Propriétés magnétiques d'un oxyde amorphe riche en fer : Fe2 O3 (30) BaO (45) B2O3 (25)

Abstract

La transition magnétique d'un oxyde amorphe riche en fer a été caractérisée par des mesures d'aimantation et susceptibilité magnétique et par spectroscopie Môssbauer de 57Fe. On note de fortes interactions antiferromagnétiques dans le verre et un comportement mictomagnétique à basse température. L'ordre magnétique au-dessous de la transition est de nature spéromagnétique

Magnetic and structural properties of iron-based oxide glasses, Fe 2O3-BaO-B2O3, from 57Fe Mössbauer spectroscopy

“…Magnetic transitions and orderings in the amorphous oxides Fe203-BaO-B203. -Combining the present Mossbauer data with the published bulk magnetic results [19,23], three types of magnetic behaviour can be identified, corresponding respectively to low -(sample D), intermediate -(samples A, B) and high -(sample C) concentration range of magnetic ions.…”

“…The increase in susceptibility below 80 K may be due to large magnetic moments localized in small clusters [8]. Thermoremanent effects are observed below 14 K for a sample cooled in a field of 18.8 kOe [19,23]. Unidirectional remanence and displaced hysteresis loops observed at 4.2 K are comparable to those reported for metallic mictomagnets [25].…”

“…Magnetization curves for this sample (A) are linear down to 4.2 K in fields up to 50 k0e except in the low field region « 5 k0e) where a very weak ferromagnetic component appears [19,20,23]. The latter behaviour probably arises from a minor contaminant of ferrimagnetic BaFe12019 which is undetected by X-ray, electron diffraction and Mossbauer analyses.…”

“…3). Among the conceivable explanations for the measured temperature dependence, small particle superparamagnetism is definitely ruled out on the basis of the following arguments : electron microscopy (resolution : -50 A) does not reveal small particles and magnetization data do not show the Q vs. HI T superposition behaviour, typical for non-interacting superparamagnetic particles [20,23]. In a true superparamagnet, the nearly saturated magnetic component should coexist in the Mossbauer spectrum with the paramagnetic doublet [31], contrary to experiment.…”