SQUID magnetometry measurements on a CuMn spin-glass reveal that the zero-fieldcooled magnetization strongly depends on the time the sample is kept at constant temperature prior to the field application. This result is evidently at variance with the common belief that an equilibrium spin-glass state is quickly obtained after cooling in zero field. The nonequilibrium behavior, as reflected in the complex time dependence of dm/dlnt f is interpreted to arise from slow dynamics of the relaxation-time spectrum.

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The magnetic properties of stoichiometric Fe2P and non-stoichiometric Fe2-xP (0 < × ⩽ 0.06) have been studied by means of magnetic susceptibility. Measurements on pure stoichiometric Fe2P samples show that there is a first order magnetic phase transition from a ferro- to a paramagnetic state at 216 ± 1 K. The transition is accompanied by a discontinuous change in the dimensions of the hexagonal unit cell with a decrease in the a-axis of 0.06% and an increase in the c-axis of 0.08% for increasing temperature. The transition is interpreted to be of magnetoelastic origin with an exchange energy critically sensitive to the interatomic spacing. Measurements on single crystals show that the spins are directed along the hexagonal c-axis with an exceedingly high axial anisotropy. The saturation moment is 1.46 μB/iron atom and the anisotropy energy as estimated from low field data is ∼ 2.5 × 106 J m-3 (2.5 × 107 erg cm-3). The transition behaviour is very sensitive to the magnitude of the external field as well as to the presence of impurities and deviations from the ideal stoichiometry in the samples.

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