence of the higher-order magnetic anisotropies. This work enriches the variety of materials exhibiting topological Hall effect and helps to clarify the mechanism of new emergent topological features in magnetic materials.

The Gilbert damping of thickness-dependent epitaxial single-crystal Heusler Co2FeAl films at various temperatures

Gilbert damping in epitaxial Heusler Co2FeAl films with thickness varying from 3 nm to 9 nm are investigated by broadband ferromagnetic resonance (FMR) with a temperature range of 5 K–300 K. Gilbert damping shows a continuous decrease with the increasing thickness of Co2FeAl films. Moreover, an enhanced peak of the Gilbert damping is observed with increasing temperature up to approximately 50 K for 3 nm, 6 nm and 9 nm thick Co2FeAl films, which may be attributed to the spin reorientation transition at Co2FeAl/MgO interface. Further, we analyzed the linewidth with a superposition of a uniaxial and a fourfold anisotropy for all samples, which suggests that FMR linewidth in epitaxial Co2FeAl films stems from two-magnon scattering. The change of Gilbert damping is confirmed to originate from various order degrees of the B2 phase with the growth of CFA film, impacting the control of magnetic damping in spin-based nanodevices.

Spin reorientation in tetragonally distorted spinel oxideNiCo2O4epitaxial films

We experimentally investigated the magnetic properties of NiCo$_2$O$_4$ epitaxial films known to be conductive oxides with perpendicular magnetic anisotropy (PMA) at room temperature. Both magneto-torque and magnetization measurements at various temperatures provide clear experimental evidence of the spin reorientation transition at which the MA changes from PMA to easy-cone magnetic anisotropy (ECMA) at a certain temperature ($T_{\rm{SR}}$). ECMA was commonly observed in films grown by pulsed laser deposition and reactive radio frequency magnetron sputtering, although $T_{\mathrm{SR}}$ is dependent on the growth method as well as the conditions. The cone angles measured from the $c$-axis increased successively at $T_{\mathrm{SR}}$ and approached a maximum of 45-50 degrees at the lowest measurement temperature of 5 K. Calculation with the cluster model suggests that the Ni$^{3+}$ ions occupying the $T_d$ site could be the origin of the ECMA. Both the magnetic properties and the results of the calculation based on the cluster model indicate that the ECMA is attributable to the cation anti-site distribution of Ni$^{3+}$, which is possibly formed during the growth process of the thin films.

Magnetic domains in a uniaxial magnet Dy3Al2

The rare-earth intermetallic Dy3Al2 is a low-temperature permanent magnet with temperature-induced spin reorientation transition. In this work, we report the observation of magnetic domains in lamellae of Dy3Al2 using Liquid-Nitrogen cryo-Lorentz transmission electronic microscopy (cryo-LTEM) above TSR (70 K). We studied the magnetic field dependence of domain evolution from stripe domains at zero magnetic field to the saturation state. When the easy axis lies within the lamella plane, stripe domains gradually narrow and disappear as the applied field increases. The saturation field decreases with the increasing temperature. In the presence of misalignment between the easy axis and external field, stripe domains evolve into type-II magnetic bubbles (as small as 50–60 nm). The spin configuration was further verified by utilizing differential phase contrast scanning transmission microscopy and micromagnetic simulations.

Investigation on X-ray photoelectron spectroscopy, structural and low temperature magnetic properties of Ni-Ti co-substituted M-type strontium hexaferrites prepared by ball milling technique

The effect of substituting Fe3+ ions by a combination of divalent Ni2+ and tetravalent Ti4+ in SrM hexaferrites synthesized by mechanical ball-milling technique were reported. Standard SrFe12O19 hexagonal ferrite (P63/mmc) was confirmed by measured XRD patterns. The phase purity was also confirmed by the XPS. The SEM images showed a clear hexagonal-shape particles in the prepared ferrites. The elemental distribution obtained from EDX spectra for SrFe12–2xNixTixO19 (x = 0.2, 0.4, 0.6 and 0.8) was consistent with stoichiometry of the starting powder. X-ray photoelectron spectra confirmed the existence of Fe2+, Fe3+, Ni2+, Ni3+ and Ti4+ ions. The presence of Fe2+ and Ni3+ was correlated with an electron transfer between Fe3+ and Ni2+. By increasing the Ni concentration, we found that some Fe3+ ions are transferred to Fe2+ ions, while some of the Ni2+ ions are transferred to Ni3+ ions. Irreversible ZFC and FC curves were recorded in the 4–300 K temperature range. The isothermal magnetization curves confirmed the ferromagnetic behavior for all synthesized samples. A small variation in the saturation and remnant magnetizations along with a sharp reduction in the coercivity fields with the increase of x were observed in a wide range of temperatures. The broad peak observed in the temperature dependence of the saturation magnetization for x = 0.8 may be referred to the spin reorientation transition. The decrease in the coercivity agrees with the behaviour of the magneto crystalline anisotropy while the first anisotropy constant exhibits a fast decrease above x = 0.6.

Unusual field-induced spin reorientation in FeCr2S4 : Field tuning of the Jahn-Teller state

The multiferroic spinel ${\mathrm{FeCr}}_{2}{\mathrm{S}}_{4}$ is a benchmark material for exploring the competition of spin-orbit (SO) and Jahn-Teller (JT) coupling. Our magnetic and thermodynamic studies of stoichiometric single-crystalline samples evidence a magnetic-field-induced spin-reorientation transition in the cooperative JT state below 10 K. At 2 K, at a critical magnetic field of 4.5 T, the magnetization measured along the hard magnetization axis $\ensuremath{\langle}111\ensuremath{\rangle}$ manifests a jump to the fully saturated state accompanied by a steplike decrease of the sound velocity and an abrupt increase of the magnetostriction. All these quantities reveal a hysteretic behavior pointing towards a first-order magnetostructural transformation. Below the JT transition, the specific heat shows a complex behavior upon the application of magnetic fields depending on the crystallographic directions. The observed reduction by 20% of the magnetic anisotropy below the JT transition is attributed to the competition of the SO and JT interactions tuned by external magnetic fields. The concomitant change of the structural symmetry results in a change of the splitting of the lowest levels of the ${}^{5}E$ doublet of the tetrahedrally coordinated ${\mathrm{Fe}}^{2+}$ ions.

Tailoring magnetism in spinel vanadate CoV2O4 epitaxial thin films

Near itinerant cubic bulk CoV2O4 is at variance with other spinel vanadates by not showing orbital ordering down to low temperature, albeit it displays fragile anomalies related to spin, and lattice structure, signaling a spin/orbital glass transition around 95 K. We investigate tetragonal-like epitaxial CoV2O4 films on SrTiO3 and (La0.3Sr0.7)(Al0.65Ta0.35)O3 substrates that exhibit pronounced signature of spin reorientation transition from to a/b plane around 90 K unlike its bulk counterpart. Using in-plane and out-of-plane magnetic measurements, we demonstrate the intricate link between Co2+ and V3+ sublattice magnetizations that give rise to anisotropic magnetic switching. In-plane magnetic measurements reveal a wasp-waist shaped M(H) loop below reorientation transition temperature, while the out-of-plane follows antiferromagnet-like M(H) response. The wasp-waist shaped feature could be linked to in-plane spin-canted (anti)ferromagnetism induced by canting away of V-spins away from antiferromagnetically coupled Co-spin direction below reorientation transition temperature. Further, we uncover the evidence for slow relaxation over a period of ∼104 s at 20 K and memory effect that indicates the possible existence for magnetic glassy phase in the low temperature regime. Using epitaxial strain as a control knob, our results inspire future study to manipulate orbital states, spin texture and itinerant electron character in tailored CoV2O4 films away from cubic lattice symmetry.

Magnetic Aspects and Large Exchange Bias of Ni0.9Co0.1/NiCoO Multilayers

Ultrathin films of Ni0.9Co0.1 were grown by radio frequency magnetron sputtering. By means of a periodic natural oxidation procedure they were transformed into Ni0.9Co0.1/NiCoO multilayers. Room temperature hysteresis loops recorded via the magneto-optic Kerr effect have revealed over all in-plane magnetic anisotropy due to magnetostatic anisotropy. Mild thermal annealing at 250 °C enhanced a tendency for perpendicular magnetic anisotropy, mainly due to an increase of the uniaxial volume anisotropy term. Spin reorientation transition, exchange bias larger than 700 Oe, and strong coercivity enhancement were observed via a superconducting quantum interference device at low temperatures after field cooling.

Tunability of Magnetism: An Interplay of Magnetic Anisotropy and Magnetoelasticity

We present theoretical study on spin reorientation transition (SRT). A phenomenological model is provided, which treats magnetic energy as sum of magnetoelasticity, magnetocrystalline anisotropy, and demagnetization contributions. We show that critical strain exists by analytically solving the phenomenological model, as a consequence of an interplay between aforementioned contributions. For more quantitative understanding, numerical estimate is performed for thin FePt and FeSUB60/SUBCoSUB40/SUB films, where experimentally accessible critical strain is 2 %. Further, this feasible strain is due to the large magnetoelastic coefficient (b₁) and the optimal saturation magnetization, which is not achievable in thin Fe film.

Magneto-structural correlation across the spin reorientation transition temperature in pure and Sm substituted TmFeO3: A temperature dependent Raman and synchrotron X-ray diffraction study

This paper presents the magneto-structural study on orthoferrite TmFeO3 and Sm substituted TmFeO3 across spin reorientation transition (SRT) temperature. A strong change in magnetic anisotropy due to the substitution of the Sm3+was observed, which is reflected as a change in spin reorientation transition (SRT) temperature. The SRT temperature of Tm0.5Sm0.5FeO3is found to be around 200–230 K, which is relatively high in comparison to TmFeO3. A sudden decrease in the value of coercivity has been observed in the SRT region for both the sample. The lattice dynamics of TmFeO3 and Tm0.5Sm0.5FeO3were investigated by temperature-dependent x-ray diffraction and Raman spectroscopy. We observed unusual contractions in the lattice parameter at low temperatures due to complex exchange interaction between RE3+ and Fe3+ ions sub-lattice. Anomalous behavior in lattice parameters was observed in the vicinity of SRT, which confirms the system’s spontaneous magnetostriction.The strong anomaly was observed in line width and phonon frequency of Raman modes of around SRT, which established the spin-lattice coupling in TmFeO3 and Tm0.5Sm0.5FeO3 nanoparticles. Observation of spin-lattice coupling utilizing Raman scattering substantiates our magnetic and structural correlation and supports its candidature for magneto-elastic applications.

The spin reorientation and improvement of magnetocaloric effect in HoCr1-xGaxO3 (0 ≤ x ≤ 0.5)

The effect of non-magnetic Ga3+ ions doping at HoCrO3 (HoCr1-xGaxO3, 0 ≤ x ≤ 0.5) on the crystal structure, electronic structure, Raman spectra, and magnetic behaviours were systematically investigated. Most strikingly, a new spin-reorientation transition (Γ2 → Γ4 →Γ2) is triggered by Ga3+ doping in HoCrO3, and the spin configuration of Γ4 is obviously displayed in ZFC and FC curves when x > 0.2. According to the XRD analysis, Ga3+ doping reduces the octahedral distortion and changes the lattice parameters, CrO and HoO bond lengths, and a turning point occurs at x = 0.2. Raman spectra further give evidence of the structural changes and suggest that spin-phonon coupling can be mediated by Ga3+ doping, illustrating the weakened effect of Ga3+ doping on the Ho and Cr interaction. The dilution of the competition between CrCr canted antiferromagnetic coupling and Ho-Cr antisymmetric coupling results in the appearance of spin configuration Γ4. Moreover, the Griffiths phase can also be observed and gradually suppressed with doping. These complex magnetic transitions in HoCr1-xGaxO3 are given in a magnetic phase diagram. From the application point of view, Ga3+ doping also improves the magneto-caloric effect (MCE) and refrigerant capacity (-ΔSM = 10.74 J/KgK, and the RC is 416 J/K at 7 T and 10 K for HoCr0.6Ga0.4O3), which sheds some light on how to optimize the MCE properties.

Magnetic order in the van der Waals antiferromagnet CrPS4 : Anisotropic H−T phase diagrams and effects of pressure

Single crystalline samples of the van der Waals antiferromagnet CrPS4 were studied by measurements of specific heat and comprehensive anisotropic temperature- and magnetic field-dependent magnetization. In addition, measurements of the heat capacity and magnetization were performed under pressures of up to ~21 kbar and ~14 kbar respectively. At ambient pressure, two magnetic transitions are observed, second order from a paramagnetic to an antiferromagnetic state at TN ~ 37 K, and a first-order spin reorientation transition at T* ~ 34 K. Anisotropic H - T phase diagrams were constructed using the M(T,H) data. As pressure is increased, TN is weakly suppressed with dTN/dP ~ -0.1 K/kbar. T*, on the other hand, is suppressed quite rapidly, with dT*/dP ~ -2 K/kbar, extrapolating to a possible quantum phase transition at Pc ~ 15 kbar.

Magnetocrystalline anisotropy and dynamic spin reorientation of half-doped Nd0.5Pr0.5FeO3 single crystal* *Project supported by the National Natural Science Foundation of China (Grant Nos. 12074242 and 51862032), the Ministry of Science and Higher Education of Russia (theme “Spin” No. AAAA-A-18-118020290104-2), and the Government of the Russian Federation (Grant No. 02.A03.21.0006)

The single crystals of Nd0.5Pr0.5FeO3 were successfully grown by optical floating zone method. Room temperature x-ray diffraction and Laue photograph declared the homogeneity and high quality of the crystal. The significant magnetic anisotropy and multiple magnetic transitions illustrate the complex magnetic structure. At high temperatures (T > 66 K), it shows the typical characteristics of Γ 4(G x , A y , F z ) state. With the decrease of the temperature, it undergoes a first-order spin reorientation transition from Γ 4(G x , A y , F z ) to Γ 2(F x , C y , G z ) state in the temperature window of 45–66 K under an applied magnetic field of 0.01 T. As the temperature drops to ∼ 17 K, a new magnetic interaction mechanism works, which results in a further enhancement of magnetization. The T–H phase diagram of Nd0.5Pr0.5FeO3 single crystal was finally constructed.

4f-3d interaction dominated field tailoring spin switching in rare earth doped Dy0.5Er0.5FeO3 single crystal

A large single crystal Dy0.5Er0.5FeO3 of 5.2 mm in diameter and 55 mm in length is prepared using the optical floating zone furnace system. The good quality of the single crystal without impurities is confirmed by powder and Laue X-ray diffraction experiments. Magnetic measurements are conducted using 1~2 millimeter cubic sample of Dy0.5Er0.5FeO3 single crystal, which experiences spin switching in two measurement modes of zero-field-cooling (ZFC) and field-cooling (FC) magnetization vs temperature (M-T) curves under magnetic fields less than 48 Oe. The co-occurrence of spin switching (i.e. magnetization drop in FC mode and magnetization jump in ZFC mode) has not been reported in the parent materials of DyFeO3 and ErFeO3 single crystals. More interestingly this kind of spin switching can be easily tailored by using low fields in a large temperature range from below 50 K to nearly 400 K. Spin reorientation transition occurs near 35.9-48 K, where the spin configuration of the iron sublattice changes from Γ4 and Γ2. The magnetic interaction between (Dy, Er)-4f and Fe-3d electrons in the two different sublattices of Dy0.5Er0.5FeO3 single crystal which governs the spin reorientation transition and spin switching under different temperature and magnetic field are discussed.

Doping tuned spin reorientation and spin switching in praseodymium–samarium orthoferrite single crystals

We investigate the detailed analysis of the magnetic properties in a series of Pr1–x Sm x FeO3 single crystals from x = 0 to 1 with an interval of 0.1. Doping controlled spin reorientation transition temperature T SR Γ4 (G x , A y , F z ) to Γ2 (F x , C y , G z ) covers a wide temperature range including room temperature. A ‘butterfly’-shape type-I spin switching with 180° magnetization reversal occurs below and above the magnetization compensation points in x = 0.4 to 0.8 compounds. Interestingly, in Pr0.6Sm0.4FeO3 single crystal, we find an inadequate spin reorientation transition accompanied by uncompleted type-I spin switching in the temperature region from 138 to 174 K. Furthermore, a type-II spin switching appears at 23 K, as evidenced from the magnetization curve in field-cooled-cooling (FCC) mode initially bifurcate from zero-field-cooled (ZFC) magnetization curve at 40 K and finally drops back to coincide the ZFC magnetization value at 23 K. Our current research reveals a strong and complex competition between Pr3+–Fe3+ and Sm3+–Fe3+ exchange interactions and more importantly renders a window to design spintronic device materials for future potential applications.

The multiple magnetic transitions and magnetic entropy change of RGa compounds

<p indent=0mm>Magnetic refrigerant materials working at middle and low temperature range have drawn much attention because they can be used for gas liquefaction such as oxygen, nitrogen, hydrogen and helium. It is continuous goal for researchers to explore and obtain magnetic refrigerant materials with large magnetic entropy change, wide refrigerant temperature span, high refrigeration capacity and large adiabatic temperature change. RGa family is a kind of rare earth based intermetallic compounds with abundant magnetic transitions. This paper reviews the results of low-temperature order-order magnetic transition, high-temperature order-disorder magnetic transition and magnetic entropy change for PrGa, NdGa, SmGa, GdGa, TbGa, DyGa, HoGa, ErGa, TmGa and Er₁₋_{<italic>x</italic>}Gd_{<italic>x</italic>}Ga compounds. The low-temperature order-order magnetic transition includes spin reorientation transition, ferromagnetic to modulated antiferromagnetic transition and cone-ferromagnetic to cone-ferromagnetic transition. There are several peaks on the magnetic entropy change curves which provide ideas for designing magnetic refrigerant materials with large temperature span. The characteristics of magnetic transitions and magnetic entropy change for RGa compounds are analyzed, the dependency relationship together with related physical mechanism are expounded and the possible research interests in the future are discussed.

Critical sample aspect ratio and magnetic field dependence for antiskyrmion formation in Mn1.4PtSn single crystals

Mn1.4PtSn is the first material in which antiskyrmions have been observed in ultra-thin single crystalline specimens. While bulk crystals exhibit fractal patterns of purely ferromagnetic domain ordering at room temperature, ultra-thin Mn1.4PtSn lamellae clearly show antiskyrmion lattices with lattice spacings up to several $\mu$m. In the work presented here, we systematically investigate the thickness region from 400 nm to 10 $\mu$m using 100 $\times$ 100 $\mu$m$^2$ -wide Mn1.4PtSn plates, and identify the critical thickness-to-width aspect ratio $\alpha_0 = 0.044$ for the ferromagnetic fractal domain to the non-collinear texture phase transition. Additionally, we also explore these non-collinear magnetic textures below the critical aspect ratio $\alpha_0$ above and below the spin-reorientation transition temperature $T_{SR}$ while applying variable external magnetic fields. What we find is a strong hysteresis for the occurrence of an antiskyrmion lattice, since the antiskyrmions preferentially nucleate by pinching them off from helical stripes in the transition to the field polarized state.

Field tunable spin switching in perovskite YbFeO3 single crystal

We report the spin reorientation transition and spin switching transition in perovskite structure YbFeO3 single crystal. A spin reorientation transition of type Г4→Г2 occurs in the temperature range of 6 ∼ 8 K, and a type-Ⅱ spin switching along c-axis is found at temperature about 20 K under an applied magnetic field of 100 Oe. In field-cooled-cooling (FCC) process, due to the spin reversal of Yb3+ magnetic moments, the magnetic moments coupling of Yb3+ and Fe3+ change from parallel to antiparallel, which leads to a significant drop in magnetization at the transition temperature. Interestingly, the Magnetization vs. magnetic field curves at various temperatures above 8 K–200 K show magnetic field induced spin switching, for which the magnetization switches from negative/positive value to positive/negative value but without change of magnitude at a magnetic field induced spin switching point. The intriguing interaction between the two magnetic sublattices of rare earth (Yb3+) and iron (Fe3+) ions is controllable by the applied magnetic field to regulate the spin switching transition temperature in YbFeO3 single crystal and make it possible as one of low field potential materials for future application in spin devices.