En las fronteras de la Materia Condensada

Among the Mn oxides exhibiting colossal magnetoresistance(CMR), the compounds with pyrochlore crystal structure stand out due to various important differences with the larger and better known family of perovskite CMR manganites, object of study since 1950. The first pyrochlore compound exhibiting CMR was found in 1996, Tl₂Mn₂O₇. One of the main questions raised thereby was whether a common fundamental mechanism could be responsible for the magnetoresistance measured in this pyrochlore and CMR in the perovskite manganese oxides. The two families of compounds differ not only in crystal structure, they also exhibit striking differences in their electronic properties. The larger experimental background now existent has put into evidence many new differences. In the present work we refer to those found in the spin dynamics, which in pyrochlores is in stark contrast to that observed in perovskite manganites. In particular we will report, and compare with available neutron scattering data, results of the spin wave calculations performed for Tl₂Mn₂O₇ (in collaboration with M.Acquarone), using the microscopic generic model proposed with M.A.Gusmao for this compound recently.