Mössbauer magnetic scans: basic principles, experimental layout and data analysis

G. A. PASQUEVICH; P. MENDOZA ZÉLIS; A. LENCINA; M. B. FERNÁNDEZ VAN RAAP; F.H. SÁNCHEZ

La Plata - Argentina

Conferencia; XI Latin American Conference on the Applications of the Mössbauer Effect; 2008

Universidad Nacional de La Plata

   Mössbauer Magnetic Scans (MMS) allow to study the response of magnetic moments to an external applied field. In the case of ferromagnetic samples, studies of domain dynamics can be performed. The important advantage offered by the MMS methodology in comparison with conventional techniques is that responses from different phases or sites can be distinguished. MMS are performed by precisely selecting Doppler velocities with a constant velocity drive [1], and measuring the transmission rate while a magnetic external field is modulated. A multiescaler is used, synchronically with the exciting ac field, to record enough magnetic sweeps as to attain the required statistics.   To understand the patterns observed in previous MMS [2] and define an analysis methodology, two α-Fe samples are studied, with thicknesses of 12 μm and of less than 1 μm.   The thin absorber results can be analysed within the well known thin absorber approach. For the thicker one, both polarization and thickness effects must be taken into account. However, more information can be retrieved in the second case. For thin absorbers, only the field dependence of the mean square projection (MSP) of the magnetic moments in the gamma rays direction is obtained. For thick samples, the asymetry on the MSP over the plane orthogonal to the gamma direction is also obtained.   For the 12μm α-Fe sample, the MSP along the gamma ray direction and the MSP asymmetry in the orthogonal plane, are presented as quasi-continuous functions of the applied field for a complete quasi-static magnetic cycle. It is shown that MSP goes slower to saturation in the sample plane than in its normal direction, reflecting the magnetic shape anysotropy of the sample.   The MMS experimental layout and experimental details are also presented.   [1] A. Veiga, N. Martínez, P. Mendoza Z ́lis, G. A. Pasquevich, F. H. Sánchez, Hyperfine Interact. 167 (2006), pp 905.   [2] G.A. Pasquevich, P. Mendoza Zelis, F.H. Sánchez, M.B. Fernandez van Raap, A.L. Veiga, N. Martínez, Physica B, 384 (2006), pp 348.