Medium range ordering and some magnetic properties of amorphous Fe90Zr7B3 alloy

High-resolution electron microscopy (HREM) reveals in the as-quenched Fe90Zr7B3 alloy the existence of medium range ordered (MRO) regions 1-2 nm in size. Transmission Mossbauer spectroscopy confirms that these regions are alpha-Fe MRO ones. Above the Curie point of the amorphous phase (T-C=(257 +/- 2)K) they behave like non-interacting superparamagnetic particles with the magnetization decreasing linearly with the temperature. For these particles the average magnetic moment of 390 mu(B) and the average size of 1.7 nm, in excellent agreement with HREM observations, were estimated. The maximum of the isothermal magnetic entropy change at the maximum magnetizing field induction of 2 T occurs at the Curie temperature of the amorphous phase and equals to 1.05 Jkg(-1) K-1. The magnetic entropy changes exhibit the linear dependence on the maximum magnetizing field induction in the range 0.5-2 T below, near and above T-C. Such correlations are attributed to superparamagnetic behavior of alpha-Fe MRO regions. (C) 2010 Elsevier B.V. All rights reserved.