Letters to Nature

Nature 389, 942-944 (30 October 1997) | doi:10.1038/40093; Received 3 April 1997; Accepted 26 August 1997

Low-field magnetoresistance in the pyrochlore Tl2Mn2O7

H. Y. Hwang1 and S.-W. Cheong1

  1. Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 07974, USA

Correspondence to: H. Y. Hwang1 Correspondence and requests for materials should be addressed to H.Y.H.

The discovery of colossal magnetoresistance in perovskite manganites derived from LaMnO3 has renewed interest in these and related materials for possible technological applications1, 2, 3, 4, 5, 6, 7. But the high magnetic fields and narrow temperature windows where the large magnetoresistive responses are observed present daunting limitations. A possible avenue for overcoming these limitations is to improve the low-field response by modifying the manganites to enhance the contribution to magnetoresistance from spin-polarized tunnelling of the conduction electrons; such tunnelling, which can be very sensitive to an applied magnetic field, takes place across grain boundaries (natural or artificial) or between the manganite planes of the layered derivatives of the perovskite compounds8, 9, 10, 11, 12, 13. Here we show that low-field (H) grain-boundary magnetoresistance can also be realized in a non-perovskite magnetoresistive oxide, the pyrochlore Tl2Mn2O7. Moreover, this low-field response, which persists for all temperatures below the transition to the ferromagnetic state, does not show the strong temperature-dependent decay characteristic of the perovskite-based systems. We suggest that this improved response is in part due to weaker electron-spin coupling and the lack of strong electron–lattice interactions in the pyrochlore.