Separation of contributions to spin valve interlayer exchange coupling field by temperature dependent coupling field measurements

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Abstract
In this work, interlayer exchange coupling fields of spin valve samples have been measured as a function of temperature, and fit to a temperature dependent combination of RKKY and Neel coupling fields. The RKKY coupling strength is assumed proportional to the form (T/T0)/sinh(T/T0), where T is temperature and T0 is characteristic temperature. [N. Persat and A. Dinia, Phys. Rev. B 56, 2676 (1997)] This allows the RKKY coupling and Neel coupling field to be separated quantitatively. The results of such an analysis on various CoFe/Cu/CoFe spin valve structures allow the extraction of a roughness parameter from the Neel model and the T0 parameter from the RKKY model. The measured roughness on the top surface was generally 2–3 times greater than the value obtained from the Neel analysis. The extracted T0 parameter was one order of magnitude smaller than that measured for bulk Cu by the de Hass–van Alphen effect. [N. Persat and A. Dinia, Phys. Rev. B. 56, 2676 (1997); B. Lengeler and W. R. Wampler, Phys. Rev. B 15, 5493 (1977)] Part of this reduction may be due to the 2D nature of the electron gas, as justified by an estimate of the 2D free electron Fermi energy calculation. However a factor of four difference remains, with the experimental value of T0 being around 100 K. This behavior, while not fully explained, is consistent with the measurements of other workers.