Symmetric and Asymmetric Magnetic Tunnel Junctions with Embedded Nanoparticles: Effects of Size Distribution and Temperature on Tunneling Magnetoresistance and Spin Transfer Torque

Abstract

The problem of the ballistic electron tunneling is considered in magnetic tunnel junction with embedded non-magnetic nanoparticles (NP-MTJ), which creates additional conducting middle layer. The strong temperature impact was found in the system with averaged NP diameter d av < 1.8 nm. Temperature simulation is consistent with experimental observations showing the transition between dip and classical dome-like tunneling magnetoresistance (TMR) voltage behaviors. The low temperature approach also predicts step-like TMR and quantized in-plane spin transfer torque (STT) effects. The robust asymmetric STT respond is found due to voltage sign inversion in NP-MTJs with barrier asymmetry. Furthermore, it is shown how size distribution of NPs as well as quantization rules modify the spin-current filtering properties of the nanoparticles in ballistic regime. Different quantization rules for the transverse component of the wave vector are considered to overpass the dimensional threshold (d av ≈ 1.8 nm) between quantum well and bulk-assisted states of the middle layer.

Ultra-giant magnetoresistance in graphene-based spin valves with gate-controlled potential barriers

“…Magnetoresistive effect in spin-valve devices has attracted considerable attention in the emerging field of spintronics because of its unique physical mechanism and magnetic properties [1][2][3][4][5]. Spin-valve devices have been recognized to be applicable in magnetic field-effect transistors [1,6], magnetic sensors [7], read heads of hard disk drives [7,8], and magnetic random access memories [4,9,10]. In general, the main structure of a typical spin valve contains a magnetic tunnel junction (MTJ), which consists of two ferromagnetic materials and an insulator as the middle spacer (F/I/F).…”

“…In addition, the degradation of the MgO barrier is another critical disadvantage that reduces device lifetime [12]. More recently, given the complex and strict manufacturing process of the excellent MgO barrier, several studies have successfully attempted the use of different insulating materials, such as hexagonal boron nitride (h-BN) [13], non-magnetic nanoparticles [7], and molybdenum disulfide (MoS 2 ) [14], as the tunneling barrier in MTJs with the expectation of simplification and structural stability, but the TMR ratios are lower than that of MgO-barrier MTJs.…”