Asymmetric spin dependent scattering at the interfaces of Si/La0.7Sr0.3MnO3/ZnO heterostructures

Abstract

A ferromagnetic 120 Å thick La0.7Sr0.3MnO3 (LSMO) film grown on (001)Si using the sputtering deposition technique demonstrates a large positive in-plane magnetoresistance (MR) at 10 K, in the field window of ±0.084 kG  to±0.405 kG, although the bulk LSMO exhibits negative MR. Around the coercive field (∼179 G), the positive MR becomes ∼ 11%. The positive MR of the LSMO thin film is explained by the charge transfer driven localized strong antiferromagnetic coupling at the Si−LSMO interface, which favors the reduction of the Curie temperature TC of LSMO compared to that of its bulk value. The construction of the interface on the top surface of LSMO with ZnO thin films further reduces TC ∼ 30 K and the positive MR decreases to ∼ 1% for 45° oriented in-plane current with the in-plane field. The coupling through Mn−O−Zn at the LSMO−ZnO interface preserves the charge state, and the weak exchange coupling at the (La/Sr)O−ZnO interface reduces the spin-dependent scattering process under the field and thereby, the negative MR. The reduced TC and in-plane low-field MR at 10 K of a series of Si/LSMO/ZnO are the same irrespective of the ZnO thickness, which confirms their interfacial origin. The presence of interfacial spin disorder at the Si−LSMO interface is further confirmed from the increase in resistance at low temperatures, which is explained by the Kondo like effect and quantum interference effect. Our investigations show that the technologically important interfacial magnetic coupling and magnetoresistance could be achieved and manipulated by the selective interfacial exchange coupling.