MAGNETIC-MOMENTS OF IRON CLUSTERS WITH 25 TO 700 ATOMS AND THEIR DEPENDENCE ON TEMPERATURE

Magnetic moments mu(N) of iron clusters in a molecular beam, with temperatures ranging from 100 to 1000 K, are investigated from their Stern-Gerlach deflections. We find that at a temperature of 120 K, mu (25 less-than-or-equal-to N less-than-or-equal-to 130) is 3mu(B) per atom, decreasing to about the bulk value (2.2mu(B) per atom) near N = 500. For all sizes, mu decreases with increasing temperature, and is approximately constant above a temperature T(C)(N). For example, T(C)(130) is about 700 K, and T(C)(550) is about 550 K (T(C) bulk = 1043 K). Limitations of the superparamagnetic model due to rotational effects are discussed.