Rare-earth Transition-metal Compounds Research Articles

Tunable microstructure and microwave absorption properties of the SmCo5/Sm2Co17 binary-phase magnetic absorbent prepared via a reduction diffusion method

Magnetic materials with highly efficient microwave absorption properties, crucial for dealing with the advanced wireless communications and radar detections, have been garnering significant attentions. Rare-earth transition-metal compounds were researched as the potential candidates but still suffer from the disadvantages of complex powder metallurgy process and low serving frequencies. In this work, the novel magnetic composites consisting of SmCo5 and Sm2Co17 are developed by a reduction diffusion method. The micromorphology and the binary phase ratios of the SmCo5/Sm2Co17 could be easily modulated by simply altering the reactant concentrations. Consequently, an optimum reflection loss of − 50.2 dB and broad absorption bandwidth of 4.95 GHz at a thickness of only 2.0 mm are achieved. The improved microwave absorption properties of the SmCo5/Sm2Co17 binary-phase magnetic absorbents can be attributed to their adjustable magnetic phases and the distinctive flaky particle shape, which greatly enhance microwave absorption capabilities. This work demonstrated a feasible reduction diffusion method and proposed a new strategy of designing binary-phase magnetic materials to achieve high microwave absorption properties.

Noncollinear commensurate antiferromagnetic structure in metallic Pr2PdAl7Ge4

We report the crystal structure, magnetic structure, magnetic properties, electrical- and magnetotransport properties, and heat capacity of the rare-earth transition-metal compound ${\mathrm{Pr}}_{2}{\mathrm{PdAl}}_{7}{\mathrm{Ge}}_{4}$. ${\mathrm{Pr}}_{2}{\mathrm{PdAl}}_{7}{\mathrm{Ge}}_{4}$ crystallizes in the noncentrosymmetric tetragonal structure $P\overline{4}{2}_{1}m$ (No. 113) with unit cell parameters $a=6.0059(3)\phantom{\rule{4pt}{0ex}}\AA{}$ and $c=15.2278(13)\phantom{\rule{4pt}{0ex}}\AA{}$. The N\'eel temperature ${T}_{\mathit{N}}$ of ${\mathrm{Pr}}_{2}{\mathrm{PdAl}}_{7}{\mathrm{Ge}}_{4}$ was determined to be 6 K by the temperature dependences of magnetization, heat capacity, and electrical resistivity. The magnetic-field-induced antiferromagnetic to ferromagnetic transition occurs for magnetic fields $H$ along both the $ab$ plane and the $c$ axis. The electrical resistivity shows a metallic behavior with an upturn at the ordering temperature due to a superzone gap. Negative linear magnetoresistance is observed since the magnetic field increases the order degree of the antiferromagnetic state, reducing the magnetic correlation scattering. Neutron powder diffraction experiments reveal that metallic ${\mathrm{Pr}}_{2}{\mathrm{PdAl}}_{7}{\mathrm{Ge}}_{4}$ has an unusual noncollinear commensurate antiferromagnetic structure with the propagation vector $\mathbit{k}=(0,\phantom{\rule{0.28em}{0ex}}0,\phantom{\rule{0.28em}{0ex}}0.5)$. Magnetic Pr atom layers stack with the ABBA sequence along the $c$ axis. Within the layers, the Pr moments lie in the $ab$ plane, and the angle between the nearest-neighbor spins is $67.{1}^{\ensuremath{\circ}}$. This magnetic structure can well explain the magnetic properties of ${\mathrm{Pr}}_{2}{\mathrm{PdAl}}_{7}{\mathrm{Ge}}_{4}$.

Novel anomalous Hall effect mechanism in ferrimagnetic GdCo alloy

In this work, we shed light on the mechanism behind the complexity of the anomalous Hall effect (AHE) in the rare earth-transition metal (RE-TM) compound. To achieve a comprehensive picture, we first theoretically investigate the pure elemental metals and observe that the AHE of RE Gd is negative while that of TM Co is positive. We then investigate magnetic properties and AHE behavior for two typical cases of TM-rich and RE-rich compositions that correspond to GdCo5 and GdCo3 alloys, respectively. The observation that net magnetization is not a decisive factor in assessing the AHE value is consistent with recent claims. Besides, our investigations reveal a significant role of the Gd sublattice to the AHE. The reduction AHE signal under a high-applied field is attributed to the counteraction between the positive and negative AHC contributions when the TM and RE sub-moments are aligned parallel. On a bright note, our new findings can be successfully employed to unravel two types of aberrant humps of AHE signals near compensation temperature.

Evolution of Compensated Magnetism and Spin-Torque Switching in Ferrimagnetic Fe1−xTbx

Compensated ferrimagnets (FIMs) made of rare-earth transition-metal compounds have stimulated increasing interest for enabling fast spin dynamics. Taking $\mathrm{Fe}$-$\mathrm{Tb}$ compounds as an example, substantial efforts have been made on the study of compensated magnetism and its potential spintronic applications. Current-induced spin-orbit torque (SOT) switching and its evolution with compensated ferrimagnetism in these compounds, however, remain to be systematically explored, which motivates the present study. By combining magnetometry and anomalous Hall effect measurements, a compositional magnetization compensation point (${x}_{c}$ = 0.25) is determined for ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}$ films of a fixed thickness of 6.5 nm. The antiferromagnetic coupling between $\mathrm{Fe}$ and $\mathrm{Tb}$ sublattices is directly revealed by conducting element-specific x-ray magnetic circular dichroism measurements. The evolution of SOT switching as a function of $\mathrm{Tb}$ concentration (x) in $\mathrm{Pt}/{\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}/\mathrm{Ta}$ multilayers is subsequently investigated. An enhanced SOT efficiency (approximately 3 times) is obtained at ${x}_{c}$ = 0.25. By conducting an endurance test, reliable SOT switching is revealed for over ${10}^{4}$ cycles. Our work suggests that compensated FIMs of composition ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}$ could be implemented for realizing efficient and stable spin-orbitronic performances.

A comparative study of the domain wall motion in ferrimagnets (Fe,Co)1-x(Gd,Tb)x.

Magnetic domain walls (DWs) in rare-earth-transition-metal (RE-TM) ferrimagnetic alloys can be used as information carriers in nonvolatile spintronic devices. Due to the rich combinations of RE-TM elements (such as CoGd, FeGd, CoTb, and FeTb in our case), it is intriguing to reveal the characteristics of DW dynamics in these wide choices of RE-TM compounds. Through a systematic study of the DW motion in thin films with different compositions of stacking order Pt(3 nm)/(Fe,Co)1-x(Gd,Tb)x(∼8 nm)/Ta(3 nm), we show that the partially compensated ferrimagnets CoGd and FeGd can exhibit a faster DW motion under various (in-plane and out-of-plane) magnetic fields driven by current-induced spin-orbit torques. In stark contrast with the fast motion of domain walls in Gd-based ferrimagnets, we find that the CoTb system exhibits much slower DW dynamics, and the FeTb system shows no motion, but evolved into a multi-domain state upon applying current pulses. Our results demonstrate that ferrimagnets CoGd and FeGd are more suitable candidates for achieving ultrafast DW motion, which could be useful for developing spintronic memory and logic devices.

Magnetoelastic coupling in DyFe11.4Nb0.6

The structural and magnetic properties of the rare-earth transition metal compound DyFe11.4Nb0.6 have been investigated over its magnetically order state by variable temperature high resolution synchrotron x-ray diffraction (85 K - 650 K) together with ac magnetic susceptibility (10 K - 300 K), DC magnetization (300 K - 600 K) and heat capacity (2 K - 300 K) measurements. The magnetic ordering temperature has been determined to be TC = 538(5) K while with decreasing temperature, two spin reorientations have been detected around Tsr1 = 265(±5 K) and Tsr2 = 140(±5) K. The Debye temperature θD = 412(±10) K derived from the specific heat measurements of DyFe11.4Nb0.6 agrees well with the values reported for related compounds, while the density of states at the Fermi level was found to be N(EF) = 3.8 ev−1 atom−1. Refinements of the synchrotron x-ray diffraction patterns indicate the occurrence of magnetoelastic couplings at all three magnetic transitions, the Curie temperature TC and spin reorientation temperatures Tsr1 and Tsr2. The linear thermal expansion has been determined over the temperature range 85 K - 650 K and substantial magneto-volume effects shown to persist at temperatures up to 596 K, significantly above the Curie temperature. Similarly, the spontaneous volume magnetostriction ωs of DyFe11.4Nb0.6 extends to 1.17 TC, well above the Curie temperature TC = 538(5) K. The spontaneous volume magnetostriction has the value ωs = 1.08 × 10−2 at 85 K. The properties of such materials offer potential for applications in functional structures.

Systematic exploration of magnetic mechanism of La3Co29Si4B10 by first principles calculation

Rare earth transition metal compounds with intrinsic and high-performance magnetic behaviors have been attractively research topic as a promising permanent magnets material. In particularly, La3Co29Si4B10 is one of typically rare earth ferromagnetism materials with large magnetic moment and high transition temperature. In order to investigate the magnetic origin of sublattice and guide the design of permanent magnet materials with high magnetic moment and high magnetic crystalline anisotropy, we adopt first principles calculations method to investigate the magnetic mechanism of La3Co29Si4B10 combine local coordination environment with density of states. The results show that the magnetic moment mainly comes from the Co atom. According to the different local symmetry and atom hybridization, the Co atoms at different crystal positions can be divided into high spin state with maximum local magnetic moment at 2c position, low spin state with minimum magnetic moment at 8i1 position and medium spin state corresponding moderate magnetic moment size at other positions. Furthermore, the strain-stress of La3Co29Si4B10 will increase the total magnetic moment. Spin orbital coupling calculation indicate that the easy magnetization direction of La3Co29Si4B10 is along in plane with magnetic crystalline anisotropy energy of 0.68 meV/unit cell, which agreement with experimental. Our calculations lay a theoretical foundation for further experimental design of high-performance permanent magnet materials.

Anomalous thermal expansion in ErFe11.4Nb0.6

The thermal expansion properties of the rare earth transition metal compound ErFe11.4Nb0.6 (Curie temperature Tc = 520(10) K) have been investigated in detail by variable temperature high resolution synchrotron x-ray diffraction measurements over the temperature range 300 K–640 K. The findings from the Rietveld analyses reveal significant anomalies in the thermal expansion of ErFe11.4Nb0.6 below the Curie temperature with negative thermal expansion also evident around Tc = 520(10) K. The structural changes that occur around the Curie temperature lead to a spontaneous volume magnetostriction of ∼6.3 × 10−3 at 300 K. The minimum values of the linear thermal expansion coefficients αa and αc for ErFe11.4Nb0.6 around TC are determined to be −3.56 × 10−6 K−1 and -1.30 × 10−6 K−1 respectively. Details of the structural features of ErFe11.4Nb0.6 (including Wigner-Seitz cell volumes and average bond lengths for Er atoms (2a site) and Fe atoms (8i, 8j, 8f sites) to neighbouring Fe atoms) that contribute to the thermal expansion behaviour have been investigated in detail. The persistence of finite magnetostriction values λa and λc (along the a-axis and the c-axis respectively) and volume magnetostriction ωs, above the magnetic transition temperature, indicates the likely occurrence of short-range magnetic correlations in this region.

Influence of strain and substitution on magnetocrystalline anisotropy of R2Fe14B (R=Pr, Dy and Y)

Abstract The intermetallic rare earth-transition metal ( R - T ) compound Nd 2 Fe 14 B has a large energy density and is an industrially important permanent magnet material. Its low Curie Temperature ( T C ) though limits its use for electric motor applications. To improve its high temperature permanent magnetic properties, the coercive field ( H C ) should be enhanced, which can be achieved by influencing intrinsic atomistic properties such as saturation magnetization ( M S ) and magnetocrystalline anisotropy energy (MAE). Strain effects and substitution are two important methods for influencing M S and MAE. Using numerical methods based on density functional theory, firstly M S and MAE of three R 2 Fe 14 B compounds with R = P r , D y and Y are calculated at 0 K. Further, the influence of changing the lattice parameter ratio c / a on MAE is studied. For increasing c / a , MAE of Y 2 F e 14 B and Pr 2 F e 14 B remains nearly constant, while MAE of Dy 2 F e 14 B decreases monotonously, up to 40 % per 1 % change in c / a . In the next step, 50 % of the R - atoms are substituted. For Pr 2 F e 14 B , MAE decreases with substitution of Dy and Y ; for Dy 2 F e 14 B it increases with Pr but decreases with Y ; for Y 2 F e 14 B it increases with Pr and Dy . The nucleation field ( H N ) of the substituted phases are estimated for different microstructures and visually compared to the non-substituted compounds, showing a large H N for P r D y F e 14 B . Further, based on DOS plots of the Y - D y F e 14 B system, the contribution of different atoms and atomic sites to MAE is discussed, and by visualizing the electronic density contours, the influence of substitution on Fe - atoms in Dy 2 F e 14 B and D y Y F e 14 B is studied.

Molecular and electronic structure of the dithiooxalato radical ligand stabilised by rare earth coordination.

Heterometallic rare earth transition metal compounds of dithioxalate (dto)2-, [NiII{(dto)LnIIITp2}2] (Ln = Y (1), Gd (2); Tp = hydrotris(pyrazol-1-yl)borate) were synthesised. The Lewis acidic rare earth ions are bound to the dioxolene and chemical reduction of 1 and 2 with cobaltocene yielded [CoCp2]+[NiII{(dto)LnIIITp2}2]˙- Ln = Y (3), Gd (4). The reduction is ligand-based and 3 and 4 are the first examples of both molecular and electronic structural characterisation of the dithiooxalato radical (dto)3˙-.

Spin Density for Intermetallic Compounds

We first performed a pure spin-polarized calculation on Nd2Fe14B using the self-consistent Full Potential Linearized Augmented Plane Wave (FPLAPW). The total charge density and the spin density calculated by taking the sum or the difference of spin-up and spin-down charge densities, respectively. In this paper, we present the spin and charge density contours for rare-earth transition metal compounds e.g. Nd2Fe14B in the (001) and (110) planes using spin-polarized only. The charge density map and the spin density map on the (001) and (110) plane of the tetragonal cell show the evidence for covalent bonding between Fe and B atoms.

The semiquinone radical anion of 1,10-phenanthroline-5,6-dione: synthesis and rare earth coordination chemistry

Reduction of 1,10-phenanthroline-5,6-dione (pd) with CoCpR2 resulted in the first molecular compounds of the pd˙- semi-quinone radical anion, [CoCpR2]+[pd]˙- (R = H, (1); R = Me4, (2)). Furthermore compounds 1 and 2 were reacted with [Y(hfac)3(thf)2] (hfac = 1,1,1-5,5,5-hexafluoroacetylacetonate) to synthesise the rare earth-transition metal heterometallic compounds, [CoCpR2]+[Y(hfac)3(N,N'-pd)]˙- (R = H, (3); R = Me4, (4)).

57 Fe Mössbauer and magnetic studies of Nd3Fe24.5Cr4.5

The structural and magnetic properties of the rare earth transition metal compound Nd 3Fe 24.5Cr 4.5 have been investigated by variable temperature high resolution x-ray diffraction together with DC magnetization and 57Fe Mossbauer effect measurements. The magnetic ordering temperature has been found to be T C= 423(5) K with spin reorientation detected below room temperature around T sr= 158(5) K. Rietveld refinements indicate that Nd 3Fe 24.5Cr 4.5 crystallizes in the Nd 3(Fe,Ti) 29-type structure with the A2/m space group and a substantial magneto-volume effect is detected around T C. The Mossbauer spectra can be fitted well using five sub-spectra. The temperature dependence of the average hyperfine field has been analysed in terms of different power laws of the reduced temperature. The Debye temperature of Nd 3Fe 24.5Cr 4.5 has been determined as 𝜃D= 400(± 30) K from a fit to the variable temperature isomer shift IS(T).

Ultrafast reduction in exchange interaction by a laser pulse: alternative path to femtomagnetism

Since the beginning of femtomagnetism, it has been hotly debated how an ultrafast laser pulse can demagnetize a sample and switch its spins within a few hundred femtoseconds, but no consensus has been reached. In this paper, we propose that an ultrafast reduction in the exchange interaction by a femtosecond laser pulse is mainly responsible for demagnetization and spin switching. The key physics is that the dipole selection rule demands two distinctive electron configurations for the ground and excited states and consequently changes the exchange interaction. Although the exchange interaction change is almost instantaneous, its effect on the spin is delayed by the finite spin wave propagation. Consistent with the experimental observation, the delay becomes longer with a stronger exchange interaction pulse. In spin-frustrated systems, the effect of the exchange interaction change is even more dramatic, where the spin can be directly switched from one direction to the other. Therefore, our theory has the potential to explain the essence of major observations in rare-earth transition metal compounds for the last seven years. Our findings are likely to motivate further research in the quest of the origin of femtomagnetism.

On the R 5d band polarization in rare-earth–transition metal compounds

Magnetic measurements and band structure calculations were performed onRT2 andRT5 compounds, where R is a heavy rare-earth andT = Fe, Co, Ni, Al, as well as on pseudobinary compoundsGdCo2 − xAx (A = Ni, Cu,Si), YFe2 − xVx and YCo4 − xNixB. The calculated moments per formula unit described well the experimentally determinedmagnetizations. By considering the 4f–5d–3d exchange interactions, we evaluate thecontributions of local 4f–5d and short range 5d–3d interactions to R 5d and Y 4d bandpolarizations. The 4f–5d induced polarizations are proportional to the De Gennes factorand are the same for a given R and a similar type structure. The R 5d and Y 4d bandpolarizations induced by R 5d–T3d or Y 4d–T3d hybridizations are proportional to thenumber of neighbouring T atoms, to a given R, and their magnetic moments. Previousresults on the matter are also discussed.

ChemInform Abstract: Structure and Ferromagnetism of the Rare-Earth Zintl Compounds: Yb14MnSb11 and Yb14MnBi11.

Rare-earth transition metal compounds Yb14MnSb11 and Yb14MnBi11 have been prepared by heating stoichiometric amounts of the elements at 1000−1200 °C. These compounds are isostructural with the Zintl compound Ca14AlSb11 and crystallize in the tetragonal space group I41/acd (Z = 8). Single-crystal X-ray data (143 K) were refined for Yb14MnSb11 [a = 16.615(2) A, c = 21.948(4) A, V = 6059(2) A3, and R1/wR2 (0.0299/0.0479)] and Yb14MnBi11 [a = 17.000(3) A, c = 22.259(6) A, V = 6433(2) A3, R1/wR2 (0.0631/0.133)]. Structural analysis is consistent with Yb2+. Temperature-dependent magnetic susceptibility data show that Yb14MnSb11 orders ferromagnetically at 56 K and Yb14MnBi11 has a ferromagnetic transition at 58 K and another transition at 28 K. High-temperature magnetic susceptibility data can be fit with a modified Curie−Weiss law and give μeff = 4.92(2)μB and μeff = 4.9(1)μB for the Sb and Bi compounds, respectively. This result is consistent with the assignment of Mn3+ (d4) and Yb2+ (f 14). Single-crystal ma...

4fcharge-density deformation and magnetostrictive bond strain observed in amorphousTbFe2by x-ray absorption spectroscopy

The giant magnetostriction observed in rare-earth transition-metal compounds such as Terfenol-D (Tb0.3Dy0.7Fe2) is commonly associated with the huge anisotropy of the 4f electron cloud. We report here the experimental observation of this phenomenon at the atomic scale, in amorphous matter. By using extended x-ray absorption fine structure spectroscopy in a differential mode, the bond strains resulting from the coupling between the anisotropic shape of the Tb 4f charge density and the environment crystalline electric field are measured. In a-TbFe2 we measure Fe-Fe and Fe-Tb bond contractions equal to 6(1)x10−4 A and of 9(2) x10−4 A, respectively. These are the smallest atomic displacements ever detected in amorphous matter.

Rare earth–transition metal compound-based MOSLM for the visible spectral range

We have demonstrated a magneto-optical spatial light modulator in which functionality is realized by (i) heating up to Curie temperature ( T c) magneto-optical elements (pixels) with a semiconductor laser and (ii) application of a switching magnetic field. The pixels were made of films of amorphous rare earth–transition metal compounds (TbFe films with T c=403 K and DyFe films with T c=343 K) having good magneto-optical responses for wavelengths from the visible spectral range. We have found that the magnetization direction of pixels can be modulated with a laser radiation density of 5 mJ/cm 2 and in a switching magnetic field of 15 Oe.

Magnetic behavior of binary intermetallic compound YPd 3

We report the results of detailed magnetic studies on binary rare-earth–transition metal compound YPd 3. The results of temperature and magnetic field dependent DC-magnetic measurements along with the results of powder X-ray diffraction measurement and electrical transport have been discussed. The X-ray data suggest a well-defined ordered crystal lattice, free from any detectable impurity phase. Magnetization data exhibits predominant diamagnetic character at higher fields. However, the compound exhibits anomalous behavior at low fields.

Large cryogenic magnetocaloric effect of DyCo2 nanoparticles without encapsulation

The structure and formation of nanoparticles without encapsulation of the intermetallic compound DyCo2 were investigated by using x-ray diffraction and high-resolution transmission electron microscopy. The DyCo2 nanoparticles are stable in air without any shell protection. A large magnetic-entropy change of 13.2Jkg−1K−1 was found at 7.5K in an applied-field change from 1to7T, which is ascribed to the large magnetic moment density and the weak interaction energy in the nanoparticles. Such oxidation-resistant rare-earth transition-metal compound nanoparticles with large cryogenic magnetocaloric effect are useful for refrigeration applications at low temperatures.