Bringing a ferromagnetic layer to resonance creates non-equilibrium magnetization dynamics which generates a spin current. The spin current propagates from the ferromagnet into a neighboring layer if permitted by the interface. This is equivalent to saying that the air-flow generated by rotating the blades of a fan can propagate in a neighboring room if the door between the rooms is open. Our experiments show that spins propagate more efficiently in a neighboring zone where the magnetic order is fluctuating rather than static. Basically, a fluctuating order allows more spin orientations to pass through the interface. These experimental findings will help us progress towards the development of more efficient spin sources, while also providing an alternative method to probe magnetic phase transitions. This type of alternative method is particularly needed to deal with the case of thin materials with no net magnetic moments, such as thin antiferromagnets. Antiferromagnetic order is expected to have a high potential in next-generation spintronic applications, a field known as antiferromagnetic spintronics.
Figure. (a) Diagram representing the spin pumping experiment. Non-equilibrium magnetization dynamics of a spin injector (NiFe) pumps a spin current (IS) into an adjacent layer, called the spin sink (IrMn). This spin sink absorbs the current to an extent which depends on its spin-dependent properties. To eliminate direct exchange interactions and focus only on the effects due to the interaction between the spin current and the spin sink, the injector and the sink are separated by an efficient spin conductor (Cu). (b) Dependence of the IrMn spin pumping contribution to the NiFe damping (αp) on temperature (T). The data are obtained from αp(T) = α(T) – α0(T), where α0 is the damping for tIrMn = 0. To facilitate reading, the data were shifted vertically. The enhanced spin pumping occurring during the IrMn magnetic phase transition is δαp. (c) Dependence of on tIrMn, where is the critical temperature for the IrMn magnetic phase transition. Fitting the data returned the spin-spin correlation length (n0).
L. Frangou, S. Oyarzun, S. Auffret, L. Vila, S. Gambarelli, and V. Baltz (vincent.baltz@cea.fr), Enhanced spin pumping efficiency in antiferromagnetic IrMn thin films around the magnetic phase transition, Phys. Rev. Lett. 116, 077203 (2016).
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.077203