Light induced magnetic order

TL;DR

This paper demonstrates that ultrafast laser pulses can reduce spin entropy and increase magnetic order in ferromagnets, challenging traditional views on heat and disorder's effects on magnetism and enabling faster spin-based information processing.

Contribution

It reveals a novel electronic mechanism where optical excitation enhances magnetic order without lattice changes, opening new avenues for ultrafast magnetic control.

Findings

Laser pulses reduce spin entropy in ferromagnets.

Magnetic order persists after electronic excitation.

Potential for ultrafast spin-based data processing.

Abstract

Heat and disorder are opponents of magnetism. This fact, expressed in Curie's law established more than a century ago, holds even in the highly non-equilibrium interaction of ultra-intense laser pulses with magnetic matter. In contradiction to this, here we demonstrate that optical excitation of a ferromagnet can abrogate the link between temperature and order and observe 100 femtosecond class laser pulses to drive a reduction in spin entropy, concomitant to an increase in spin polarization and magnetic moment persisting after relaxation back to local charge equilibrium. This both establishes disorder as an unexpected resource for magnetic control at ultrafast times and, by the provision of a purely electronic mechanism that does not involve reconfiguration of the crystal lattice, suggests a novel scheme for spin-based signal processing and information storage significantly faster than current methodology.