Spin Torque Ferromagnetic Resonance (ST-FMR)

The figure shows the actual set-up for field modulated (FM)-STFMR. In this technique, we modulated the static magnetic field by a small ac field of 5 Oe, produced by a pair of Helmholtz coils. These coils are supplied with the reference frequency (98Hz) from a lock-in amplifier, which also measures the spin-torque diode voltage. The applied Irf excites the magnetization dynamics of the free layer and causes the resistance to oscillate when the frf is near to the resonance of the magnetic free layer. The precession of magnetic moment produces time dependent resistance oscillations. The voltage V(t) = I(t)R(t) contains the mixing between Irf and resistance oscillations. When the frequency of the Irf, i.e., frf, is near to the Eigen frequency of precession of the magnetic moment, a voltage Vmix develops over the device which is measured across the lock-in amplifier. We have a custom made probe station based broad band ST-FMR set-up working in the range of 100 MHz to 20 GHz. The set-up includes a GMW projectile magnet which provides 360o rotation of magnetic field, making the measurement in three dimensional magnetic field.