Spin Reorientation Temperature Research Articles

Intrinsic magnetism and practical potential of 2:14:1-type magnet with rare earth supplied only by misch-metal

2:14:1-type rare earth (R) permanent magnet R2Fe14B, as a functional material, plays an indispensable role in transportation, machinery, energy and other fields. Under the pressure of resources, cost and environment, special attention has been devoted to magnets replaced by high-abundance rare earth. But until now, 2:14:1 phase containing only misch-metal (MM) is not considered suitable for practical production. In this work, from the perspective of intrinsic properties, it is confirmed for the first time that MM2Fe14B with MM (La, Ce and other high-abundance rare earth content as high as 80%) has the potential to become a permanent material. The saturation magnetization Ms at 300 K is 27.36 μB/f.u, and the anisotropy parameters are μ0Ha = 4.2 T, K1 = 1.39 MJ/m3 and K2 = 0.42 MJ/m3. We noted that the temperature dependence of Ms, K1 and K2 are very similar to Nd2Fe14B. Curie temperature TC and spin reorientation temperature Tsr of MM2Fe14B are 488 K and 74 K, respectively. When the temperature is lower than Tsr, the anisotropy changes from easy-uniaxial to easy-cone. The spin reorientation angle θs is about 18° at 4.2 K, less than Nd2Fe14B. Small θs means that strong uniaxial anisotropy can be maintained, which is important to achieve high-performance. Micromagnetic simulation was also introduced to confirm the effect of θs and grain boundary on MM-Fe-B performance. The intrinsic magnetism not only provides strong evidence for the practicability of MM-Fe-B, but also of great significance for further study on the mechanism of rare earth magnets with high-performance and high-abundance.

Near room temperature hexagonal multiferroic (Yb0.25Lu0.25In0.25Sc0.25)FeO3 high-entropy ceramics

In this work, h-RFeO3 multiferroic high-entropy ceramics are designed by introducing high-entropy concept with four elements (Yb, Lu, In, Sc) for R site. (Yb0.25Lu0.25In0.25Sc0.25)FeO3 high-entropy ceramics are prepared by the standard solid-state reaction methods. The samples prepared with precursors were identified to crystalize in the pure hexagonal structure with polar space group (P63cm) at room temperature. By the analysis of the variable XRD patterns, it is speculated that the ferroelectric transition temperature of the sample is above 773 K. Meanwhile, three magnetic anomalies are determined for high-entropy ceramics, which is the antiferromagnetic transition at Néel temperature TÑ280 K, the spin-reorientation temperature TSR∼145 K and the reasonable ferromagnetic-like clusters without long ordering in TN < T < TA (∼397 K). Besides, it is observed that the peak intensity of the pyroelectric current around TN can be tuned by magnetic field, which is indicated the magnetoelectric coupling effect in (Yb0.25Lu0.25In0.25Sc0.25)FeO3 high-entropy ceramics. These results indicate the ferroelectric and antiferromagnetic orders are coexist in the h-RFeO3 high-entropy ceramics as promising near room temperature multiferroic materials, and it is an effective way to obtain a new type single-phase multiferroic materials.

Tunable magnetic phase transition in thulium–samarium orthoferrite single crystals

Spintronics and condensed matter physics are in pursuit of materials that can serve as carriers for novel quantum devices. Antiferromagnetic rare earth orthoferrites (RFeO3, where R is rare earth or Y), are potential functional materials for magnetic information processing. They exhibit temperature-controlled spin reorientation transition (SRT) and magnetic field/temperature-induced spin switching (SSW) properties. As such, RFeO3 is expected to be used in spintronic devices that can easily control the spin. With the advancement of research, the co-doping of rare earth ions has emerged as a prominent area of investigation in RFeO3. In this work, we have grown a series of Tm1-xSmxFeO3 (TSFO, x = 0, 0.2, 0.3, 0.4) single crystals via a four-mirror optical floating zone furnace. Crystal axes and single phase of these single crystals were determined using Laue back reflection camera and X-ray diffractometer. We observed that the doping of Sm ions can effectively regulate the spin reorientation temperature of the parent material TmFeO3. Both type-I and type-II SSW have been observed when the doping rate x is 0.2 or 0.4, perfectly integrating the magnetic properties of TmFeO3 and SmFeO3 single crystals. Furthermore, the spin switching in TSFO (x = 0.2, 0.3, 0.4) can be manipulated by applying low magnetic fields with tens of Oe. On the other hand, when the doping rate x reaches 0.4, the magnetic compensation phenomenon and the Néer temperature of rare earth ions occurred. The super-exchange interaction between R3+ and Fe3+ magnetic sublattices leads to these interesting phenomena.

Bipolar magnetic switching and large exchange-bias in Fe-substituted SmCrO3

Rare-earth orthochromite is an interesting system in the view of its complex magnetic ordering due to competing interaction between different magnetic ions. Here, Fe-substituted SmCrO3 samples were prepared by solid-state route to investigate their intriguing magnetic properties towards exploring its application potential. The magnetic studies revealed antiferromagnetic (AFM) ordering at Nèel temperature (T N) ∼ 181 K, magnetic compensation temperatures (T COMP) at ∼137 K and 50 K, and spin-reorientation temperature (T SR) at 64 K in SmCr0.8Fe0.2O3 sample. Additionally, the system exhibited negative magnetization under field-cooled conditions which allowed the field as well as temperature controllable magnetization switching behavior. Notably, the Fe-substituted SmCrO3 sample displayed a remarkable exchange bias (H EB) value of ∼1.39 T at 10 K due to the coexistence of ferromagnetic and AFM ordering at different cationic sites. The M–H loops recorded under positive and negative field-cooled conditions ruled out the minor-loop effect. Theoretical models applied on the training effect studies confirmed the observed exchange-bias effect.

Structure and stripe domain of melt-spun HoMn6Sn6-xGax ribbons

Topological magnetic skyrmions are expected to become a new generation of information carrier units, and exploring new magnetic skyrmion host materials and their magnetic domain structures is critical. This paper prepared HoMn6Sn6-xGax ribbons by melt-spinning and annealing and studied the effects of the second phase and doping Ga on the structure and magnetic domain of the ribbons. The results show that doped Ga only replaces the Sn sites in the HoMn6Sn6 phase, and the maximum substitution rate of Ga in the HoMn6Sn6 phase is close to 1/6. The unequal substitution of crystal positions causes the lattice to bear considerable compressive stress and negative strain. With an increase in doped Ga content, the lattice constant and cell volume of the HoMn6Sn6-xGax phase gradually decrease, and the substitution positions also change from mainly occupying Sn(2c) sites to occupying Sn(2e) and Sn(2d) sites simultaneously. Doping Ga enhances the preferential orientation in the grains, Ga occupying Sn(2d) sites enhances 〈009〉 orientation, and occupying Sn(2e) sites contributes to the enhancement in 〈204〉 orientation. Whether doped with Ga or not, the ribbons have stable stripe domains with HoMn6Sn6 structure. Increasing Ga content from x = 0.3 to x = 1.6 decreases the spin reorientation temperature, Curie temperatures, and the difference between the two temperatures.

Influence of Mn content on the magnetic properties of the hexagonal Mn(Co,Ge)2 phase

Herein, we report on the effect of Mn content on the magnetic properties of the hexagonal Mn(Co,Ge)2 with composition Mn36+xCo49-xGe15.This compound was previously described as Mn2Co3Ge (MgZn2-type structure), but later as Mn(Co,Ge)2 with its own structure type, all samples in this work follow the same superstructure model. Samples were synthesized by induction melting, the crystal structures were evaluated using a combination of X-ray diffraction together with scanning electron microscopy equipped and an energy dispersive X-ray spectroscopy detector. The Curie temperature (TC) is shifted towards lower temperature as the Mn content is increased. On the other hand, the spin reorientation temperature (TSRT) increases and the magnetic moment decreases as the Mn content is increased. The magnetocaloric properties were investigated for the x=1 alloy, Mn37Co48Ge15. It was found that the isothermal entropy change is 2 J kg−1 K−1 at room temperature for an applied field of 5 T.

Investigation of spin reorientation and magnetocaloric behavior in PrCo[formula omitted]Cu[formula omitted] compounds

In the present work, we have studied the structural and magnetic properties of the compounds PrCo2Cu3, PrCo2.5Cu2.5 and PrCo3Cu2 as well as their spin reorientation transition and magnetocaloric behavior. All three compounds crystallize in the hexagonal CaCu5-type structure. The lattice parameters increase when copper replaces cobalt. The temperature dependence of the magnetization has been determined at low and high temperatures. It revealed that the Curie temperature decreases from ∼ 1000 K to 310 K after the substitution of cobalt by copper (PrCo2Cu3). For the copper-rich compound, a merging of the transition from the planar ferromagnetic state to the axial ferromagnetic one and the transition from the ferromagnetic state to the paramagnetic one is observed. A constant entropy variation is observed over a wide temperature range centered around room temperature. It results from the merging of the entropy measured around the spin reorientation temperature and that measured around Curie temperature.

Tuning the spin-reorientation towards room temperature and the evidence for spin-phonon coupling in modified SmFeO3

The spin-reorientation phenomenon exhibited by rare-earth based ferrite systems generate lot of interest due to its application potential in related fields like spintronic devices. In this work, it was demonstrated that the spin-reorientation temperature (TSR) of SmFeO3 was tuned towards near room temperature by Cr doping. The SmFe1-xCrxO3 (x = 0.0, 0.1, 0.3 and 0.4) samples were prepared by solid state reaction method and the structural refinements carried out on the x-ray diffraction patterns revealed that the samples were crystallized in orthorhombic structure with Pbnm space group. The magnetic measurements displayed that the samples were all ordered antiferromagnetically and the ordering temperature (TN) shows decreasing trend with increase in Cr doping. Furthermore, TSR was tuned from 472 K to 317 K when the composition was changed from x = 0.0 to x = 0.4. The temperature-dependent Raman spectroscopic studies on x = 0.4 sample revealed the existence of the spin-phonon coupling. In addition, this sample also displayed an interesting negative magnetization and compensation temperature. The details are discussed in this work.

Insight into the intrinsic magnetic properties of dual-main-phase Ce magnets through Ce chemical state

The dual-main-phase (DMP) Ce magnet with isostructural heterogenous Ce-rich and Nd-rich main phase contributes remarkably to balance the utilization of high-abundance rare earths and the performance. The intrinsic magnetic properties and Ce chemical state of DMP magnets are still a gap. In this work, we prepared a series of DMP (Nd1-xCex)30FebalAl0.1Cu0.1B1 magnets and systematically investigated the intrinsic magnetic properties for the first time through the chemical states of Ce elements. The XRD crystal structure analysis shows that the lattice parameters of the DMP Ce magnets do not vary monotonically with increasing Ce content, which is correlated with the chemical state of the Ce elements and demonstrated by XPS analysis. The results of the thermal expansion properties further demonstrate that the spin reorientation is only a change in the magnetic structure and is not accompanied by a contraction of the lattice. In addition, the application temperature window is broadened by regulating the spin reorientation temperature, contributing to the understanding of the regulation mechanism of the intrinsic magnetic property of DMP Ce magnets.

Combined pressure and magnetic field induced caloric effects in Fe7Se8 single crystals doped with Ni and Co ions

The influence of Co and Ni ion doping on the crystal structure, phase transitions, and magnetic properties of the Fe7Se8 system has been investigated. The compounds studied are (Fe0.987Ni0.013)7Se8, (Fe0.955Ni0.045)7Se8, (Fe0.915Ni0.085)7Se8, (Fe0.89Ni0.11)7Se8, (Fe0.79Ni0.21)7Se8, (Fe0.975Co0.025)7Se8, (Fe0.951Co0.049)7Se8, and (Fe0.91Co0.09)7Se8 as well as the parent compound Fe7Se8. The crystals are grown using a modified Bridgman method and exist as a hexagonal NiAs-like structure with an ordered distribution of Fe vacancies that determine their magnetic properties. The substitution effect, inducing a systematic decrease in the unit-cell volume due to the ionic radii of doping ions being smaller than the radii of Fe2+ ions, is a source of chemical pressure, acting on the magnetic subsystem and determining the magnetic ordering temperature TC and the spin-reorientation temperature (TSRT). As the most important result of this paper, it was shown that hydrostatic and chemical pressures are strongly correlated in the investigated system. The character of magnetic phase transitions has been designated in the vicinity of TC and TSRT temperatures, and the magnetic entropy change ΔSm and refrigeration potential magnitudes have been determined for this temperature range. These magnetocaloric parameters were shown to depend strongly on chemical pressure. A phenomenological model developed based on the experimental measurements demonstrated that the magnetic properties of the system depend strongly on the crystal field acting on Fe2+ ions and the ratio of the numbers of Fe2+ and Fe3+ ions.

Correlation between linear magnetostriction and magnetocaloric effect in the Fe7Se8 single crystals

The effect of the change in size under the influence of an applied magnetic field (magnetostriction) was studied in Fe7Se8 single crystals. It was shown that a systematic change in the unit-cell constants, induced by an external magnetic field and dependent on the direction and magnitude of this field, strongly correlates with the change in the spin reorientation temperature (T SRT) and the magnetic entropy change, which is strongly dependent on T SRT and magnetization. The obtained results suggest that the relation between magnetostriction and the change in magnetic entropy (ΔS m), reported previously for different materials, seems to have universal character, and magnetostriction can be used as an indirect method to estimate the change in magnetic entropy in Fe7Se8 single crystals substituted with transition metals.

Magnetic and structural properties of the Fe5Si1-xGexB2 system

A series of compounds with compositions Fe5Si1-xGexB2 were synthesised and their structural and magnetic properties were investigated. The Mo5SiB2-type structure with tetragonal I4/mcm space group is maintained for all compounds with x<0.15, which is estimated as the compositional limit of the system. The unit cell parameters expand with Ge content before reaching a plateau of a ​= ​5.5581(1) and c ​= ​10.3545(1) Å at x=0.15. The saturation magnetisation (MS) decreased slightly with increasing Ge content whilst the magnetocrystalline anisotropy energy (MAE) remains almost unaffected. The Curie temperature for all compounds studied is at 790 ​K whilst the spin-reorientation temperature shows suppression from 172 ​K to 101 ​K where x=0.15. Ab Initio calculations reveal an increase in MAE for compositions up to x= 0.25 and a decreased magnitude of MAE of −0.14 ​MJ/m3 for the hypothetical compound Fe5GeB2 relative to the parent compound Fe5SiB2.

Spin switching in room temperature spin reorientation transition process of Sm0.8Yb0.2FeO3 single crystal

We report that the introduction of a certain proportion of Yb ions into SmFeO3 single crystal can modulate the reduction of the spin reorientation (SR) transition temperature down to the room temperature region. Simultaneously, it maintains the spin configuration change between Γ2 (Cy, Gz, Fx) and Γ4 (Gx, Ay, Fz) and raises the magnetization compensation temperature of the single crystal. Both Zero-Field-Cooling (ZFC) and Field-Cooled-Cooling (FCC) modes along the a-axis are present with two type-I spin switching effects, which can be effectively regulated by the applied magnetic field. Interestingly, the type-II spin switching effect is observable along the c-axis in the ZFC mode under lower magnetic fields during the SR transition process at room temperature, an interesting magnetization phenomenon that is suppressed when the magnetic field is greater than 38 Oe. This type of spin switching effect arises from a partial flip of the moments of Sm3+. Additionally, the sharp spin switching induced by the magnetic field is also observed along the a- and c-axes with the variation of the magnetization with the applied magnetic field (M-H). This work is valuable for providing an insight into the magnetic coupling and competition between the two sublattices in the RFeO3 system and for facilitating the practical application of relevant spin switching materials.

Structural and magnetic properties of DyCrO3

In this contribution, the structural and magnetic properties of DyCrO3 are studied, along with the magnetocaloric effect in this compound. The susceptibility as a function of temperature, χ(T), indicates that DyCrO3 has a G-type antiferromagnetic behaviour with weak ferromagnetism below Néel temperature, TNCr, at 147.1 ± 0.1 K, attributed to the ordering of Cr moments. The Dy moments orders antiferromagnetically below the spin reorientation temperature TSR = 4.81 ± 0.04 K. The dependence of magnetization on the applied magnetic field, Mμ0H, shows a behaviour that corresponds to the χ(T) data. Arrott plots reflect the various magnetic orderings with a change in the gradient of the curves. For the first time, the magnetocaloric effect of sol-gel synthesized DyCrO3 is studied having an average particle size 215 ± 3 nm as obtained from transmission electron microscopy (TEM). Large magnetocaloric effects (MCE) are observed in the temperature range of 10 to 80 K for DyCrO3. The compound shows a relatively large magnetic entropy change (ΔSM) of 21 J.Kg−1.K−1 and relative cooling power (RCP) of 498 J.Kg−1 at 7 T and 10 K. Assuming the relations |ΔSmT,H|=a(H)n and RCP=CH1+1δ, with critical exponents n = 1 and δ → ∞ were obtained from the linearization, confirming the weak ferromagnetic behaviour.

Magnetic, dielectric and structural properties of nanocrystalline Lu1−xHoxFeO3 orthoferrite solid solutions

This work reports on the magnetic, dielectric and structural properties of the nanocrystalline Lu1-xHoxFeO3 (x = 0.0 – 1.0) solid solutions. Ho substitution at the Lu site increases the ground state magnetic moment from 0.245(1) μB per f.u. at x = 0.0 to 4.7 μB per f.u. at x = 1.0. The spin reorientation temperature, TSR, and compensation temperarure, Tcomp, increase with x as ~x2 whereas the Néel temperature, TN, increases as ~x0.4. The variations with x of the ‘field-cooled’ (FC) magnetization, MFC(T=3K,H=100Oe) and the magnetocrystalline anisotropy constant, K1(T=3K), assert that the percolation of the Ho3+ moments and single-ion magnetic anisotropy on the Ho3+ sub-lattices occurs above the threshold concentration of xc≈0.05, which is the minimum Ho concentration for the stabilization of orthorhombic structure in the nanocrystalline Lu1-xHoxFeO3 orthoferrites. A striking similarity between the functional dependences on x of the coercive field, HC, and the magnetocrystalline anisotropy field, HK=2K1/Msat (Msat is the satutation magnetization), indicates that the magnetocrystalline anisotropy on the Ho3+ sub-lattices essentially governs HC(x) at 3 K. Several experimental observations, that firmly support type II multiferroicity in nanocrystalline Lu1-xHoxFeO3, are presented.

Spin Switching in Room Temperature Spin Reorientation Transition Process of Sm0.8yb0.2feo3 Single Crystal

Spin Switching in Room Temperature Spin Reorientation Transition Process of Sm0.8yb0.2feo3 Single Crystal

Retaining the Curie temperature of Ce substituted Nd-Fe-B nano-ribbons by Alnico elements substitution

A balanced consumption of the rare earth resources can be realized by increasing the content of Ce in Nd-Fe-B magnetic alloys. However, the substitution of Ce for Nd reduces the magnetic properties and the Curie temperature of the 2:14:1 phase resulting in limited application fields. In this manuscript, targeting to increase the Curie temperature by maintaining the magnetic properties at acceptably high level, Fe in 25% Ce substituted Nd-Ce-Fe-B alloys has been substituted by Alnico constituent elements. The Curie temperature of the main phase for 25% Ce substitution (544 K) is enhanced to 589 K by 20% Alnico substitution which is higher than the Curie temperature of the pure Nd2Fe14B compound (⁓585 K). The magnetic properties initially increased as a result of Alnico element substitution, and then slightly decreased. Maximum energy density of 100 kJ/m3 and Curie temperature of 582 K is obtained by substituting 15% Alnico. These properties are comparable to Ce-free Nd-Fe-B melt spun alloys. The working temperature range increased by the increase of Curie temperature and the decrease of spin reorientation temperature. Due to the accumulation of ferromagnetic element, Ni, at the grain boundary and triple junction phases and the refined grains, the short-range exchange interactions among the nanograins increased which helped to obtain high energy density in the alloys.

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.

Structural and optical properties along with magnetization reversal and bipolar switching in CeCr1−xFexO3 (x = 0 and 0.05) nanoparticles

Nano-crystalline, CeCr1−xFexO3 (x = 0 and 0.05) compounds synthesized by a facile nitrate-solution combustion method are crystallized in orthorhombic, Pnma structure. Reitveld refinement of diffraction patterns reveal an expansion of lattice parameter and lattice volume after the substitution of Fe. Structural analysis evidences an increase in distortion in orthorhombic structure due to bending of Cr-O6 octahedra which is a sheer consequence of the lattice expansion. The optical band gap decreases from 2.9 to 2.6 eV due to the increase in particle size and decrease in strain after Fe substitution estimated from Williamson-Hall analysis. Besides the decrease in Neel temperature from 260 to 253 K after Fe incorporation, temperature-dependent magnetization exhibits some peculiar features such as compensation temperature, Tcomp, and spin reorientation temperature, TSR. While TSR enhances from 15 to 30 K, we observe two Tcomp at 13 and 110 K for x = 0.05 in contrast to only one Tcomp at 61 K for the pristine phase. Moreover, we for the first time demonstrate a stable switching behavior of magnetization by varying the external field in the same direction. The increase in Tcomp and TSR along with a decrease in band gap from 2.9 eV to 2.6 eV makes this material suitable for bipolar magnetic switching and photocatalytic applications.