First-order Spin Reorientation Transition Research Articles

Thermal and magnetic properties of Fe7Se8 studied on single crystals

Specific heat, thermal expansion and magnetic measurements on single crystalline samples have been employed to study the interplay between the lattice and the magnetic state in the layered iron selenide compound Fe7Se8, which exhibits a ferrimagnetic order below TN ≈ 440 K and a spin reorientation transition upon cooling below Tsr ∼ 115 K. Thermal expansion measurements performed on single-crystal samples revealed significant anisotropic deformations of the crystal lattice with decreasing temperature below TN, an increase in the c/a ratio, and negative volume spontaneous magnetostriction (ωs ∼ −5.3⋅10−3 at 120 K). The first-order spin reorientation transition in Fe7Se8 is found to be accompanied by a hysteretic behavior of the specific heat and thermal expansion, and an anomaly in the ωs vs T dependence. The results obtained are indicative of a strong influence of the magnetoelastic interactions on the properties of Fe7Se8.

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.

Room-temperature magnetization reversal and magnetocaloric switching in Fe substituted GdMnO3

Room-temperature tunable bipolar magnetization switching and magnetically switchable magnetocaloric phenomena having numerous application potentials are reported in $\mathrm{GdM}{\mathrm{n}}_{1\ensuremath{-}x}\mathrm{F}{\mathrm{e}}_{x}{\mathrm{O}}_{3}$ ($x=0.55$ and 0.60) polycrystalline samples. Substitution of Fe in antiferromagnetic $\mathrm{GdMn}{\mathrm{O}}_{3}$ induces a first-order spin-reorientation transition $({T}_{SR})$, which along with antiferromagnetic ordering transition $({T}_{\mathrm{N}})$ gives rise to anomalies in dielectric spectra, a signature of magnetodielectric effect. Temperature-dependent Raman spectra confirm the spin-phonon coupling which could be the origin of the magnetodielectric effect in the system. Notably, low-field magnetically tunable magnetization reversal is found to appear between ${T}_{\mathrm{SR}}$ and ${T}_{\mathrm{N}}$ in these compounds owing to the competition between single-ion magnetic anisotropy and antisymmetric Dzyaloshinsky-Moriya interaction. Additionally, the $\mathrm{GdM}{\mathrm{n}}_{0.40}\mathrm{F}{\mathrm{e}}_{0.60}{\mathrm{O}}_{3}$ sample reveals the coexistence of magnetically switchable conventional and inverse magnetocaloric effect at 250 and 310 K. The tailoring of these coexisting room-temperature magnetization reversal and magnetocaloric phenomena in a single-phase system suggests a route to design the material suitable for potential applications in electromagnetic and memory devices.

Experimental Investigation on the Low-Temperature Anomalies in Dysprosium Iron Garnet (DyIG)

The anomalous physical properties of dysprosium iron garnet Dy3Fe5O12 or DyIG single crystals have been revisited at low temperatures. This paper presents results of experimental investigation based on specific heat, magnetization, and Faraday rotation measurements. The distinguishing features are the occurrence of two types of anomalies in the temperature dependences of some judicious quantities. The first one coincides with the previous first-order spin reorientation transition at TSR = 15 K where the iron sublattice magnetization vector MFe changes from the axis at high temperature toward the low angular phases below TSR. The second one takes place around the “low-temperature Belov point” TB = 42 K, confirming what had already been predicted previously about the paraprocess effect in this ferrimagnet. The results are compared with previous findings and discussed taking into account the coexistence of some concomitant phenomena such the magnetodielectric and Schottky effects which cause anomalies, respectively near TSR and TB.

Interplay of rare-earth and transition-metal subsystems inCu3Yb(SeO3)2O2Cl

We present the synthesis and the experimental and theoretical study of the new member of the francisite family, $\mathrm{C}{\mathrm{u}}_{3}\mathrm{Yb}{(\mathrm{Se}{\mathrm{O}}_{3})}_{2}{\mathrm{O}}_{2}\mathrm{Cl}$. The compound reaches an antiferromagnetic order at ${T}_{\mathrm{N}}=36.7\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and experiences first-order spin-reorientation transition to weakly ferromagnetic phase at ${T}_{\mathrm{R}}=8.7\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ evidenced in specific heat ${C}_{\mathrm{p}}$ and magnetic susceptibility \ensuremath{\chi} measurements. Distinctly different magnetization loops in $T<{T}_{\mathrm{R}}$ and ${T}_{\mathrm{R}}<T<{T}_{\mathrm{N}}$ temperature ranges reflect the interplay of rare-earth and transition-metal subsystems. At low temperatures, the saturation magnetization ${M}_{\mathrm{s}}\ensuremath{\sim}5.2\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ is reached in pulsed magnetic-field measurements. The electron spin resonance data reveal the complicated character of the absorption line attributed to response from both copper and ytterbium ions. Critical broadening of the linewidth at the phase transitions points to quasi-two-dimensional character of the magnetic correlations. The spectroscopy of $\mathrm{Y}{\mathrm{b}}^{3+}$ ions evidences splitting of the lowest-energy Kramers doublet of ${}^{2}{F}_{5/2}$ excited multiplet at ${T}_{\mathrm{R}}<T<{T}_{\mathrm{N}}$ while the ground Kramers doublet splits only at $T<{T}_{\mathrm{R}}$. We describe the magnetic properties both above and below the spin-reorientation transition in the framework of a unified approach based on the mean-field approximation and crystal-field calculations.

Spin reorientations and crystal field modification in Ho1−y GdyAl2 compounds

We have performed an experimental and theoretical investigation on the spin reorientation transitions Ho1−y GdyAl2 compounds. Crystallographic, magnetic and calorimetric measurements have been performed for five selected samples in the Ho1−y GdyAl2 series (y = 0, 0.25, 0.5, 0.75 and 1.0). From the results, a linear increase in the lattice parameter as a function of Gd-content (y) is observed. Magnetization measurements show that all samples present collinear ferromagnetism. Specific heat measurements were performed in order to detail the first-order spin reorientation transition (FOSRT) that appears for HoAl2 around 20 K. Furthermore, we investigated how the increase in Gd content affects the character of such phase transition. Our results show a slightly modification in the spin reorientation transition temperature, which moves to lower temperatures as Gd is increased in HoAl2, whereas for the selected concentrations up to x = 0.75 the first-order character of the transition is maintained. The theoretical analysis by means of a model Hamiltonian that includes crystal field, exchange and Zeeman interactions reveals a modification in the crystal-field acting on Ho ions as Gd-content is increased.

Phase transitions of anisotropic and exchange origins inTmFe5Al7

Magnetization and sound propagation reveal a number of unusual spontaneous and field-induced transformations in ferrimagnetic ${\mathrm{TmFe}}_{5}{\mathrm{Al}}_{7}$ (${T}_{\mathrm{C}}$ = 193 K). The rare-earth sublattice was found to provide a uniaxial magnetic anisotropy, whereas the iron sublattice favors an easy-plane anisotropy. A competition between them results in a first-order spin-reorientation transition at 64 K as the magnetic moments rotate from the $c$ axis to the basal plane of a tetragonal structure. The transition is preceded by a first-order magnetization process of type II along the hard axis. Remarkably, the intersublattice Tm-Fe exchange interaction is weakened at the spin-reorientation transition. Concomitantly, the spontaneous magnetic moment disappears, and the ferrimagnetic state changes to antiferromagnetic. With increasing temperature, the strength of the Tm-Fe exchange is recovered, and the ferrimagnetism is restored at 82 K through another first-order phase transformation. Below 40 K, a first-order field-induced transition occurs for a magnetic field applied along the easy [001] axis. It reflects a rotation of the magnetic moments towards the forced ferromagnetic state observed above 30 T. Along the hard [100] axis the ferromagnetic saturation is not reached even at 60 T.

First-order spin reorientation transition and specific-heat anomaly in CeFeO3

We report the successful synthesis of single-phase polycrystalline CeFeO3, and a thorough study of its magnetic and thermal properties. An abrupt spin reorientation transition occurs at T = 240 K, indicating a first-order phase transition from Γ4 (Gx, Ay, Fz) to Γ1 (Ax, Gy, Cz). A distinct thermal anomaly in the specific heat due to spin reorientation has been detected, with the onset and completion of the spin reorientation at 240 K and 220 K, respectively. The low-temperature specific heat exhibits a Schottky anomaly caused by paramagnetic Ce3+. The very-low-temperature specific heat increases with increasing the applied magnetic field, suggesting an antiferromagnetic transition of Ce3+ exists below T = 1.8 K.

Spin reorientation and magnetization reversal in the perovskite oxides, YFe1−xMnxO3 (0≤x≤0.45): A neutron diffraction study

Members of the YFe1−xMnxO3 (0≤x≤0.45) family crystallize in the GdFeO3 type orthorhombic perovskite structure (space group Pnma) where the Fe and Mn ions are disordered at the 4b crystallographic site. Upon substitution of Mn at the Fe-site in the canted antiferromagnetic YFeO3 (TN=640K), a first-order spin-reorientation transition occurs at a temperature, TSR, where the magnetic structure changes from the canted to a collinear state. With increasing Mn-concentration, TSR increases whereas TN decreases. Neutron diffraction studies on the x=0.4 sample reveal that the spin structure changes from Γ4 to Γ1 below TSR. Intriguingly, when x=0.4 and 0.45, a temperature-induced magnetization reversal is observed below a compensation temperature T⁎ (T⁎<TSR<TN). The reversal is explained on the basis of a ferrimagnetic ground state resulting from antiferromagnetic coupling of the canted moments of Fe–O–Fe and Mn–O–Mn with that of Fe–O–Mn ordering.

Magnetism of Ho1−xTbxAl2alloys: Critical dependence of a first-order transition on Tb concentration

HoAl${}_{2}$ exhibits a first-order spin reorientation transition at 20 K, which is manifested as a sharp peak in the heat capacity. When Ho is partially replaced by only 5$%$ of Tb, the sharp heat-capacity peak in ${\mathrm{Ho}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}{\mathrm{Al}}_{2}$ ($x$ = 0.05) disappears, and then reappears again for $x$ \ensuremath{\ge} 0.07. For $x$ = 0.05, the anomaly corresponding to the spin reorientation transition is barely seen in the heat capacity, but as $x$ exceeds 0.07 the weak anomaly transforms to a sharp peak. The spin reorientation transition temperature increases to 29 K for $x$ = 0.05, and as $x$ increases further the transition shifts to lower temperature and returns to \ensuremath{\sim}20 K for $x$ = 0.25. The transition is no longer observed when $x$ exceeds 0.60. Temperature-dependent x-ray powder-diffraction data confirm the first-order nature of the spin reorientation transition for the alloy with $x$ = 0.40, and indicate that the compound retains the room-temperature cubic structure within the sensitivity of the technique. Experimental observations are discussed considering the easy magnetization directions of HoAl${}_{2}$ and TbAl${}_{2}$.

Mössbauer spectroscopic study of spin reorientation in Mn-substituted yttrium orthoferrite

The first-order spin-reorientation transition in the Mn-substituted yttrium orthoferrites, YFe1−xMnxO3 (x = 0.1, 0.15 and 0.2), has been investigated using 57Fe Mössbauer spectroscopy. Owing to its large anisotropy, substitution of Mn3+ ions in YFeO3 induces a spin-reorientation transition from the low-temperature antiferromagnetic state to a high-temperature weak ferromagnetic state. With increasing x, the spin-reorientation transition temperature (TSR) increases whereas the Néel temperature (TN) decreases. Analysis of the Mössbauer spectra unambiguously confirms the occurrence of spin reorientation relative to crystal axes. At a given temperature, the mean hyperfine field decreases with the increasing Mn concentration. The variation of canting angle with temperature for YFe0.85Mn0.15O3 has been estimated.

Spin-Reorientation, Ferroelectricity, and Magnetodielectric Effect inYFe1−xMnxO3(0.1≤x≤0.40)

We report the observation of magnetoelectric and magnetodielectric effects at different temperatures in Mn-substituted yttrium orthoferrite, YFe(1-x)Mn(x)O(3)(0.1 ≤ x ≤ 0.40). Substitution of Mn in antiferromagnetic YFeO(3)(T(N) = 640 K) induces a first-order spin-reorientation transition at a temperature, T(SR), which increases with x whereas the Néel temperature (T(N)) decreases. While the magnetodielectric effect occurs at T(SR) and T(N), the ferroelectricity appears rather at low temperatures. The origin of magnetodielectric effect is attributed to spin-phonon coupling as evidenced from the temperature dependence of Raman phonon modes. The large magnetocapacitance (18% at 50 kOe) near T(SR) = 320 K and high ferroelectric transition temperature (∼115 K) observed for x = 0.4 suggest routes to enhance magnetoelectric effect near room temperature for practical applications.

ChemInform Abstract: Hydrogenation, Crystal Structure and Magnetic Ordering of R2Fe14C (R: Sm, Er, Tm).

Abstract The influence of hydrogen absorption on the magnetic properties of the compounds Sm 2 Fe 14 C, Er 2 Fe 14 C and Tm 2 Fe 14 C was studied using X-ray diffraction and measurements of the temperature dependences of the magnetization, the a.c.-susceptibility and the resistivity. The latter two compounds have a first-order spin reorientation transition close to room temperature, as confirmed by DSC measurements. It is shown that this property is largely retained upon hydrogen absorption although the corresponding Curie temperatures increase strongly with hydrogen concentration. The maximum hydrogen concentration decreases with increasing atomic number of the R component in the R 2 Fe 14 C compounds investigated.

The influence of spontaneous and field induced spin reorientation transitions on the magnetocaloric properties in rare earth intermetallic compounds: Application to TbZn

We report a theoretical investigation on the magnetocaloric properties of the cubic CsCl-type TbZn compound. Two successive peaks in the magnetocaloric quantities are observed and attributed to different types of phase transitions. For the magnetic field applied in the ⟨110⟩ direction, the first peak is ascribed to a spontaneous first-order spin reorientation transition (SRT) at T1=63 K, and the second one to the ferroparamagnetic phase transition. The application of an external magnetic field of 2 T along this direction leads to a tablelike behavior in the magnetocaloric quantities (ΔST and ΔTS) as a consequence of two successive second-order SRTs at TSR1=71 K and at TSR2=160 K. Applying a magnetic field of 5 T suppress the flat behavior but a high refrigeration capacity of 352 J/kg is predicted in a wide temperature range from 62 to 258 K. When the magnetic field is applied along the ⟨100⟩ direction an inverse magnetocaloric effect is observed in the temperature range below T1. The system was studied throughout a Hamiltonian that takes into account the Zeeman, exchange, and crystal field interactions.

Magnetoelectric effect and spontaneous polarization inHoFe3(BO3)4andHo0.5Nd0.5Fe3(BO3)4

The thermodynamic, magnetic, dielectric, and magnetoelectric properties of ${\text{HoFe}}_{3}{({\text{BO}}_{3})}_{4}$ and ${\text{Ho}}_{0.5}{\text{Nd}}_{0.5}{\text{Fe}}_{3}{({\text{BO}}_{3})}_{4}$ are investigated. Both compounds show a second order Ne\'el transition above 30 K and a first-order spin reorientation transition below 10 K. ${\text{HoFe}}_{3}{({\text{BO}}_{3})}_{4}$ develops a spontaneous electrical polarization below the Ne\'el temperature $({T}_{N})$ which is diminished in external magnetic fields. No magnetic-field induced increase of the polarization could be observed in ${\text{HoFe}}_{3}{({\text{BO}}_{3})}_{4}$. In contrast, the solid solution ${\text{Ho}}_{0.5}{\text{Nd}}_{0.5}{\text{Fe}}_{3}{({\text{BO}}_{3})}_{4}$ exhibits both, a spontaneous polarization below ${T}_{N}$ and a positive magnetoelectric effect at higher fields that extends to high temperatures. The superposition of spontaneous polarization, induced by the internal magnetic field in the ordered state, and the magnetoelectric polarizations due to the external field results in a complex behavior of the total polarization measured as a function of temperature and field.

A high-field magnetization study of aNd2Fe14Si3 single crystal

Magnetization study of a single crystal ofNd2Fe14Si3 (with therhombohedral Th2Zn17-type structure) reveals that the compound is a ferromagnet with a spontaneous magnetic moment of32.3μB per formulaunit (at T = 2 K) and a Curie temperature equal to 495 K. The easy-magnetization direction lies close to theb-axis, tiltingslightly towards the c-axis. (The b-axis [120] is not a high-symmetry direction in the crystallographic classD3d.) The observed strong magnetic anisotropy is attributed almostentirely to the Nd sublattice, as concluded from comparison with aY2Fe14Si3 single crystal. A magnetic field applied along thec-axis induces a first-order spin reorientation transition atBFOMP = 20 T. In the process of magnetization the Nd and Fe sublattices behave as essentiallynon-collinear. This is manifest particularly in the downward curvature of the first(pre-FOMP) stage of the magnetization curve. It is proposed to regard this curvature as avalidity criterion for the single-sublattice approximation.

Spin reorientation and crystal-field interaction inTbFe12−xTixsingle crystals

The magnetic properties of ${\mathrm{TbFe}}_{12\ensuremath{-}x}{\mathrm{Ti}}_{x}$ single crystals with $x=0.8--1.4$ have been investigated in detail using ac and dc susceptibility and high-field magnetization measurements. A first-order spin reorientation transition from a basal plane easy magnetization direction at low temperatures to an axial easy magnetization direction at high temperatures occurs for all the investigated compounds. The spin reorientation temperatures have been determined by combining ac and dc susceptibility measurements and its dependence on both the Ti content and the applied magnetic field has been studied. A first-order magnetization process is observed below a certain temperature when the magnetic field is applied along the [001] crystallographic direction. The dependence of the transition critical field on the Ti content has been analyzed. The magnetic behavior has been interpreted using a two-sublattices model for the magnetic structure, in the frame of a crystal-electric-field--mean-field model. The parameters describing the crystal-field interaction in ${\mathrm{TbFe}}_{12\ensuremath{-}x}{\mathrm{Ti}}_{x}$ compounds have been determined. The calculated magnetic behavior shows a good agreement with experimental results in a wide temperature range.

Non-collinear magnetic structures and first-order magnetization process in rare-earth systems

First-order field-induced spin reorientation transitions in multisublattice intermetallic compounds are considered within an anisotropic Heisenberg model, only leading-order anisotropy constants being included. The exchange interactions both between the rare-earth (RE) and transition metal sublattices and within the RE sublattice play an important role in the model. The latter interaction results in the occurrence of metastable states corresponding to a non-collinear magnetic structure. The possible FOMP scenarios for R 2Fe 17, HoFe 11Ti, and TbMn 6Sn 6 systems are discussed.

On the gradual character of the first-order spin reorientation transition in DyFe11Ti

Proceeding from recently published crystal field parameters, I demonstrate that the first-order spin reorientation transition point in DyFe12−xTix depends strongly on the value of titanium content x. This leads, due to inevitable small spatial variation of composition, to significant broadening of the first-order transition, giving it an appearance of a continuous process. Yet it can be unmistakably identified as a first-order phase transition, thanks to the characteristic shape of the temperature dependence of the spin orientation angle θ. What makes first- and second-order spin reorientation transitions clearly distinct is the shape, rather than width, of the “step” in the θ(T) dependence. Small differences of composition are also found to account for the outstanding discrepancies between the experimental studies carried out on different single crystals of DyFe11Ti, thus bringing the decade-long controversy to an end.