The suppression of spin–orbit coupling effect by the ZnO layer of La0.7Sr0.3MnO3/ZnO heterostructures grown on (001) oriented Si restores the negative magnetoresistance

Abstract

Dual sign magnetoresistance (MR) and spin-glass state are achieved by stabilizing 120 Å thick La_0.7Sr_0.3MnO₃ (LSMO) film on a (001) oriented Si substrate using pulsed sputtered plasma deposition method. The growth of the ZnO film on top of LSMO suppresses the Curie temperature around 30 K, and reduces the out-of-plane positive MR to zero. On increasing the paramagnetic ZnO film thickness, the out-of-plane negative MR and net magnetic moment increase with the same Curie temperature. At the same time, the band gap decreases, and is attributed to the grain size. The existence of the spin-glass state designates the presence of the non-collinear Mn ion spins, which formed because of the competing double exchange and superexchange interactions. The spin-glass state in the LSMO film is rich in the charge transfer driven localized strong antiferromagnetic coupling at the Si–LSMO interface. The localized strong antiferromagnetic coupling and spin–orbit coupling induced weak antilocalization favor positive MR and reduce the Curie temperature in LSMO. In contrast, the strong magnetic scattering and the loss of the 2D confinement of the charge carrier in LSMO–ZnO heterostructures favor the negative MR. Our investigations show that the technologically important interfacial magnetic coupling and magnetoresistance could be achieved in a bottom interface, and can be manipulated by the top interface of the semiconducting–ferromagnetic–semiconducting heterostructures.