Large magnetoresistance over a wide temperature range in Eu_0.99La_0.01TiO₃

Physics Department, Faculty of Science, National University of Singapore - 2 Science Drive 3, Singapore 117551, Republic of Singapore

^(a) phyrm@nus.edu.sg (corresponding author)

Received: 22 May 2017
Accepted: 25 July 2017

Abstract

We report the magnetization (M), electrical resistivity and magnetoresistance (MR) in the electron-doped antiferromagnet Eu_0.99La_0.01TiO₃. While M(T) measured upon cooling indicates the occurrence of a paramagnetic to antiferromagnetic transition at , zero field goes through a broad maximum at . The application of an external magnetic field raises the value of T_p and decreases the magnitude of ρ at T_p leading to a negative magnetoresistance (MR) effect. A large MR of for is observed at 2.5 K with a remarkable change occurring in sub-tesla magnetic fields ( for ). In addition, significant MR prevails even up to 10 T_N ( at 50 K). While MR over a wide field range for can be satisfactorily described by the equation , MR scales with M below T_N. Unlike the resistivity, thermopower is insensitive to magnetic fields. Our results indicate that electrons doped into the Ti-3d conduction band are strongly coupled to localized 4f⁷ spins of Eu²⁺ ions via the exchange interaction. We suggest that the observed MR is most likely caused by the field-induced suppression of 4f spin fluctuations and the subsequent reduction of the scattering of 3d electrons. This is a unique example in perovskite oxides where the magnetoresistance of 3d electrons is controlled by spin fluctuations associated with 4f localized electrons of a rare-earth ion.