Competing sweep-rate dependent effects in the hard loop of spin-valve multilayers

Sweep-rate-dependent effects due to time-dependent magnetisation reversal of the pinned layer in spin-valve structures based on the Ta/NiFeCo/Cu/NiFeCo/FeMn system have been studied. By measuring the demagnetising branch of the hard loop of a spin-valve at different sweep rates, after holding the pinned layer at saturation in the opposite direction to the pinning field for different amounts of time, we have observed competing sweep-rate-dependent effects. Our results show that the effect which dominates depends upon the length of time the pinned layer is held at saturation and a critical saturation time exists where the two effects are equal.