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 Å Fe/17 Å Cr)₉, exhibits a room temperature remanent magnetic structure consisting of successive Fe layer moments aligned at 50° 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 Å Fe/88 Å 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° 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.