First-order Spin Reorientation 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.

Neutron Diffraction Investigation of the DyFe11Ti Magnetic Structure and Its Spin Reorientations

Abstract In this article, we report on the magnetic structure of DyFe11Ti and its thermal evolution as probed by neutron powder diffraction. A thermodiffraction technique was used to follow the temperature dependence of the magnetic moments, as well as their orientation. The Dy and Fe moments were coupled to each other in an antiparallel manner to form a ferrimagnet, where the easy magnetization direction at 2 K was the [110] axis in the basal (a, b) plane. This magnetic structure underwent two successive spin reorientation phenomena with increasing temperature. A large Dy magnetic moment of 9.7 Bohr magneton (μB) was obtained at low temperatures, and the magnitude decreased rapidly to 7.5μB at 200 K. The largest Fe magnetic moment was observed on the Fe 8i position. A ThMn12-type crystal structure was preserved in the studied temperature range, despite the large changes of the magnetic structure. A sharp tilt was observed at the first-order spin reorientation, TSR1; the angle between the easy magnetization axis and the crystal c axis was reduced from 90° at 2 K to about 20° at 200 K (where c is the easy axis above 200 K); and the Dy and Fe magnetic moments maintained an antiparallel coupling.

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.

Magnetic, magneto-optical and specific heat studies of the low temperature anomalies in the magnetodielectric DyIG ferrite garnet

Abstract Measurements of magnetization and Cotton Mouton effect (CM) under external magnetic field (Hex) combined with specific heat experiments at Hex = 0, were performed on dysprosium iron garnet Dy3Fe5O12 (or DyIG) single crystals. The low-temperature dependences of some magnetic, magneto-optical and thermodynamic quantities, such as spontaneous magnetization, both magnetic and CM susceptibilities and the excess specific heat due to the contribution of the Dy3+ ions only, give rise to the appearance of two types of anomalies. The first one which is related to the ‘low temperature paraprocess’ effect, occurs in the region of the ‘Belov point’ TB predicted at 42 K. Whereas the second one, which is due to the previous first-order spin reorientation phase transition, takes place at TSR = 15 K. The easy axis of magnetization defined by the resultant iron sublattice magnetization vector MFe, which remains along the 〈1 1 1〉 direction above TSR, changes spontaneously below TSR and becomes aligned along the low symmetry angular 〈u u w〉 phase. The results are analyzed taking into account those reported earlier, such as the negative magnetodielectric property for Hex

Femtosecond single-shot imaging and control of a laser-induced first-order phase transition in HoFeO3

Excitation of antiferromagnetic HoFeO3 with a single 80 fs laser pulse triggers a first-order spin-reorientation phase transition. In the ultrafast kinetics of the transition one can distinguish the processes of impulsive excitation of spin precession, nucleation of the new domain and growth of the nuclei. The orientation of the spins in the nuclei is defined by the phase of the laser-induced coherent spin precession. The growth of the nuclei is further promoted by heating induced by the laser excitation. Hereby we demonstrate that in HoFeO3 coherent control of the spin precession allows an effective control of the route of the heat-induced first-order magnetic phase transition. The theoretical description of the excitation of the spin precession by linearly-polarized ultrashort laser pulses is developed with the sigma model. The analysis showed high sensitivity of the excited dynamics to the initial spin orientations with respect to the crystallographic axes of the material.

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.

β-NMR Investigation of the Depth-Dependent Magnetic Properties of an Antiferromagnetic Surface.

By measuring the prototypical antiferromagnet α-Fe_{2}O_{3}, we show that it is possible to determine the static spin orientation and dynamic spin correlations within nanometers from an antiferromagnetic surface using the nuclear spin polarization of implanted ^{8}Li^{+} ions detected with β-NMR. Remarkably, the first-order Morin spin reorientation in single crystal α-Fe_{2}O_{3} occurs at the same temperature at all depths between 1 and 100 nm from the (110) surface; however, the implanted nuclear spin experiences an increased 1/T_{1} relaxation rate at shallow depths revealing soft-surface magnons. The surface-localized dynamics decay towards the bulk with a characteristic length of ε=11±1 nm, closely matching the finite-size thresholds of hematite nanostructures.

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.

INFLUENCE OF AN EXTERNAL MAGNETIC FIELD ON THE DYNAMICS OF A NEW-PHASE NUCLEUS IN THE VICINITY OF THE FIRST-ORDER PHASE TRANSITION IN MAGNETS WITH DEFECTS PRESENT

Theoretically, with the aid of a soliton model, the evolution of a new-phase nucleus near the first-order spin-reorientation phase transition in magnets has been investigated in an external magnetic field. The influence of an external field and one-dimensional defects of magnetic anisotropy on the dynamics of such nucleus has been demonstrated. The conditions for the localization of the new-phase nucleus in the region of the magnetic anisotropy defect and for its escape from the defect have been determined. The values of the critical fields which bring about the sample magnetization reversal have been identified and estimated.

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.

Influence of one-dimensional “defects” on the new-phase nucleation dynamics near the first-order transition in magnets

The evolution of a new-phase nucleus near the first-order spin-reorientation phase transition in magnets has been investigated. A strong influence of one-dimensional magnetic anisotropy “defects” on the nucleation dynamics has been shown. The conditions of the localization of the new-phase nucleus in the region of the magnetic anisotropy “defect” have been determined.

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.