Study of Magnetic Materials by Mössbauer Thermal Scans. Application to Nanocrystalline Systems

F. H. SÁNCHEZ; G. A. PASQUEVICH; P.MENDOZA ZÉLIS; F. A. CABRERA

Foz do Iguaçu-Brazil

Workshop; II Workshop on Metastable and Nanostructured Materials NanoMat; 2003

Constant Doppler velocity Mössbauer thermal scans (MTS) were experimented by U. Gonser[1], C.L. Chien[2] and others, especially to extract semi-quantitative information on magnetic ordering temperatures. Here we focuss on a more general aproach in which a set of temperature dependent Mössbauer spectra can be regarded as a two dimentional pattern (v, T), were v is the source-absorber Doppler velocity (determining the gamma ray energy relative to the absorber) and T is the temperature. Intersections of this pattern with planes of constant T lead to the conventional Mössbauer spectra while intersections with constant v planes correspond to the thermal scans. Same considerations are in order for a (v, t) space in the case of isothermal time (t) - dependent experiments. MTS results can be analyzed on the same theoretical background of Mössbauer spectra providing that transformation dependent phenomena such as saturation effects and phonon softening are taking into account. Recently we have reported on a quantitative description and application of MTS results[3]. In this contribution the basis of the quantitative description of the technique is presented along with first applications to: (i) determination of the internal magnetic field temperature dependence in a bulk antiferromagnet (FeSn2) and in an amorphous alloy (Fe73.5Si13.5Nb3Cu1B9), (ii) temperature driven structural and magnetic transformations of Fe73.5Si13.5Nb3Cu1B9, (iii) kinetics of nanocrystallization in Fe73.5Si13.5Nb3Cu1B9. This presentation will address the potential offered by the technique, when adequately combined with conventional Mössbauer spectrometry, to investigate properties of nanostructured systems [1] U. Gonser, C.J. Meechan, A.H. Muir, H. Wiedersich, J. Appl. Phys. 34 (1963) 2373. [2] C.L. Chien, Phys. Rev. B 18 (1978) 1003. [3] P. Mendoza Zélis, G. Paquevich, F.H. Sánchez, N. Martínez and A. Veiga, Phys. Lett. A 298 (2002) 55.