Mike Street

Increasing the Néel temperature of magnetoelectric chromia for voltage-controlled spintronics

Boron doped chromia (Cr2O3) thin films with substitutional doping levels between zero and 3% are grown using pulsed laser deposition in borane background gases. Magnetometry reveals a tunable increase in the Neel temperature of the (0001) textured Cr2BxO3−x thin films at a rate of about 10% with 1% oxygen site substitution preserving a net boundary magnetization. Spin resolved inverse photoemission measured after magnetoelectric annealing in subsequently reversed electric fields evidences voltage-controlled reversal of boundary magnetization and thus magnetoelectricity of Cr2BxO3−x. Conservation of magnetoelectricity far above room temperature makes ultra-low power voltage-controlled spintronic devices feasible.

Magnetization at the interface of Cr2O3and paramagnets with large stoner susceptibility

From the Cr 2p3/2 x-ray magnetic circular dichroism signal, there is clear evidence of interface polarization with overlayers of both Pd and Pt on chromia (Cr2O3). The residual boundary polarization of chomia is stronger for a Pt overlayer than in the case of a Pd overlayer. The reduction of chromia boundary magnetization with a paramagnetic metal overlayer, compared to the free surface, is interpreted as a response to the induced spin polarization in Pt and Pd. Magnetization induced in a Pt overlayer, via proximity to the chromia boundary magnetization, is evident in the polar magneto-optical Kerr measurements. These results are essential to explainations why Pt and Pd are excellent spacer layers for voltage controlled exchange bias, in the [Pd/Co] n /Pd/Cr2O3 and [Pt/Co] n /Pt/Cr2O3 perpendicular magneto-electric exchange bias systems. The findings pave the way to realize ultra-fast reversal of induced magnetization in a free moment paramagnetic layer, with possible application in voltage-controlled magnetic random access memory.

Magnetoelectric device feasibility demonstration — Voltage control of exchange bias in perpendicular Cr 2 O 3 Hall bar device

Several emerging mechanisms using voltage to control the magnetism have recently been proposed because of their possible applications in energy-efficient spintronic devices [1]. Among others, one promising way to reach this goal is to use voltage to control the exchange bias of the magnetoelectric (ME) antiferromagnet Cr2O3 (Fig. 1) [2]. In this work, we demonstrate the ME effect in the device level using a bilayer thin film structure Cr2O3/[Co/Pd]n.