Temperature dependence of the magnetization of superlattices with variable interlayer magnetic couplings

A Heisenberg model is solved for the coupling of two-dimensional ferromagnetic layers separated by nonmagnetic spacer layers in a superlattice configuration. The cases of noncoupling, and ferromagnetic and anti-ferromagnetic interlayer couplings, are solved for the temperature dependence of the magnetization at low temperature; the results yield linear, ${\mathit{T}}^{3/2}$ and ${\mathit{T}}^2$ power laws, respectively. Experimental realization of the coupling cases was then sought. Three sputtered Fe/Cr superlattices with 10 Å Fe layers and Cr-layer thicknesses of 100, 20, and 10 Å were chosen to span the three cases, respectively. Superconducting-quantum-interference-device magnetometry yields linear and ${\mathit{T}}^{3/2}$ behavior for the first two cases. Mössbauer spectroscopy in zero field indicates an approximately ${\mathit{T}}^2$ behavior for the antiferromagnetically coupled sample. The results are discussed and related to recent magnetotransport work.