Microchemical induced magnetic changes in thermally oxidized Sm2(Co, Fe, Cu, Zr)17 alloys

Abstract

Permanent loss of hard ferromagnetic characteristics in Sm₂(Co, Fe, Cu, Zr)₁₇ (2:17) alloys on account of disruption in microchemical characteristics of their cellular nanostructure due to thermal oxidation, is a key determinant for their selection concerning prolonged application cycles under extreme conditions. However, studies in the context of microchemical induced magnetic changes in thermally oxidized 2:17 alloys are found to be limited in the literature. In this regard, this study systematically investigates the bulk and the surface magnetic changes induced in thermally oxidized (in the temperature range of 373 K to 973 K at P = 1.013 × 10⁵ Pa) 2:17 permanent magnets of two different alloy grades. Changes in the bulk and the surface magnetic properties are then systematically correlated with the associated microchemical alterations observed in these oxidized alloys. Whereas formation of distinct deterioration zone(s), in varied volume fractions at different oxidation conditions at the expense of hard magnetic phases are attributed to the overall decline in the bulk magnetic characteristics, formation of transition-metal oxides, like, Fe₃O₄, Co₃O₄, CuO and Cu₂O near the alloy/oxide-ambient interface are attributed to the observed increase in in-plane magnetic anisotropy. In the end, operating conditions and strategies to combat the irrecoverable losses of magnetic properties are outlined.