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-x)Gd(x)O, we thereby demonstrate the strengthening as well as the weakening of the magnetic order by ~10% and within ≤3 ps by optically controlling the magnetic exchange interaction.
Highlights
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
This involves the quenching of magnetic order and is often described by a three-temperature model (3TM), where the coupled electron, spin and lattice subsystems are each assumed to be in equilibrium at their respective temperatures[1,7]
We have presented experimental and theoretical evidence according to which magnetization-induced second harmonic generation (MSHG) reveals the dynamics of the magnetization M and of the magnetic exchange interaction strength Jex
Summary
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. 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. Transient enhancement of ferromagnetism in a diluted magnetic semiconductor is mediated by photoexcited mobile carriers connecting magnetic ions (‘p–d exchange’)[11] These observations raise the question of whether criteria can be identified that allow us to enhance or attenuate the magnetic order of a system at will. In contrast to systems with a high carrier concentration like transition-metal, rare-earth or certain diluted-magnetic-semiconductor ferromagnets, the sub-ps carrier dynamics in low-doped Eu1 À xGdxO is far from equilibrium due to a substantially longer electron thermalization time. Aside from the generalized insight into ultrafast spin as well as charge dynamics, a key requirement for spintronics technology, our investigation provides guiding information for the selection and design of materials for ultrafast optical control of magnetic order
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