In the work a brief discussion of the structural and magnetic properties of the manganites from the point of view of the micro- and macrostructures is presented. The influence of stoichiometry with the different oxygen parameter δ and doped atoms is discussed. The correlation between the crystal structure parameters and magnetic properties for some manganites is presented.
The magnetic and magnetocaloric properties of Sm_{1-x}Gd_{x}Mn_{2}Ge_{2} compounds with 0 ≤ x ≤ 0.10 have been studied. SmMn_{2}Ge_{2} is antiferromagnetic below the Néel temperature T_{N} ( ≈ 400 K). Further cooling leeds to canted ferromagnetic phase below T_C = 341 K. With decreasing temperature, two metamagnetic phase transitions are observed: F2-AF1 at T_2 = 153 K and AF1-F1 at T_1 = 106 K. The maximum values of magnetic entropy change | Δ S_m | are found to be 1.5 J K^{-1} kg^{-1} at T_{1} and 2.0 J K^{-1} kg^{-1} at T_{2} in SmMn_{2}Ge_{2}. The MCE is found to increase with Gd concentration, | Δ S_{m}(T_{1}) | = 3.3 J K^{-1} kg^{-1}, while | Δ S_{m}(T_{2})| is slightly enhanced for x = 0.1. The magnetocaloric effect is found to be positive at T_{1} and negative at T_{2}.
The electronic structure of Ce_{1-x}La_{x}PtIn is studied by means of ab initio full-potential local orbital basis (coherent potential approximation) (FPLO-CPA) and spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR-CPA) methods within the densities functional methodologies. In both methods, we have observed decrease of the density of states at the Fermi level versus of La concentration. The theoretical photoemission spectra of LaPtIn and CePtIn are compared with the experimental data and the agreement is good. We have also reported the optical properties of LaPtIn and CePtIn compounds obtained in GGA and GGA+U approximation.
We report on the magnetic and thermal properties of a few TmTX compounds, where T = d-electron metal and X = p-electron element. In all these ternaries but TmRuGe the thulium magnetic moments order antiferro- or ferromagnetically at low temperatures. The specific heat data confirms the magnetic orderings and reveals the influence of crystalline electric field effects.
The magnetic data for the polycrystalline samples of RIrSi (R = Tb, Dy and Ho) compounds are reported. These compounds are antiferromagnets with the Néel temperatures equal to 32 K (R = Tb), 7.0 K (R = Dy) and 4.8 K (R = Ho), respectively. The external magnetic field induces the one step for TbIrSi and two step for DyIrSi and HoIrSi metamagnetic phase transitions. The values of the critical field as Néel temperatures decrease with increase of the number of 4f electrons. The magnetic phase diagrams (H, T) are determined.
The magnetic ordering in Ni_{1-x}Cu_{x}MnSb alloys changes from ferromagnetic (x=0) to antiferromagnetic (x=1). The X-ray and neutron diffraction showed that the systems crystallise in C1_{b} type structure. We present an influence of the local chemical ordering on the electronic and magnetic properties of Ni_{1-x}Cu_{x}MnSb alloys. The band structure and the magnetic moments were calculated by the spin-polarised linear muffin-tin orbital in the atomic sphere approximation method for the experimental values of the lattice parameters. The magnetic moment of Mn increases from 3.8 μ_{B} for x=0 to 4.18 μ_{B} for x=1.
The magnetic data for R_5Rh_4Ge_{10} (R = Tb, Dy, Ho, Er, and Tm) compounds was investigated by means of the dc magnetization and dc and ac magnetic susceptibility. At low temperature all these compounds are antiferromagnets. For these with R = Tb, Ho and Er below T_{N} the additional phase transitions are observed. The obtained data are compared with the neutron diffraction results.
Polycrystalline samples of Tb_{1 - x}Y_{x}NiIn (x = 0.2 and 0.4) were prepared and studied by powder X-ray diffraction and AC and DC magnetic measurements. The compounds crystallize in the hexagonal ZrNiAl-type structure. At low temperatures the ferromagnetic properties are detected. With increasing Y content a change in the magnetic properties, decrease of the Curie temperatures and magnetic moment in the ordered state are observed.
We present here temperature dependent X-ray photoemission measurements on polycrystalline Yb_2CuGe_6. The analysis of these data shows the change in the effective valence, determined directly from the 4f intensity ratio, as a function of temperature.
The electronic structure of the ternary RPtIn (R = La, Ce) compounds, which crystallize in the hexagonal ZrNiAl-type structure, was studied by X-ray photoelectron spectroscopy measurements and calculation using the ab initio methods (linear muffin-tin orbital in the atomic sphere approximation, full potential linear muffin-tin orbital, full potential linear orbital). The results showed that the valence band in these compounds is formed by the Pt 5d and In 5s and 5p states. The band calculations with spin-orbit coupling have shown that the Ce 4f peaks consist of two peaks above the Fermi level that correspond to the Ce 4 f_{7/2} and 4 f_{5/2} doublet and wide peaks corresponding to the La 4f states. The analysis of Ce 3d spectra on the basis of the Gunnarsson-Schönhammer model gives hybridization of 4f orbitals with the conduction electron band equal to 170 meV.
In the paper the results of the powder neutron diffraction measurements of RAuIn (R = Ce, Tb, Dy, and Er) and ZnFe_2O_4 compounds at low temperatures are presented. For the RAuIn compounds, which crystallize in the hexagonal ZrNiAl-type structure, the rare-earth moments lie in the ab-plane and form a typical triangle non-collinear structure. ZnFe_2O_4 has the normal spinel structure in which the Fe^{3+} ions occupy the B sites, forming the corner-shared tetrahedra of the Fe spins. At low temperatures experimental data indicate the coexistence of the long-range and the short-range magnetic order. The obtained results suggest that the important factor which influences the magnetic ordering in these compounds is geometrical frustration of magnetic moments.
The neutron powder diffraction measurements of the TmRu₂Si₂ compound in the temperature range 0.47-2.5 K have been performed. The obtained results confirm that this compound in low temperature has a tetragonal ThCr₂Si₂-type crystal structure (space group I4/mmm). The long range magnetic ordering was not detected up to 0.47 K.
X-ray diffraction and magnetic measurements of Ho_{5}Ni_{2}In_{4} are reported. This compound crystallizes in the orthorhombic Lu_{5}Ni_{2}In_{4}-type structure. Magnetic data indicate ferromagnetic properties below T_c = 30 K.
Powder neutron diffraction measurements of PrNi₅Sn performed in the temperature range 1.5-76 K indicate that the compound crystallizes in a hexagonal CeNi₅Sn-type crystal structure (space group P6₃/mmc). The a lattice parameter and the unit cell volume V increase while the c lattice parameter does not change with increasing temperature. No long range magnetic ordering was detected down to 1.5 K, in contradiction to bulk magnetometric results.
The electronic structure of the ternary CeTIn (T = Ni, Cu, Pd, Au) compounds was investigated by means of X-ray photoelectron spectroscopy. Our interest was aimed mainly to the valence bands and the Ce3d core levels of investigated compounds. Analysis of the valence bands indicates that they are mainly determined by the Tnd band, whereas a share of the R4f states can be estimated to be about a few percent only. The analysis of the differential valence bands spectra between CeTIn and LaTIn analogues suggests that the Ce4f^1 ground states shift deeper below the Fermi level with an increase in the 4f level occupation factor. The analysis of the Ce3d spectra made on the basis of the Gunnarsson-Schönhammer model indicates the hybridization parameter equal to 148 meV for CeNiIn, 45 meV for CeCuIn, 177 meV for CePdIn, and 123 meV for CeAuIn.
Ternary Ho_3Cu_4X_4 compounds exhibit very complex magnetic phase diagrams. The rare earth ions occupy two non-equivalent crystal positions. Within both magnetic sublattices, magnetic moments exhibit different magnetic ordering temperatures. Moreover, in light of our results, it seems that both sublattices are weakly coupled between each other. This may be observed as independent changes of propagation vectors etc. The major difference of ordering temperatures between both compounds is likely related to substantial change of interatomic distances. Consequently, completely different crystalline electric field effects are observed.
Magnetization curves up to 140 kOe have been measured in the temperature range 4.2-100 K on polycrystalline oriented samples for some RT_{2}X_{2}, RTX_{2} RTX compounds. The magnetic phase diagrams for all samples are determined.
Magnetic and specific heat data of the TmRhX (X = Ga, Ge) compounds are reported. These compounds crystallize in an orthorhombic crystal structure of the TiNiSi-type (space group Pnma). Magnetic data indicate that the compounds are antiferromagnets with the Néel temperature T_{N} equal to 3.9 K for TmRhGa and 6.0 K for TmRhGe. Magnetic susceptibility of TmRhGe has an additional peak at T_{t} = 10.6 K. In TmRhGe temperature dependence of χ"(T), the positions of both the peaks at T_{N} and T_{t} change with frequency indicating a relaxation process. These data suggest that with the decreasing temperature, first a cluster glass state and next the long-range aniferromagnetic order exists.
X-ray and neutron diffraction as well as magnetometric methods were used in order to investigate crystal and magnetic structure together with magnetic properties of nickel oxide NiO obtained from thermal decomposition of Ni(OH)₂. It has been found that crystal unit cell volume and crystal unit cell deformation parameter decrease with increasing decomposition temperature T_{d} while grain size increases. The results of magnetization, magnetic susceptibility and neutron diffraction measurements reveal a formation of antiferromagnetic order with uncompensated magnetic moment below the Néel temperature. Magnetization together with coercive field decreases with increasing T_{d}. The neutron diffractogram of sample obtained at 240°C indicates broadening of both the peaks of nuclear and magnetic origin. The magnetic ordering may be described by a propagation vector k=[½,½,½].
Magnetic measurements of HoAl_{2} are reported. The compound crystallizes in the cubic MgCu_{2}-type crystal structure. HoAl_{2} exhibits two successive magnetic transitions: below T_{c} = 29 K a ferromagnetic order is formed while anomaly at T_{t} = 20 K is related to reorientation of magnetic moment. Near transition temperatures a magnetocaloric effect with magnetic entropy changes -ΔS_{m} equal to 6.3 J/(mol K) at T_{c} and 5.0 J/(mol K) at T_{t} for an external field μ_{0}H = 9 T is observed.
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