MAGNETIC-SUSCEPTIBILITY OF PURE GADOLINIUM AS FUNCTION OF THE FIELD IN THE SPIN REORIENTATION REGION

A.c. magnetic susceptibilities chi of a 99.99% nominal purity gadolini um polycrystal have been measured in the temperature range 110 - 295 K as a function of applied magnetic fields (0.3 G less-than-or-equal-to H less-than-or-equal-to 2600 G). For weak fields and increasing tempe rature, chi(T) goes through a maximum at T(M) = 208 K then it decrease s slightly until it reaches the temperature T2 = 223 K where it falls precipitously. The temperature corresponding to the sharp fall of chi decreases when H is augmented but T(M) remains unaffected as long as H has not reached a critical field H(c). The shape of chi(T) changes dr astically above H(c); for H = 1040 G for example T(M) shifts to 141 K and T2 emerges as a local minimum in chi. We discuss these effects in terms of the variable angle between the ferromagnetic spins and the he xagonal c-axis of Gd. This fine structure of X in the region of T2 has not been detected in a 99.9% pure polycrystal.