Electrical Noise Studies of the Re-Entrant Spinglass Nickel-Manganese

NiMn is known as a re-entrant spinglass. In some range of Mn concentrations it exhibits a transition from the paramagnetic to ferromagnetic states as it cools, and then crosses over into a regime with many magnetic properties similar to a spinglass but with a spontaneous moment. It has often been suggested that NiMn in this "ferro-spinglass" regime is a spinglass in the components of spins transverse to the overall ferromagnetic moment. Electrical noise and other transport data presented here, however, as well as a careful review of all the literature, suggests a different picture for at least thin film systems with partial short -range atomic order. In this picture it is clusters of spins rather than individual spins that have a random transverse component of magnetization. In addition to these results, electrical noise arising from the dynamics of ferromagnetic domains and domain walls is considered. The noise provides several examples of two-level systems that reveal the ferromagnetic structure and dynamics in different ranges of temperatures and domain sizes.