Second-order magnetic phase transition in amorphous Fe₁₀Ni₇₀B₁₉Si₁

Abstract

Magnetic measurements performed on the amorphous Fe₁₀Ni₇₀B₁₉Si₁ alloy in the critical region (145-210 K) in fields up to 10 kOe reveal that this alloy exhibits a well-defined magnetic phase transition at 186.5± 0.3 K with the critical exponents β=0.42± 0.02, γ=1.35± 0.04 and δ=4.49± 0.05 satisfying an equality relation resulting from the static scaling hypothesis and with the reduced magnetization and field following a magnetic equation of state derived for the second-order phase transition over a wide temperature range. A reasonably good agreement between the present exponent values and those derived from the theories based on the Heisenberg spin model has been observed. Long range forces (such as dipole forces) are shown to have negligible influence on the critical fluctuations of magnetization. A detailed analysis of the magnetization versus field isotherms taken above the Curie temperature demonstrates the existence of giant super-paramagnetic clusters.