CMR induced in pure lanthanum manganite - Dr. Ho-Kwang Mao

AUGUST 12, 2015

Colossal magnetoresistance (CMR) is a property with practical applications in a wide array of electronictools including magnetic sensors and magnetic RAM. New research from a team including HPSTAR director Dr. Ho-Kwang “Dave” Mao, used high-pressure techniques to induce CMR for the first time in a pure sample, lanthanum manganite, LaMnO₃. The work is published by Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1424866112).

Manganite compounds, such as LaMnO₃ studied by the research team, are particularly promising when it comes to colossal magnetoresistance, because the change from insulator to metal is several orders of magnitude stronger than in other types of compounds. But controlling and the intrinsic mechanism  underlying the CMR has remained largely elusive. It was only found before in chemically doped manganite samples, but not in a pure one until this study.

High pressure transport measurements were performed in a pure compound, LaMnO₃ with varying temperature and magnetic field.  Around 320, 000 atmospheric pressure (32 gigapasals), LaMnO₃ separates into two distinct phases, one metallic and one non-metallic. Interestingly, the chemical structure of the non-metallic phase is distorted, while the metallic phase is not. The insulator-to-metal transition occurs when the metallic phase exceeds the non-metallic one by a certain threshold confirmed by theoretical predictions. But the existence of a period when the two phases are mixed together is the crucial ingredient for inducing colossal magnetoresistance. The CMR occurs when the competition between the two phases is at its maximum. The physical separation of the two phases and the interplay between the deformed structure and the non-deformed structures is the key to driving the colossal magnetoresistance.

"The ability to induce colossal magnetoresistance by applying pressure to a pure, un-doped sample is a major step forward in understanding the physics underlying the phenomenon and to potentially harnessing it for practical purposes,” Baldini said, the leader of the research.

Caption: CMR induced in pure lanthanum manganite at 32 GPa in megnetic field.

Adapted from Carnegie Institution for Science, USA.