Spin-glass/ferromagnetic transitions and multicritical points in amorphous transition metal alloys (invited)

Experimental results on a number of amorphous alloys with compositions (M1−xM′x)75P16B6Al3, with M either Fe or Co and M′ either Mn or Ni are summarized for compositions in the vicinity of the boundary between ferromagnetic and spin-glass behavior. The qualitative nature of the phase boundary is very similar to that of the Sherrington-Kirkpatrick model, but with non-classical values for the critical exponents. Critical behavior along the ferromagnetic-paramagnetic, ferromagnetic-spin glass, and spin glass-paramagnetic lines are discussed. Some evidence for a qualitative change within the ferromagnetic phase near the spin-glass transition is also given. These represent the first detailed critical-point studies of such a phase diagram.