Hysteretic behavior of the diluted random-field Ising system ${\mathrm{Fe}}_{0.70}$${\mathrm{Mg}}_{0.30}$${\mathrm{Cl}}_2$

We report a systematic neutron scattering study of the hysteretic behavior of the randomly diluted metamagnet ${\mathrm{Fe}}_{0.70}$ ${\mathrm{Mg}}_{0.30}$ ${\mathrm{Cl}}_2$ in magnetic fields, which is presumed to correspond to the three-dimensional Ising model in random fields. In general, we find that the low-temperature state of the system is disordered if it is approached from the disordered paramagnetic phase, but ordered if it is approached from the zero-field-ordered phase. In contrast to typical spin-glass systems, time dependence is observed for the field-cooled states. Plausible explanations for these phenomena and further experiments are suggested.