Solid-state synthesis, magnetic and structural properties of interfacial B2-FeRh(001) layers in Rh/Fe(001) films.

Here we first report results of the start of the solid-state reaction at the Rh/Fe(001) interface and the structural and magnetic phase transformations in 52Rh/48Fe(001), 45Rh/55Fe(001), 68Rh/32Fe(001) bilayers from room temperature to 800 °C. For all bilayers the non-magnetic nanocrystalline phase with a B2 structure (nfm-B2) is the first phase that is formed on the Rh/Fe(001) interface near 100 °C. Above 300 °C, without changing the nanocrystalline B2 structure, the phase grows into the low-magnetization modification αl' (MSl ~ 825 emu/cm3) of the ferromagnetic α' phase which has a reversible αl' ↔ α" transition. After annealing 52Rh/48Fe(001) bilayers above 600 °C the αl' phase increases in grain size and either develops into αh' with high magnetization (MSh ~ 1,220 emu/cm3) or remains in the αl' phase. In contrast to αl', the αh' ↔ α" transition in the αh' films is completely suppressed. When the annealing temperature of the 45Rh/55Fe(001) samples is increased from 450 to 800 °C the low-magnetization nanocrystalline αl' films develop into high crystalline perfection epitaxial αh'(001) layers, which have a high magnetization of ~ 1,275 emu/cm3. αh'(001) films do not undergo a transition to an antiferromagnetic α" phase. In 68Rh/32Fe(001) samples above 500 °C non-magnetic epitaxial γ(001) layers grow on the Fe(001) interface as a result of the solid-state reaction between the epitaxial αl'(001) and polycrystalline Rh films. Our results demonstrate not only the complex nature of chemical interactions at the low-temperature synthesis of the nfm-B2 and αl' phases in Rh/Fe(001) bilayers, but also establish their continuous link with chemical mechanisms underlying reversible αl' ↔ α" transitions.

Characterization of the iron oxide phases formed during the synthesis of core-shell FexOy@C nanoparticles modified with Ag.

Core-shell FexOy@C nanoparticles (NPs) modified with Ag were studied with x-ray diffraction, transmission electron microscopy, energy dispersive elemental mapping, Mössbauer spectroscopy, static magnetic measurements, and optical magnetic circular dichroism (MCD). FexOy@C NPs synthesized by the pyrolysis process of the mixture of Fe(NO3)3 · 9H2O with oleylamine and oleic acid were added to a heated mixture of oleylamine and AgNO3 in different concentrations. The final product was a mixture of iron oxide crystalline NPs in an amorphous carbon shell and Ag crystalline NPs. The iron oxide NPs were presented by two magnetic phases with extremely close crystal structures: Fe3O4 and γ-Fe2O3. Ag is shown to form crystalline NPs located very close to the iron oxide NPs. An assumption is made about the formation of hybrid FexOy@C-Ag NPs. Correlations were obtained between the Ag concentration in the fabricated samples, their magnetic properties and the MCD spectrum shape. Introducing Ag led to a approximately linear decrease of the NPs saturation magnetization depending upon the Ag concentration, it also resulted into the MCD spectrum shift to the lower light wave energies. MCD was also studied for the Fe3O4@C NPs synthesized earlier with the same one-step process using different heat treatment temperatures, and MCD spectra were compared for two series of NPs. A possible contribution of the surface plasmon excitation in Ag NPs to the MCD spectrum of the FexOy@C-Ag NPs is discussed.

Transformation from an easy-plane to an easy-axis antiferromagnetic structure in the mixed rare-earth ferroborates Pr x Y1-x Fe3(BO3)4: magnetic properties and crystal field calculations.

The magnetic structure of the mixed rare-earth system Pr x Y1-x Fe3(BO3)4 (x = 0.75, 0.67, 0.55, 0.45, 0.25) was studied via magnetic and resonance measurements. These data evidence the successive spin reorientation from the easy-axis antiferromagnetic structure formed in PrFe3(BO3)4 to the easy-plane one of YFe3(BO3)4 associated with the weakening of the magnetic anisotropy of the Pr subsystem due to its diamagnetic dilution by nonmagnetic Y. This reorientation occurs through the formation of an inclined magnetic structure, as was confirmed by our previous neutron research in the range of x = 0.67 ÷ 0.45. In the compounds with x = 0.75 and 0.67 whose magnetic structure is close to the easy-axis one, a two-step spin reorientation takes place in the magnetic field H||c. Such a peculiarity is explained by the formation of an interjacent inclined magnetic structure with magnetic moments of Fe ions located closer to the basal plane than in the initial state, with these intermediate states remaining stable in some ranges of the magnetic field. An approach based on a crystal field model for the Pr(3+) ion and the molecular-field approximation is used to describe the magnetic characteristics of the system Pr x Y1-x Fe3(BO3)4. With the parameters of the d-d and f-d exchange interactions, of the magnetic anisotropy of the iron subsystem and of the crystal field parameters of praseodymium thus determined, it is possible to achieve a good agreement between the experimental and calculated temperature and field dependences of the magnetization curves (up to 90 kOe) and magnetic susceptibilities (2-300 K).

Magnetic phase diagram of the olivine-type Mn2GeO4 single crystal estimated from magnetic, resonance and thermodynamic properties.

Mn2GeO4 single crystals with the olivine structure grown by the modified flux method have been investigated. Pronounced magnetic phase transitions at T1 = 47.7 K, T2 = 17 K and T3 = 5.5 K, with T2 being dependent on an applied magnetic field, have been found. Based on the data of magnetic, resonance and temperature measurements, the entire phase diagram of Mn2GeO4 has been built. Mn2GeO4 is shown to be a material with a complex magnetic structure consisting of two magnetic subsystems.

Magnetic and thermophysical properties of Gd(X)Mn(1-X)S solid solutions.

The structural, magnetic, and thermophysical properties of cation-substituted sulfides Gd(X)Mn(1-X)S (0.04 ≤ X ≤ 0.25) with the NaCl-type face-centered cubic lattice have been investigated. The range of existence of long-range antiferromagnetic order has been established. The anomalies observed in the temperature dependence of the specific heat correspond to the temperatures of the magnetic phase transition. The anomaly in the specific heat caused by electron transitions between the 4f levels and d band states has been observed. It has been found that the coefficient of thermal expansion decreases with increasing concentration of substituents in the magnetically ordered region and remains nearly invariable in the paramagnetic phase.