We exploit nanoscale metallic contacts for detection of ferromagnetic resonance. In our experiments we use mechanical point contacts between a copper wire tip and a ferromagnetic sample of interest to inject both dc and microwave currents into the sample. A small dc voltage develops across the contact subject to microwaves that can be attributed to rectification processes in the contact. The rectification signal was found to increase linearly with the applied dc current as expected for a point contact in the thermal regime. Here the point contact acts as a nanoscale bolometer which monitors the microwave current absorbed by the sample. When the microwave absorption increases at ferromagnetic resonance the rectification signal reveals the resonance. Our point-contact technique enables the electrical detection of ferromagnetic resonance in sample volumes as small as a few cubic nanometers.
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 = NixFe1-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.