Itinerant Electron Metamagnetism Research Articles

Origin of the metamagnetic transitions in Y0.9Tb0.1Fe2D4.3

Deuterium insertion was used to tune the magnetic properties of Y0.9Tb0.1Fe2 Laves phase towards an itinerant electron metamagnetic (IEM) behavior. The latter is highly sensitive to chemical changes and external parameters. The structural and magnetic properties of Y0.9Tb0.1Fe2D4.3 were investigated using various neutron powder diffraction experiments in addition to magnetic measurements under steady and pulsed high magnetic fields up to 60 T. The deuteride crystallizes in a monoclinic structure (Pc space group) with 4.3 D atoms located in 18 tetrahedral interstitial sites. At zero field, it undergoes a ferrimagnetic-antiferromagnetic (FiM-AFM) transition at TM0 = 90 K, accompanied by an anisotropic magnetostriction and a negative cell volume expansion of 0.6%. A second AFM-PM transition is observed at 146 K. Under pulsed magnetic field at 4.2 K, the deuteride displays a multistep magnetic behavior from ferrimagnetic to a ferromagnetic state, which can be attributed to a stepwise rotation of the Tb moments. The ZFC-FC magnetization curves at low fields exhibit an irreversibility below 90 K, followed by a sharp decrease in magnetization at the FM-AFM transition. Between 90 K and 130 K, the magnetization curves display an IEM behavior, with the transition field increasing linearly with temperature.

Hall effect of itinerant electron metamagnet Co(S1-xSex)2

We have studied the Hall effect of Co(S1-xSex)2 with 0.08 ≤ x ≤ 0.14, which shows itinerant electron metamagnetism (IEM). The Hall resistivity ρxy was measured as a function of the magnetic field B at various temperatures. It is found that ρxy decreases nearly linearly with increasing B in the paramagnetic state, while it has a positive slope in the ferromagnetic state. Abrupt drops were observed at around the metamagnetic transition field in the ρxy – B curves, which are attributable to the anomalous Hall effect. From the analyses of the ρxy – B curves and the magnetization curves, we estimated the anomalous Hall coefficient, the normal (ordinary) Hall coefficient in the ferromagnetic state, and that in the paramagnetic state. Appearance of both ferromagnetic and paramagnetic states depending on a magnetic field in IEM makes it possible to estimate these values, simultaneously. The estimated normal Hall coefficients are compared with the theoretical values calculated from the energy band structures. The present study has demonstrated that IEM provides a suitable stage to understand the electronic structures of both ferromagnetic and paramagnetic states of the itinerant electron system at the same temperature.

Effects of the Substitution of 20% Nd for La or Doping with 20% C on the Magnetic Properties and Magnetocaloric Effect in LaFe11.5Si1.5 Compound

The effects of element substitution and element doping on the magnetic properties and magnetocaloric effect of the LaFe11.5Si1.5 compound were investigated. The crystals of the LaFe11.5Si1.5, La0.8Nd0.2Fe11.5Si1.5, and LaFe11.5Si1.5C0.2 compounds all showed cubic NaZn13-type structures, but the lattice of the La0.8Nd0.2Fe11.5Si1.5 shrank and the lattice of the LaFe11.5Si1.5C0.2 expanded. All three compounds had the characteristic of first-order magnetic transition due to the obvious itinerant-electron metamagnetic (IEM) transition occurring above Curie temperature (TC). For the LaFe11.5Si1.5, La0.8Nd0.2Fe11.5Si1.5, and LaFe11.5Si1.5C0.2 compounds, the TC were approximately 194 K, 188 K, and 232 K, respectively. Meanwhile, the maximum magnetic entropy changes (−ΔSM) under a magnetic field change of 0–3 T were approximately 18.7 J/kg·K, 22.8 J/kg·K, and 16.4 J/kg·K, respectively. The TC was mainly affected by the lattice constant. Furthermore, the −ΔSM was mainly affected by the latent heat of the first-order magnetic transition.

Achievement of promising cryogenic magnetocaloric performances in La1-xPrxFe12B6 compounds

The magnetic refrigeration (MR) utilizing magnetocaloric effect (MCE) has been recognized as an environmentally friendly and energy efficiency technology. Here we presented the magnetic properties and MCE in Pr-doped La1-xPrxFe12B6 (x=0.05-0.2) itinerant-electron metamagnetic (IEM) compounds. A small amount of Pr doping La site can greatly improve the peak values in the magnetic entropy change ΔSM(T) curves, especially under relatively low magnetic field changes (ΔH). Additionally, the peak temperature increases gradually and the magnetic hysteresis reduces gradually with increasing x. The observed MCE in present La1-xPrxFe12B6 compounds is related to its field-induced first-ordered IEM transition. The peak values of ΔSM for La1-xPrxFe12B6 compounds reach 13.4, 15.4, 12.5 and 13.0 J/(kg K) at TC ~58, 68, 72 and 89 K for x=0.05, 0.10, 0.15 and 0.2 under ΔH of 0-7 T, respectively. The corresponding relative cooling power values are 462.3, 480.7, 372.4 and 375.7 J/kg. The present La1-xPrxFe12B6 compounds could be good candidates for active MR application if the magnetic and thermal hysteresis can be further reduced. The present work indicates that the LaFe12B6-based material system could also exhibit promising magnetocaloric performances.

Influence of hydrogenation on the vibrational density of states of magnetocaloric LaFe11.4Si1.6H1.6

We report on the impact of magnetoelastic coupling on the magnetocaloric properties of LaFe$_{11.4}$Si$_{1.6}$H$_{1.6}$ in terms of the vibrational density of states, which we determined with $^{57}$Fe nuclear resonant inelastic X-ray scattering measurements and with density-functional-theory based first-principles calculations in the ferromagnetic low-temperature and paramagnetic high-temperature phase. In experiments and calculations, we observe pronounced differences in the shape of the Fe-partial VDOS between non-hydrogenated and hydrogenated samples. This shows that hydrogen does not only shift the temperature of the first-order phase transition, but also affects the elastic response of the Fe-subsystem significantly. In turn, the anomalous redshift of the Fe VDOS, observed by going to the low-volume PM phase, survives hydrogenation. As a consequence, the change in the Fe specific vibrational entropy $\Delta S_\mathrm{lat}$ across the phase transition has the same sign as the magnetic and electronic contribution. DFT calculations show that the same mechanism, which is a consequence of the itinerant electron metamagnetism associated with the Fe subsystem, is effective in both the hydrogenated and he hydrogen-free compounds. Although reduced by 50 % as compared to the hydrogen-free system, the measured change $\Delta S_\mathrm{lat}$ of 3.2\pm1.9 J/kgK across the FM to PM transition contributes with 35 % significantly and cooperatively to the total isothermal entropy change $\Delta S_\mathrm{iso}$. Hydrogenation is observed to induce an overall blueshift of the Fe-VDOS with respect to the H-free compound; this effect, together with the enhanced Debye temperature observed, is a fingerprint of the hardening of the Fe sublattice by hydrogen incorporation. In addition, the mean Debye velocity of sound of LaFe$_{11.4}$Si$_{1.6}$H$_{1.6}$ was determined from the NRIXS and the DFT data.

Corrosion behavior and magnetocaloric effect of FeNi (1J85) coated LaFe11.6Si1.4/Sn composites

The FeNi coated LaFe11.6Si1.4/Sn composites were prepared by hot pressing (HP). The microstructure, corrosion behavior and magnetocaloric effect (MCE) of FeNi coated LaFe11.6Si1.4/Sn composites were investigated systematically. The results show that the corrosion resistance of FeNi coated LaFe11.6Si1.4/Sn composites is better than that of LaFe11.6Si1.4/Sn composites in deionized water. The maximum magnetic entropy change ((–ΔSM)max) and relative cooling power (RCP) of FeNi coated LaFe11.6Si1.4/Sn composites are 13.30 J/(kg·K) and 146.25 J/kg, respectively, which are larger than that ((–ΔSM)max, 10.65 J/(kg·K) and RCP, 106.53 J/kg) of LaFe11.6Si1.4/Sn composites in a low magnetic field change of 2 T. FeNi coated LaFe11.6Si1.4/Sn composites possess a more negative slope. The improvement of magnetic properties is due to high permeability FeNi permalloy (1J85) which improves the itinerant-electron metamagnetic (IEM) transition. So, the method of coating FeNi can provide a new idea for enhancing the corrosion resistance and magnetocaloric effect of La(FexSi1–x)13-based materials.

Exchange interaction in itinerant-electron metamagnetism

Abstract The exchange interaction in itinerant-electron metamagnetism is investigated theoretically. In fact, by considering spin-up and spin-down electrons in an itinerant-electron metamagnetic gas in the presence of an external magnetic field, we show that the difference between the Fermi energies of the spin-up and spin-down electrons equals, up to a multiplicative constant, the absolute value of the matrix element of the Hamiltonian operator relative to the interaction in question. Furthermore, the Stoner formula for the electronic energy of the gas is used to study the size of the exchange interaction.

Element-specific observation of the ferromagnetic ordering process in UCoAl via soft x-ray magnetic circular dichroism

We have performed soft x-ray magnetic circular dichroism (XMCD) experiments on the itinerant-electron metamagnet UCoAl at the U $4d\ensuremath{-}5f({N}_{4,5})$ and Co $2p\ensuremath{-}3d({L}_{2,3})$ absorption edges in order to investigate the magnetic properties of the U $5f$ and Co $3d$ electrons separately. From the line shape of the XMCD spectrum, it is deduced that the orbital magnetic moment of the Co $3d$ electrons is unusually large. Through the systematic temperature $(T)$- and magnetic field $(H)$-dependent XMCD measurements, we have obtained two types of the magnetization curve as a function of $H$ and $T$ (M-H curve and M-T curve, respectively). The metamagnetic transition from a paramagnetic state to a field-induced ferromagnetic state was clearly observed under 15 K at ${H}_{\mathrm{M}}$. The value of the ${H}_{\mathrm{M}}$ and its $T$ dependence agree well between the U and Co sites, and the bulk magnetization. Whereas, we have discovered the remarkable differences in the M-H and M-T curves between the U and Co sites. The present findings clearly show that the role of the Co $3d$ electrons should be considered more carefully in order to understand the origin of the magnetic ordering in UCoAl.

Structural disorder effects on the magnetic entropy change of DyCo2 intermetallic: Mechanical milling and the weakening of the itinerant electron metamagnetism mechanism

Magnetocaloric properties of the intermetallic DyCo2 compound (in the form of reduced size particles) and its correlations with the itinerant electron metamagnetism (IEM) phenomenon and structural disorders are investigated and discussed. Micrometric-sized particles were prepared by a mechanical milling technique for two low milling times (4 and 8 h) and characterized by means of X-ray diffraction, scanning and high-resolution transmission electron microscopy as well as magnetic measurements as a function of an applied external magnetic field and temperature. The results show that the particles have irregular-shaped and amorphous “edges/ledges” with embedded randomly oriented DyCo2 nanocrystallites. The average particle size practically does not change with increasing milling time, whereas the average crystallite size is slightly diminished. In contrast, microstrain values that indicate lattice deformation degree were rather increased after the milling processes. Structural disorders and surface effects, features resulting from mechanical impact, disturb the Dy-Co sublattice coupling and weaken the IEM mechanism responsible for the high magnetocaloric effect found for the DyCo2 bulk sample. For the milled samples, it was observed reductions in the peak intensity of the magnetic entropy change (−ΔSM) and substantial broadenings of the distribution profiles which have contributed to an increase of the working temperature range of the investigated magnetocaloric material.

Pressure-induced itinerant electron metamagnetism in UCo0.995Os0.005Al ferromagnet

The effect of external hydrostatic pressure on magnetic properties is studied for the UCo0.995Os0.005Al single crystal. At ambient pressure, the ground state is ferromagnetic. Even lowest applied pressure 0.11GPa is sufficient to suppress ferromagnetism. A sharp metamagnetic transition is observed only in magnetic fields along the c axis of the crystal, similar to previously studied itinerant electron metamagnet UCoAl. Temperature dependence of the susceptibility for various pressures shows a broad maximum at Tmax ~ 20K. The experimental data are analyzed with the theory of itinerant electron metamagnetism, which considers anisotropic thermal fluctuations of the uranium magnetic moment. The observed pressure dependence of the susceptibility at Tmax and the temperature for the disappearance of the first-order metamagnetic transition are explained with the theory.

Alloying and pressure effects on itinerant-electron metamagnetism of the UCoAl-based compounds

With the UCo1-xOsxAl single crystals, we studied interplay between alloying and pressure effects on magnetism of the itinerant electron metamagnet UCoAl. The Os alloying for x ≥ 0.005 switches the UCoAl to ferromagnetism. For the UCo0.995Os0.005Al single crystal, even lowest applied pressure 0.11 GPa is sufficient to suppress ferromagnetism. A sharp metamagnetic transition for various pressures is observed in magnetic fields along the c axis of the crystal. Concentration magnetic phase diagram of the UCo1-xOsxAl, which includes the quantum phase transition from ferromagnetic to metamagnetic state, and P–T–H phase diagram of the UCo0.995Os0.005Al are determined using the data of magnetization measurements at various pressures and temperatures.

Interplay between crystal and magnetic structures in YFe2(HαD1−α)4.2 compounds studied by neutron diffraction

We report a detailed magnetic structure investigation of YFe2(HαD1−α)4.2 (α=0, 0.64, 1) compounds presenting a strong (H,D) isotope effect by neutron diffraction and Mössbauer spectroscopy analysis. They crystallize in the same monoclinic structure (Pc space group) with 8 inequivalent Fe sites having different H(D) environment. At low temperature, the compounds are ferromagnetic (FM) and show an easy magnetization axis perpendicular to the b axis and only slightly tilted away from the c axis. Upon heating, they display a first order transition from a ferromagnetic towards an antiferromagnetic (AFM) structure at TM0 which is sensitive to the H/D isotope nature. The AFM cell is described by doubling the crystal cell along the monoclinic b axis. It presents an unusual coexistence of non magnetic Fe layer sandwiched by two thicker ferromagnetic Fe layers which are antiparallel to each other. This FM-AFM transition is driven by the loss of ordered moment on one Fe site (Fe7) through an itinerant electron metamagnetic (IEM) behaviour. The key role of the Fe7 position is assigned to both its hydrogen rich atomic environment and its geometric position. Above TM0 a field induced metamagnetic transition is observed from the AFM towards the FM structure accompanied by a cell volume increase. Both thermal and magnetic field dependence of the magnetic structure are found strongly related to the anisotropic cell distortion induced by (H,D) order in interstitial sites.

Magnetocaloric effect suppression induced by mechanical milling on intermetallic DyCO2.

Structural and magnetic properties of mechanically milled samples of intermetallic DyCo2 were investigated by x-ray diffraction and magnetization measurements. The results show that the average crystallite size is reduced down to 35 nm for the sample milled for 8 h. The milling process induces structural disorder as evidenced by x-ray diffraction data, leading to a weakening of Itinerant Electron Metamagnetism (IEM) mechanism and suppression of the magnetocaloric effect. The RCP values of milled samples were not significantly reduced in comparison with the bulk sample due to the broadening of magnetic entropy change peak.

High-field transport properties of itinerant electron metamagnetic Co(S1-Se )2

Abstract The Co(S1-xSex)2 compounds are known to exhibit itinerant electron metamagnetism (IEM). We present field dependence of electrical resistivity and Hall effect of the compounds with 0 ≤ x

Magnetic Phase Relations of RCo3

In recent years, the rare earth-cobalt compounds with a formula of RCo 3 (R=rare earth) have received much attention due to their complex magnetic properties such as antiferromagnetic, temperature-induced itinerant-electron metamagnetism, magnetocaroric effect, spin reorientation etc[1-3]. However, these magnetic phenomena occur in low temperature regime. It's known that the binary rare-earth (R) intermetallic compounds RCo 3 crystallise in the PuNi 3 -type rhombohedral structure (space group R-3m). In this lattice, the R atoms occupy 3a and 6c sites, while cobalt atoms are distributed on 3b, 6c and 18h positions. In the RCo 3 compounds (except R=Tm and Y) the Co sublattice is in a strong ferromagnetic(SFM) ground state. Both the Co-Co and the R-Co exchange interactions influence strongly the magnetic state of the Co sublattice. In this study, the magnetism and relationship between the rare earth elements and magnetic property of RCo 3 in high temperature have been systematically.

Itinerant-electron metamagnetism of the Hf1−xTaxFe2 (x=0.125 and 0.14) compounds under high pressure

The effect of hydrostatic pressure on the magnetic properties has been investigated for itinerant-electron metamagnetic Hf1−xTaxFe2 (x=0.125 and 0.14) compounds which exhibit a temperature-induced transition from the ferromagnetic (FM) to the antiferromagnetic (AFM) state upon heating. Both the magnetic transition temperature TFM–AFM and the spontaneous magnetization MS decreases with increasing pressure. The application of an external pressure leads also to the strong increase of the AFM–FM transition field μ0Hcr. The magnitude of the pressure coefficient, dln(TFM–AFM)/dP, is much larger than that of dln(MS)/dP. This extremely large difference between the pressure coefficients is explained by the influence of spin fluctuations on the magnetovolume effects in the compounds Hf0.875Ta0.125Fe2 and Hf0.86Ta0.14Fe2.

Quantum critical point and unusual phase diagram in the itinerant-electron metamagnet UCoAl

We present the temperature--pressure--magnetic-field phase diagram of the itinerant-electron metamagnet UCoAl determined from the ac susceptibility measurement. The quantum critical point (QCP) was found to be located at $2.9\ifmmode\pm\else\textpm\fi{}0.2$ GPa ($\ensuremath{\equiv}{P}_{\mathrm{QCP}}$) and $130\ifmmode\pm\else\textpm\fi{}5$ kOe. In addition to the determination of the phase diagram, we report magnetic and transport properties in the paramagnetic state and around the phase boundary. The critical divergence of the magnetic susceptibility is suppressed toward the QCP. From the longitudinal magnetoresistance and the resistivity under magnetic fields, enhancement of the resistivity is observed in the so-called supercritical region. In the paramagnetic region, the magnetoresistance and temperature dependence of the resistivity exhibit complex behaviors, especially in the vicinity of 1.5 GPa and ${P}_{\mathrm{QCP}}$.

Magnetic coupling in transition-metal–doped LaSiFe11.5 TM0.5 (TM=Cr, Mn, Co and Ni)

This study describes the effect of small concentration of transition metal (TM) dopants on the nature of magnetic and electronic structure of the metamagnetic La-Si-Fe. In agreement with experimental results, all of the investigated dopants are found to reduce the overall magnetisation of the parent compound, regardeless of the nature of actual spin arrangement. The large magnetic moment of Cr (−1.87μB) and Mn (−2.35μB) prefers to couple antiferromagnetically to the magnetic moments of Fe (2.22μB), whilst the Co and Ni spins are aligned ferromagnetically but with a lower magnetic moment of 1.40 and , respectively. The variation of electronic entropy due to the change in with the dopants suggests a reshaped metamagnetic energy landscape that can lead to an altered itinerant-electron metamagnetic (IEM) transition.

Magnetocaloric effect of nonstoichiometric La1−xFe11.4+xSi1.6 alloys with first-order and second-order magnetic transitions

Variation from a first-order magnetoelastic transition (FOMT) to a second-order magnetic transition (SOMT) could be controlled by finely adjusting the Fe/La ratio in the non-stoichiometric La1−xFe11.4+xSi1.6 (x = 0, 0.05, 0.10, 0.15 and 0.20) alloys. Particularly, a nearly stoichiometric ratio of NaZn13-type phase was obtained with an addition of excess 0.15 at% Fe. When x value increased from 0 to 0.20, the Curie temperature (TC) increased from 198.6 to 216.6 K due to lattice shrinkage and the magnetic entropy change (−ΔSM) decreased from 18.4 to 8.0 J/(kg·K) (at 0−2 T) and from 22.5 to 13.8 J/(kg·K) (at 0−5 T), which may be ascribed to the change from the itinerant-electron metamagnetism (IEM) to second order magnetic transition. Thus their effective refrigeration capacities declined from 347.6 to 245.9 J kg−1 under 0–5 T, which values were comparable to the Gd5Si2Ge1.9Fe0.1. The Fe/La ratio in NaZn13-phase was possibly dominant to induce the transition from first to second order among La1−xFe11.4+xSi1.6 alloys. The thermal hysteresis decreased by 87% to 0.3 K and magnetic hysteresis losses reduced by 90% to 1.4 J kg−1 under 0–5 T. Near the transition border, the alloys with x = 0.15 produced a giant magnetocaloric effect of about 11.8 J/(kg·K) under 0–2 T at TC = 205.6 K. The magnetic hysteresis was 3.01 J kg−1 and the thermal hysteresis was 1.9 K. The material near the border of transition could be suitable for future magnetic refrigeration application.

Sequential cobalt magnetization collapse in ErCo2: beyond the limits of itinerant electron metamagnetism.

The itinerant electron metamagnetism (IEM) is an essential physical concept, describing magnetic properties of rare earth – transition metal (R-TM) intermetallics, demonstrating technologically important giant magnetoresistance and magnetocaloric effects. It considers an appearance of TM magnetization induced by spontaneous magnetization of surrounding R atoms, which provides significant response of the magnetic and transport properties on variation of external parameters (temperature, pressure, magnetic field) due to strong coupling between magnetic sublattices. The RCo2 compounds were generally considered as model systems for understanding of basic properties of IEM intermetallics. However, microscopic nature of magnetic properties still remains unclear. In our experimental and theoretical study of ErCo2 in a wide range of thermodynamic parameters a sequential collapse of cobalt sublattice magnetization in the background of nearly unchanged Er sublattice magnetization was revealed. The uncoupled magnetizations behavior challenges the IEM concept applicability and evidences more complex nature of magnetism in ErCo2 and related RCo2 systems.