Hyperfine interactions in Ho(Fe_1−xCo_x)₂compounds at 77 K

Abstract

Synthesized, x-ray studied Ho(Fe 1−x Co x ) 2 compounds (x = 0-1) have a pure cubic Fd3m, C15, MgCu 2 -type crystal phase. The unit cell parameter decreases nonlinearly with the composition parameter x. Mössbauer effect spectra collected at 77 K for the Ho(Fe 1−x Co x ) 2 series were composed of a number of locally originated subspectra due to random Fe/Co nearest neighbourhoods. Hyperfine interaction parameters, i.e. the isomer shift, the magnetic hyperfine field and the quadrupole interaction parameter, were determined from the fitting procedure of the spectra for the individual nearest neighbourhoods and also as average values for the sample as bulk. As a result of Fe/Co substitution, Slater-Pauling-type dependences for magnetic hyperfine fields corresponding to both the local area and the sample as bulk were observed. A correlation between the local magnetic hyperfine fields and the average magnetic hyperfine fields was noticed, and this was related to weak and strong ferromagnetism of the transition metal sublattice. The obtained magnetic hyperfine fields were compared to analogous data known for compounds with other rare earths. A numerical formula for describing the magnetic hyperfine field as a function of the composition parameter x and rare earth spin S was proposed.

Mössbauer effect and full-potential linearized augmented plane wave band structure studies on Ho(Fe1−xCox)2intermetallics

“…Since all compounds have Curie temperatures far above the temperature of measurement it may be expected that compounds are close to their magnetic saturation [1,[10][11][12][13][14][15][16][17]. The spectra were fitted considering both the [100] easy axis of magnetization and an assumed random distribution of Fe and Co atoms in the transition metal sublattice, in line with a method described previously elsewhere [7,18].…”

“…is described by a binomial distribution formula [7], in a form adapted to the Ho(Fe 1−x Co x ) 2 series [19]. A fitting procedure was performed, assuming that amplitudes A(k) of the particular subspectra follow probabilities P(6; k) [7].…”

“…Previously, the significance of 3d electrons was experimentally tested for the Ho(Fe 1−x Co x ) 2 series using the 57 Fe Mössbauer effect at temperatures 77 and 295 K [6,7]. It was found that the magnetic hyperfine field µ 0 H hf (µ 0 is the magnetic permeability) measured at 57 Fe nuclei treated as a function of the average number n of 3d electrons calculated per atom in the transition metal 3d band follows a Slater-Pauling-type dependence [6,7].…”

Electrical resistivity, Curie temperature and band structure of Ho(Fe1−xCox)2compounds

“…The factor 0.5 in formula ( 10) is added to omit double counting the same Fe-Co exchange energy (or the same magnetic binding) between neighbouring Fe and Co atoms. After using the formula for p i− j probabilities introduced above and considering that parameters c i− j are symmetrical, the c Fe-Co = c Co-Fe formula (10) takes the form…”

“…Previously, the results of the changing number of 3d electrons in the transition metal sublattice have been studied in Ho(Fe 1−x Co x ) 2 compounds using the Mössbauer effect [9][10][11]. Some results of electronic band structure using the full-potential linearized plane wave (FLAPW) method have also been presented [11].…”