Background

The advent of femtosecond laser in the field of solid state physics has been at the origin of many discoveries. For instance, in the field of magnetism it was possible to understand how fwmtosecond optical demagnetizationcan probe the exchange interaction in ferromagnetic metals. The core of the project is to explore how optically generated acoustic waves interact with magnetization of a thin film, and vice versa, how femtosecond demagnetization can lead to longitudinal and shear acoustic waves exitation from release of magnetostrictive stresses. The later relevant physical framework is known as direct magnetostriction, which is the property of ferromagnetic material that causes them to change their shape or dimentions during the process of magnetization/demagnetization. Te revers phenomenon appears when an applied exterlal stress modifies statically or dynamically the magnetization configuration of a ferromagnet. A number of novel physical phenomena can be expected to arise when an ultrafast acoustic pulse, exited through absorption of a femtosecond laser pulse in a photoacoustic transducer, is injected through a ferromagnetic sample.

Our goals

1) Direct ultrafast magnetostriction, generation of THz longitudinal and shear acoustic pulses through laser mediated release of magnetostrictive stress in ferromagnetic compouns. Master and understand how to generate laser mediated ultrafast longitudinal and, more originally, shear acoustic pulses. The idea is to develope 'smart' hybrid structures with improved magneto-elastic coupling using rare earth based compounds.

2) Inverse ultrafast magnetostriction, investigation of ultrafast interaction of laser generated ultrasonic pulses with spins and magnons in hybrid metal/ferromagnet multilayer structures. Learn how to dynamically control the magnetization state with acoustic pulses.

Why ?

The discovery of giant magnetoresistance (GNR) effect in hybrid metal/ferromagnet layers in the late 80's represents on of the most facinating examples of a hybrid structure, which combines in an intelligent way, electronic and magnetic properties of its compounds. This discovery became a major operating principle in magnetic data storage devices. Another trend in modern ultrafast optics is driven by progress in picosecond ultrasonics. Notably, the possibility to trigger magnetic precession ina very short time scale through acoustic pulses has been demonstrated very recently. However, the magnitude of the effect, the underlying physical mechanism, and the swiching speed are not fully understood. For the moment, efficient and simple ultrafast shear transducers are lacking and a new generation of THz shear transducers based on laser-mediated release of magnetostrictive stresses would be a great interest for the viscoelastic investigation of many material families (liquids, glasses, mixes multiferroics, correlated electron systems and magnetic materials).

 

Perspectives

The success of UltrAMOX would open the way of the bottom-up approach pf acousto-spintronics in spin based devices where ultrafast acoustic pulses could be utilized to modify the magnetization in addition to more conventional spin injection. It would permit the experimental studies of several new fundamental effects related to magnetostriction. Finally, it could have significant impact in several fields of applications: Brillouin spectroscopy, magnetic data recording, microwave devices, etc.