Marked enhancement of Néel temperature in strained YMnO₃ thin films probed by femtosecond spectroscopy

¹ Department of Electrophysics, National Chiao Tung University - Hsinchu 300, Taiwan
² Institute of Physics, National Chiao Tung University - Hsinchu 300, Taiwan
³ Department of Applied Physics and Chemistry and Institute for Laser Science, The University of Electro-Communications - Chofugaoka 1-5-1, Chofu, Tokyo 182-8585 Japan
⁴ Institute of Solid State Physics, Bulgarian Academy of Sciences - 1784 Sofia, Bulgaria, EU

^a khwu@cc.nctu.edu.tw

Received: 21 December 2010
Accepted: 19 March 2011

Abstract

In this paper, the (001)-oriented hexagonal YMnO₃ (h-YMO) thin films with various nominal strain states were deposited on MgO(100), MgO(111) and YSZ(111) substrates by pulsed laser deposition. The ultrafast dynamics probed by wavelength-tunable femtosecond pump-probe spectroscopy was performed to disclose the effects of the epitaxial strain on the electronic structure and associated magnetism. Analyses based on the measured transient-reflectivity-change (ΔR/R) curves revealed that while the magnitude of the on-site Mn d-d transition energy E_dd(T) changes only slightly with the variation of the lattice constant ratio c/a, a marked shift in the antiferromagnetic (AFM) Néel temperature T_N was observed and the direction of shift was dependent on the type of strain. The possible mechanism for the observed strain effect on the AFM ordering is discussed.