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Spin-dependent tunnelling junctions with amorphous CoNbHfFe
Sharma, Manish; Tran, Lung T.; Anthony, Thomas C.; Warot, Benedicte; Petford-Long, Amanda K.
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Abstract: We report on using amorphous Co77Nb16Hf6Fe1` (CoNbHfFe) as the ferromagnetic electrode in bottom-pinned magnetic tunnel junctions (MTJ's). Exchange bias with CoNbHfFe was achieved with Mn75Ir25 as the antiferromagnetic pinning layer. In a first sample with both pinned and sense layers being CoNbHfFe, a tunnelling magnetoresistance ratio (TMR) of 5% was found. In comparison, a TMR of 16.4% was found in a second sample with a pinned Co50Fe50 electrode and a sense CoNbHfFe electrode. This leads to a low spin-polarization of about 15% for CoNbHfFe at room temperature. High- resolution transmission electron microscopy (HREM) images show that while the first sample has a fully amorphous sense layer, the sense layer in the second sample is largely amorphous with nano-crystalline inclusions. Both pinned layers are found to be highly textured and crystalline. To study switching distributions, large MTJ arrays were patterned using electron-beam lithography and the magneto-optic kerr effect (MOKE) was used to measure the switching of the sense layer. MOKE results for the two samples are compared in arrays with devices of different sizes.
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