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...

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