Hard-magnetic properties and microstructure of Sm(Co,Cu)z compounds

Magnetic measurements and metallographic investigations are reported on Sm(Co,Cu)z alloys. The compositions lie between the rare-earth (RE) to transition-metal (TM) ratios of 1 : 5 and 2 : 17 with a content of copper of up to 35% of the TM fraction. The materials were analyzed both in the as-cast and heat-treatment conditions. The remanence BR scales with composition. The coercivity IHc showed a maximum along a tieline from the off-stochiometric Sm(Co0.65Cu0.35)5.6 to the Sm2Co17 phase. In the as-cast state the hysteresis loops are not square. High-temperature homogenization yields ideal demagnetization curves. Subsequent annealing at lower temperatures T resulted in two coercivity peaks as a function of T. The peak temperatures decrease with increasing Cu concentration, e.g., for 35% Cu of TM 450 and 650 °C and for 20% Cu of TM 650 and 850 °C were found. Alloys near the 2 : 17 phase boundary contain 2 : 17 as a massive primary phase in a 1 : 5 matrix. The squareness of the hysteresis loops implies that the 2 : 17 phase itself is magnetically hardened. The results are discussed on a pinning model under consideration of the metallurgical properties of the RE-TM alloys.