Spin Reorientation Transition Research Articles

Effects of 4d transition metal Pd doping on the magnetic and superconducting properties of 112-type iron pnictide EuFeAs2

The recently discovered 112-type EuFeAs2 compound that shows complex Eu-spin magnetism provides a new platform to study the interplay between superconductivity (SC) and magnetism in iron pnictide superconductors. In this paper, by substituting Fe with the 4d transition metal (TM) Pd, we have synthesized a series of EuFe1−x Pd x As2 (0 ⩽ x ⩽ 0.08) samples and studied the doping effect on SC and magnetism by means of electrical transport and magnetization measurements. The systematic evolution of the lattice parameters indicates that the Pd atoms have been successfully substituted into the Fe sites. With Pd doping, the Fe-related spin density wave transition at in the parent phase is rapidly suppressed, and SC simultaneously emerges, exhibiting a domelike shape with a maximum onset transition temperature of around 18.5 K at x = 0.04. On the other hand, the Eu-related antiferromagnetic order at is suppressed very slowly and persists up to x = 0.08, covering the whole SC dome region. Also, the reentrant spin-glass and spin-reorientation transitions below remain unchanged with Pd doping. All these results indicate that the Eu spins have little effect on SC in EuFe1−x Pd x As2. Finally, based on the resistivity and magnetization data, the T − x phase diagram of EuFe1−x Pd x As2 is constructed and compared with those of 3d TMs Co/Ni and La doped ones.

Exploring the possible origin of the spin reorientation transition in NdCrO3

Spin reorientation transitions and other related magnetic phenomena, which owe their origin to the complex interplay between multiple magnetic sublattices, have long attracted scientific attention both from the perspective of fundamental curiosity and technological applications. In this study, combining first principles calculations together with finite temperature Monte Carlo simulations, we explore the possible origins of reorientation transition of Cr spins in ${\mathrm{NdCrO}}_{3}$. We construct a ${\mathrm{NdCrO}}_{3}$ specific magnetic model, consisting of symmetric superexchange interactions between magnetic ions, as well as their magnetic anisotropy. We show that the observed spin reorientation in ${\mathrm{NdCrO}}_{3}$ arises out of a delicate balance between $\mathrm{Nd}\text{\ensuremath{-}}\mathrm{Cr}$ magnetic exchange interactions, single ion anisotropy of Nd spins, and single ion anisotropy of Cr spins. Moreover, though our model does not take into consideration the effect of antisymmetric and anisotropic-symmetric magnetic exchanges, the qualitative as well as quantitative agreement of the theoretically derived and the experimentally observed spin-reorientation transition in ${\mathrm{NdCrO}}_{3}$ confirms the merit of our proposed microscopic model. Our results also propose a hitherto unobserved collective magnetic ordering in the Nd sublattice, which is challenging to detect as it is an extreme low temperature phenomena, which therefore calls for further investigations.

Thermal control magnetic switching dominated by spin reorientation transition in Mn-doped PrFeO3 single crystals

Thermal control magnetic switching dominated by spin reorientation transition in Mn-doped PrFeO3 single crystals

A comparative study on magnetic behaviors and magnetocaloric effect in heavy rare-earth antiferromagnetic orthoferrites RFeO3 (R = Dy, Ho and Er)

The heavy rare-earth GdFeO 3 -type RFeO 3 (R = Dy, Ho and Er) orthoferrites (space group Pnma, N 62) show spin reorientation transition characterized by a turning point on the magnetization curves. The basic Arrott plots curves showing positive slopes confirm the second-order nature of the spin reorientation and the transition temperature T SR is estimated to be ∼45 K, ∼53 K and ∼94 K for DyFeO 3 , HoFeO 3 and ErFeO 3 , respectively. In addition, magnetic entropy change − Δ S M of the three samples is calculated to be 11.4, 9.8 and 7.4 J kg −1 K −1 at 10 K and 50 kOe, respectively. The field sensitive antiferromagnetic state and competitive magnetocaloric performances in RFeO 3 have been attracting considerable interest for the possible applications in spintronic devices.

Emergence of the topological Hall effect in a tetragonal compensated ferrimagnet Mn2.3Pd0.7Ga

Topological spin textures such as magnetic skyrmions have attracted considerable interest due to their potential application in spintronic devices. However, there still remain several challenges to overcome before their practical application, for instance, achieving high scalability and thermal stability. Recent experiments have proposed a new class of skyrmion materials in the Heusler family, Mn1.4Pt0.9Pd0.1Sn and Mn2Rh0.95Ir0.05Sn, which possess noncollinear magnetic structures. Motivated by these experimental results, we suggest another Heusler compound hosted by Mn3Ga to overcome the above limitations. We fabricate Mn3-xPdxGa thin films, focusing on the magnetic compensation point. In Mn2.3Pd0.7Ga, we find a spin-reorientation transition around TSR = 320 K. Below the TSR, we observe the topological Hall effect and a positive magnetic entropy change, which are the hallmarks of a chiral noncollinear spin texture. By integrating all the data, we determine the magnetic phase diagram, displaying a wide chiral noncollinear spin phase even at room temperature. We believe that this compensated ferrimagnet shows promise for opening a new avenue toward chiral spin-based, high-density, and low-power devices.

Field tuning magnetic phase transition in Dy0.5Tb0.5FeO3 single crystal

RFeO3 is an ideal candidate for the fabrication of spintronic devices, and its rare earth site doping is an important means to regulate and produce many unique spin behaviors. In this work, we report a high-quality Dy0.5Tb0.5FeO3 single crystal grown by optical floating zone method and its magnetic properties are studied explicitly. A type-Ⅱ spin switching effect and suppressed spin reorientation transition are found in the Magnetization vs Temperature curves in Dy0.5Tb0.5FeO3. In the temperature region of spin reorientation transition, the transition of Fe3+ magnetic sublattice configuration becomes very complicated by the influence of competitive interaction with magnetic Dy3+/Tb3+ ions. Interestingly, a field tunable double-hysteresis loop is observed near the antiferromagnetic transition temperature of rare earth ions sublattice, which has never been reported in RFeO3 family compounds. By studying the dependence of double-hysteresis loop at different temperatures, the magnetic phase transition and spin reorientation transition induced by the applied magnetic field are inferred. This novel physical phenomenon helps us understand the mechanism of spin configuration transition better at low temperatures.

Role of magnetocrystalline anisotropy on anisotropic magnetocaloric effect in single crystals

The role of magnetocrystalline anisotropy in single crystals played on the anisotropic magnetocaloric effect is studied based on Monte Carlo simulation. By taking into account the anisotropy, the spin reorientation transition (SRT) temperature (TSRT) may be higher than the Curie temperature and enhanced with larger anisotropy, and the magnetization behaviors at low temperatures below TSRT and under weak fields are highly sensitive to the anisotropy. The anisotropy of entropy change is the most significant when the magnetic field is parallel to the easy axis, while the maximum entropy change may increase or decrease with the anisotropy constant in a given direction depending on the magnetic field strength. Power-law fits have been conducted on the field dependence of the maximum entropy change and relative cooling power, which not only indicate a characteristic of the second-order phase transition but also demonstrate effect of anisotropy on magnetic order and dynamics during the SRT to contribute to the anisotropic magnetocaloric effect.

Structural, electronic and magnetocaloric properties of antiskyrmion hosting Heusler compounds: Mn2PtSn and Mn1.4PtSn

In this work, we have studied the structure, electronic and magnetic properties of Mn2PtSn and Mn1.4PtSn by using the ab initio calculations and Monte Carlo study. The ab initio calculations, based on the functional theory of density combined with the method of linear augmented plane waves at potential, are performed to investigate both electronic and magnetic properties of the two compounds. The total and partial densities of two systems have been calculated. Mn1.4PtSn, the first known Heusler tetragonal (Mn vacancy-induced) superstructure compound, opens a new direction of research for superstructure-related properties in a family containing multiple compounds. We have deduced the total magnetic moment of the two systems. We observe an anisotropic fractal magnetic pattern of zero-field closing domains above the spin-reorientation transition temperature, which transforms into a set of high-field bubble domains. Below the spin-reorientation transition temperature, the strong in-plane anisotropy as well as the zero-field fractal self-affinity is gradually lost, while the formation of high-field bubble domains remains robust. The magnetization, specific heat and magnetic entropy change have been obtained by using the Monte Carlo simulations. The relative cooling power has been obtained for different values of external magnetic field and temperatures.

Scaling of the Thermally Induced Sign Inversion of Longitudinal Spin Seebeck Effect in a Compensated Ferrimagnet: Role of Magnetic Anisotropy

AbstractThe authors report on a systematic investigation of the longitudinal spin Seebeck effect (LSSE) in a GGG(Gd3Ga5O12)/GdIG(Gd3Fe5O12)/Pt film series exhibiting an in‐plane magnetic easy axis with a compensation temperature (TComp) that decreases from 270 to 220 K when decreasing GdIG film thickness from 272 to 31 nm, respectively. For all the films, the LSSE signal flips its sign below TComp. The authors demonstrate a universal scaling behavior of the temperature dependence of LSSE signal for the GdIG films around their respective TComp. Additionally, the authors demonstrate LSSE in a 31 nm GdIG film grown on a lattice‐mismatched GSGG (Gd3Sc2Ga3O12) substrate that exhibits an out‐of‐plane magnetic easy axis at room temperature. However, this sample reveals a spin reorientation transition where the magnetic easy axis changes its orientation to in‐plane at low temperatures. A clear distinction is observed in the LSSE signal for the GSGG/GdIG(31 nm)/Pt heterostructure, relative to GGG/GdIG(31 nm)/Pt showing an in‐plane magnetic easy axis. The findings underscore a strong correlation between the LSSE signal and the orientation of magnetic easy axis in compensated ferrimagnets and opens the possibility to tune LSSE through effective anisotropy.

Terahertz spectroscopy of antiferromagnetic resonances in YFe1−xMnxO3 ≤x≤0.4 across a spin reorientation transition

We have conducted a terahertz spectroscopic study of antiferromagnetic resonances in bulk orthoferrite YFe1−xMnxO3 0≤x≤0.4. Both the quasi-ferromagnetic resonance mode and the quasi-antiferromagnetic resonance mode in the weak ferromagnetic Γ4 phase disappear near the spin reorientation temperature, TSR, for the onset of the collinear antiferromagnetic Γ1 phase (x ≥ 0.1). Below TSR, an antiferromagnetic resonance mode emerges and exhibits a large blueshift with decreasing temperature. However, below 50 K, this mode softens considerably, and this tendency becomes stronger with Mn doping. We provide a deeper understanding of such behaviors of the antiferromagnetic resonance modes in terms of the influence of the Mn3+ ions on the magnetocrystalline anisotropy. Our results show that terahertz time-domain spectroscopy is a useful, complementary tool in tracking magnetic transitions and probing the interaction between disparate magnetic subsystems in antiferromagnetic materials with multiple ionic species.

Controlling Spin Orientation and Metamagnetic Transitions in Anisotropic van der Waals Antiferromagnet CrPS4 by Hydrostatic Pressure

AbstractControlling the phases of matter is a central task in condensed matter physics and materials science. In 2D magnets, manipulating spin orientation is of great significance in the context of the Mermin–Wagner theorem. Herein, a systematic study of temperature‐ and pressure‐dependent magnetic properties up to 1 GPa in van der Waals CrPS4 is reported. Owing to the temperature‐dependent change of the magnetic anisotropy energy, the material undergoes a first‐order spin reorientation transition with magnetic moments realigning from being almost parallel with the c axis in the ac plane to the quasi‐1D chains of CrS6 octahedra along the b axis upon heating. The spin reorientation temperature is suppressed after applying pressure, shifting the high‐temperature phase to lower temperatures with the emergence of spin‐flop transitions under magnetic fields applied along the b axis. The saturation field increases with pressure, indicating the enhancement of interlayer antiferromagnetic coupling. However, the Néel temperature is slightly reduced, which is ascribed to the suppression of intralayer ferromagnetic coupling. The work demonstrates the control of spin orientation and metamagnetic transitions in layered antiferromagnets, which may provide new perspectives for exploring 2D magnetism and related spintronic devices.

Altering magnetic and optical features of rare earth orthoferrite LuFeO3 ceramics via substitution of Ir into Fe sites

LuFeO3 and LuFe1-xIrxO3 ceramics with x ​= ​0.05 and 0.10 have been obtained by solid-state reaction process. Scanning electron microscope (SEM) analyses have revealed the existence of both particle agglomeration and porosity of nature of the studied samples. The X-ray photoelectron spectroscopy (XPS) investigations have revealed that while Lu has 3+, Fe has mix valence states, 2+ and 3+. On the other hand, the Ir dopant has metallic and 4+ valence states in the study samples. The Raman investigations unveiled i) the Raman peak intensity reduces with Ir doping until ∼600 ​cm−1, ii) the peaks appearing between 200 ​cm−1 and 600 ​cm−1 wavenumbers shift toward the smaller values. Magnetic measurements, conducted by vibrating sample magnetometer (VSM), have shown the spin re-orientation (SR) transition temperature around 47 ​K for all the investigated samples. Furthermore, it is noticed the 5 ​mol % Ir doped sample has higher magnetization than other samples owing to existence of magnetic impurities such as Lu3Fe5O12. M ​− ​H loops have unveiled that Ir doping advances both Hc and Mr values compared to the undoped LFO sample. This increase in both Hc and Mr values could be due to 1) the variation of the canted angels of Fe3+ moments, 2) the advancement of energy of magnetocrystalline anisotropy, and 3) formation of secondary phases such as Lu3Fe5O12 and Fe3O4. Furthermore, the optical band gap examinations have revealed that the band gap of LFO reduces from 2.19 ​eV to 2.

Competing magnetic interactions and magnetocaloric effect in Ho5Sn3

The rare-earth intermetallic compound Ho5Sn3 demonstrates fascinating magnetic properties, which include temperature-driven multiple magnetic transitions and field-driven metamagnetism. We address the magnetic character of this exciting compound through a combined experimental and theoretical studies. Ho5Sn3 orders antiferromagnetically below 28 K, and shows further spin reorientation transitions at 16 K and 12 K. We observe a sizable amount of low-temperature magnetocaloric effect (MEC) in Ho5Sn3 with a maximum value of entropy change ΔS = −9.5 J Kg−1 K−1 for an applied field of H = 50 kOe at around 30 K. The field hysteresis is almost zero above 15 K where the MEC is important. Interestingly, ΔS is found to change its sign from positive to negative as the temperature is increased above about 8 K, which can be linked to the multiple spin reorientation transitions. The signature of the metamagnetism is visible in the ΔS versus H plot. The magnetic ground state, obtained from the density functional theory based calculation, is susceptible to the effective Coulomb interaction (U eff) between electrons. Depending upon the value of U eff, the ground state can be ferromagnetic or antiferromagnetic. The compound shows large relaxation (14% change in magnetisation in 60 min) in the field cooled state with a logarithmic time variation, which may be connected to the competing magnetic correlations observed in our theoretical calculations. The competing magnetic ground states are equally evident from the small value of the paramagnetic Curie–Weiss temperature.

Thermal Stability, Blocking Regime and Superparamagnetic Behavior in Mn-Al-C Melt Spun Ribbons.

Alloys possessing nominal compositions Mn53Al45C2 and Mn52Al46C2 were prepared by the melt spinning method and were subjected to complex structural, morphological and magnetic investigations. As these alloys can exhibit tetragonal L10-type and τ phase, they have good potential as rare earth (RE)—free magnets. It is, therefore, important to monitor the ε–τ phase transformation and the stability and the magnetic features of the tetragonal phase in an entire temperature interval. By using synchrotron X-ray diffraction, it has been proven that the ε–τ phase transformation occurs gradually, with the τ phase becoming predominant only after 450 °C. Moreover, this phase has been proven to be quite stable without any grain growth even at the highest temperature investigated at 800 °C. Low temperature behavior was thoroughly investigated by using a complex combination of major and minor hysteresis loops combined with the zero field cooled-field cooled magnetization protocols (ZFC-FC). Two different regimes, blocking and superparamagnetic, were documented. A spin reorientation transition was proven to occur at 55 K while a maximum magnetization observed in ZFC-FC curves proved that at about 75 K, a transition from ferro to superparamagnetic state occurs. The existence of a blocking regime below 55 K that is characteristic to nanogranular systems with superparamagnetic behavior has shown further development towards obtaining RE-free magnets.

Large magnetization jumps in Ca-doped bismuth ferromanganite

Magnetic properties of the phase-separated (antiferromagnetic + glassy) Bi0·85Ca0·15Fe0·6Mn0·4O3 multiferroic have been studied over a wide temperature range. It has been found that the material exhibits a metamagnetic transition (shifting toward smaller fields with decreasing temperature) which is accompanied by the magnetization jumps whose value (up to ∼4 emu/g at T = 2 K) far exceeds that characteristic of the field-driven transformation from the cycloidal to the canted antiferromagnetic order in the pure BiFeO3. The metamagnetic behavior can be explained as originating from the spin-reorientation transition in the long range-ordered antiferromagnetic phase and involving magnetic moments from the glassy-like phase. The obtained results shed new light on the conditions favoring the coexistence of large switchable magnetization and spontaneous electric polarization in BiFeO3-based multiferroics.

Magnetothermal properties of [formula omitted] (x = 0, 0.05, 0.10, 0.15, 0.25 and 0.50) compounds

Magnetic and magnetocaloric properties of Ho1-xDyxAl2 compounds with x=0,0.05,0.10,0.15,0.25 and 0.50, modelled using a Hamiltonian that includes the exchange interactions between Ho-Dy, Ho-Ho and Dy-Dy ions in addition to the crystalline electric field and the Zeeman effects, have been compared with those determined experimentally. In order to reproduce experimentally observed global ferromagnetic ordering temperatures and spin reorientation transition temperatures as xDy varies, the exchange interactions between Ho-Dy and Ho-Ho were set as free parameters and adjusted to match the experimental results. We demonstrate that heat capacity of polycrystalline materials in non-zero magnetic fields can be satisfactory reproduced by using the average of multiple magnetic field directions with respect to the crystallographic coordinate system, while reasonably good agreement between experimentally determined and theoretically predicted magnetocaloric effects can be achieved considering an average of only three field directions.

Spin dynamics in bulk MnNiGa and Mn1.4Pt0.9Pd0.1Sn investigated by muon spin relaxation

We report the results of muon-spin relaxation and magnetometry investigations of bulk ${\mathrm{Mn}}_{1.4}{\mathrm{Pt}}_{0.9}{\mathrm{Pd}}_{0.1}\mathrm{Sn}$ and MnNiGa, two materials that have been proposed to host topological magnetic states in thin lamellae (antiskyrmions for ${\mathrm{Mn}}_{1.4}{\mathrm{Pt}}_{0.9}{\mathrm{Pd}}_{0.1}\mathrm{Sn}$ and biskyrmions for MnNiGa), and show spin reorientation transitions in the bulk. Our measurements reveal dynamic fluctuations surrounding the magnetic phase transitions in each material. In particular, we demonstrate that the behavior approaching the higher-temperature transitions reflects a decrease in the frequency of dynamics with increasing temperature. At low temperatures the two systems both show spin dynamics over a broad range of frequencies that persist below the respective spin reorientation transitions.

Field-free topological behavior in the magnetic domain wall of ferrimagnetic GdFeCo

Exploring and controlling topological textures such as merons and skyrmions has attracted enormous interests from the perspective of fundamental research and spintronic applications. It has been predicted theoretically and proved experimentally that the lattice form of topological meron-skyrmion transformation can be realized with the requirement of external magnetic fields in chiral ferromagnets. However, such topological transition behavior has yet to be verified in other materials. Here, we report real-space observation of magnetic topology transformation between meron pairs and skyrmions in the localized domain wall of ferrimagnetic GdFeCo films without the need of magnetic fields. The topological transformation in the domain wall of ferrimagnet is introduced by temperature-induced spin reorientation transition (SRT) and the underlying mechanism is revealed by micromagnetic simulations. The convenient electric-controlling topology transformation and driving motion along the confined domain wall is further anticipated, which will enable advanced application in magnetic devices.

Multiferroic properties in [formula omitted] ceramics

The effect of Er3+ substitution on the physical properties of SmFeO3 was studied through magnetic and electrical measurements. The X-ray diffraction patterns of Sm1-xErxFeO3 samples showed that the lattice constants decrease with increasing Er content. As a result, the distortion of Er -doped SmFeO3became significant. The magnetic hysteresis loops of samples indicate that the antiferromagnetic trend increases with Er concentration. The anomaly in Ac susceptibility (χ) and dielectric constant curves for Sm1-xErxFeO3 provided evidence for occurring spin reorientation transition (SRT) in these compounds and are also observed the gradual decrease in SR temperature with increasing Er3+ions. Furthermore, the electrical measurements exhibited a considerable enhancement in the dielectric constant. Sm0.3Er0.7FeO3 is the only compound that presented a colossal dielectric constant (CDC) (103) at room temperature which is attributed to relaxor-ferroelectrics. Likewise, the appearance of magnetic and ferroelectric hysteresis loops indicated the coexistence of magnetism and ferroelectricity.

Ultrafast Control of Magnetic Anisotropy by Resonant Excitation of 4f Electrons and Phonons in Sm0.7Er0.3FeO3

We compare the ultrafast dynamics of the spin reorientation transition in the orthoferrite ${\mathrm{Sm}}_{0.7}{\mathrm{Er}}_{0.3}{\mathrm{FeO}}_{3}$ following two different pumping mechanisms. Intense few-cycle pulses in the midinfrared selectively excite either the $f\text{\ensuremath{-}}f$ electronic transition of ${\mathrm{Sm}}^{3+}$ or optical phonons. With phonon pumping, a finite time delay exists for the spin reorientation, reflecting the energy transfer between the lattice and $4f$ system. In contrast, an instantaneous response is found for resonant $f\text{\ensuremath{-}}f$ excitation. This suggests that $4f$ electronic pumping can directly alter the magnetic anisotropy due to the modification of $4f\text{\ensuremath{-}}3d$ exchange at femtosecond timescales, without involving lattice thermalization.