ATOMIC AND MAGNETIC SHORT-RANGE ORDER IN AG-MN SPIN-GLASS ALLOYS

To understand the relationship between the magnetic properties and local arrangements of Mn spins in Ag-Mn spin-glass alloys, we have measured the magnetic susceptibility, and x-ray and diffuse-neutron-scattering intensities for three single crystals. The x-ray results show that the Mn atoms are found to have a preference for linking up along [100] directions. This tendency increases with increasing Mn content up to around 20.8 at.% Mn. However, this tendency decreases abruptly at 28.1 at.% Mn. The neutron results for the spin-glass state of Ag-20.8 at.% Mn alloy show that the nearest spin pairs have strong antiferromagnetic coupling and the second-nearest spin pairs along the [100] directions are correlated ferromagnetically with each other. These ferromagnetic spin chains are found to develop inside the atomic short-range-ordered region of Mn atoms. In addition to the existence of these spin chains, we have also observed longer-range spin correlation with about twice the correlation length of the atomic one. The amplitude of the magnetic susceptibility at the freezing temperature and the paramagnetic Curie temperature are found to have a strong relationship with the short-range spin structure. We believe that the longer-range spin correlations cannot grow without conflicting with the short-range spin structures inside the atomic short-range-ordered region of Mn atoms. This may become a key point to understand the spin-glass freezing mechanism.