First-order transition and phase separation in pyrochlores with colossal magnetoresistance - art. no. 104412

摘要

Tl2Mn2O7 pyrochlores present colossal magnetoresistance (CMR) around the long-range ferromagnetic ordering temperature (T-C). The character of this magnetic phase transition has been determined to be first order, by purely magnetic methods, in contrast to the second order character previously reported by Zhao Phys. Rev. Lett. 83, 219 (1999). The highest CMR effect, as in Tl1.8Cd0.2Mn2O7, corresponds to a stronger first order character. This character implies a second type of magnetic interaction, in addition to the direct superexchange between the Mn4+ ions, as well as a phase coexistence. A model is proposed, with a complete Hamiltonian (including superexchange and an indirect interaction), which reproduce the observed phenomenology. References: 29