P. Renaudin

Mössbauer studies of FeAl2O4 and FeIn2S4 spin glass spinels

Mössbauer experiments were performed on iron spinels in which spin-glass-like properties are observed. The spin glass character of FeIn2S4 cannot be considered as canonical due to the existence of a relaxation-time distribution nearTg. A surprising first-order transition atTg has been evidenced for FeAl2O4.

Mössbauer studies of granular Fe/Al2O3 films

Results from low temperature Mössbauer measurements upon several samples of dispersed small Fe particles in an alumina matrix are presented. The nature and population of the various iron species are deduced and discussed in relation to the particle mean diameters. An evaluation of the blocking temperature for one sample has been attempted.

Hyperfine parameters of amorphous Fe64Cr16B20 particles dispersed in an alumina matrix

Mössbauer spectra of amorphous Fe64Cr16B20 particles dispersed in an alumina matrix are compared to those of the corresponding amorphous ribbon. The slight variations between the hyperfine parameters of the granular samples are mainly assigned to disorders at the particle surface. The behaviour of the blocking temperatures versus frequency deduced from A.C. susceptibility measurements and Mössbauer spectroscopy is governed by particle interactions.

Properties of a new metal-ferrite composite as seen by Mössbauer spectroscopy

Several samples of a new metal-ferrrite composite made up of Fe-Co alloy and mixed Fe-Co ferrite have been studied by Mössbauer spectroscopy with and without applied field. The general chemical formulas have been established and the non-collinear magnetic structure has been evidenced at low temperature due to anisotropic Fe2+ and Co2+ ions.

Mössbauer studies of CdCr2xIn2−2xS4:57Fe solid solutions: Reentrant and spin glass like properties

Mössbauer spectroscopy has been performed in CdCr2xIn2−2xS4 spinel solid solutions (0.7⩽x⩽0.95). For x>0.85, reentrant properties are observed: For T<Tc, finite clusters occurs, decoupled of the ferromagnetic matrix; at low temperature, the ferromagnetic order seems to vanish and a spin glass state occurs. For x⩽0.85, a spin glass state is observed and the properties are coherent rather with a phase transition.

Quadrupole splittings and hyperfine fields in CdCr2xIn2−2xS4 spin glass system

CdCr2xIn2−2xS4 spinels show spin glass and reentrant properties. The quadrupole splitting variations with composition and temperature are determined from paramagnetic spectra and interpreted from crystal field theory and partial quadrupole splitting treatment.

Mössbauer study of mineral glasses: East rhodope perlites

Several perlites of different colours originating from east Rhodope (Bulgaria) have been studied by Mössbauer spectroscopy. Several types of iron are revealed (i) paramagnetic Fe2+ and Fe3+ down 4.2K which correspond to iron dispersed into the glass matrix (ii) small aggregates of Fe2+ and hematite in colloidal type phase with superparamagnetic properties (iii) large aggregates and microlites of hematite and magnetite. Alteration effects and colour problem are discussed.

Mössbauer studies of Ni70Fe10Si8B12 metglass: Reentrant properties

Amorphous metal Fe10Ni70Si8B12 has been studied by Mössbauer spectroscopy without and with an weak applied field in the plane of ribbons. Reentrant properties have been confirmed with the existence of a canted state at low temperature. Studies with different values of the applied field have shown that a field near 50 0e is sufficient to saturate the average direction of the ferromagnetism.