P.C.M. Gubbens

Mossbauer effect investigation of Y-Fe compounds

Mossbauer spectra were taken of the compounds YFe2, YFe3, Y6Fe23 and Y2Fe17 at temperatures ranging from 15K to well above the Curie temperatures (Tc=540, 538, 496 and 358K, respectively). The various spectra were analysed by means of subspectra due to the different nonequivalent Fe sites occurring in these compounds. For each of these sites the temperature dependence of the hyperfine field was determined and shown to be similar for different sites within the same compound.

Magnetic properties of the ternary carbides Tm2Fe17Cx

Abstract We have investigated the crystallographic and magnetic properties of the ternary carbides Tm2Fe17Cx by means of X-ray diffraction, 57Fe Mossbauer spectroscopy, 169Tm Mossbauer spectroscopy and magnetic measurements. It is shown that small amounts of carbon raise the Curie temperature in Tm2Fe17Cx from below room temperature to about 500 K, at the same time increasing the average Fe moment. Important conclusions regarding the rare-earth sublattice anisotropy were derived from the quadrupole splitting of the 169Tm Mossbauer spectra and from the strong concentration dependence of the spin reorientation temperature in Tm2Fe17Cx.

57Fe and 169Tm Mössbauer effect and magnetic properties of Tm2Fe15M2 (M ≡ Al, Ga, Si)

Abstract The Curie temperatures Tc and spin reorientation temperatures TSR were found to increase strongly when aluminium, gallium or silicon was substituted for iron in Tm2Fe17. By means of 57Fe Mossbauer spectroscopy we were able to show that there is no preferential substitution of these elements into the 4f or dumbbell site. The 169Tm Mossbauer effect was studied in Tm2Fe15Si2. We found that silicon substitution has led to a marked shift of the second-order crystal field parameter A02 to more negative values, the corresponding increase in K1 explaining the shift of TSR towards higher temperatures.

Magnetic properties of rare earth-transition metal compounds

A survey is given of results obtained by means of rare earth and57Fe Mössbauer spectroscopy on intermetallic compounds of rare earths (R) and 3d metals (M). It is shown how these results can be used to obtain experimental information on crystal field effects, magnetic anisotropy, magnetic moments and magnetic coupling constants. The types of compounds considered in this review comprise RM5, R2M17, R2Fe14B, R2Fe14C, R2Fe17Cx and RFe10V2. The results obtained by Mössbauer spectroscopy are compared with other techniques and the discussion of relevant theoretical models is included.

Crystal field effects in Tm2M17 compounds studied by 169Tm Mössbauer spectroscopy

Abstract 169Tm Mossbauer spectra of the compounds Tm2Fe17 and Tm2Co17 were measured at various temperatures between 4.2 and 300 K. The spectra were analysed in terms of crystal fields and exchange fields and the presence of two crystallographically nonequivalent Tm sites in these compounds. The crystal field parameters derived from this analysis were used to derive approximate values of the anisotropy constants of these materials.

RFe10V2 compounds studied by57Fe,161Dy,166Er and169Tm Mössbauer spectroscopy

The RFe10V2 compounds are studied with57Fe,161Dy,166Er and169Tm Mössbauer spectroscopy. Parameters as the magnetic moments, the magnetic coupling constants, the easy magnetization directions and the crystal field parameters are determined.

Magnetic density of states at low energy in geometrically frustrated systems

Using muon-spin-relaxation measurements we show that the pyrochlore compound Gd(2)Ti(2)O(7), in its magnetically ordered phase below approximately 1 K, displays persistent spin dynamics down to temperatures as low as 20 mK. The characteristics of the induced muon relaxation can be accounted for by a scattering process involving two magnetic excitations, with a density of states characterized by an upturn at low energy and a small gap depending linearly on the temperature. We propose that such a density of states is a generic feature of geometrically frustrated magnetic materials.

μSR study of RNi5 intermetallics where R=La, Gd or Tb

Zero-field μSR studies of some hexagonal intermetallic compounds are described. Our LaNI5 data provide information on the muon localisation site. This site could be one of the deuterium sites deduced from neutron diffraction. A comparison of the temperature dependence of the exponential damping rate, λ(T), of our samples shows that λ(T) is strongly influenced by crystal field effects. The TbNi5 spectra exhibit two components forT<60 K. We discuss the possible explanations of this result. We see a μSR signal below the magnetic phase transition in GdNi5. This makes the study of the spin-lattice relaxation rate possible in the ordered magnetic state.

Concentration dependence of the Fe moments in rare earth iron compounds

A linear relationhip has been found between the hyperfine fields observed at the various Fe sites in rare earth iron compounds RxFey and the relative number of near neighbour Fe atoms corresponding to these sites. From these results it is concluded that the concentration dependence of the magnitude of the Fe moments in these compounds is largely determined by the local environment.

Influence of the magnetic anisotropy on the relaxation behaviour in DyCu2 and ErCu2

Abstract The orthorhombic intermetallic compounds DyCu 2 and ErCu 2 were measured with 161 Dy and 166 Er Mossbauer spectroscopy, respectively. DyCu 2 , which has a weak magnetic anisotropy parallel to the a -axis, shows no relaxation traject above T N . In contrast, ErCu 2 has a strong magnetic anisotropy parallel to the b -axis and shows a long relaxation traject above T N = 11.5 up to 45 K. A very good correspondence is found between the results of ErCu 2 obtained by inelastic neutron scattering and by 166 Er Mossbauer spectroscopy.