Pressure-induced magnetic transition in Fe2P

The weak field ac susceptibility and the resistivity of Fe₂P single crystals were measured as functions of temperature from 4.2–300 K and as functions of hydrostatic pressures up to 20 kbar, using a newly designed clamp-type pressure cell. The Curie temperature, and the first-order transition temperature, decreased rapidly with increasing pressure, and ferromagnetism vanished at about 13 kbar at 0 K. A second-order transition temperature, as well as the first-order transition, appeared in the region below 170 K and above 5 kbar (triple point) and a new pressure-induced magnetic phase was found. The phase is proposed to be antiferromagnetic for reasons discussed in the paper.     

μSR study of Fe2P in the paramagnetic state

Using transverse field μSR measurements, a search for longlived magnetic correlations in the itinerant ferromagnet Fe₂P at temperatures significantly above the Curie temperatures has been made. No correlations with a lifetime longer than ≈ 10^-10 s could be found.     

Magnetocaloric properties of the (La-Gd)Fe11.4Si1.6 metamagnetic compound

The effect of the partial substitution of La by Gd atoms on the magnetic entropy change of the LaFe_11.4Si_1.6 metamagnetic compound was studied using Mössbauer spectroscopy and DC magnetization measurements. A considerable enhancement of the magnetic entropy change was observed in Gd-substituted compounds, while the Curie temperature slightly decreased with the increase of the Gd content. For the 20% Gd-substituted compound, a giant magnetic entropy change value of −16 J/kg K at 190 K was attained under a field varying from 0 to 2 T.     

Submillimeter wave ESR measurements of metamagnetic Y2Cu2O5

Submillimeter wave ESR system in Kobe University is presented. It covers the frequency region from 60 to 383GHz and can apply the pulsed magnetic field up to 30T. The measurement of Y₂Cu₂O₅ single crystals using our system is presented.     

Microscope studies of the metamagnetic transition in FeCl2

Using a polarizing microscope with its optical axis along the field of an electromagnet, we have studied the metamagnetic transition in thin flakes of FeCl₂ at pumped helium temperatures. Among the interesting nucleation phenomena observed was the precipitation of paramagnetic phase on lines interpreted to be antiferromagnetic domain walls.     

Magnetic and optical properties of Fe2VAl and Fe3Al

Full-potential linearized augmented plane wave plus local orbital method (FPLAPW + lo) calculations were performed for Fe₂VAl and Fe₃Al in order to investigate magnetic and optical properties and to show the origin of various optical transitions. It was found that the lattice constant and spin magnetic moments with the GGA method differ more from the respective experimental values than those calculated with the LSDA method. Furthermore, our calculated lattice constant and spin magnetic moments with the LSDA method were in overall better agreement with experiment. Our predictions agreed well with recent experimental reflectivity spectra. Meanwhile, the spectral peaks at the transitions were analyzed from the imaginary part of the dielectric function.     

Interplay of metamagnetic and structural transitions in Ca2-xSrxRuO4

Metamagnetism in layered ruthenates has been interpreted as a novel kind of quantum critical behavior. In an external magnetic field, Ca_2-xSr_xRuO₄ undergoes a metamagnetic transition accompanied by a pronounced magnetostriction effect. In this paper we present a mean-field study for a microscopic model that naturally reproduces the key features of this system. The phase diagram calculated is equivalent to the experimental T-x phase diagram. The presented model also gives a good basis to discuss the critical metamagnetic behavior measured in the system.     

Magnetic phase transitions in Fe1−xCoxCl2: A computer simulation

The equation of motion method has been used to calculate the $\text{q}\text{= 0}$ magnon in Fe_1?xCo_xCl₂. For a certain range of concentrations, a response at negative frequency is found, which implies that there is a new magnetic phase intermediate between FeCl₂ and CoCl₂ in this composition region. The boundaries of this phase are in good agreement with the available experimental data.     

Electron localization in Fe2PO5

Fe₂PO₅ is a mixed valence compound where Fe^II and Fe^III are in face sharing octahedra with a short Fe^II - Fe^III distance, so that electron delocalization along chains parallel to the $\text{b}$ axis of the orthorhombic cell was worth to investigate. From Mössbauer experiments, carried out up to 600°C, it appears that the 4 lines spectra evolution, as regards Isomer Shift, Quadrupolar Splitting, and Linewidth, is only consistent with a localized electron pattern. This result is interpreted from the unequivalence of the 2 sites. The strong Fe^II quadrupolar splitting decrease allows the determination of the energy gap between the d_xy and d_yz-d_zx orbitals.     

Electronic structure of Fe2CrSn

From the first principles calculation based on the density functional theory, we find that consideration of electron–electron correlation drives Fe₂CrSn from a barely half-metallic state to a magnetic semiconductor. However, in both cases, the magnetic state remains ferrimagnetic with a total spin moment of 2μ_B$2{\mathrm{\mu }}_{\mathrm{B}}$, with Cr carrying a large local moment that is oppositely aligned to that of Fe.     

Magnetic phase transitions in PrCo2Si2

Magnetic phases in PrCo₂Si₂ have been studied by measurements of magnetization, neutron diffraction and electrical resistivity. For <9 K, the magnetic structure with a propagation vector k = (0,0,1) [2π/c] is stable. Incommensurate structures k = (0,0,0.926) and (0,0,0.777) appear for 9 K < T <17 K and 17 K < T <30 K, respectively.     

Electrical conduction in Fe2O3 and Cr2O3

The influence of some impurities on the conduction properties of Cr₂O₃ and Fe₂O₃ are examined and contrasted. A mechanism is proposed to account for the effect of Ti in Cr₂O₃.     

Flat bands and enigma of metamagnetic quantum critical regime in Sr3Ru2O7

Understanding the nature of field-tuned metamagnetic quantum criticality in the ruthenate Sr₃Ru₂O₇ has presented a significant challenge within condensed matter physics. It is known from experiments that the entropy within the ordered phase forms a peak, and is unexpectedly higher than that outside, while the magnetoresistivity experiences steep jumps near the ordered phase. We find a challenging connection between Sr₃Ru₂O₇ and heavy-fermion metals expressing universal physics that transcends microscopic details. Our construction of the T–B$T\text{–}B$ phase diagram of Sr₃Ru₂O₇ permits us to explain main features of the experimental one, and unambiguously implies an interpretation of its extraordinary low-temperature thermodynamic in terms of fermion condensation quantum phase transition leading to the formation of a flat band at the restricted range of magnetic fields B. We show that it is the flat band that generates both the entropy peak and the resistivity jumps at the QCPs.     

Large magnetoresistance in metamagnetic CoMnSi0.88Ge0.12 alloy

The magneto-transport properties are investigated in metamagnetic CoMnSi0.88Ge0.12 alloy.By applying a magnetic field or increasing temperature,a metamagnetic phase transition from antiferromagnetic to ferromagnetic is observed in this alloy.Around the metamagnetic phase transition,CoMnSi0.88Ge0.12 alloy exhibits a large and negative magnetoresistance effect(～32%) under a magnetic field of 20 kOe(1 Oe = 79.5775 A/m),which is ascribed to the spin-dependent scattering of conduction electrons.     

Structural properties of amorphous Fe2O3 nanoparticles

We have investigated the microstructure of amorphous Fe₂O₃ nanoparticles by using molecular dynamics (MD) simulations. Non-periodic boundary conditions with Born-Mayer type pair potentials were used to simulate a spherical model of different diameters of 2, 3, 4 and 5 nm. Structural properties of an amorphous model obtained at 350 K have been analyzed in detail through the partial radial distribution functions (PRPFs), coordination number distributions, bond-angle distributions and interatomic distances. Calculations showed that structural characteristics of the model are in qualitative agreement with the experimental data. The observation of a large amount of structural defects as the particle size is decreased suggested that surface structure strongly depends on the size of nanoparticles. In addition, surface structure of amorphous Fe₂O₃ nanoparticles have been studied and compared with that observed in the core and in the bulk counterpart. Radial density profiles and stoichiometry in morphous Fe₂O₃ nanoparticles were also found and discussed.     

Optical emissions of products sputtered from Fe, Fe2O3 and Fe3O4 powders

Powder iron has been bombarded by a 5 keV Kr⁺ ions in a vacuum better than 10^-7 torr and under few 10^-6 torr ultra pure oxygen partial pressure. The optical spectra of the sputtered particles were recorded between 340.0 nm and 410.0 nm. These spectra exhibit discrete lines, which are attributed to neutral excited atoms of iron. Two iron oxides, namely hematite (Fe₂O₃)_{3}) and magnetite (Fe₃O₄)_{4}), in powder form, were studied under the same experimental conditions and identical lines were observed in the obtained spectra. The absolute intensities of the spectral lines in all spectra were measured and the differences in the recorded yield photons were discussed in term of electron-transfer processes between the excited sputtered atom and the bombarded surface. In accordance with the proposed interpretation, we suggest values for the energy gaps and electronic affinities for the studied oxides and for the oxide layer that might be formed by the adsorption of oxygen atoms.     

Influence of hydrogenation on the electronic structure and the itinerant-electron metamagnetic transition in strong magnetocaloric compound La(Fe0.88Si0.12)13

The influence of interstitial hydrogen on the electronic structure and the itinerant-electron metamagnetic (IEM) transition in strong magnetocaloric compound La(Fe_0.88Si_0.12)₁₃H_1.6 has been investigated by Mössbauer spectroscopy. A slight change in the average hyperfine field at 4.2 K was observed after hydrogen absorption. In contrast, the thermally induced first-order transition related to the IEM transition for y=1.6 appears at the Curie temperature T_C=330 K, much higher than T_C=195 K for y=0.0. The increase of isomer shift δ_IS at 4.2 K indicates that the valence electron transfer from hydrogen to Fe is negligibly small, hence the change in the magnetic state is closely associated with a volume expansion after hydrogen absorption. No change in shape by hydrogenation for the Mössbauer spectra in the paramagnetic state has been observed except for a difference in only δ_IS, indicating the volume expansion by hydrogenation is isotropic. Accordingly, the significant increase of T_C by hydrogen absorption is attributed to the magnetovolume effect associated with characteristic feature in IEM compounds. A discontinuous change of ferromagnetic moment, ΔM, around T_C has been observed by Mössbauer spectra, as expected from the magnetization measurement. The value of ΔM is slightly decreased by increase of T_C after hydrogenation but its magnitude is almost the same due to the stabilization of ferromagnetic moment. As a result, strong magnetocaloric effect is maintained up to room temperature after hydrogenation.     

Chemical quenching of positronium in Fe2O3/Al2O3 catalysts

Fe₂O₃/Al₂O₃ catalysts were prepared by solid state reaction method using α-Fe₂O₃ and γ-Al₂O₃ nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimes τ₃ and τ₄ are attributed to positronium annihilation in two types of pores distributed inside Al₂O₃ grain and between the grains, respectively. With increasing Fe₂O₃ content from 3 wt% to 40 wt%, the lifetime τ₃ keeps nearly unchanged, while the longest lifetime τ₄ shows decrease from 96 ns to 64 ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe₂O₃ content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease of τ₄ is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores.