M. Tsoi

Spintronics is about control and manipulation of magnetic moments for new and improved functionality in electronic devices. The phenomenon of spin transfer emerged as a unique tool to control the magnetic state of a ferromagnet (F) with an electrical current. MacDonald and co-workers predicted that spin transfer could also occur in an antiferromagnet (AFM), where it might be even stronger under certain conditions. We recently showed that the exchange bias at an AFM/F interface, with AFM = FeMn and F = CoFe, could be either increased or decreased depending upon the polarity of the applied current. We attributed these changes to effects of the current on the AFM. Here we extend that study to a new AFM = IrMn and to a new F = Py = Ni_xFe_1-x with x ~ 0.2. Using exchange-biased spin-valves (EBSVs) of the form AFM/F(pinned)/Cu/F(free), where both Fs are the same alloy, we first compare data for F = CoFe with AFMs = FeMn or IrMn. The data for FeMn and IrMn are generally similar, with the current having clear effects upon the exchange bias, but little or none on the coercive field of the 'free' CoFe-layer. We then present data for F = Py with AFMs = FeMn or IrMn. With Py, the current generally affects both the exchange bias and the coercive field of the 'free' layer, in ways that we are not yet able to simply correlate with layer thicknesses or AFM.

The magnetic state of a ferromagnet can affect the electrical transport properties of the material; for example, the relative orientation of the magnetic moments in magnetic multilayers¹ underlies the phenomenon of giant magnetoresistance. The inverse effect—in which a large electrical current density can perturb the magnetic state of a multilayer—has been predicted^2,3,4,5,6,7 and observed experimentally with point contacts^8,9 and lithographically patterned samples^10,11. Some of these observations were taken as indirect evidence for current-induced excitation of spin waves, or ‘magnons’. Here we probe directly the high-frequency behaviour and partial phase coherence of such current-induced excitations, by externally irradiating a point contact with microwaves. We determine the magnon spectrum and investigate how the magnon frequency and amplitude vary with the exciting current. Our observations support the feasibility of a spin-wave maser² or ‘SWASER’ (spin-wave amplification by stimulated emission of radiation).

A technique for studying conduction electron/interface interactions is used to study reflection and refraction of an electron beam at a Bi intercrystalline boundary. The technique involves scanning a small laser spot over the surface of a bicrystal, exciting conduction electrons locally, and using a magnetic field to focus excited electrons onto a fixed point contact (an electron collector), after the electrons have been reflected from, or transmitted through, the intercrystalline boundary. Refraction of conduction electrons, high bicrystal interface transparency, and a correlated electron transmission through the interface have all been observed.