Contribution of Pt impurities to spin configurations in the reentrant spin glass NiMn

We have measured the temperature-dependent linear and nonlinear susceptibilities of the reentrant spin glass Ni_100-xMn_x (x = 22.4, 23.0 and 23.4) and Pt-doped samples Ni_100-x-yPt_yMn_x (x = 23.5, y = 0.6 and 1.1) in order to elucidate the thermal evolution of spin configurations in the low-temperature states. The nonlinear susceptibility in the reentrant spin glasses Ni_77.0Mn_23.0 and Ni_76.6Mn_23.4 shows a peak corresponding to the appearance of the vortex-like spin structure in addition to conventional phase transitions. Such an extra peak becomes more pronounced in Ni_75.9Pt_0.6Mn_23.5 and Ni_75.4Pt_1.1Mn_23.5 with increasing Pt content, suggesting the appearance of a long-range vortical spin arrangement above the spin freezing temperature. In these Pt-doped samples, the singularity due to the spin glass transition becomes indistinct and the ferromagnetic transition disappears. We explain this contribution of Pt to the spin configuration in terms of the enhanced magnetic anisotropy due to a Dzyaloshinsky-Moriya-type interaction.