Robust isothermal electric control of exchange bias at room temperature

Abstract

Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with highspeed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr 2 O 3 has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr 2 O 3 single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Néel temperature.S pintronics strives to exploit the spin degree of freedom of electrons for an advanced generation of electronic devices 1,2 . In particular, voltage-controlled spin electronics is of vital importance to continue progress in information technology. The main objective of such an advanced technology is to reduce power consumption while enhancing processing speed, integration density and functionality in comparison with presentday complementary metal-oxide-semiconductor electronics [3][4][5][6] . Almost all existing and prototypical solid-state spintronic devices rely on tailored interface magnetism, enabling spin-selective transmission or scattering of electrons. Controlling magnetism at thin-film interfaces, preferably by purely electrical means, is a key challenge to better spintronics [7][8][9][10] . The absence of direct coupling between magnetization and electric field makes the electric control of collective magnetism in general, and surface and interface magnetism in particular, a scientific challenge. The significance of controlled interface magnetism started with the exchange-bias effect. Exchange bias is a coupling phenomenon at magnetic interfaces that manifests itself most prominently in the shift of the ferromagnetic hysteresis loop along the magnetic-field axis and is quantified by the magnitude µ 0 H EB of the shift 11 . The exchange-bias pinning of ferromagnetic thin films is employed in giant magnetoresistance and tunnelling magnetoresistance structures of magnetic-field sensors and modern magnetic read heads 12 . Electric control of exchange bias has been proposed for various spintronic applications that go beyond giant magnetoresistance and tunnelling magnetoresistance technology 5 . One approach to such voltage control requires a reversible, laterally uniform, isothermal electric tuning of the exchange-bias field at room temperature, which remains a significant challenge.Early attemp...

Non-volatile electrically-driven repeatable magnetization reversal with no applied magnetic field

“…Demonstrating electrical control of coercivity 19,24 , exchange bias 25,26 or magnetic anisotropy 20,27 is insufficient because, respectively, an electrically addressable coercivity is inextricably linked with an applied magnetic field; because exchange bias is an interfacial phenomenon that cannot readily drive magnetization reversal throughout a film of significant thickness; and because no new magnetic anisotropy axis can lie more than 901 from the anisotropy axis along which the local magnetization initially lies. It has been suggested that this latter challenge may be overcome by applying a suitable sequence of normal stresses near the pre-existing magnetic anisotropy axes of a small homogeneously magnetized Stoner-Wohlfarth particle 28,29 , but this has not been experimentally realised.…”

Interplay of chemical structure and magnetic order coupling at the interface between Cr2O3 and Fe3O4 in hybrid nanocomposites

“…This boundary polarization, roughness insensitive, has been demonstrated to contribute to the magnetization. 27,28 Accordingly, the hysteresis loops included in Fig. 4 can be associated with these two main contributions; one responsible for the large magnetization values due to the ferrimagnetic (FiM) magnetite nanoparticles, which superimposes the antiferromagnetic contribution responsible for the subtle slope and almost non-saturation of the magnetization at high field values that corresponds to the chromium oxide magnetic phase identified.…”

Nucleation of Graphene Layers on Magnetic Oxides: Co3O4(111) and Cr2O3(0001) from Theory and Experiment

“…For spintronic device applications growing similar films on Cr 2 O 3 (0001) would offer several important advantages compared to other oxides because of its magnetoelectric properties 5,10 and the ability to produce a single magnetic domain via field cooling. 11 However, we find that C MBE on chromia yields only disordered graphite below ~ 800 K and the desorption of C above this temperature. In this paper, we use experiment and DFT to understand the origin of this dramatic difference between growth of graphene on Co 3 O 4 (111) compared to Cr 2 O 3 (0001) to provide insight into developing guidelines for obtaining cohesive graphene/oxide films.…”