[en] A NdCr₂Si₂C polycrystal has been prepared and characterized by heat-capacity and magnetization, X-ray and neutron powder diffraction measurements. Ferromagnetism below T_C = 21 K with Nd magnetic moments aligned parallel to the c-axis has been confirmed. We also studied the electronic structure of NdCr₂Si₂C by first-principles calculations, which predict the ordered magnetic moment both on the Nd and Cr sites. The magnetization and neutron diffraction data, however, do not allow resolving the question of existence of the Cr moment unambiguously.

[en] PbFe_0.5Nb_0.5O₃ compound (PFN) is a well-known multiferroic material undergoing a paraelectric(PE)-to-ferroelectric(FE) phase transition at ∼ 380 K. The cubic structure in the PE state is distorted in the FE state to the tetragonal (below 376 K), and subsequently to the monoclinic structure. Inspecting magnetism, two diffuse magnetic phase transitions were reported at T_N = 150 K and T_m = 10 K. In our work, we have investigated samples derived from the PFN, prepared by different methods. The crystal structure, grain size and phase composition of the materials was determined by powder XRD and SEM analysis. Study of magnetization and a.c. susceptibility confirmed presence of the two anomalies of magnetic origin at 150 K and 10 K, respectively, in most of the samples.

[en] We have prepared a NdCr₂Si₂C single crystal by Czochralski technique and investigated it by heat capacity and magnetization measurements in the temperature range 2-300 K and magnetic fields up to 6 T applied parallel to the principal crystallographic axes. A strongly anisotropic ferromagnetism has been observed with the T_C = 24 K and the ordered magnetic moment oriented entirely along the c-axis of the tetragonal structure whereas the basal plane response is weak paramagnetic. We also studied the electronic structure of the compound by first-principles DFT calculations, which predict existence of a stable Cr magnetic moment. Results of our present experiments do not allow resolving the question on the existence of the ordered Cr moments unambiguously.

[en] We report on magnetic properties of RCr₂Si₂ compounds with R=Tb, Er. The polycrystalline samples were characterized by powder X-ray diffraction and found to be isostructurally crystallizing in the ThCr₂Si₂-type tetragonal structure. The samples were further investigated by specific heat, AC-susceptibility and magnetization methods in the temperature range 2-900 K and in magnetic fields up to 9 T. The magnetic measurements revealed the magnetic ordering of the rare-earth moments below about 2 K, whilst no high-temperature ordering of the Cr moments was observed. The evidence of for Cr magnetism is corroborated by results of first-principles calculations based on the density functional theory (DFT).

[en] A series of UCoGe and U₃Co₄Ge₇ polycrystalline samples has been prepared by arc melting and studied with respect to the phase composition and crystal structure, magnetization, a.c. susceptibility, electrical-resistivity and specific-heat behavior (down to 350 mK). U₃Co₄Ge₇ has been found to exhibit a spontaneous magnetization below T_C=21 K. Clear anomalies at T_C typical for a ferromagnetic transition have been observed in a.c. susceptibility, electrical-resistivity and specific-heat data. No additional anomaly, which would indicate the second magnetic phase transition below T_C reported in the literature, has been indicated. In all our UCoGe samples a transition to superconductivity has been revealed. On the other hand, no clear evidence of any transition to ferromagnetism with zero-field cooling down to 1.8 K has been obtained. The zero-field state is most probably governed by strong ferromagnetic spin fluctuations and seems to transform to a ferromagnetic state only when applying a magnetic field ≥10 mT. Simultaneously, an increase of the superconducting transition temperature is increasing with a magnetic field up to 10 mT and starts to decrease when increasing the field above this value. Measurements on bulk samples, which are by rule textured, indicate strong magnetocrystalline anisotropy in both investigated compounds.

[en] In magnetism of nanoparticles, surface spin effects play a key role. The so-called spin canting at the surface leads either to lowering of saturation magnetization, or even to lack of saturation in high magnetic fields. The value of the saturation magnetization depends on cation distribution within the spinel network and on the spin canting angles. We have investigated structure and magnetic behavior of CoFe₂O₄ nanoparticles doped with La (Co_1-xLa_xFe₂O₄, x = 0.05 - 0.5 and CoLa_xFe_2-xO₄, x = 0.05 - 0.2) embedded in amorphous silica matrix prepared by a sol-gel method. The samples were characterized using X-ray diffraction and TEM. The zero-field cooled and field cooled measurements of magnetization showed that the blocking temperature is well above the room temperature. The high coercivity was observed (up to 2 T at 10 K) and no saturation of the magnetization even in applied field of 7 T was obtained, suggesting considerable spin canting effects. Finally, the Mossbauer spectroscopy under magnetic field and down to low temperature was performed to determine the cation distribution and the spin canting angles.

[en] We have studied magnetic properties of TCr₂O₄ (T = Co, Ni) fine powders, obtained by the citric acid method, and TCr₂O₄/SiO₂ nanocomposites, constituted of spinel nanoparticles embedded in silica matrix fabricated by a modified sol gel method. All samples were characterized by powder X-ray diffraction, scanning electron microscopy and microprobe analysis. The profile analysis of the powder X-ray diffraction revealed that the particle size is larger for the fine powder samples, as expected. Detailed measurements of magnetization, hysteresis loops and a.c. susceptibility demonstrate significant differences in magnetic properties of the fine powders in comparison to the nanocomposite samples. The values of the coercitivity at 10 K ranges from ∼ 2T for NiCr₂O₄ fine powders to ∼ 0.6 T for CoCr₂O₄/SiO₂ nanocomposites. Moreover, the hysteresis loops of the NiCr₂O₄/SiO₂ samples are brightly asymmetric. The phenomenon will be discussed in context of the exchange-bias originated by presence of a tiny amount of the antiferromagnetic phase, Cr₂O₃ in the samples.

[en] Research highlights: → YPd₂Al₃-a new metallic superconductor belonging to RENi₂Al₃ structure type. → Polycrystalline material was prepared by standard arc melting under the pure Ar. → Strong increase of T_SC was induced by heat treatment at 700 deg. C. → Maximum T_SC = 2.2 K. → All results are supported and in good agreement with electronic structure calculation. - Abstract: We have prepared a polycrystalline sample of YPd₂Al₃ - a so far unknown member of the well-known group of intermetallic compounds REPd₂Al₃ (RE = rare earth elements). The XRPD analysis revealed that the YPd₂Al₃ compound crystallizes in the hexagonal crystal structure adopted by the entire REPd₂Al₃ family, too. For the new material we have measured the magnetization, AC susceptibility, specific heat and electrical resistivity with respect to temperature and magnetic field. We have observed superconductivity with T_SC ∼ 2.2 K in well-annealed samples and Pauli paramagnetism in normal state. We have also performed ab initio electronic structure calculations and found reasonable agreement between experimental findings and corresponding results of theoretical calculations.

[en] We have studied the influence of Pt-Ni substitution on the crystal structure and magnetic behavior of the PrNi_1-x Pt _x pseudobinary compounds. The orthorhombic CrB-type structure owned by PrNi was found to remain conserved when substituting Pt for Ni while the unit cell volume linearly increased. The polycrystalline PrNi_1-x Pt _x samples were investigated by measuring the specific heat (C_P ) and magnetization (M) as function of temperature and magnetic field. All studied compounds were found to order ferromagnetically; the Curie temperature T _C is linearly decreasing with increasing Pt content. The magnetocaloric effect (the isothermal magnetic entropy change ΔS _mag) was determined consistently from the specific heat and magnetization data. The maximum values of ΔS _mag are the same for the boundary compounds PrNi and PrPt but become somewhat reduced in solid solutions

[en] We have prepared the RE₂Fe_17-x Cr _x compounds for RE=Pr, Gd and x=0, 1 in polycrystalline form and characterized by the powder X-ray diffraction and the ⁵⁷Fe Moessbauer spectroscopy. The Pr₂Fe_17-x Cr _x compounds are rhombohedral with the space group P-3m and the Gd₂Fe_17-x Cr _x ones are hexagonal with space group P/6₃ mmc. The magnetization and the ⁵⁷Fe Moessbauer spectra were measured as functions of temperature and the applied magnetic field. All the studied compounds are ferromagnetic. The doping by Cr yields enhancement of the Curie temperature by ∼50 K in both systems. In the vicinity of the magnetic ordering transition, the magnetocaloric effect was studied, as well