Rare-earth Iron Research Articles

Epitaxial growth of Ho<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub> films with perpendicular magnetic anisotropy and spin transport properties in Ho<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub>/Pt heterostructures

Rare-earth iron garnet films with perpendicular magnetic anisotropy could open new perspectives for spintronics. Holmium iron garnet (Ho<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub>, HoIG) films with thickness ranging from 2 to 100 nm are epitaxially grown on (111) orientated gadolinium gallium garnet single crystal substrate doped with yttrium and scandium (Gd<sub>0.63</sub>Y<sub>2.37</sub>Sc<sub>2</sub>Ga<sub>3</sub>O<sub>12</sub>, GYSGG) by ultra-high vacuum magnetron sputtering. A 3-nm Pt film is further deposited on each of the HoIG films. The magnetic anisotropy and magneto-transport properties of heterostructures at room temperature are investigated. It is shown that the HoIG film as thin as 2 nm (less than two unit cells in thickness) exhibits the ferromagnetic properties at room temperature, and perpendicular magnetic anisotropy is achieved in the 2-60 nm thick films, and a maximum effective perpendicular anisotropy field reaches 350 mT due to the strain induced magnetoelastic anisotropy. The HoIG/Pt heterostructure shows significant anomalous Hall effect (AHE) and appreciable spin-Hall magnetoresistance (SMR) and/or anisotropic magnetoresistance (AMR). Remarkably, the AHE starts to decline gradually when the HoIG thickness is less than 4 nm, but the magnetoresistance decreases rapidly with the HoIG layer becoming less than 7 nm in thickness. The fact that the AHE in the heterostructure is less sensitive to the HoIG thickness suggests that the interface effect is more dominant in the AHE mechanism, whereas the bulk magnetic properties of the HoIG plays a more important role for the observed magnetoresistance. In addition, the spin Seebeck effect decreases exponentially with the decrease of HoIG thickness till the ultrathin limit, which was previously validated in the micrometer-thick YIG/Pt stacks in the frame of thermally excited magnon accumulation and propagation. The present results show that the nanometer HoIG/Pt heterostructure with tunable perpendicular magnetic anisotropy and efficient interfacial spin exchange interaction could be a promising candidate for insulating magnet based spintronic devices.

Effect of calcination temperature on rare earth tailing catalysts for catalytic methane combustion

AbstractBayan Obo tailings are rich in rare earth elements (REEs), iron, and other catalytic active substances. In this study, mine tailings were calcined at different temperatures and tested for the catalytic combustion of low-concentration methane. Upon calcination at 600°C, high catalytic activity was revealed, with 50% CH4 conversion at 587°C (space velocity of 12,000 mL/g h). The physicochemical properties of catalysts were characterized using thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, hydrogen temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). Compared to the raw ore sample, the diffraction peak intensity of Fe2O3 increased post calcination, whereas that of CeCO3F decreased. A porous structure appeared after the catalyst was calcined at 600°C. Additionally, Fe, Ce, Ti, and other metal elements were more highly dispersed on the catalyst surface. H2-TPR results revealed a broadening of the reduction temperature range for the catalyst calcined at 600°C and an increase in the reduction peak. XPS analysis indicated the presence of Ce in the form of Ce3+ and Ce4+ oxidation states and the coexistence of Fe in the form of Fe2+ and Fe3+. Moreover, XPS revealed a higher surface Oads/Olatt ratio. This study provides evidence for the green reuse of Bayan Obo mine tailings in secondary resources.

Cleaner and effective extraction and separation of iron from vanadium slag by carbothermic reduction-chlorination-molten salt electrolysis

In this work, a cleaner and effective method for selective extraction of iron from vanadium slag was developed, including carbothermal reduction of iron from vanadium slag, chlorination of reduced slag, and electrolysis of chlorinated slag. In the reduction process of vanadium slag, the influence of temperature and C/slag mass ratio on the reduction percentage of FeO, V2O3, Cr2O3, MnO and TiO2 were also investigated by isothermal method. Under the optimal process conditions, the reduction percentage of FeO, V2O3, Cr2O3, MnO, and TiO2 in vanadium slag is 38.6% at 1100 °C for 135 min and the metallization ratio of Fe is 85.4%. After carbothermal reduction of vanadium slag, the unreduced iron oxide is chlorinated to obtain FeCl2 and the chlorination rate of unreduced iron oxide is 85.6% at 900 °C for 4 h. In the electrolysis process, the selective electrolysis of iron ions is achieved by controlling the potential of electrolysis to obtain metal Fe (95 wt%) with 0.9 wt% of V and 0.25 wt% of Cr at 1.6 V. This is a new and cleaner method for the selective removal of Fe from vanadium slag. This novel and cleaner process has potential application for processing materials with high Fe content and low content of other valuable elements (Ti, Cr, V, Nb, etc) such as rare earth iron ore, vanadium titanomagnetite ore, and chromite ore.

Finite-temperature properties of rare-earth iron garnets in a magnetic field

An ab initio scheme is developed and used to investigate finite-temperature properties of a prototype of the complex rare-earth iron garnets, namely, $\mathrm{G}{\mathrm{d}}_{3}\mathrm{F}{\mathrm{e}}_{5}{\mathrm{O}}_{12}$ (that is, possessing gadolinium as its rare-earth ion), under applied magnetic fields. It is found that such a system undergoes a field-induced transition at a critical temperature, ${T}_{\mathrm{rev}}$, at which all magnetic ions reverse the direction of their spins. This ${T}_{\mathrm{rev}}$ critical temperature is well seen via a peak in the specific heat versus temperature curve under field and depends on different magnetic fields' magnitude regimes: (1) for fields up to about 20 T, it is field independent, rather sudden, and coincides with the so-called compensation temperature, ${T}_{M}\ensuremath{\sim}286$ K, at which the sum of all local magnetic moments is annihilated; (2) for fields larger than 70 T, there is no more full cancellation of these local magnetic moments for any temperature and ${T}_{\mathrm{rev}}$ is also field independent but now occurs via rotation of the local magnetic moments and at a temperature smaller than the zero-field ${T}_{M}$ by about 100 K; and (3) for intermediate fields ranging between 20 and 70 T, ${T}_{\mathrm{rev}}$ is now field dependent and decreases with the field's magnitude while also being associated with a rotation of these local magnetic moments. Our calculations also highlight the predominant role of the spins of the Gd ions in all these effects.

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

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

Magnetic-Domain-Wall-Induced Electrical Polarization in Rare-Earth Iron Garnet Systems: A First-Principles Study.

First-principles methods are employed to understand the existence of magnetic-domain-wall-induced electric polarization observed in rare-earth iron garnets. In contrast with previous beliefs, it is found that the occurrence of such polarization neither requires the local magnetic moments of the rare-earth ions nor noncollinear magnetism. It can rather be understood as originating from a magnetoelectric effect arising from ferromagnetic interactions between octahedral and tetrahedral Fe ions at the domain walls, and the mechanism behind is found to be a symmetric exchange-striction mechanism.

The Tb-Fe-Ga system at 870 ​K as a representative of rare-earth iron gallides: Crystal structure and magnetic properties

The Tb-Fe-Ga system has been investigated at 870 ​K by X-ray powder, microprobe elemental analyses and magnetic measurements. The existence of the known compounds TbFe6.2-5.5Ga5.8-6.5 (ScFe6Ga6-type), TbFe5.5-4.9Ga6.5-7.1 (ThMn12-type), TbFe2.4-2.2Ga0.6-0.8 (CeNi3-type), Tb4FeGa12 (Y4PdGa12-type) and quasibinary solid solutions Th2Zn17-type Tb2Fe17-10.6Ga0-6.4, PuNi3-type TbFe3-2.73Ga0-0.23 and MgCu2-type TbFe2-1.57Ga0-0.43 has been confirmed, meanwhile new Th2Ni17-type Tb1.85Fe15.2Ga1.8 and AlB2-type TbFe0-0.3Ga2-1.7 were detected at 870 ​K. The appreciable solubility was no observed at the other binary compounds in the Tb-Fe-Ga system. Tb4FeGa12 is pure antiferromagnetic and TbFe0.3Ga1.7 shows mixed field-sensitive ferro-antiferromagnetic ordering. TbFe6.2Ga5.8, TbFe5.5Ga6.5, TbFe2.4Ga0.6, and TbFe1.42Ga0.58 exhibit ferrimagnetic ordering of Tb- and Fe-sublattices, which are soft ferromagnets at room temperature and hard magnets at low temperatures.

Structural, Spectroscopic and Magnetic Study of Nanocrystalline Terbium–Nickel Ferrite by Oxalate Co-Precipitation Method

Rare earth element terbium (Tb3+), nickel (Ni2+) and iron oxide are incorporated ferrites (Ni0.5MTb0.5MFe2MO4/PVP) by the oxalate co-precipitation method. This oxalate helps get free of extra terbium and nickel by binding with iron oxide. XRD declared that the polycrystalline microstructure of synthesized materials. FT-IR spectra noted that the two prestigious vibration band coordination’s at (584–610 cm−1) and (412–422 cm−1) and promoted to an inverse spinel structure. TEM reveals the spherical shape for the Magnetostrictive effect. VSM reveals the super-paramagnetic properties of synthesized mixed ferrite materials. EPR study shows the grain/lattice development of the symmetry/asymmetry nature of ferrite particles. TGA/DSC reveal that the ferrite formation (ferritization) gets completed at a thermal activation temperature (678.84 °C). Such optimized super-paramagnetic nanoparticles could be a good promising candidate for their use in high-frequency applications.

Carbothermal Reduction, Melting Separation, and Structural Analysis of Carbon-bearing Rare Earth Iron Ore Pellets

Carbothermal Reduction, Melting Separation, and Structural Analysis of Carbon-bearing Rare Earth Iron Ore Pellets

Perpendicular magnetic anisotropy and anomalous Hall effect in (YBiLuCa)3(FeGe)5O12 garnet films

Rare-earth iron garnet (RIG) thin films with perpendicular magnetic anisotropy (PMA) property have recently attracted a great deal of attention for spintronic applications. In this paper, thin (YBiLuCa)3(FeGe)5O12 garnet films were prepared on gadolinium gallium garnet (GGG) substrate by liquid phase epitaxial (LPE) method showing large PMA property. Microstructural properties, chemical composition, magnetic and anomalous Hall effect (AHE) properties of the films were discussed in detail. And we found that the PMA property of this kind of films was mainly controlled by stress-induced anisotropy and growth-induced anisotropy, which were mainly affected by growth temperature. As the growth temperature decreased, the films turned from tensile stress to compressive stress, however, the growth-induced anisotropy increased and would further dominant PMA. By analyzing AHE curves, the thinner films were easier to realize magnetization reversal due to the influence of domains width and interface reflection.

High-efficiency simultaneous extraction of rare earth elements and iron from NdFeB waste by oxalic acid leaching

Iron can not be recovered at high value because only rare earth elements are effectively recovered from NdFeB waste via oxidation roasting-hydrochloric acid leaching process. In this study, a new method for leaching NdFeB waste with oxalic acid was developed. The high-efficiency, simultaneous and high-value recovery of rare earth elements and iron was realized to simplify the process and improve the economic benefit. Results of the oxalic acid leaching experiments show that under the optimum leaching conditions at 90 °C for 6 h in the aqueous solution of oxalic acid (2 mol/L) with a liquid–solid ratio of 60 mL/g, the iron leaching efficiency and precipitation rate of rare earth oxalate reach 93.89% and 93.17%, respectively. Rare earth oxalate and Fe(C2O4)33− were left in the residue and the leaching solution, respectively. The leaching mechanism was further analyzed by characterising the leach residues obtained through X-ray powder diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). Results of the leaching kinetics study indicate that the process of oxalic acid leaching follows the shrinking nucleus model, and the leaching kinetics model is controlled by the mixed factors of diffusion and chemical reaction. The leaching residue was calcined at 850 °C for 3 h and then decomposed into rare earth oxide, which can be directly used to prepare rare earth alloy via molten salt electrolysis. For the leaching solution, ferric oxalate solution was reduced using Fe powder to prepare the ferrous oxalate (FeC2O4·2H2O).

Spin reorientation, normal and inverse magnetocaloric effects in heavy rare-earth iron garnets

Experiments for heavy rare-earth iron garnets Ho3Fe5O12 and Er3Fe5O12 show a compensation effect characterized by a near zero magnetization at 134 K and 80 K, respectively. The magnetic entropy change calculated according to the Maxwell's relation is shown to be positive and negative, indicating both normal and inverse magnetocaloric effects exist in the sample. The critical temperature (134 K for Ho3Fe5O12, 80 K for Er3Fe5O12) of the two types of magnetocaloric effect occurs at almost the same temperature as the compensation point. However, the compensation effect is attributed to the multiple exchange interactions among the octahedral sites Fe3+, the tetrahedral sites Fe3+ and the dodecahedral sites R3+, while the reversal of the magnetocaloric effect is originated from the spin reorientation. The maximum magnetic entropy change of the normal magnetocaloric effect is 4.72 J kg−1 K−1 for Ho3Fe5O12 at 34 K and 4.94 J kg−1 K−1 for Er3Fe5O12 at 24 K, respectively. Moreover, all the positive slopes of basic Arrott plots suggest only the second-order phase transition existing in Ho3Fe5O12 and Er3Fe5O12.

Tunable magnetoelastic anisotropy in epitaxial (111) Tm3Fe5O12 thin films

Ferrimagnetic insulators with perpendicular magnetic anisotropy are of particular interest for spintronics due to their ability to mitigate current shunting in spin–orbit torque heterostructures and enable low switching energy, high-density storage magnetic devices. Rare earth iron garnet Tm3Fe5O12 (TmIG) is one such material where prior studies have shown that the negative magnetostriction coefficient and isotropic in-plane tensile strain enable the magnetoelastic anisotropy to overcome the demagnetization energy and stabilize perpendicular magnetic anisotropy. However, the investigation of the tunability of the magnetoelastic anisotropy between thin films that possess perpendicular magnetization and quantification of the magnetoelastic constants has not been reported. Here, we quantify the evolution of magnetic anisotropy in (111)-oriented, epitaxial, 17 nm thick thin films of TmIG using a systematic variation of in-plane epitaxial strain (ranging 0.49%–1.83%) imposed by a suite of commercially available garnet substrates. Within the confines of the imposed strain range and deposition condition, the distortion from cubic symmetry is found to be approximately linear within the in-plane strain. The magnetic anisotropy field can be tuned by a factor of 14 in this strain range. The magnetoelastic anisotropy constant, B2, is found to be approximately constant (∼2500 kJ m−3) and more than 2× larger than the reported bulk value (∼1200 kJ m−3) for a cubic distortion between 90.17° and 90.71°. B2 is found to decrease at cubic distortions of 90.74° and larger. Our results highlight strain engineering, and its limitations, for control of perpendicular magnetic anisotropy.

Application of iron nitride compound as alternative permanent magnet for designing linear generators to harvest oceanic wave energy

Most of the conventional linear generator is constructed with either Alnico (specially AlNiCo-9) or Neodymium iron boron (NdFeB) permanent magnets (PMs) for harvesting oceanic wave energy. Alnico is a composition of aluminium (Al), nickel (Ni), and cobalt (Co) added to iron, which is its major volumetric component. Alnico has a poor magnetic energy product, and NdFeB contains a rare earth element. To overcome this issue, a recently developed rare-earth free iron nitride (Fe16N2) compound-based PM linear generator (PMLG) is proposed in this study as an alternative solution for avoiding rare earth material while obtaining high output power. To the best of authors’ knowledge, newly invented Fe16N2 is not proposed, analysed, and investigated in any electrical generator. In this context, Fe16N2 is proposed in a linear generator as PM for producing adequate magnetic flux. For analysis and testing the performance of the proposed material, a PMLG is designed. The performances are compared for using Fe16N2 and AlNiCo PMs in the same PMLG design for a fair comparison. It is considered that the proposed PMLG is connected to a direct drive power take-off system. Simulation results show that the proposed PMLG having Fe16N2 generates 55% more electrical power than that of using AlNiCo. The voltage, current, magnetic flux linkage, power, and magnetic flux density of the proposed PMLG are investigated extensively and compared with those of AlNiCo. The finite element method is applied in the ANSYS/Maxwell software environment for testing the PMLG with the conventional and the proposed PMs as well as results are presented. The proposed design is also validated with a small laboratory prototype.

Phase Composition and Magnetic Properties of Fast-Quenched Co-Sm-La and Co-Sm-Ce Alloys

The intermetallic compounds of rare-earth metals (REM) and iron triad metals have unique properties that are increasingly exploited in cutting-edge technology both as individual materials and as phase components that give the alloy its desired properties.Of greatest interest are the intermetallic compounds (IMC) of cobalt based on light REMs. Proper processing imbues these compounds with considerable coercivity on the order of 104E. Thus, spinning that is used for the superfast quenching of melts (v=106 K/s) can produce intermetallic compounds in microcrystal state, in which crystals have distorted crystal lattices. In such cases, phases have high coercivity. Experimentally obtained magnetization and coercivity values of fast-quenched alloys (FQA) in the Sm2Co17 plane of Co-Sm-La and Co-Sm-Ce systems are significantly higher than the equilibrium values.

The submicron garnet film with perpendicular magnetic anisotropy prepared by liquid phase epitaxy method

Rare-earth iron garnet thin films with perpendicular magnetic anisotropy (PMA) have recently attracted a great deal of attention for spintronic applications. In this study, magnetic anisotropy of epitaxial garnet films was analyzed theoretically, and (YBiLuCa)3(FeGe)5O12 mono-crystalline films with PMA have been successfully grown with liquid phase epitaxial (LPE) method on Gd3Ga5O12 (GGG) substrates. Microstructural properties, chemical composition and magnetic properties of the epitaxial films were discussed in detail. We found that growth temperatures played a significant role in the uniaxial anisotropy of the epitaxial (YBiLuCa)3(FeGe)5O12 mono-crystalline films. Ferromagnetic resonance linewidth of (YBiLuCa)3(FeGe)5O12 films with thickness of 170 nm was 8.06 Oe@12 GHz, which indicated that the epitaxial (YBiLuCa)3(FeGe)5O12 mono-crystalline films had a great potential application in spintronic devices.

Visualization of stray-field distribution by charged domain-walls in rare-earth substituted iron garnets

Magnetic-optical methods are used to investigate the magnetic microstructure of an epitaxial film of (Lu,Bi) substituted rare earth iron garnet. In particular, we focused our study on a bi-dimensional domain configuration, the Néel spike, which is induced and pinned at defects inside the sample or at its edges. Imaging of magnetic domains and domain-walls is obtained by direct magneto-optical interaction in the sample under study. The visualization of the stray-field distribution that is generated by single domain-walls is achieved by means of magneto-optical imaging with an indicator film. Furthermore, magnetostatic calculations were performed in order to correlate the net magnetic charge of the Néel spike domain and domain-walls with the measured stray-field. It results that the measured magnetic field intensity nearby the Néel spike tip is compatible with a Bloch-to-Néel wall transition.

Thermal nucleation and high-resolution imaging of submicrometer magnetic bubbles in thin thulium iron garnet films with perpendicular anisotropy

Nanometer-thin rare-earth iron garnet films with perpendicular magnetic anisotropy are among the most promising materials for fast and low-energy spintronics applications. Here, the authors demonstrate ultrafast control of intrinsically stabilized submicrometer bubble domains in these materials. By employing powerful x-ray imaging techniques both in transmission and with surface sensitivity, and by combining this with nanosecond electrical pulses and femtosecond laser excitation, they deterministically create, and image, these bubble states $i\phantom{\rule{0}{0ex}}n$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$. The topology, the chirality, and the switching phase diagram of these twisted spin structures are all resolved by direct imaging.

Structural properties, optical, electrical and magnetic behavior of bismuth doped Gd3Fe5O12 prototype garnet

The co-existence of magnetism and semi-conducting property in a material around room temperature has potential for application in the field of spintronics. The rare-earth iron garnets with high Curie temperature can be tuned by doping them with suitable elements to have properties useful for device applications. In this context, the structural, optical, electrical, and magnetic properties of bismuth doped Gd3−xBixFe5O12 (x = 0.05 & 0.09), synthesized from ball milled stoichiometric oxide precursors, are studied. Structural deformation due to doping is not prominent from the Rietveld refinement of X-ray diffractograms. A minimal increase in the band gap is observed with increase in Bi concentration. A shift in the Curie point towards the high temperature region is observed, ascribed to the stabilizing effect of Bi ion on magnetic ordering. The P–E loops show low coercivity dictating their linear capacitive behavior.

Spin–Orbit Torque Switching in Low-Damping Magnetic Insulators: A Micromagnetic Study

Magnetic insulators, in particular, rare-earth iron garnets, have low damping compared to metallic ferromagnetic materials due to lack of conduction electrons. In analogy to spin-transfer-torque devices, the low-damping nature is presumed to be an advantage for spintronic applications. We report that perpendicular magnetic anisotropy material with low damping actually does not favor reliable spin–orbit torque (SOT) switching. Increasing damping, introducing interfacial Dzyaloshinskii–Moriya interactions, or field-like torques may help SOT switching in some cases. Having notches in a nanometer-scale element, which is a more realistic size for practical applications, can also improve switching stability.