Simultaneous measurements of terahertz emission and magneto-optical Kerr effect for resolving ultrafast laser-induced demagnetization dynamics

T. J. Huisman, R. V. Mikhaylovskiy, A. Tsukamoto, Th. Rasing, and A. V. Kimel

Phys. Rev. B 92, 104419 – Published 17 September 2015

Abstract

Simultaneous detection of terahertz (THz) emission and transient magneto-optical response is employed to study ultrafast laser-induced magnetization dynamics in three different types of amorphous metallic alloys: Co, GdFeCo, and NdFeCo. A satisfactory agreement between the dynamics revealed with the help of these two techniques is obtained for Co and GdFeCo. For NdFeCo the THz emission indicates faster dynamics than the magneto-optical response. This observation indicates that in addition to spin dynamics of Fe, ultrafast laser excitation of NdFeCo triggers faster magnetization dynamics of Nd originating from its orbital momentum.

Received 17 December 2014

DOI:https://doi.org/10.1103/PhysRevB.92.104419

Authors & Affiliations

T. J. Huisman¹, R. V. Mikhaylovskiy¹, A. Tsukamoto², Th. Rasing¹, and A. V. Kimel¹

¹Radboud University Nijmegen, Institute for Molecules and Materials, 6525 AJ Nijmegen, Netherlands
²College of Science and Technology, Nihon University, 7-24-1 Funabashi, Chiba, Japan

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 92, Iss. 10 — 1 September 2015

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) The layered structure under study and the scheme of the experiment. Re is rare earth, being either Nd or Gd. The reflected probe pulse is used to measure the MOKE signal. The electric field of the THz emission is detected with the help of electro-optic (EO) detection. A field of $\pm 1 kG$ is applied in plane. (b) Ultrafast magnetization dynamics as deduced from time-resolved MOKE measurements. The solid lines are fitting functions as expressed in Eqs. (10) and (11). (c) Electric field of the emitted THz radiation as a function of time. The position of zero time delay is chosen arbitrarily so that the position of the peak of the pump pulse is close to zero. The traces are vertically shifted with respect to each other.
Reuse & Permissions
Figure 2
(a) Electric field of the emitted THz radiation from the $N d_{0.2} {(F e_{0.87} C o_{0.13})}_{0.8}$ sample as a function of time. The measurements have been performed in an external magnetic field of 1 kG and $- 1 kG$ ( $+ B$ and $- B$ ). The wave forms are measured for two orientations of the sample as indicated next to the curves. The inset shows the hysteresis of the peak amplitude when the pump pulse excites the sample from the side of the substrate. (b) MOKE measured demagnetization for $G d_{0.18} {(F e_{0.87} C o_{0.13})}_{0.82}$ and $G d_{0.3} {(F e_{0.87} C o_{0.13})}_{0.7}$ . The solid lines are fitting functions as expressed in Eqs. (10) and (11). (c) Measured demagnetization emission of $G d_{0.18} {(F e_{0.87} C o_{0.13})}_{0.82}$ and $G d_{0.3} {(F e_{0.87} C o_{0.13})}_{0.7}$ . The traces are vertically shifted with respect to each other. The position of zero time is chosen arbitrarily so that the position of the peak of the pump pulse is close to zero.
Reuse & Permissions
Figure 3
(a) A laser pump pulse initiates magnetization dynamics in the sample which is accompanied by the emission of electromagnetic radiation. (b) Response of the spectrometer as a function of frequency.
Reuse & Permissions
Figure 4
(a) The calculated spectra of the emitted electromagnetic radiation inferred from the time-resolved magneto-optical data shown in Fig. 1, using Eq. (7). (b) The detected spectra of the THz emission. The solid lines (1) are spectra obtained with the help of the Fourier transform of the measured THz wave forms. The dashed lines (2) indicate the calculated spectra of (a) and taking into account the spectrometer response for THz radiation. The calculated spectra of GdFeCo and NdFeCo are shown multiplied by 2 and 1.8, respectively. The shaded areas are meant to highlight the difference between the calculated and measured spectra.
Reuse & Permissions
Figure 5
(a) The transmission of $N d_{0.2} {(F e_{0.87} C o_{0.13})}_{0.8}$ normalized to the transmission of $G d_{0.3} {(F e_{0.87} C o_{0.13})}_{0.7}$ . The solid line is a polynomial fit. (b) The solid line (1) is the spectrum obtained with the help of the Fourier transform of the measured THz emission from $N d_{0.2} {(F e_{0.87} C o_{0.13})}_{0.8}$ . The dashed line (2) indicates the calculated spectrum from the MOKE and taking into account the spectrometer response for THz radiation. The dotted line (2′) indicates a possible correction to the calculated spectrum using the transmission data of (a). The calculated spectra are shown multiplied by 1.8.
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics