Solid State Phenomena Vol. 190

Abstract: The X-ray diffraction and specific heat measurements have been performed for the ferromagnetic compounds (MnCo)_1-xGe within the concentration range 0.02 x 0.035. The compounds possess the hexagonal Ni₂In-type structure at elevated temperatures, while for the composition with x = 0.02 and 0.03 a spontaneous martensitic-type transition to the orthorhombic TiNiSi-type phase occurs at 283 and 221 K, respectively. We studied the entropy changes associated with the first-order structural transition and estimated the changes in magnetic, lattice, electronic entropies.

Abstract: We report magneto-optical spectra of the Heusler bulk alloys Ni-Mn-In, thin films Ni-Mn-Ga, microwires Ni-Mn-In and Ni-Mn-Ga in martensitic and austenitic states. Transversal Kerr effect (TKE) was studied at an angle of light incidence of 68° with respect to the sample plane, in the energy range 0.5 eV < E < 4.0 eV, at 50 350 K temperatures, and in magnetic fields up to 3.5 kOe. The TKE spectra profile does not change too much at martensitic transformation in Ni₂MnGa thin films, only magnitudes of characteristic maxima decrease. The magneto-optical response of Ni₂MnGa microwires is very similar to that for Ni₂MnGa thin films. For most of studied bulk samples, the TKE signal is very weak (about 10^-5), about two orders of magnitude smaller than for thin films, and in many cases could not be detected at all. It indicates the strong dependence of the magneto-optical response of Heusler alloys on the quality of optically or electrochemically polished surfaces and their microstructure.

Abstract: The direct measurements of the magnetocaloric effect (MCE) and the magnetization have been conducted for a large number of compounds based on RCo₂ (R = Tb, Ho) with substitutions by nonmagnetic elements (Y, Al, Ga) in rare earth and 3d- sublattices. The concentration dependencies of the Curie temperature and the value of MCE are discussed. The linear dependencies of the value of the MCE from the second power of the magnetization were find out at the region of the phase transition of the second type .

Abstract: The MCE in MnAs and doped Mn (As,Sb) compounds with low concentration of Sb has been studied by direct investigation. It was shown that for MnAs the maximum value of MCE is ΔT = 0.28 K on heating (at 308 K) and ΔT = 0.88 K on cooling (at T = 306 K) in magnetic filed 12.5 kOe. In doped Mn (As,Sb) compounds the temperature dependence of MCE is similar to MnAs. All investigated compounds demonstrate a strong temperature and field hysteresis of magnetic properties in magnetic field less than 40 kOe. It was established that a small concentration of Sb leads to decrease of MCE hysteresis and preserves the phase transition at room temperature region.

Abstract: In our work the temperature dependencies of magnetization, entropy changes, and the Curie temperature (T_C) of La_1-xCa_xMnO₃ (x = 0.33 and 0.5) were investigated using Monte Carlo method and Heisenberg model. In our simulation, magnetic Mn³⁺ and Mn⁴⁺ ions are described by classical Heisenberg spins, while oxygen, lanthanum and calcium ions are considered as non-magnetic. The Mn magnetic ions are distributed on a simple cubic lattice according to the perovskite structure of the manganite. The theoretical Curie temperatures and magnetocaloric values are in a good agreement well with experimental data.

Abstract: The studies of X-ray diffraction, magnetization, magnetocaloric effect, and 57Fe Mössbauer spectra have been performed in a bulk sample of RhFe compound synthesized under high pressure. It have been found that RhFe has fcc-type of crystal structure at room temperature and, shows the first order magnetic transition from the antiferromagnetic-like to ferromagnetic state close to 338 K at 5T magnetic field. This type of behavior has been verified by differential scanning calorimetry, magnetization and Mössbauer techniques. The irreversible transition from antiferromagnetic to stable ferromagnetic state has been observed after heating of sample up to 573K.

Abstract: The liquid quenched Gd₃Ni alloy is observed to exhibit a ferromagnetic behavior below T_C = 117 K unlike crystalline compound having an antiferromagnetic order at T < T_N = 99 K. Rapid quenching from the melt results in a considerable enhancement of the magnetocaloric effect in Gd₃Ni at low magnetic fields. The maximal value of the isothermal magnetic entropy change at a magnetic field change of 20 kOe for the amorphous Gd₃Ni surpasses by more than 8 times the S_M value for the polycrystalline counterpart. The relative cooling power for the amorphous Gd₃Ni alloy is estimated as 265 J kg^-1 and 676 J kg^-1 at a magnetic field change of 20 kOe and 50 kOe, respectively.

Abstract: Spectral and field dependencies of Transversal Kerr Effect (TKE) for [(Co45Fe45Zr10)Z(Al2O3)100-Z(X)/α-Si:H(Y)] n multilayers have been studied in the energy range 0.5 - 4.0 eV. It was found that TKE field dependencies in the nearest IR energy range exhibit anomalous behavior for structures only with thin Si layers and this behavior vanishes with increasing of the Si layer thickness. TKE spectra measured in small and large magnetic fields were essentially different. It was shown that magneto-optical response of multilayered structure composite-silicon is the sum of contributions from two composites: (Co45Fe45Zr10) - Al2O3 + Si + silicides and (Co45Fe45Zr10) - Si + silicides, which have a different sign of TKE in the nearest IR spectrum and their magnetic states depend both on composite and semiconducting layer thicknesses.

Abstract: The paper is devoted to experimental study of Faraday Effect enhancement. The experimental structure consists of photonic crystal, loaded with ferrite, which in turn is covered by thin metal layer or wire medium. An analysis of the transmission/reflection spectra for both unloaded and loaded photonic crystals shows that the surface oscillation mode (the surface state) is formed in the crystal band gap. A good agreement exists between experimental data and numerical calculations.

Abstract: t is shown that the inverse Faraday effect appears in the case of surface plasmon polariton propagation near a metal-paramagnetic interface. The inverse Faraday effect in nanostructured periodically perforated metaldielectric films increases because of the excitation of surface plasmon polaritons. In this case, a stationary magnetic field is amplified by more than an order of magnitude compared to the case of a smooth paramagnetic film. The distribution of an electromagnetic field is sensitive to the wavelength and the angle of incidence of light, which allows one to efficiently control the local magnetization arising due to the inverse Faraday effect.