Inverse magneto-refraction as a mechanism for laser modification of spin-spin exchange parameters and subsequent terahertz emission from iron oxides

TL;DR

This paper introduces a novel optical mechanism called inverse magneto-refraction that enables ultrafast, non-thermal control of spin interactions in iron oxides, leading to terahertz emission and potential magnetic property manipulation.

Contribution

It proposes and experimentally demonstrates a new opto-magnetic effect allowing light to modify exchange interactions in magnetic materials regardless of symmetry.

Findings

Observation of THz emission from iron oxides upon optical excitation.

Estimation that a sub-picosecond laser pulse can induce an effective magnetic field of 0.01 Tesla.

Theoretical support for light-induced modification of exchange interactions over 1%.

Abstract

Ultrafast non-thermal manipulation of magnetization by light relies on either indirect coupling of the electric field component of the light with spins via spin-orbit interaction or direct coupling between the magnetic field component and spins. Here we propose a novel scenario for coupling between the electric field of light and spins via optical modification of the exchange interaction, one of the strongest quantum effects, the strength of which can reach 1000 Tesla. We demonstrate that this isotropic opto-magnetic effect, which can be called the inverse magneto-refraction, is allowed in a material of any symmetry. Its existence is corroborated by the experimental observation of THz emission by magnetic-dipole active spin resonances optically excited in a broad class of iron oxides with a canted spin configuration. From its strength we estimate that a sub-picosecond laser pulse with a moderate fluence of ~ 1 mJ/cm^2 acts as a pulsed effective magnetic field of 0.01 Tesla, arising from the optically perturbed balance between the exchange parameters. Our findings are supported by a low-energy theory for the microscopic magnetic interactions between non-equilibrium electrons subjected to an optical field which suggests a possibility to modify the exchange interactions by light over 1 %.