Ultrafast optical tuning of ferromagnetism via the carrier density

Abstract

Interest in manipulating the magnetic order by ultrashort laser pulses has thrived since it was observed that such pulses can be used to alter the magnetization on a sub-picosecond timescale. Usually this involves demagnetization by laser heating or, in rare cases, a transient increase of magnetization. Here we demonstrate a mechanism that allows the magnetic order of a material to be enhanced or attenuated at will. This is possible in systems simultaneously possessing a low, tunable density of conduction band carriers and a high density of magnetic moments. In such systems, the thermalization time can be set such that adiabatic processes dominate the photoinduced change of the magnetic order-the three-temperature model for interacting thermalized electron, spin and lattice reservoirs is bypassed. In ferromagnetic Eu 1 À x Gd x O, we thereby demonstrate the strengthening as well as the weakening of the magnetic order by B10% and within r3 ps by optically controlling the magnetic exchange interaction.

Ultrafast Quenching of the Exchange Interaction in a Mott Insulator

“…In principle, laser-excitation can effect J ex by modulating the electronic structure (electron hopping, Coulomb repulsion) and by creating a nonequilibrium distribution of photoexcited carriers (photodoping). A modification of J ex has been discussed within the context of experiments on manganites [2-4], magnetic semi-conductors [5], and, using static field gradients, ultracold atoms in optical lattices [6,7]. While it might play a role as well in metallic ferromagnets [8][9][10][11], ultrafast demagnetization [12] and laser-induced magnetization reversal [13][14][15] seem at least partly understood in terms of a given time-independent J ex .…”

Annealing rate tuned magnetization level in polycrystalline ZnO:Cu films

“…It's believed that the application of DMSs will revolutionize the performance of various commercial devices, such as flash memories, low current semiconductor lasers and spin light-emitting diode (LED) [1e4]. And it has already demonstrated these DMSs show strong magnetoelectric effects [5,6] and magneto-optical effects [7,8] that could possibly allow them used as magnetoresistance devices as well as in photomagnetic devices. Since its Curie temperature (T c ) was theoretically predicted to be above room temperature [9], TMdoped ZnO has been extensively studied and room temperature ferromagnetism (RTFM) has been experimentally observed in Co-, Mn-, Cu-doped ZnO system [10].…”

Theory of Curie temperature enhancement in electron-doped EuO

“…Electrondoped europium monoxide (EuO) is a promising candidate for this purpose, as it undergoes a simultaneous ferromagnetic (FM) and insulator-to-semimetal transition [1], exhibiting an outstanding magneto-electric response, including the strongest colossal magnetoresistance effect known [2,3], magneto-optical effects [4][5][6][7], and a spin polarization of the conduction band of nearly 100 % in the FM state [8,9]. Improved sample fabrication techniques [10,11] and europium monoxide's epitaxial integrability into Si [9] and GaAs [12] structures have renewed and intensified the interest in this material during the past few years.…”