Carrier-Induced Magnetic Circular Dichloism in the Magnetoresistive Pyrochlore Tl2Mn2O7

TL;DR

This study investigates the magneto-optical properties of Tl2Mn2O7, revealing a unique magnetic circular dichroism behavior linked to classical magnetoplasma resonance rather than magnetization, indicating weak spin-orbit coupling.

Contribution

It demonstrates that MCD in Tl2Mn2O7 is driven by magnetoplasma resonance, not magnetization, highlighting a different mechanism from conventional ferromagnets.

Findings

MCD signal appears at the plasma edge near T_c

MCD grows with magnetic field, not magnetization

Weak spin-orbit coupling inferred from results

Abstract

Infrared magnetic circular dichloism (MCD), or equivalently magneto-optical Kerr effect, has been measured on the Tl2Mn2O7 pyrochlore, which is well known for exhibiting a large magnetoresistance around the Curie temperature T_C ~ 120 K. A circularly polarized, infrared synchrotron radiation is used as the light source. A pronounced MCD signal is observed exactly at the plasma edge of the reflectivity near and below T_c. However, contrary to the conventional behavior of MCD for ferromagnets, the observed MCD of Tl2Mn2O7 grows with the applied magnetic field, and not scaled with the internal magnetization. It is shown that these results can be basically understood in terms of a classical magnetoplasma resonance. The absence of a magnetization-scaled MCD indicates a weak spin-orbit coupling of the carriers in Tl2Mn2O7. We discuss the present results in terms of the microscopic electronic structures of Tl2Mn2O7.