Thickness effect on ferro/antiferromagnetic coupling of Co/CrMnPt systems

To investigate ferro/antiferromagnetic coupling in Co/CrMnPt layers of spin valve films, spin valve films of glass/Ta/NiFe/CoFe/Cu/Co 30 Å/CrMnPt D Å/Ta 30 Å were made with various CrMnPt thicknesses indicated D. Shift fields of the hysteresis loop indicated Hp and coercivities indicated H_c were evaluated. With the increase of D from 150 to 1000 Å, the blocking temperature increases from RT to 340 °C. By increasing the temperature, the coercivity H_c increases, peaks at around the blocking temperature and then decreases. The temperature at which H_c peaks increases with an increase of D. The maximum value of H_c decreases with the increase of D. The grain size distribution of CrMnPt was measured and temperature dependencies of H_p and H_c were calculated based on a thermal fluctuation model using the grain size distribution. Quantitatively, the calculated results agree with the experimental results. The change of temperature dependence of H_p and H _c are explained by the change of the local blocking temperature distribution. With the increase of D, the mean blocking temperature becomes higher and the local blocking temperature shows narrower distributions. The anisotropy constant of the antiferromagnet K_a0, which is a fitting parameter, increases with the increase of D and saturates at above 400 Å.