A. Kowalczyk

Magnetic characteristics of RNi4B compounds (R=Y, Pr, Sm, Tb, Ho and Er)

The magnetic properties of RNi4B compounds with R=Y, Pr, Sm, Tb, Ho and Er have been studied. These compounds crystallize in a hexagonal structure with the P6/mmm space group. YNi4B shows superconducting behavior below ∼12 K, while PrNi4B is paramagnetic but contains a contribution of a ferromagnetic impurity phase. For compounds with R=Sm, Tb, Ho and Er transitions to magnetically ordered state are visible at 38, 21, 6 and 12 K, respectively. A large hysteresis loop is observed for the SmNi4B compound with a coercive field HC>7.0 T, whereas the RNi4B compounds of the other rare earths are characterized by an HC lower than 0.06 T at 5 K.

X-ray photoemission spectra of La0.7Sr0.3MnO3 perovskite

Abstract X-ray photoemission (XPS) measurements of the core levels and valence electronic structure of La0.7Sr0.3MnO3 are presented. The ferromagnetic phase La0.7Sr0.3MnO3 is half-metallic, which is important in the relation to colossal magnetoresistance properties of this compound. Comparing XPS measurements, and the LMTO band-structure calculations for La0.75Sr0.25MnO3, one concludes that the electronic structure of La0.7Sr0.3MnO3 compound consists mainly Mn 3d and O 2p states. In addition, the Mn 3d and O 2p states are hybridized over whole valence band. States of 3d character localized in Mn site predominate near the top of the valence band.

The influence of partial substitution of Co by Al atoms on the magnetic properties of DyCo2 compound

Abstract New results of experimental investigations of the physical properties of Dy(Co 1− x Al x ) 2 compounds, where x = 0.0, 0.1 and 0.2, are presented. These systems crystallize in the whole range of the concentration x in the Laves-phase MgCu 2 crystal structure. The zero field cooled (ZFC) and field cooled (FC) magnetization measurements were performed on the pseudobinary Dy(Co 1− x Al x ) 2 cubic compounds. The composition dependence of the Curie temperature is discussed on the basis of electronic structure calculations.

Structural and magnetic properties of RFe10Cr2 compounds

Abstract The structure and magnetic properties of RFe 10 Cr 2 compounds where R = Y, Nd, Gd, Tb, Dy, Ho, Er, Tm are investigated. X-ray analysis reveals that RFe 10 Cr 2 alloys are of the tetragonal ThMn 12 structure. The lattice constants, Curie temperature, saturation magnetization at 77 and 295 K and the anisotropy field at 295 K are determined. The mean-field approximation is applied to obtain the R-Fe coupling constant. The properties of these compounds are compared with those of R 2 Fe 14 B alloys.

Structural and magnetic characteristics of R2Fe14−xCuxB systems (R = Y, Nd and Gd)

Abstract Structural and magnetic characteristics of R2Fe14-xCuxB systems (R = Y, Nd and Gd) have been investigated. These compounds crystallize in a tetragonal system of P42/mnm-type for a Cu content up to x⩽1.5. The Curie temperature and lattice parameters a and c increase with substitution of Fe by Cu. The spin-reorientation temperature in the Nd2Fe14B compound is lowered when Cu replaces Fe. The effects of Fe substitution by Cu on the saturation magnetization and the anisotropy field are presented.

Magnetic and resistivity investigation of Dy(Co1−xSix)2 (if0 < x ⩽ 0.2) compounds

Abstract The results of experimental investigations of the magnetic and transport (electrical resistivity) properties of Dy(Co 1− x Si x ) 2 , where x = 0.0, 0.1 and 0.2 compounds are presented. These systems crystallize in the whole concentration range of x , in the MgCu 2 Laves-phase-type crystal structure. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements were performed on the pseudobinary Dy(Co 1− x Si x ) 2 cubic compounds. The thermomagnetic cycle of ZFC and FC processes exhibits an irreversible behaviour. The composition dependence of the Curie temperature, 3d-magnetic moment and electrical resistivity is discussed.

Electronic Structure of GdNi4B Compound

The GdNi 4 B compound is studied both experimentally and theoretically by X-ray photoemission spectroscopy and self-consistent tight binding linear muffin-tin orbital calculations, respectively. The density of states at the Fermi level and the magnetic moments are obtained including the influence of various atomic positions in the unit cell. The calculated magnetic moment of Ni atoms is antiparallel to the magnetic moment of Gd and depends on the local environment.

The intrinsic magnetic properties of R2Co7B3 (R = rare earth) intermetallic compounds

Abstract The magnetic properties of polycrystalline intermetallics R 2 Co 7 B 3 with R = Y, Nd, Gd, Tb, Dy, Ho, Er and Tm have been studied. The R 2 Co 7 B 3 compounds crystallize in a hexagonal structure and having the P6/mmm space group. The compounds belong to the R n +1 Co 3 n +5 B 2 n family. All the compounds order magnetically between T C = 310 K for Y 2 Co 7 B 3 and T C = 375 K for Gd 2 Co 7 B 3 . From the measured magnetization, it is evident that the light rare earths are coupled ferromagnetically with the Co moments, whereas with heavy rare lanthanides, antiferromagnetic coupling of the R and Co moments was found. The experimental results are compared with magnetic properties of other RCoB compounds.

Effect of silicon additions on the magnetic properties of Nd2Fe12Co2B alloy

Abstract The results of magnetic measurements performed on Nd 2 Fe 12−x Si x Co 2 B alloys with 0⩽ x ⩽0.6 are presented. All the compound studied crystallize in the tetragonal Nd 2 Fe 14 B structure. The unit cell volume is found to decrease by introducing Si. With substitution of Fe by Si, the saturation moments decrease, but theanisotropy fields and Curie temperatures are found to increase significantly. For example, in Nd 2 Fe 11.5 Si 0.5 Co 2 b, at room temperature, μ s =28.4 μ B , H A =80 kOe and T c =736 K.

X-ray photoemission spectra and electronic structure of GdCo4B

Abstract New results on the electronic properties of GdCo 4 B are reported. This compound crystallizes in the hexagonal CeCo 4 B type structure. The electronic structure has been studied by X-ray photoemission spectroscopy (XPS). The valence band (VB) of the X-ray photoemission spectra is determined mainly by the Co(3d) and Gd(4f) bands. The VB spectrum is compared with ab initio electronic structure calculations performed with the linearized muffin-tin orbital (LMTO) method. The calculated magnetic moment of 3.276 μ B /f.u. is in good agreement with the experimental value, 2.96 μ B /f.u., of the saturation magnetization.