Open AccessThickness dependent terahertz emission from cobalt thin films
Author(s) -
N. V. Narendra Kumar,
Ruud Hendrikx,
A.J.L. Adam,
Paul C. M. Planken
Publication year - 2015
Publication title -
optics express
Language(s) - Uncategorized
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.23.014252
Subject(s) - magnetization , materials science , terahertz radiation , femtosecond , optics , laser , cobalt , thin film , azimuth , magnetic field , optoelectronics , physics , nanotechnology , quantum mechanics , metallurgy
When cobalt thin films are illuminated with femtosecond laser pulses, we observe the emission of terahertz pulses. For a cobalt film thickness less than about 40 nm, the THz electric field direction rotates when the sample is rotated about the surface normal. This azimuthal angle-dependent emission is consistent with the assumption that laser-induced changes in an in-plane magnetization are responsible for the emission. For thicker layers, however, we observe the development of an azimuthal angle-independent contribution to the THz emission which we attribute to laser-induced changes in an out-of-plane magnetization component. We show that the relative contribution of this component grows when the cobalt film thickness increases. Our observations are supported by magnetic force microscopy measurements which show that for film thicknesses below 40 nm, the magnetization is predominantly in-plane whereas for thicknesses larger than 40 nm, an out-of-plane magnetization component develops.