Materials dependence of the spin-momentum transfer efficiency and critical current in ferromagnetic metal/Cu multilayers

We have quantitatively compared spin-momentum transfer effects in FM/Cu multilayers, with FM=Co, Co90Fe10, Ni80Fe20, Ni40Fe10Cu50, and Fe. All of the measured multilayers exhibited an abrupt step up in resistance at a critical current Ic, the value of which was a linear function of applied magnetic field Happ. The spin-transfer efficiencies determined from these data were in substantial agreement with their predicted values over the range of materials studied. Ic(Happ), when evaluated at zero net field, was found to increase with the exchange energy density of the ferromagnet, demonstrating the tunability of the critical current by materials selection.

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