Giant magnetic viscosity in SmCo5-xCux alloys

Hysteresis loops in SmCo5-xCux as-cast and annealed magnets (1 < x less tha n or equal to 3) were measured at room temperature using a pulsed-field mag netometer and a static vibrating sample magnetometer. At field sweeps betwe en 2 and 17 (GA/m)/s a giant-in this field range nearly constant-magnetic v iscosity S-v was obtained. The viscosity is approximately proportional to t he Cu concentration and to the coercive field. A heat treatment at 1273 K f or three weeks changes the microstructure and enhances strongly the intensi ty and the time dependence of the coercivity. The decay of the inverse of t he coercive field H-c with time follows a simple ln(t) relation between 10( -5) and 10 s. Data analysis allows a density of stacking faults N to be ext racted for each sample. S-v (and H-c) increases with N which increases with x. (C) 1999 American Institute of Physics. [S0021-8979(99)07721-X].