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Detecting Magnetic Order when Magnetization is Absent

Schematics of the physical principle to discriminate two ordered states of a magnetoelectric antiferromagnet. In the presence of applied voltage, the polarization plane of linearly polarized light rotates in opposite directions when light is transmitted through the domains with reversed spins.

Antiferromagnets are magnetically ordered materials which lack the net magnetization known for ferromagnets. In an antiferromagnet, spins arrange in opposing sublattices with mutually compensating magnetization. Not unlike ferromagnets, antiferromagnets can have domains. In a simple case, the domains are differentiated through spin reversal. Identifying a specific antiferromagnetic domain is a notoriously difficult experimental problem.

Nebraska MRSEC researchers developed a magneto-optical table-top setup (Phys. Rev. Applied 5, 031001 (2016)) that allows detecting magnetic order in magnetoelectric antiferromagnets, such as chromia, which rotate the plane of polarization of transmitted light in response to electric fields. Probing with light of a specific wavelength allows determining the domain state from the sign of the rotation angle. In chromia, domain states can not only be detected but also selected through voltage. This property plays a key role in potential ultra-low power spintronic memory and logic devices. Advancing them requires investigation of antiferromagnetic domains.