Studies of Interface Induced Phenomena: Magnetic Proximity effect and Spin Hall Magnetoresistance

  • 黃 舜漁

Student thesis: Doctoral Thesis

Abstract

In this thesis we separate into two parts: magnetic proximity effect and spin Hall magnetoresistance In the first part we investigated the proximity effect in topological insulator (TI) and magnetic insulator bilayer system (Bi1-xSbx)2Se3/CoFe2O4 (CFO) heterostructure was fabricated using molecular beam epitaxy and pulsed laser deposition system respectively As revealed from the magnetoresistance measurement the weak anti-localization (WAL) is strongly suppressed by proximity effect in (Bi1-xSbx)2Se3/CFO interface Modified Hikama-Larkin-Nagaoka equation was used to fit the WAL results so that the size of surface state gap can be extracted successfully The temperature-dependent resistance of the heterostructures at small and large perpendicular magnetic fields were also measured and analyzed The results indicate that the surface band gap can be induced in TI and continuously enlarged up to 9T indicating the gradual alignment of the magnetic moment in CFO under perpendicular magnetic field The approaches and results accommodated in this work show that CFO can effectively magnetize (Bi1-xSbx)2Se3 and the heterostructures are promising for TI-based spintronic device applications Meanwhile in the second part we integrated bilayer structure of covered Pt on nickel zinc ferrite (NZFO) and CoFe/Pt/NZFO tri-layer structure by pulsed laser deposition system for a spin Hall magnetoresistance (SMR) study In the bilayer structure the angular-dependent magnetoresistance (MR) results indicate that Pt/NZFO has a well-defined SMR behavior Moreover the spin Hall angle and the spin diffusion length which were 0 0705 and 0 85 nm respectively can be fitted by changing the Pt thickness in the SMR equation Particularly the MR ratio of the bilayer structure (Pt/NZFO) has the highest changing ratio (about 0 135%) compared to the prototype structure Pt/Y3Fe5O12 (YIG) because the NZFO has higher magnetization Meanwhile the tri-layer samples (CoFe/Pt/NZFO) indicate that the MR behavior is related with CoFe thickness as revealed in angular-dependent MR measurement Additionally comparison between the tri-layer structure with Pt/NZFO and CoFe/Pt bilayer systems suggests that the SMR ratio can be enhanced by more than 70% indicating that additional spin current should be injected into Pt layer
Date of Award2017 Aug 4
Original languageEnglish
SupervisorJung-Chun Huang (Supervisor)

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