Pressure Dependence of Ferromagnetic Curie Temperature and Colossal Magnetoresistance Effect in Pyrochlore Manganites
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Negative pressure dependence of ferromagnetic Curie temperature T<SUB>c</SUB> is established by the susceptibility measurements on a series of isostructural pyrochlores A<SUB>2</SUB>Mn<SUB>2</SUB>O<SUB>7</SUB>, (A=Tl, In, Y, Lu). At temperatures well below and above T<SUB>c</SUB> the pronounced magnetothermohistory effects are revealed, indicating the presence of competing antiferromagnetic interaction. The results contradict not only the double exchange model, which dictates positive pressure shift of T<SUB>c</SUB>, but also the simple superexchange scenario where the ferromagnetic character of the nearest-neighbor interaction allows no deviations from the standard ferromagnetic behaviour. We propose a model where a long-range ferromagnetic ordering originates from next-near-neighbor ferromagnetic interactions which compete with the antiferromagnetic nearest-neighbor superexchange, greatly reduced by the frustrated topology of pyrochlores. We also report a dramatic increase under pressure of the colossal magnetoresistance effect.
- The Review of High Pressure Science and Technology
The Review of High Pressure Science and Technology 7, 505-507, 1998
The Japan Society of High Pressure Science and Technology