Magnetoelectric Evidence for the Attainability of Time-Reversed Antiferromagnetic Configurations by Metamagnetic Transitions in DyPO4

Abstract

The observation of the linear magnetoelectric (ME) effect in the metamagnetic antiferromagnet DyPO4 is reported. Also presented is a new quantum-mechanical mechanism of the ME effect which is, in contrast to previous mechanisms, specifically designed for DyPO4 and other magnetically ordered materials containing rare-earth ions. These results are shown to provide evidence for the feasibility of isothermal forced switching between time-reversed antiferromagnetic configurations by means of metamagnetic transitions. The optically deduced1 magnetic structure of DyPO4 is shown to require 4′/m′mm′ symmetry so that the ME susceptibility tensor has only one independent component α. It is found experimentally that |α| decreases monotonically with increasing temperature from roughly 2×10−4 Gaussian units at 1.5°K to zero at the Néel temperature of about 3.38°K. Application of a sufficiently large, static, magnetic field Hc along the antiferromagnetic axis (which is the crystalline c axis) causes not only a metamagnetic increase of the magnetization to its saturation value but (due to the transition to 4/mm′m′ symmetry) also an even more abrupt decrease of |α| to zero. The relative sign of α is determined, rather remarkably, solely by the sign of that Hc which caused the most recent metamagnetic transition prior to the measurement of α. This new switching method is potentially applicable to an isothermal storage and retrieval of information in materials which are both metamagnetic and magnetoelectric. All the above-mentioned work is described more fully elsewhere.2 Subsequently, appropriate ME annealing produced a larger value of |α| (≈1×10−3 Gaussian units) so that a non-ME-annealed DyPO4 crystal is not a single antiferromagnetic domain.