The Role of Disorder in the Magnetic Properties of Mechanically Milled Nanostructured Alloys

Abstract

ABSTRACTMechanical milling provides a unique means of studying the influence of grain size and disorder on the magnetic properties of nanostructured alloys. This paper compares the role of milling in the nanostructure evolution of two ferromagnets – SmCo5 and GdAl2 – and the subsequent impact of nanostructure on magnetic properties and phase transitions. The ferromagnetic properties of SmCo5 are enhanced by short (< 2 hours) milling times, producing up to an eight-fold increase in coercivity and high remanence ratios. The coercivity increase is attributed to defect formation and strain. Additional milling increases the disorder and produces a mix of ferromagnetic and antiferromagnetic interactions that form a magnetically glassy phase. GdAl2, which changes from ferromagnetic in its crystalline form to spin-glass-like in its amorphous form, is a model system for studying the dependence of magnetically glassy behavior on grain size and disorder. Nanostructured GdAl2 with a mean grain size of 8 nm shows a combination of ferromagnetic and magnetically glassy behavior, in contrast to previous studies of nanostructured GdAl2 with a grain size of 20 nm that show only spin-glass-like behavior.