Temperature dependence of noncollinear magnetic coupling in Fe/Cr(001) superlattices

Using polarized-neutron reflectivity, we have measured the temperature dependence of the noncollinear magnetic coupling of ferromagnetic iron across chromium interlayers in two superlattice samples. The first sample, (52 Angstrom Fe/17 Angstrom Cr)(9), exhibits a room temperature remanent magnetic structure consisting of successive Fe layer moments aligned at 50 degrees relative to each other. This magnetic structure remains unchanged upon cooling the sample to 42 K. In contrast, a superlattice with a thicker Cr interlayer, [44 Angstrom Fe/88 Angstrom Cr](30), passes in a 20 K-wide transition centered on T-N = 240 K from a room temperature state with Fe moments aligned at 90 degrees to an uncoupled state. The formation of the incommensurate Cr spin density wave state below T-N suppresses the interlayer coupling. The thinner Cr interlayers do not undergo a transition to this bulk structure, hence exhibit no suppression of coupling. In both samples, the coupling strength decreases for temperatures at and above room temperature. (C) 1997 American Institute of Physics.