Spin Reorientation Phase Transition Research Articles

Study on microscopic origin of spin excitation in TmFeO3 by time-resolved multicolor optical pump-probe spectroscopy

Spin dynamics of TmFeO3, mainly induced by two different mechanisms, were investigated by time-resolved multicolor pump-probe spectroscopy using femtosecond laser pulses. The spin dynamics, caused either by spin-reorientation phase transition or optical polarization-dependent effect, were distinguished by investigating their dependencies on external magnetic field and optical polarization. Spectral-dependent magneto-optic studies of the spin phase transition-induced spin dynamics revealed that laser-induced nonthermal exchange interaction between the electron states of iron (Fe3+) and thulium (Tm3+) ions is crucial for subsequent spin dynamics. This exchange interaction is influenced by the population change of the 4f electron states of Tm3+ ions, making the spin wave generation highly dependent on crystal temperature. However, spectroscopic studies of the polarization-dependent spin dynamics show that they are only related to the 3d electrons of Fe3+ ions, therefore, the spin dynamics appear to be a universal effect over a wide temperature range. Our observation can be further applied to study extended orthoferrite systems with other rare earth atoms.

2D-Perovskite Multiferroics: Interface-Induced Magnetoelectric Effect in Perovskite-Based Multiferroic Superlattices

Multiferroics are materials crucial for energy-efficient scalable electronics. The implementation of an effective combination of ferroic orderings on the nanoscale requires the design of new multiferroic materials. Recently, there have been observations of magnetoelectricity in the antiferromagnetic Ruddlesden-Popper and perovskite oxides with the interfacial Dzyaloshinskii-Moriya interaction. We propose a model for studying magnetic states and magnetoelectric effects in magnetoelectrically coupled antiferromagnetic–ferroelectric bi-layers with the interfacial Dzyaloshinskii–Moriya interaction. The ground magnetic states are calculated for a system on a rectangular lattice, with Heisenberg spins interacting with each other via an antiferromagnetic exchange interaction and a Dzyaloshinskii–Moriya interaction in the absence of an external magnetic field. Our calculations show that the interfacial Dzyaloshinskii-Moriya interaction in the considered system leads to the stabilization of topological skyrmionic states in a zero magnetic field. We explore transformations of magnetic states considering the changes in the in-plane magnetic anisotropy constant and the magnetoelectric coupling parameter. Our findings have shown the possibility of the existence of several magnetic configurations: a skyrmion lattice, a skyrmion state, and a uniform antiferromagnetic ordering realized at a definite ratio of the system parameters. We determine the areas of the phases existence and the conditions required for spin-reorientation phase transitions.

Observation of c -axis magnetization at low temperatures in the weak ferromagnet FeBO3 reveals a spin-reorientation transition

The weak ferromagnet $\mathrm{Fe}{\mathrm{BO}}_{3}$ is well known for being a unique system for modeling and testing magnetic dynamics primarily due to relatively simple and localized magnetic structure and its interesting spin wave dynamics. At room temperature, it has slightly canted iron moments lying in the $a\text{\ensuremath{-}}b$ plane that result in a strong antiferromagnetic moment and a weak ferromagnetic moment, which results in pronounced ferromagnetic and antiferromagnetic spin modes. However, some previous studies have shown unusual low-temperature behavior that suggests a phase transition. By performing low-temperature magnetization measurements, both in bulk and on the mesoscale, we have observed a low-temperature magnetic texture in this material in which a large $c$-axis magnetization occurs. Magnetic fields along the $c$ axis as high as 1300 Oe were observed close to the sample's surface. This presents evidence for the onset of a Morin transition or another type of spin-reorientation phase transition wherein the ${\mathrm{Fe}}^{3+}$ moments would acquire a $c$-axis component to their canting below a critical temperature. The observation of this $c$-axis magnetization suggests that there is a different ground state in this material than has been previously expected and could be due to as yet unexplored intricacies of the Dzyaloshinskii-Moriya interaction.

Microscopic description of magnetic nonequilibrium phenomena in erbium orthoferrite

A model of nonequilibrium thermodynamics of erbium orthoferrite is presented. The quantum-mechanical effects in arbitrary magnetic fields, related both to the direction of a general quantization axis and an influence of anisotropic exchange interactions on the magnetic structure, spin-reorientation phase transition, spin reversals, and hysteresis, are considered. Based on recent experimental data on temperature-induced spin switching [Phys. Rev. B 105, 094424 (2022)], a possible mechanism for the exchange bias of magnetic hysteresis loops is proposed. The main parameters of the model Hamiltonian are determined, which point out a strongly competitive character of exchange interactions in erbium orthoferrite.

Transformation of 5I8→5F5 Ho absorption band in Ho0.75Nd0.25Fe3(BO3)4 crystal during spin-reorientation transition

Polarized absorption spectra of crystal Ho0.75Nd0.25Fe3(BO3)4 in the region of the 5I8→5F5 absorption band of Ho ions were investigated depending on temperature in the range of 5–20 K. Absorption spectra are decomposed into components of the Lorentz form. The spin-reorientation phase transition was detected at 6.9 K. The observed line position shifts during the reorientation transition were different for different lines, which indicated different local magnetic anisotropy of the Ho ion in its excited states. Significant changes in absorption line intensities as a function of temperature were observed during the reorientation transition and above. These were explained as a consequence of the change in even components of the local crystal field in excited states. These components mix the closely spaced 4f states. Distortion of local symmetry in the ground state was detected at one of the electron transitions.

Laser-driven first-order spin reorientation and Verwey phase transitions in magnetite Fe3O4 beyond the range of thermodynamic equilibrium

Ultrafast photo-induced phase transitions occurring under the impact of femtosecond laser pulses provide versatile opportunities for switching solids between distinctly-different crystalline, electronic, and magnetic states and thus modify their functional properties in a significant way. In this paper, we report on the laser-induced spin reorientation and Verwey phase transitions in a single crystalline ferrimagnetic magnetite ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$. Using femtosecond optical and magneto-optical pump-probe techniques, we define the range of the initial sample temperatures and laser fluences when partial or complete photo-induced phase transitions occur from a monoclinic insulating to a cubic metallic state with concomitant switching of magnetic anisotropy from the uniaxial to the cubic one. We thus reveal a connection between these phase transitions when driven by femtosecond laser pulses. Using transient linear and quadratic magneto-optical effects, we examine magnetization dynamics launched the switching of the magnetic anisotropy axis. We unveil the presence of the domains undergoing the laser-induced phase transitions even below the established threshold fluence for the transitions, as well as when the material is initially in the cubic phase. This is the manifestation of the first order of these both laser-induced phase transitions beyond the range of thermodynamic equilibrium.

First-order nature of the spin-reorientation phase transition in SmCrO3

The ever expected canted antiferromagnetic (CAFM) $Pb\ensuremath{'}n\ensuremath{'}m:{\mathrm{\ensuremath{\Gamma}}}_{4}({\mathbit{G}}_{\mathbit{x}},{A}_{y},{F}_{Z};{F}_{Z}^{R})$ to $Pbn\ensuremath{'}m\ensuremath{'}:{\mathrm{\ensuremath{\Gamma}}}_{2}({F}_{x},{C}_{y},{\mathbit{G}}_{\mathbit{Z}};{F}_{x}^{R}, {\mathbit{C}}_{\mathbit{y}}^{\mathbit{R}})$ spin reorientation phase transition (SRPT) has only recently been confirmed through high-resolution time-of-flight neutron scattering studies by Sau et al. [Phys. Rev. B 103, 144418 (2021)]. Despite several studies on $\mathrm{SmCr}{\mathrm{O}}_{3}$, the nature of its SRPT still remains debatable. In the present study, we revisit the issue through dc $M(T)$ and ac-susceptibility, ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$, measurements. Repeated cycle field-cooled-cooling and field-cooled-warming dc $M(T)$ measurements clearly expose a temperature point differentiating the regimes of continuous and discontinuous parts of the SRPT. The discontinuous part has a tiny but clear hysteresis in $M(T)$, confirming the first-order nature of the SRPT with supercooling $({T}^{*})$ and superheating $({T}^{**})$ temperatures to be $\ensuremath{\sim}33$ and $\ensuremath{\sim}36\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, respectively. The hysteresis in the $M(T)$ is strongly supported by the occurrence of hysteresis in the nondispersing peaks in ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$, measured using a 3 Oe ac signal amplitude during cooling and heating under zero dc-bias. Below SRPT, the complete reversibility of $M(T)$ and ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$ confirms the second-order nature of the ${\mathrm{Sm}}^{3+}$ ordering at ${T}_{\mathrm{N}2}$, which arises due to independent ${\mathrm{Sm}}^{3+}\text{\ensuremath{-}}{\mathrm{Sm}}^{3+}$ interaction. Similarly, the absence of hysteresis in $M(T)$ as well as in ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$, across the paramagnetic to CAFM ${\mathrm{\ensuremath{\Gamma}}}_{4}$ phase transition, proves the second-order nature of this phase transition.

Perspective on synthesis, structure, and magnetic properties of R–Fe–H hydrides

The structural and magnetic properties of the multicomponent R–Fe–H compounds with a high content of Fe and H are reported. The process of synthesis of the hydrides (R,R′)2Fe14BH5.5 [where R and R′ are light (Nd) and heavy (Dy, Ho, Er, Tm) rare earth metals, respectively] with a maximum hydrogen content is described in detail. The paper also provides insights into the synthesis of single-crystalline hydrides using the example of the R2(Fe,Co)14BH3 series. The hydrides (R,Nd)2Fe14BH5.5, R2(Fe,Co)14BH3, R2(Fe,Al)17H3 have a significantly increased volume as compared to the parent materials. High-field magnetization results of both parent and hydrogenated compounds at low temperatures are presented. Spin–reorientation phase transitions induced by an external magnetic field are observed. The parameter of the intersublattice exchange interaction and the influence of hydrogen on it are estimated within the framework of the mean field theory. The magnetocaloric effect of the compounds with a magnetic compensation point is studied with a special emphasis placed on the change of the sign of the effect.

Magnetic Domain Control of ErFeO3 by Intense Terahertz Free Electron Laser Pulses

The control of magnetic domain in correlated spin systems by optical pulses has been gaining importance in spintronics and related fields. In particular, ultrafast control of magnetic domain is one of the top areas of interest. Herein we demonstrate the magnetic domain control in ErFeO3 single crystal, a weak ferromagnet, induced by high-intensity terahertz (THz) pulse excitation from a free-electron laser. THz pulses with a central frequency of 4 THz and pulse energy in the order of 10 mJ were used. The microscopic images of the magnetic domain inversion induced by the THz irradiation were recorded by the Faraday-rotation method using a He–Ne probe laser. The experimental results of the THz pulse irradiation at room temperature and at low temperature around the spin reorientation phase transition are presented. We show that the THz pulse excitation can expand the minor magnetic domain toward the direction of the THz beam spot. The magnetic domain inversion is caused by the combination of depinning of the magnetic domain due to local heating and the entropic force owing to the thermal gradient induced by THz irradiation.

High-resolution time of flight neutron diffraction and magnetization studies of spin reorientation and polar transitions in SmCrO3

Rare-earth chromates have always been of interest due to temperature-induced magnetization reversal and spin-reorientation phase transitions (SRPTs). In orthochromates containing magnetic rare earths, the spin configuration is supposed to undergo a characteristic changeover across the SRPT followed by an independent ordering of rare-earth moments leading to polar order. However, due to the presence of nearly 14% of highly neutron-absorbing isotope $^{149}\mathrm{Sm}$ in natural Sm based compounds, correct magnetic structure determination of ${\mathrm{SmCrO}}_{3}$ through neutron diffraction measurements has been a challenge. In the present study we investigate the pre- and post-SRPT spin configurations in well characterized ${\mathrm{SmCrO}}_{3}$ through time of flight neutron diffraction measurements carried out in zero field at the high-resolution high-flux WISH beam line of ISIS, in the United Kingdom. Magnetization measurement shows a canted antiferromagnetic phase transition at ${T}_{N1}=192\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, giving rise to a weak ferromagnetism, which undergoes a SRPT at 37 K. Rietveld analysis of the neutron powder diffraction data shows that below ${T}_{N1}=192\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ the ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Sm}}^{3+}$ moments order in a $P{b}^{\ensuremath{'}}{n}^{\ensuremath{'}}m$:${\mathrm{\ensuremath{\Gamma}}}_{4}$(${\mathbit{G}}_{\mathbit{x}},{A}_{y},{F}_{Z};{F}_{Z}^{R}$) spin configuration with their tiny ferromagnetic components ${F}_{Z}$ and $\phantom{\rule{0.28em}{0ex}}{F}_{Z}^{R},$ giving rise to weak ferromagnetism. Below 37 K the $P{b}^{\ensuremath{'}}{n}^{\ensuremath{'}}m$:${\mathrm{\ensuremath{\Gamma}}}_{4}$(${\mathbit{G}}_{\mathbit{x}},{A}_{y},{F}_{Z};{F}_{Z}^{R}$) configuration transforms to $Pb{n}^{\ensuremath{'}}{m}^{\ensuremath{'}}:{\mathrm{\ensuremath{\Gamma}}}_{2}$(${F}_{x},{C}_{y},{\mathbit{G}}_{\mathbit{Z}};{F}_{x}^{R},\phantom{\rule{0.16em}{0ex}}{\mathbit{C}}_{\mathbit{y}}^{\mathbit{R}}$) as a result of continuous rotation of ${\mathrm{Cr}}^{3+}$ moments, while approaching SRPT below ${T}_{N1}$. At still lower temperatures the $Pb{n}^{\ensuremath{'}}{m}^{\ensuremath{'}}:{\mathrm{\ensuremath{\Gamma}}}_{2}$(${F}_{x},{C}_{y},{\mathbit{G}}_{\mathbit{Z}};{F}_{x}^{R},\phantom{\rule{0.16em}{0ex}}{\mathbit{C}}_{\mathbit{y}}^{\mathbit{R}}$) phase transforms to polar phases, either the $P{2}_{1}^{\ensuremath{'}}{2}_{1}^{\ensuremath{'}}{2}_{1}:{\mathrm{\ensuremath{\Gamma}}}_{26}$(${C}_{x},{\mathbit{G}}_{\mathbit{y}},{F}_{z};{\mathbit{C}}_{\mathbit{x}}^{\mathbit{R}},\phantom{\rule{0.16em}{0ex}}{A}_{y}^{R},\phantom{\rule{0.16em}{0ex}}{F}_{z}^{R}$) or the $P{n}^{\ensuremath{'}}a{2}_{1}^{\ensuremath{'}}:{\mathrm{\ensuremath{\Gamma}}}_{27}$(${F}_{x},{C}_{y},{\mathbit{G}}_{\mathbit{z}};{F}_{x}^{R},\phantom{\rule{0.16em}{0ex}}{\mathbit{C}}_{\mathbit{y}}^{\mathbit{R}},{G}_{z}^{R}$) phase, as a result of independent antiferromagnetic ordering of ${\mathrm{Sm}}^{3+}$ moments at ${T}_{N2}l4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ through ${\mathrm{Sm}}^{3+}\text{\ensuremath{-}}{\mathrm{Sm}}^{3+}$ direct interaction. Our result of the transformation of ${\mathrm{SmCrO}}_{3}$ from ${\mathrm{\ensuremath{\Gamma}}}_{4}$ to ${\mathrm{\ensuremath{\Gamma}}}_{2}$ below SRPT is in contradiction with the ${\mathrm{\ensuremath{\Gamma}}}_{1}$(${A}_{x},{\mathbit{G}}_{\mathbit{y}},{C}_{Z};{C}_{z}^{R}$) spin configuration as reported in Tripathi et al. [Phys. Rev. B 96, 174421 (2017)]. This issue has been independently settled through ground-state energy calculation using spin-dependent density functional theory confirming the ${\mathrm{\ensuremath{\Gamma}}}_{2}$ spin configuration to be of lower energy as compared to that of the ${\mathrm{\ensuremath{\Gamma}}}_{1}$. The role of magnetocrystalline anisotropy in the occurrence of SRPT has been discussed.

Magnetic order of Dy3+ and Fe3+ moments in antiferromagnetic DyFeO3 probed by spin Hall magnetoresistance and spin Seebeck effect

We report on spin Hall magnetoresistance (SMR) and spin Seebeck effect (SSE) in single crystal of the rare-earth antiferromagnet DyFeO$_{3}$ with a thin Pt film contact. The angular shape and symmetry of the SMR at elevated temperatures reflect the antiferromagnetic order of the Fe$^{3+}$ moments as governed by the Zeeman energy, the magnetocrystalline anisotropy and the Dzyaloshinskii-Moriya interaction. We interpret the observed linear dependence of the signal on the magnetic field strength as evidence for field-induced order of the Dy$^{3+}$ moments up to room temperature. At and below the Morin temperature of 50$\,$K, the SMR monitors the spin-reorientation phase transition of Fe$^{3+}$ spins. Below 23$\,$K, additional features emerge that persist below 4$\,$K, the ordering temperature of the Dy$^{3+}$ magnetic sublattice. We conclude that the combination of SMR and SSE is a simple and efficient tool to study spin reorientation phase transitions and sublattice magnetizations.

Synthesis, structure and magnetic properties of Sm1.2Ho0.8Fe17Нx (x = 0; 4.4)

Intermetallic compounds based on rare-earth metals and iron are by far the most promising materials for permanent magnets. In this work, the multicomponent compound Sm1.2Ho0.8Fe17 was prepared by induction melting. The hydride Sm1.2Ho0.8Fe17H4.4 with a high hydrogen content was obtained by direct hydrogenation of the intermetallic compound. The rhombohedral Th2Zn17-type of structure (space group R3¯m) is inherent to parent compound and hydride as well. The effect of hydrogenation on the magnetic properties of Sm1.2Ho0.8Fe17 was investigated. Curie temperature of the hydride Sm1.2Ho0.8-Fe17H4.4 is higher than that of parent compound by ΔTC = 138 K. The hydrogen embedded in Sm1.2Но0.8Fe17 crystal lattice increases the saturation magnetization (σS) at T = 300 K, but does not significantly affect σS at Т = 4.2 K. The ferrimagnetic structure is retained in magnetic fields up to 58 T in the parent compound, while, in the hydride, there is a spin-reorientation phase transition observed at 55 T. It is found that the parameter of the intersublattice exchange interaction decreases significantly in the hydride Sm1.2Ho0.8Fe17H4.4 (and in the nitride Sm1.2Ho0.8Fe17N2.4) which is associated with boosting of the unit-cell volume and distances between magnetic ions.

Dzyaloshinskii – Moriya interaction, epitaxial strains, phase transitions in multiferroics with cycloidal structure

In this paper, we explore magnetic phases and spin reorientation phase transitions (SRPT) in the BiFeO3 – like multiferroics. We consider the Dzyaloshinskii – Moriya exchange interaction (DMI) as the principle mechanism responsible for appearance of spin space modulated structures (SSMS) in BiFeO3 and focus the peculiar features of the DMI manifestation in single crystals and films. As an example we take a (110) – oriented BiFeO3 film whose thickness is much lower than the period of SSMS (dfilm≪λ) and construct phase diagram in terms “magnetic field H – perpendicular magnetic anisotropy (PMA) constant κ” accounting the PMA dependence on the strains, where the tensile strains correspond to the situation κ > 0; the compressive strains correspond to the situation κ < 0. Our findings shows that at the condition (dfilm≪λ) the SSMS modulated along the [001] axis with spin rotating in a plane (110) exists as the ground magnetic state in a definite range of the control parameters (H, ±κ). We show that magnetic field applied along the normal to the film along with strains leads to the transition into homogeneous magnetic state of the “easy plane” type at κ > 0 and tilted phase at κ < 0. As well as in the single crystals at the positive values κ > 0 phase transition from SSMS into homogeneous “easy plane” phase goes through the cone SSMS whose existence was recently experimentally confirmed [S. Kawachi, et al, Phys. Rev. Mater. 1, 024, 408 (2017)]. We believe that our findings performed for the (110) BiFeO3 film will be of interest for further experimental and theoretical research and the implementations of BiFeO3 based technologies.

Simulating the Hysteretic Characteristics of Hard Magnetic Materials Based on Nd2Fe14B and Ce2Fe14B Intermetallics

The Ce2Fe14B intermetallic, like Nd2Fe14B, has the tetragonal Nd2Fe14B-type structure (space group P42/mnm), in which Ce ions have a mixed-valence state characterized by the coexistence of trivalent 4f1 and tetravalent 4f0 electron states. Despite the fact that the saturation magnetization, magnetic anisotropy field, and Curie temperature of the Ce2Fe14B intermetallic are substantially lower than those of Nd2Fe14B and Pr2Fe14B, Ce2Fe14B retains the capacity of being able to be used in the manufacturing of rare-earth permanent magnets. Moreover, at low temperatures, the anisotropy field of Се2Fe14B is higher than that of Nd2Fe14B, and Се2Fe14B does not undergo the spin-reorientation transition. In this respect, studies of (Nd, Ce)-Fe-B alloys, which are intended for the improvement of the service characteristics-to-cost ratio, are very relevant. A model and algorithm for calculating the hysteresis loops of uniaxial hard magnetic materials with allowance for the K1 and K2 (K2 &gt; 0 and K1 &gt; 0 and K1 &lt; 0) magnetic anisotropy constants were developed and allowed us to obtain data on their effect on the parameters of hysteresis loops for a wide temperature range (0–300 K). The simulation and analysis of hysteresis loops of the quasi-ternary intermetallics (Nd1−хСех)2Fe14B (х = 0–1) was performed. Results of the simulation indicate that the alloying of the Nd2Fe14B intermetallic with Ce to x = 0.94 (1) does not completely eliminate the negative effect of spin-reorientation phase transition on the residual magnetization of the (Nd1−хCeх)2Fe14B intermetallic and (2) slightly decreases the slope of magnetization reversal curve.

Features of magnetic and magnetoelectric properties, H-T phase diagram of GdCr3(BO3)4

Comprehensive studies of magnetic properties of GdCr3(BO3)4 single crystal have been carried out. The integrals of intrachain (J/k = 4 ± 1 K) and interchain (J΄/k ≈ −0.7 K) exchange interactions in the Cr subsystem have been determined and the strength of Cr-Gd exchange interaction (JCr-Gd/k ~ −0.2 K) has been estimated. The values of the exchange field 2HE ≈ 17 T and the effective magnetic anisotropy field HA ≈ 0.05 T of GdCr3(BO3)4 have been estimated. The electric polarization ΔPa along the a axis in the longitudinal geometry of the experiment has been detected. Correlations between the electric polarization and the magnetization of the studied compound have been found. The spin-reorientation phase transition in the magnetically ordered state has been found. This transition exists for the external magnetic field applied along any crystallographic direction and the transition field depends weakly on the direction of the field. Nature of the spin-reorientation phase transition has been discussed. Magnetic phase diagram has been constructed and spin configurations for the low-field and high-field phases have been proposed.

Strengthening the Intersublattice Exchange Interaction in R(Fe,Ti)$${}_{12}$$N (R = Ho and Er) Nitrides

The field dependences of the magnetization of nitrogen-containing compounds R(Fe,Ti) $${}_{12}$$ N (R = Ho and Er) are analyzed. It was found that the initial HoFe $${}_{11}$$ Ti sample at $$T=4.2$$ K exhibits the eaxy-axis anisotropy; however, as a result of nitriding, the anisotropy type changes to the easy cone of magnetization. As in the original samples of HoFe $${}_{11}$$ Ti and ErFe $${}_{11}$$ Ti, in HoFe $${}_{11}$$ TiN and ErFe $${}_{11}$$ TiN nitrides the cascade of spin-reorientation phase transitions is observed which is induced by external magnetic field. In the framework of the molecular field theory, the effect of nitriding on the interlattice exchange interactions is estimated. It is established that the molecular field that acts from the iron sublattice on rare-earth ions (holmium and erbium) is enhanced. The effect of nitriding and hydrogenation on the intersublattice exchange is compared.

Magnetic Domain-Wall Induced Electric Polarization in NdCrO3 Polycrystalline Ceramic.

We reported the magnetic, dielectric and magnetoelectric properties of NdCrO3 polycrystalline ceramics. Magnetization curves revealed two magnetic transitions at 227 K and 38 K, which corresponded to Cr3+ canted antiferromagnetic ordering and Cr3+ spin reorientation phase transition, respectively. At 11.5 K, a Schottky-type anomaly was observed, caused by Nd3+ ground doublet Zeeman splitting. High-temperature dielectric relaxation exhibited a type of thermally activated relaxation process, which mainly resulted from the Maxwell–Wagner effect. The spin-reorientation of Cr3+ ions and the Nd3+ ground doublet splitting were observed to be accompanied by an electric polarization. The polarization could be induced by the presence of the antiferromagnetic-type domain walls, which led to spatial inversion symmetry breaking.

Spontaneous Rotation of Ferrimagnetism Driven by Antiferromagnetic Spin Canting.

Spin-reorientation phase transitions that involve the rotation of a crystal's magnetization have been well characterized in distorted-perovskite oxides such as orthoferrites. In these systems spin reorientation occurs due to competing rare-earth and transition metal anisotropies coupled via f-d exchange. Here, we demonstrate an alternative paradigm for spin reorientation in distorted perovskites. We show that the R_{2}CuMnMn_{4}O_{12} (R=Y or Dy) triple A-site columnar-ordered quadruple perovskites have three ordered magnetic phases and up to two spin-reorientation phase transitions. Unlike the spin-reorientation phenomena in other distorted perovskites, these transitions are independent of rare-earth magnetism, but are instead driven by an instability towards antiferromagnetic spin canting likely originating in frustrated Heisenberg exchange interactions, and the competition between Dzyaloshinskii-Moriya and single-ion anisotropies.

Unusual Field Dependence of the Anomalous Hall Effect in Ta/Tb−Fe−Co

Experimental studies of anomalous Hall effect are performed for thin filmed Ta/TbFeCo in a wide range of temperatures and magnetic fields up to 3 T. While far from the compensation temperature (TM=277 K) the field dependence has a conventional shape of a single hysteresis loop, just below the compensation point the dependence is anomalous having the shape of a triple hysteresis. To understand this behavior, we experimentally reveal the magnetic phase diagram and theoretically analyze it in terms of spin-reorientation phase transitions. We show that one should expect anomalous hysteresis loops below the compensation point if in the vicinity of it the magnetic anisotropy is dominated by FeCo sublattice due to interaction with Ta.

Anomalies in the magnetic properties of some terbium-yttrium iron garnets at low temperatures

This work is aimed to study the influence of the replacement of the magnetic cations Tb3+ by diamagnetic cations Y3+ on the low-temperature point’, TB predicted by Belov for ferrimagnets with and without magnetic compensation point, Tcomp. Isothermal magnetizations, MT(H) are carried out on single crystals of two mixed terbium-yttrium ferrite garnets TbxY3-xFe5O12 (x = 1.98 and 0.37). The measurements are performed using DC magnetic field, H up to 80 kOe applied along the <111> and <100> crystallographic directions in the 1.5-300 temperature range. From the approximation to the second order of H, the expansion of MT(H) is analyzed on the basis of the T-dependences of the spontaneous magnetization, MS, the paraprocess magnetic susceptibility, χp and the parameter, |b| of the bH2 term. The manifestation of ferromagnetic-and antiferromagnetic-type low-temperature paraprocess and other concomitant effects is observed in the temperature dependences of the derivative, dMS/dT where MS exhibits Néel’s-type curves, i.e., N-type with Tcomp = 137 K for x = 1.98 and P-type without a Tcomp point for x = 0.37). It was established that low-T anomalies appear in the area of TB = 58 K reported before for the pure TbIG. The results obtained for x = 0.37 in the case of the free sphere show that |b| undergo changes at TSR1 = 40 K, TSR2 = 140 K, and TSR3 = 232 K. Thus, we suggest that as T increase, the previous spin reorientation phase transition occurs in a wide T-range, (40-232 K) from the easy axis of magnetization <100> via stable and intermediate low-symmetry angular phases <uuw> towards the high symmetry phase <111>.