| AVS 63rd International Symposium & Exhibition | |
| Novel Trends in Synchrotron and FEL-Based Analysis Focus Topic | Monday Sessions |
| Session SA+AS-MoA |
| Session: | Frontiers of Photoemission with Synchrotron and XFEL Radiation/Advances in High-resolution Imaging Techniques |
| Presenter: | Tommaso Pincelli, Università di Milano, Italy |
| Authors: | T. Pincelli, Università di Milano, Italy A.Yu. Petrov, Laboratorio TASC, IOM-CNR, Italy G. Panaccione, Laboratorio TASC, IOM-CNR, Italy M. Oura, RIKEN SPring-8, Japan T.L. Lee, Diamond Light Source Ltd., UK G. Rossi, Università di Milano, Italy |
| Correspondent: | Click to Email |
Hole-doped rare-earth manganites, like La0.66Sr0.33MnO3 (LSMO), display exotic phenomena such as concurrent colossal magnetoresistance and half-metallicity which originate from the interplay of charge, spin, and orbital degrees of freedom [1]. The peculiar transport properties of LSMO thin films combined with the ferromagnetic order that persists up to about 350 K [2] render such system a most technologically attractive material for spin injection: the spin polarization at the Fermi level reaches about 100% for T<TCurie [3].
The ultrafast manipulation of spin states in LSMO can be tested by state-of-the-art time-resolved pump-probe techniques. Previous studies by optical pump-probe spectroscopy have given evidence of photoinduced effects in ferromagnetic manganites [4].
Photo-Electron Spectroscopy (PES) allows a direct measurement of the electronic structure; time-resolved PES is able to disentangle the delicate out-of-equilibrium interplay between electronic, spin and lattice degrees of freedom [5], an essential feature in the case of highly correlated materials. HArd X-ray PhotoElectron Spectroscopy (HAXPES) extends the probing depth of PES to the bulk of the solid (tens of nm), and therefore does not suffer of the modification induced by the surface.
We present here a pump-probe HAXPES study of the relaxation dynamics of LSMO thin films. We study the structure of the Mn 2p core level and, in particular, the bulk-only screening channel proportional to the metallic and ferromagnetic state in LSMO. We observe a large and ‘slow’ reduced lineshape change up to 200 picoseconds after the IR pumping. By comparison with all-optical techniques (Time-Resolved Magneto-Optical Kerr effect, TR-MOKE) we are able to attribute the observed quenching to a collapse of magnetic order. The sudden demagnetization reduces the mobility of electrons in the solid, inducing a localization similar to a metal-insulator transition.
Since LSMO is half-metallic, the direct exchange of energy between the optically excited electrons and the magnetic order is inhibited by the absence of final states for spin-flip scattering [3]. So we can follow the relaxation dynamics as the energy is first dissipated in the lattice and then in a reduction of the magnetic order.
References
[1] Y. Tokura et al. J. Magn. & Magn. Mater. 200, 1 (1999).
[2] K. Horiba et al. Phys. Rev. B 71, 155420 (2005).
[3] G.M. Müller et al. Nat. Mat. 8, 56 (2009); J.-H. Park, et al. Nature, 392, 794 (1998).
[4] A.I. Lobad et al. Appl. Phys. Lett. 77, 4025 (2000); K. Matsuda et al. Phys. Rev. B 58, 4203 (1998).
[5] B. Frietsch et. al. Nature Communications, 6, 8262 (2015).