Phase(?) Transitions in Systems with Spin Glass and Long-Range Order Regimes

Abstract

Some of the first spin glasses studied were created by slight modifications of the structural parameters of systems possessing long-range order, and it is of interest to look for general features of systems in which a spin-glass transition intersects a line of Curie or Neel temperatures as the concentration of magnetic sites increases in a random A-B solid solution where A is non-magnetic and B magnetic. Metallic systems are of particular interest since fairly high temperature spin glass transitions can be expected to follow from the RKKY coupling of solute B atoms, but straightforward tests of percolation ideas can be complicated by the presence of two families of interactions, nearest neighbour and RKKY. An added problem in metallic systems is that when strong mixing exists between the conduction electrons of metal A and the part-filled electron shell providing the B moments the B atom may not carry a moment when in dilute solution. (We shall not here discuss the question of whether this situation is better described as a non-magnetic ground state of the Friedel-Anderson approach or of the Kondo problem, but it should be borne in mind that in principle a singlet of the crystal field Hamiltonian, the spin-orbit interaction or even the hyperfine interaction can have an effect which is formally very similar.)