Spin Dynamics of the Low-Temperature Magnetic Relaxation in Disordered Fe<sub>35</sub>Al<sub>50</sub>B<sub>15</sub> Alloys

Abstract

An alloy of Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">35</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> has been prepared by milling under vacuum for 840 h. The X-ray diffraction pattern shows only two broad peaks stemming from a highly disordered structural state. The magnetic state was characterized by AC susceptibility. It displays sharp maxima around 20 K (21 K) in the real (complex) components. The maxima are due to the onset of a spin frozen disordered arrangement, and shift to higher temperature with increasing frequency. The magnetic dynamics is accounted for a power-law in the vicinity of the transition. Values of zv = 9.0(3) and T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 19.5(1) K are obtained. Complex susceptibility dynamic scaling results in a large β = 1.3(1). The values extracted for the critical exponents are close to those of glassy magnets and are an indication of a nonconventional transition. The nonlinear susceptibility reveals a peak at the transition, which is affected by the oscillating h <; 5 Oe and biasing (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> ≤ 40 Oe) fields. The results are interpreted in terms of the freezing of very fine Fe-rich magnetic particles which are present as the result of an incomplete compositional homogenization despite the long milling time.