Spin Reorientation Transition Research Articles

Electrical detection of the spin reorientation transition in antiferromagnetic TmFeO3 thin films by spin Hall magnetoresistance

TmFeO$_3$ (TFO) is a canted antiferromagnet that undergoes a spin reorientation transition (SRT) with temperature between 82 K and 94 K in single crystals. In this temperature region, the N\'eel vector continuously rotates from the crystallographic $c$-axis (below 82 K) to the $a$-axis (above 94 K). The SRT allows for a temperature control of distinct antiferromagnetic states without the need for a magnetic field, making it apt for applications working at THz frequencies. For device applications, thin films of TFO are required as well as an electrical technique for reading out the magnetic state. Here we demonstrate that orthorhombic TFO thin films can be grown by pulsed laser deposition and the detection of the SRT in TFO thin films can be accessed by making use of the all electrical spin Hall magnetoresistance (SMR), in good agreement for the temperature range where the SRT occurs. Our results demonstrate that one can electrically detect the SRT in insulators.

Polarization control of THz emission using spin-reorientation transition in spintronic heterostructure

Polarization of electromagnetic waves plays an extremely important role in interaction of radiation with matter. In particular, interaction of polarized waves with ordered matter strongly depends on orientation and symmetry of vibrations of chemical bonds in crystals. In quantum technologies, the polarization of photons is considered as a “degree of freedom”, which is one of the main parameters that ensure efficient quantum computing. However, even for visible light, polarization control is in most cases separated from light emission. In this paper, we report on a new type of polarization control, implemented directly in a spintronic terahertz emitter. The principle of control, realized by a weak magnetic field at room temperature, is based on a spin-reorientation transition (SRT) in an intermetallic heterostructure TbCo2/FeCo with uniaxial in-plane magnetic anisotropy. SRT is implemented under magnetic field of variable strength but of a fixed direction, orthogonal to the easy magnetization axis. Variation of the magnetic field strength in the angular (canted) phase of the SRT causes magnetization rotation without changing its magnitude. The charge current excited by the spin-to-charge conversion is orthogonal to the magnetization. As a result, THz polarization rotates synchronously with magnetization when magnetic field strength changes. Importantly, the radiation intensity does not change in this case. Control of polarization by SRT is applicable regardless of the spintronic mechanism of the THz emission, provided that the polarization direction is determined by the magnetic moment orientation. The results obtained open the prospect for the development of the SRT approach for THz emission control.

Unique magnetic properties of Nd based cuprate francisite: Major enhancement upon Co doping

To understand the physical mechanism of intralayer ferromagnetic (FM) and interlayer antiferromagnetic (AFM) interactions in quasi-two-dimensional model of a real three-dimensional system, rare earth (RE)-Nd based cuprate francisite, Cu3Nd(SeO3)2O2Cl (NdCufr) was doped with Co and studied using structural (X-ray diffraction technique), magnetic (temperature and field dependent magnetization and specific heat measurements) and local structural (X-ray absorption technique) techniques supported by first principle theoretical calculation. The structure of the samples is orthorhombic and doped specimens indicate more or less substitutional incorporation of Co at Cu site. The magnetic properties highlighted with two transitions, viz. AFM to paramagnetic (PM) transition around 30 K and a spin reorientation transition (SRT) below 10 K. Two phenomena viz. magnetic hysteresis below SRT and magnetic field induced metamagnetic transition (MMT) were observed. Co doping significantly enhanced these two phenomena in addition to change the transition temperatures. The concomitant change and enhancement of magnetic properties by Co doping has been interpreted using splitting scheme of Cu-d and Nd-f states. The local structure study corroborates the overall findings and detects the cause of unexpected trend of magnetism with increasing Co doping.

Non-monotonic magnetic anisotropy behavior as a function of adsorbate coverage in Fe ultrathin films near the spin reorientation transition

Carbon monoxide (CO) adsorption on ultrathin fcc Fe films is known to result in the rotation of magnetization from out-of-plane to in-plane.

Thermal decomposition of GdCrO4 to GdCrO3: Structure and magnetism

Rare-earth orthochromites (RCrO3) with orthorhombically distorted perovskite (ABO3) structure exhibit a wealth of magnetic phenomena including temperature-induced magnetization reversal (TMR), spin-reorientation (SR), spin-flipping (SF) and exchange-bias (EB). These occur as a result of magnetic interactions among the cations such as Cr3+–Cr3+, Cr3+–R3+ and R3+–R3+, where R is the rare earth element. In the present work, GdCrO4 samples were prepared using the sol-gel technique. The as-synthesized samples are amorphous in nature. Calcination of the samples at 600 °C for 1 h leads to the formation of the GdCrO4 phase whereas increasing the calcination temperature to 1000 °C for 1 h triggers the decomposition of GdCrO4 into GdCrO3. The role of thermal decomposition of GdCrO4 to GdCrO3 on crystal structure and magnetic transitions are discussed in this paper. Microstructure analyses show that the GdCrO4 powders have an intercalated porous structure that comprises a core-shell like construction with undistinguishable grain boundaries, whereas the morphology of the GdCrO3 demonstrates bulk nature with particles having micrometer size. Magnetization measurements as a function of temperature (M-T) with different probing magnetic fields show the ferromagnetic Curie temperature, (TC), of the GdCrO4 sample to be 24 K. GdCrO3 orders antiferromagnetically with a Néel temperature, TN (Cr), ascribed to the Cr magnetic moment at 171 K. A spin-flip transition (TSF) occurred at 22 K indicating the flipping of Cr3+ and Gd3+ spins and the spin-reorientation (TSR) transition is located at 5 K. The hysteresis loops measured across the transition temperatures validate the magnetic transitions as observed in the M-T curves.

Observation of Spin Reorientation Transitions in Lead and Titanium‐Modified BiFeO3 Multiferroics

We report the synthesis and basic characterization details of bulk Bi1 − xPbxFe1 − xTixO3 (x = 0.05 and 0.1) polycrystalline samples, which have been synthesized using the conventional solid‐state route. We studied the effects of partially doping of Pb and Ti ion on structural, vibrational, and magnetic properties of multiferroic BiFeO3. X‐ray diffraction (XRD) was used for crystallographic studies, followed by Rietveld refinement, and phase formation of the compounds was confirmed, which indicates that the sample has rhombohedral (R3c, 100%) symmetry for x = 0.05 and R3c (98%) + P4mm (2%) symmetry for x = 0.1. X‐ray absorption spectroscopy has been probed at Fe L2,3 and O K edges to determine the valence (charge) state of Fe in BiFeO3. Interestingly, the magnetic measurement results revealed the existence of spin reorientation transition in Pb and Ti‐modified BiFeO3, which indicates that the BiFeO3 samples studied may find promising applications in memory and spintronic devices.

ОСОБЕННОСТИ МАГНИТНОГО СОСТОЯНИЯ В АМОРФНЫХ МАГНЕТИКАХ RE–TM и RE–TM–B (обзор)

Provides an overview of the magnetism features of amorphous magnets of the RE–TM and RE–TM–B alloys (RE – rare earth metal, TM – transition metal, B – boron). Magnetic states in amorphous alloys, the effect of the single-ionic anisotropy of heavy rare-earth metals on local disorder and spin frustrations in an amorphous body, and some spin-reorientation transitions observed in such compounds are presented. It is shown that the identification of the spin-glass state can be achieved by detecting specific features on the field and temperature dependences of the magnetic moment and magnetic susceptibility of the sample.

Синтез, структурные, магнитные и теплофизические свойства Pb-=SUB=-3-=/SUB=-Mn-=SUB=-7-=/SUB=-O-=SUB=-15-=/SUB=-, допированного ионами титана

Crystals of Pb3Mn7O15 doped with titanium ions have been synthesized. The study of the structural properties showed that titanium ions occupy positions in the “columns” between the planes, which leads to a weakening of the exchange interaction between the planes. The temperature dependences of magnetization and heat capacity revealed two anomalies at 62 K and 35 K. At 62 K, a long-range magnetic order presumably appears, and at 35 K a spin-reorientation transition occurs, as in Pb3Mn7O15.

Ionic radii correlative study on LaFe0.5Cr0.5O3 and YbFe0.5Cr0.5O3magnetic double perovskites

Comparative study on the iso-structural compounds LaFe0.5Cr0.5O3 (LFCO) and YbFe0.5Cr0.5O3 (YFCO) are carried out to investigate the structural, optical and magnetic properties. Rietveld refinement and the derived structural parameters disclose the extent of distortion exhibited by the ions substituted in the orthorhombic lattice. Raman analysis describes the genuine differences in the phonon modes. Contradictory Raman shift observed in the oxygen breathing mode at ~679 cm−1 denotes the existence of the multi-valence state in LFCO than YFCO. EPR and XPS analysis validates the multi-valence state of Cr3+/4+/6 ions present in the LFCO compound. The optical transition between the Cr3+/Fe3+ ions is studied by diffuse reflectance spectroscopy, where the direct bandgap energy (Eg) is 2.05 and 2.08 eV, respectively. Magnetic measurement reveals complex magnetic Phenomena such as magnetisation reversal and spin reorientation transition, illustrating a contrast in the magnetic interaction present due to La3+(non-magnetic) and Yb3+ (magnetic) ion and with the interplay of Cr3+/Fe3+ ion between their sublattices.

Magnetic properties, 57Fe Mössbauer spectroscopy and 1H NMR relaxometry of ε-Fe2−xGaxO3 nanoparticles: The effect of gallium doping on magnetic and MRI performance

Magnetic nanoparticles of ε-Fe1.76Ga0.24O3 were prepared by thermal treatment of a mesoporous silica matrix impregnated with nitrates. The chosen Ga-doping enhanced magnetization and suppressed the low-temperature spin-reorientation transition typical for ε-Fe2O3. Despite the small mean size of 11 nm, the nanoparticles were in the blocked state over the whole temperature range under study, unlike standard superparamagnetic contrast agents based on other iron oxides or ferrites. The role of Ga-doping in local magnetic properties of the epsilon polymorph of ferric oxide was probed by 57Fe Mössbauer spectroscopy. The particles were further coated with silica and their performance in MRI was tested both in relaxometry and ultra-high-field imaging. The obtained dependences of relaxivity on temperature and thickness of the coating were placed in the context of relevant theoretical models of particle-induced relaxation – motional averaging and static dephasing regimes.

Two-layer compounds in rare earth-{Fe, Co, Ni, Rh, Pd, Pt}-Te systems: crystal structure and magnetic properties

The partial isothermal sections of {Gd, Ho}-Ni-Te and Gd-Co-Te systems (~40–100 ​at. % of rare earth) have been investigated at 1070 ​K by X-ray and electron microprobe analysis. The Y5Ni2Te2-type {Tb, Dy, Ho}5Fe2Te2 and {Gd, Tb, Dy, Ho}5{Co, Ni}2Te2 (space group Cmcm, No. 63, oC36), Er7Ni2Te2-type Er7Co2Te2, {Y, Dy, Ho}7Ni2Te2, Ho7{Rh, Pd}2Te2 and {Y, Gd}7Pt2Te2 (space group Imm2, No. 44, oI22), Fe2P-type Ho6NiTe2 (space group P-62m, No. 189, hP9) and Sc6PdTe2-type Ho6{Rh, Pd}Te2 and {Y, Gd}6PtTe2 (space group Pnma, No. 62, oP36) compounds have been established using powder X-ray diffraction studies. Magnetization measurements show that the Y5Ni2Te2-type {Tb, Dy, Ho}5Fe2Te2, {Gd, Tb, Dy}5Co2Te2 and {Tb, Ho}5Ni2Te2 compounds exhibit a high-temperature ferromagnetic ordering with low-temperature spin-reorientation transition for Tb-, Dy- and Ho-containing compounds. Below Curie temperature, Tb5Fe2Te2, Tb5Co2Te2 and Ho5Ni2Te2 are soft ferromagnets, while they show hard magnetic properties below spin-reorientation transition. At 2 ​K, Tb5Co2Te2 and Tb5Fe2Te2 exhibit a coercive field of 35 ​kOe and ~30 ​kOe and the residual magnetization of 17.2 μB and 22.9 μB per formula unit, leading to theoretical maximum energy product of ~620 ​kJ/m3 and ~700 ​kJ/m3, respectively. Ho5Ni2Te2 reaches a maximum magnetic entropy change of −10.0 ​J/kg⋅K and −9.4 ​J/kg⋅K for a magnetic field change of 0–50 ​kOe ​at 45 ​K and 20 ​K, respectively.

NMR study of magnetic structure and hyperfine interactions in the binary helimagnet FeP

We report a detailed study of the ground state helical magnetic structure in monophosphide FeP by means of ${}^{31}$P NMR spectroscopy. We show that the zero-field NMR spectrum of the polycrystalline sample provides strong evidence of an anisotropic distribution of local magnetic fields at the P site with substantially lower anharmonicity than that found at the Fe site by M\"{o}ssbauer spectroscopy. From field-sweep ${}^{31}$P NMR spectra we conclude that a continuous spin-reorientation transition occurs in an external magnetic field range of 4 - 7 T, which is also confirmed by specific-heat measurements. We observe two pairs of magnetically inequivalent phosphorus positions resulting in a pronounced four-peak structure of the single crystal ${}^{31}$P NMR spectra characteristic of an incommensurate helimagnetic ground state. We revealed a spatial redistribution of local fields at the P sites caused by Fe spin-reorientation transition in high fields and developed an effective approach to account for it. We demonstrate that all observed ${}^{31}$P spectra can be treated within a model of an isotropic helix of Fe magnetic moments in the ($ab$)-plane with a phase shift of 36$^{\circ}$ and 176$^{\circ}$ between Fe1-Fe3 (Fe2-Fe4) and Fe1-Fe2 (Fe3-Fe4) sites, respectively, in accordance with the neutron scattering data.

Evidence of magneto-structural coupling during the spin reorientation process in TmFeO3 single crystal

We report the growth of a TmFeO3 single crystal, its magnetic and structural properties upon varying temperature, magnetic field, and hydrostatic pressure. The abrupt change related to the spin reorientation (SR) process vanishes under a 30 kOe magnetic field in both thermomagnetic and strain curves, indicating strong magneto-structural coupling in such orthoferrite. Interestingly, the thermomagnetic curve under hydrostatic pressure reveals that the SR shifts towards higher temperatures and its temperature interval widens upon the application of external hydrostatic pressure. Combining the strain data obtained under similar conditions, the onset temperature shift of SR is concluded to originate from changes in structural parameters and widening of the SR transition is attributed to the presence of an intermediate phase. These findings may shed light on the envisage of potential uses in magneto-mechanical and transducer devices, based on the interaction between structure and magnetism.

Tunable magnetic properties and magnetocaloric effect of TmGa by Ho substitution

The influence of Ho substitution for Tm atoms on the magnetic properties and magnetocaloric effect (MCE) of TmGa compound was systematically investigated according to magnetic measurements and neutron powder diffraction (NPD) experiments. The magnetic transitions of ${\mathrm{Tm}}_{1\ensuremath{-}x}{\mathrm{Ho}}_{x}\mathrm{Ga}$ compounds show different types by Ho substitution due to the variation of spin and orbital angular momentum quantum number and the complete magnetic diagram of ${\mathrm{Tm}}_{1\ensuremath{-}x}{\mathrm{Ho}}_{x}\mathrm{Ga}$ compounds was obtained. The spin reorientation (SR) transition of ${\mathrm{Tm}}_{0.1}{\mathrm{Ho}}_{0.9}\mathrm{Ga}$ compound was directly confirmed by variable-temperature NPD experiments. Results show that the magnetic moment orders along the $c$ axis at the temperatures between ${T}_{\mathrm{SR}}$ and ${T}_{\mathrm{C}}$ and it cants away from the $c$ axis towards the $ab$ plane upon cooling below ${T}_{\mathrm{SR}}$. Furthermore, Ho substitution plays a dominant role in MCE of ${\mathrm{Tm}}_{1\ensuremath{-}x}{\mathrm{Ho}}_{x}\mathrm{Ga}$ compounds. When $x=0.15$, the peak value of magnetic entropy change reaches the maximum value of 18.0 J/kg K under field change of 0--2 T. The refrigerant temperature span ($\ensuremath{\delta}{T}_{\mathrm{FWHM}}$) and refrigeration capacity of ${\mathrm{Tm}}_{0.85}{\mathrm{Ho}}_{0.15}\mathrm{Ga}$ compound show enhancement of 23.0 and 21.6%, correspondingly, compared with TmGa compound. The giant MCE of ${\mathrm{Tm}}_{0.85}{\mathrm{Ho}}_{0.15}\mathrm{Ga}$ compound results from the optimization of spin and total angular momentum quantum number by Ho substitution.

Anisotropic fractal magnetic domain pattern in bulk Mn1.4PtSn

The tetragonal compound Mn$_{1.4}$PtSn with the $D_{2d}$ symmetry recently attracted attention as the first known material that hosts magnetic antiskyrmions, which differ from the so far known skyrmions by their internal structure. The latter have been found in a number of magnets with the chiral crystal structure. In previous works, the existence of antiskyrmions in Mn$_{1.4}$PtSn was unambiguously demonstrated in real space by means of Lorentz transmission electron microscopy on thin-plate samples ($\sim$100~nm thick). In the present study, we used small-angle neutron scattering and magnetic force microscopy to perform reciprocal- and real-space imaging of the magnetic texture of bulk Mn$_{1.4}$PtSn single-crystals at different temperatures and in applied magnetic field. We found that the magnetic texture in the bulk differs significantly from that of thin-plate samples. Instead of spin helices or an antiskyrmion lattice, we observe an anisotropic fractal magnetic pattern of closure domains in zero field above the spin-reorientation transition temperature, which transforms into a set of bubble domains in high field. Below the spin-reorientation transition temperature the strong in-plane anisotropy as well as the fractal self-affinity in zero field is gradually lost, while the formation of bubble domains in high field remains robust. The results of our study highlight the importance of dipole-dipole interactions in thin-plate samples for the stabilization of antiskyrmions and identify criteria which should guide the search for potential (anti)skyrmion host materials. Moreover, they provide consistent interpretations of the previously reported magnetotransport anomalies of the bulk crystals.

Quantification of residual stress governing the spin-reorientation transition (SRT) in amorphous magnetic thin films

Soft magnetic thin films with in-plane uniaxial magnetic anisotropy are of significant importance for a broad range of technological applications, including high-frequency power conversion. In-plane uniaxial anisotropy in amorphous films is of particular interest for ultra-low materials loss and MHz frequency operations. The present work is focused on one of the fundamental mechanisms, i.e., residual stress, that can negate the uniaxial anisotropy in amorphous films by engendering perpendicular magnetisation and hence, undermining the soft magnetic performance. It is quantified how the nature of residual stress, compressive or tensile, transforms the magnetisation from an in-plane to an out-of-plane configuration, also well-known as spin-reorientation transition (SRT). A correlation between engineered residual stress in multilayer stacks, induced by the uneven expansion of metallic/dielectric layers following a thermal-shock scheme, and SRT mechanism demonstrates tensile stress inside the films undermines the soft magnetic performance. We suggest the magnetic softness can be retained by eluding sources of tensile stress during fabrication or post-processing of the amorphous films.

On the Structural and Magnetic Properties of Mn-Bi Alloy Jet Milled at Different Feed Rates

Mn50Bi50 alloy was prepared using arc melting method with subsequent homogenization treatment. The homogenized alloy was crushed and subjected to jet mill at different feed rates. The weight fraction of the LTP MnBi phase determined by the Rietveld refinement of the XRD pattern was found to be 89% in the as-homogenized and crushed alloy. The crushed alloy was subjected to jet milling at different feed rates from 0.5 to 1.5 g/min. Structural studies show that increase in feed rate leads to phase decomposition. Magnetic studies show that as-homogenized crushed alloy exhibits a magnetization of 60 emu/g. Jet milling leads to increase in coercivity and a decrease in magnetization. However, it was found that increase in the feed rate during jet milling leads to decrease of both coercivity and magnetization. Microstructural studies show that jet milling leads to decrease in particle size. Jet milling done at a lower feed rate helps in yielding the lowest average particle size compared to remaining feed rates in the Mn-Bi alloy. The spin reorientation transition temperature of the Mn-Bi alloy decreases with jet milling and varies at different feed rates. The coercivity of the Mn-Bi powder jet milled with a lower feed rate increases from 14.7 kOe at room temperature to 19.4 kOe at 400 K.

Engineering perpendicular magnetic anisotropy in Tb-Fe-Co thin films using ion-beam irradiation

This paper presents engineering perpendicular magnetic anisotropy in amorphous Tb-Fe-Co thin films employing irradiation of Ar+ ions at 200 and 250 keV energies with various fluences. The pristine film depicts a rectangular hysteresis loop with high perpendicular magnetic anisotropy, showing elongated, inter-connected maze-like magnetic domains. Irradiation at higher fluences (≥1015 ions cm−2) results in the transformation of magnetization reversal mechanism from rapid domain wall motion to nucleation and propagation of reverse domains due to the pinning of domain walls. The elongated magnetic domains get fragmented with reduced contrast and interestingly inhomogeneous flux-closure patterns are observed at higher fluences, indicating a spin reorientation transition. The modifications in magnetic properties are correlated with the structural investigations which reveal the crystallization of the Fe-Co phase in an amorphous Tb-Fe-Co matrix at higher energy and fluences of the projectile ions. Micromagnetic simulations complement the experimental results of domain modification.

Magnetothermal properties of [formula omitted] ([formula omitted] 0.25, 0.50 and 0.75)

We describe magnetic, thermal, and magnetocaloric properties of rare earth intermetallic compounds TmxDy1−xAl2 with x= 0.25, 0.5 and 0.75. Using model Hamiltonian we consider contributions of the crystalline electric field anisotropy in both Tm and Dy magnetic sublattices, disorder in exchange interactions among Tm-Tm, Dy-Dy and Tm-Dy magnetic ions, and the Zeeman effect. Employing earlier reported and new experimental measurements, we first determine a single free variable – the intersublattice magnetic exchange parameter – to properly model the temperature and magnetic field dependencies of heat capacity and magnetization, and then use the modeling results to explain the emergence of an anomalous spin reorientation transition and its influence on the magnetocaloric effect in the title compounds. Theoretical results agree with experimental data reasonably well.

The effect of composite configurations of Fe ionic spins on the dielectric properties in Sm-doped CeFeO3 ceramics

The Sm-doping effect on the crystal structure, dielectric and magnetic properties of CeFeO3 ceramics are systemically investigated. A giant dielectric response with high dielectric constant and low dielectric loss at room temperature (RT) is observed in Ce0.5Sm0.5FeO3 compounds. The increase of the dielectric constant is attributed to the increase of the ratio of Fe2+/Fe3+ ionic contents due to the charge transfer between Ce3+ and Fe3+ ions induced by Sm doping. Besides, the starting temperature T1 of spin-reorientation transition from Γ4 (Gx, Ay, Fz) to Γ1 (Ax, Gy, Cz) increases with Sm doping, and even reaches to a higher one than RT. Meanwhile, composite spin configurations of Fe3+ ions containing Γ1 and/or Γ2 (Fx, Cy, Gz) are found at RT in 0.2≤x ≤ 0.5 samples (x is Sm doping level), besides Γ4 state, whose formation originates from the strengthening of the anisotropic exchange interactions between Fe3+ and Ce3+/Sm3+ spins and the coexistence of Ce- and Sm-rich regions caused by Sm doping. It is suggested that the combining and competing functions of the Fe2+-Fe3+ ferromagnetic double-exchange interaction related to the Fe2+ ionic content and the composite spin configurations of Fe3+ ions containing Γ1 and/or Γ2 dominate the dielectric loss of Ce1-xSmxFeO3 ceramics. The results provide a different view for the physical theory and adjustment of the dielectric properties for applications.