  Information technologies require entangling data stability with encryption
for a next generation of secure data storage. Current magnetic memories,
ranging from low-density stripes up to high-density hard drives, can ultimately
be detected using routinely available probes or manipulated by external
magnetic perturbations. Antiferromagnetic resistors feature unrivalled
robustness but the stable resistive states reported scarcely differ by more
than a fraction of a percent at room temperature. Here we show that the
metamagnetic (ferromagnetic to antiferromagnetic) transition in intermetallic
Fe0.50Rh0.50 can be electrically controlled in a magnetoelectric
heterostructure to reveal or cloak a given ferromagnetic state. From an aligned
ferromagnetic phase, magnetic states are frozen into the antiferromagnetic
phase by the application of an electric field, thus eliminating the stray field
and likewise making it insensitive to external magnetic field. Application of a
reverse electric field reverts the antiferromagnetic state to the original
ferromagnetic state. Our work demonstrates the building blocks of a feasible,
extremely stable, non-volatile, electrically addressable, low-energy
dissipation, magnetoelectric multiferroic memory.
