Interlayer interaction in a Fe/Cr/Fe system: Dependence on the thickness of the chrome interlayer and on temperature

A three-layer sample of Fe(100 A)/Cr(0–20 A)/Fe(100 A) is used to study the dependence of inter-layer exchange on the thickness of the chrome interlayer and on temperature. The method of Kerr magnetometry in the temperature range from 77 to 473 K and the method of Brillouin scattering of light by spin waves at room temperature are used. The data for magnetization curves and spin wave spectra are treated in the model of biquadratic exchange. The range of validity of this model is established, which is apparently determined by interlayer exchange. The resultant dependence of the constant of bilinear interaction on the interlayer thickness demonstrates an oscillating behavior with two oscillation periods of about 3 and 18 A. Within the experimental error, the magnitude of this constant, the amplitude, and the period and phase of its oscillation are independent of temperature. It is found that the constant of biquadratic exchange decreases in inverse proportion to the chrome thickness, the proportionality factor decreasing linearly as the temperature rises. In order to interpret the observed singularities in the behavior of the biquadratic exchange constant, a theoretical model is suggested which includes the nonideality of the interface and the presence of magnetic hardness in the chrome interlayer. This rigidity exceeds in magnitude the interaction on the interface between iron and chrome. The suggested model gives an adequate qualitative description of the experimental results.