Chemical ordering dependence of interlayer exchange coupling in Co-Mn-Si/Cr/Co-Mn-Si trilayer structures

The effect of chemical ordering of a half-metallic full-Heusler alloy Co2 MnSi (CMS) on interlayer exchange coupling (IEC) behavior was investigated in Co-Mn-Si(20 nm)/Cr(1.2 nm)/Co-Mn-Si(7 nm) trilayers. Two types of experimental investigations were employed, namely, the variations in IEC with changing the annealing temperature of the bottom CMS from room temperature to 500°C and with changing the Co concentration in top and bottom Co-Mn-Si layers. The 90°coupling parameter J2 and the bilinear coupling parameter J1 were estimated from the numerical simulations of magnetization curves. Only the strong 90° coupling with almost the same strength was observed in both the completely B2 ordered and in a mixture of ordered L 21 and B2 structures. The degree of B2 ordering as well as the strength of 90° coupling was observed to decrease simultaneously with the Co concentration in Co-Mn-Si and 180° coupling appeared in highly Co antisite defective (A2) structures, i.e., for the Co concentration over 73at.%. This observation showed a clear relationship between the degree of B2 ordering and the IEC behavior in full-Heusler Co-Mn-Si-based structures.