Electrical detection of millimeter-waves by magnetic tunnel junctions using perpendicular magnetized L 1₀-FePd free layer

Spin dynamics excited by spin-polarized current in magnetic tunnel junctions (MTJs) is potentially useful in nanoscale electrical oscillation sources and detection devices. A spin oscillator/detector should work at a high frequency, such as that of a millimeter-wave, where the quality of a semiconductor device is restricted by carrier mobility, the CR time constant, and so on. Developers of spin systems for practical use need to find out how to excite spin dynamics (i) in the millimeter-wave region, (ii) with low power consumption (ex: no external magnetic field, low damping material), and (iii) for broad frequency modulation. Here L1₀-ordered FePd alloy with perpendicular magnetocrystalline anisotropy (PMA) and a low damping constant, 0.007, was used for the free layer in the MTJs, and a homodyne-detected ferromagnetic resonance (FMR) signal was obtained at around 30 GHz together with the possibility of one-octave frequency modulation. The FMR signal in out-of-plane magnetized L1₀-ordered FePd free layer could be excited without an external magnetic field by injecting in-plane spin polarized alternating current. This study shows the potential utility of L1₀-ordered alloy materials such as FePt, CoPt, MnAl, and MnGa in a variety of millimeter-wave spin devices.