We fabricated a magnetic tunnel junction (MTJ) using an MgO barrier and MnGa electrode, which shows large magnetic anisotropy, and we investigated the spin torque diode effect in the MTJ. The magnetoresistance ratio increased up to approximately 40% by inserting thin FeB/Fe layers at the MnGa/MgO interface. The obtained diode effect was as high as 70 GHz, which is thought to occur due to the coupled precession acoustic mode in the MnGa/Fe-B multi-layer. Numerical simulation suggests that a very high frequency diode signal of more than 150 GHz can be expected in the optical mode precession.
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