Novel room-temperature spin-valve-like magnetoresistance in magnetically coupled nano-column Fe3O4/Ni heterostructure

Abstract

Herein, we design a room-temperature spin-valve-like magnetoresistance in a nano-column Fe₃O₄/Ni heterostructure without using a non-magnetic spacer or pinning layer. An Fe₃O₄ nano-column film is self-assembled on a Ni underlayer by the thermal decomposition method. The wet-chemical self-assembly is facile, economical and scalable. The magnetoresistance (MR) response of the Ni underlayer in the heterostructure under positive and negative out-of-plane magnetic fields differ by ∼0.25 at room temperature and ∼0.43 at 100 K. We attribute the spin-valve-like magnetoresistance to the unidirectional magnetic anisotropy of the Ni underlayer when being magnetically coupled by the Fe₃O₄ nano-column film. The out-of-plane negative-field magnetization is higher than the positive-field magnetization, affirming the unidirectional magnetic anisotropy of the Fe₃O₄/Ni heterostructure. Temperature-dependent magnetic and resistivity studies illustrate a close correlation between the magnetization transition of Fe₃O₄ and resistivity transition of Ni and prove a magnetic coupling between the Fe₃O₄ and Ni. First-principles calculations reveal that the Fe₃O₄/Ni model under a negative magnetic field is energetically more stable than that under a positive magnetic field. Furthermore, partial density of states (PDOS) analysis demonstrates the unidirectional magnetic anisotropy of the Ni 3d orbital. This is induced by the strong ferromagnetic coupling between Fe₃O₄ and Ni via oxygen-mediated Fe 3d–O 2p–Ni 3d hybridizations.