S. Yamada, N. Abe, H. Sagayama, K. Ogawa, T. Yamagami, and T. Arima

We have discovered room-temperature low-field colossal magnetoresistance (CMR) in an A-site ordered NdBaMn₂O₆ crystal. The resistance changes more than 2 orders of magnitude at a magnetic field lower than 2 T near 300 K. When the temperature and magnetic field sweep from an insulating (metallic) phase to a metallic (insulating) phase, the insulating (metallic) conduction changes to the metallic (insulating) conduction within 1 K and 0.5 T, respectively. The CMR is ascribed to the melting of the charge and orbital ordering. The entropy change which is estimated from the B?T phase diagram is smaller than what is expected for the charge and orbital ordering. The suppression of the entropy change is attributable to the loss of the short-range ferromagnetic fluctuation of Mn spin moments, which is an important key of the high temperature and low magnetic field CMR effect.

DOI:https://doi.org/10.1103/PhysRevLett.123.126602