Colossal Magnetoresistance by Avoiding a Ferromagnetic State in the Mott System Ca3Ru2O7

TL;DR

This study investigates the anisotropic magnetic and transport properties of Ca3Ru2O7, revealing that colossal magnetoresistance occurs without a ferromagnetic state, driven by orbital degrees of freedom near the Mott transition.

Contribution

It demonstrates that colossal magnetoresistance in Ca3Ru2O7 arises without ferromagnetic order, highlighting the role of orbital degrees of freedom in this Mott system.

Findings

Colossal magnetoresistance occurs only for B||b-axis.

Ferromagnetic state is achieved for B||a-axis but not associated with colossal MR.

Unusual spin-charge-lattice coupling observed near the Mott transition.

Abstract

Transport and magnetic studies of Ca3Ru2O7 for temperatures ranging from 0.4 K to 56 K and magnetic fields, B, up to 45 T leads to strikingly different behavior when the field is applied along the different crystal axes. A ferromagnetic (FM) state with full spin polarization is achieved for B||a-axis, but colossal magnetoresistance is realized only for B||b-axis. For B||c-axis, Shubnikov-de Haas oscillations are observed and followed by a less resistive state than for B||a. Hence, in contrast to standard colossal magnetoresistive materials, the FM phase is the least favorable for electron hopping. These properties together with highly unusual spin-charge-lattice coupling near the Mott transition (48 K) are driven by the orbital degrees of freedom.