Magnetic properties of mechanically milled Sm-Co permanent magnetic materials with the structure

The magnetic properties of Sm(Co,Fe,Cu,Zr) 7 compound with the TbCu 7 structure are studied for the mechanically milled samples. The coercivity could be varied, without affecting the saturation magnetization, from 44 kA/m for the micron sized particles to 280 kA/m by reducing the particle size to sub-micron size (600-900 nm) using high-energy ball milling. The enhancement in the coercivity is attributed to the particles approaching single domain size. The presence of dipolar coupling suggests that the grain sizes are well above the exchange length for the milled samples. The thermal measurements indicate that the compound with the TbCu 7 structure is not stable at high temperatures beyond 743 K