Colossal Magnetoresistance without Mixed Valence in a Layered Phosphide Crystal.

Materials with strong magnetoresistive responses are the backbone of spintronic technology, magnetic sensors, and hard drives. Among them, manganese oxides with a mixed valence and a cubic perovskite structure stand out due to their colossal magnetoresistance (CMR). A double exchange interaction underlies the CMR in manganates, whereby charge transport is enhanced when the spins on neighboring Mn ³⁺ and Mn ⁴⁺ ions are parallel. Prior efforts to find different materials or mechanisms for CMR resulted in a much smaller effect. Here an enormous CMR at low temperatures in EuCd ₂ P ₂ without manganese, oxygen, mixed valence, or cubic perovskite structure is shown. EuCd ₂ P ₂ has a layered trigonal lattice and exhibits antiferromagnetic ordering at 11 K. The magnitude of CMR (10 ⁴ %) in as-grown crystals of EuCd ₂ P ₂ rivals the magnitude in optimized thin films of manganates. The magnetization, transport, and synchrotron X-ray data suggest that strong magnetic fluctuations are responsible for this phenomenon. The realization of CMR at low temperatures without heterovalency leads to a new regime for materials and technologies related to antiferromagnetic spintronics.
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