ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Recent magnetoresistance experiments1,2 on Fe/Cr/Fe sandwiches and superlattices show that the critical magnetic field for saturation varies linearly with temperature from liquid helium to room temperature. The drop in critical field is as large as 30%, even though the reduction in Fe magnetization is negligible over this temperature range. In order to gain some insight into the physical origin of this softening of the critical field, which is a measure of the antiferromagnetic interlayer coupling, we have studied a phenomenological model of an Fe/Cr/Fe sandwich structure which consists of two Fe films coupled at their interface by an antiferromagnetic exchange at zero temperature. The Fe films themselves are ferromagnetic and subjected to an external field and uniaxial in-plane anisotropy. The Fe spins are confined to the film plane. The temperature dependence of the critical field, i.e., the field below which the spins in the two films deviate from the direction of the field, arises from fluctuations in these spin deviations, which are present for any temperature greater than zero. Using an approximation in which these fluctuations are treated classically, the critical field decreased linearly with temperature, with a coefficient that increases logarithmically with the transverse dimension of the films. Interpreting this length to be of the order of the grain size in polycrystalline films or a coverage terrace width in epitaxially grown material, we can directly relate the temperature variation of the antiferromagnetic interaction to film quality. The larger this dimension, the greater the decrease of the coupling with temperature; hence, "better'' films are expected to show weaker (or zero) coupling at room temperature. Conversely, the magnetization of the Fe films is not critically dependent on this dimension. Extension of the model to include spin-wave effects will be discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.350117
