Ultrafast all-optical magnetic switching in NaTb„WO
4
…
2
Zuanming Jin,
1
Hong Ma,
1
Lihua Wang,
1
Guohong Ma,
1,a͒
Feiyun Guo,
2
and
Jianzhong Chen
2
1
Department of Physics, Shanghai University, 99 Shangda Road, Shanghai 200444,
People’s Republic of China
2
College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou 350002,
People’s Republic of China
͑Received 14 March 2010; accepted 28 April 2010; published online 21 May 2010͒
The operation of an all-optical magnetic switching based on the paramagnetic NaTb͑WO
4
͒
2
crystals
is carried out by the time-resolved magneto-optical Faraday effect. Our results demonstrate that the
switching time can be as fast as ϳ500 fs at room temperature. The switching amplitude shows a
linear dependence on the excitation intensity, which is proportional to the magnetization induced by
the circularly polarized light. Based on the inverse Faraday effect in magneto-optical crystal, the
switching mechanisms arising from circular dichroism and birefringence are discussed. By tailoring
the magneto-optical properties of NaTb͑WO
4
͒
2
crystal, the switching magnitude can be
modulated. © 2010 American Institute of Physics. ͓doi:10.1063/1.3432072͔
Laser-induced switching and manipulation on electron
spins in magnetic materials are of great interest for the fur-
ther development of magnetic storage, spin electronics and
quantum computing.
1,2
A lot of experiments have shown a
fast decay of the magneto-optical signal occurring on the
subpicosecond time scale in magnetic materials using the
time-resolved magneto-optical Kerr effect.
3,4
Recently, the
excitation of magnetic oscillations through nonthermal opti-
cal processes had been demonstrated in DyFeO
3
by Kimel
et al.
5
The excitation process was interpreted by the effect
named inverse Faraday effect or optomagnetic effect. A cir-
cularly polarized light propagating through a transparent
magnetic medium induces a spin-orbit split via stimulated
Raman scattering, as a result, an effective magnetic field is
generated, which will create a predominant orientation of
electron spins in the medium. Vahaplar et al.
2
put forward a
prospect in application as all-optical magnetic recording, in
which the fastest record and readout within 30 ps was
achieved. These results inspire us to investigate one possible
option for the speedup of magnetic switching, namely, the
use of ultrashort laser pulses together with the leveraging of
inverse Faraday effect for all-optical magnetic switching,
6
which is in great demand for a large variety of photonic
applications, such as optical interconnects, optical communi-
cation networks and data processing.
In order to achieve all-optical magnetic switching, the
candidate materials should have low absorption in visible
and infrared spectral region, and exhibit large magneto-
optical effects. Additionally, the magneto-optical properties
can be tailored over a wide range through varying their
growth conditions or chemical substitution. For these rea-
sons, paramagnetic magneto-optical crystal NaTb͑WO
4
͒
2
͑Refs. 7 and 8͒ is an alternative choice for the ultrafast all-
optical magnetic switching.
In this letter, we investigate the all-optical magnetic
switching based on the inverse Faraday effect in the
magneto-optical crystal NaTb͑WO
4
͒
2
. The results demon-
strate that the switching time is reached as fast as ϳ500 fs at
room temperature. The switching amplitude is dependent lin-
early on the magnetization of the crystal induced by the cir-
cularly polarized light. The polarization state of the signal
pulse can be selectively modulated by changing the helicity
of the control pulse. Finally, the strength of switching is
discussed by tailoring the magneto-optical properties of
NaTb͑WO
4
͒
2
crystal.
The single crystal NaTb͑WO
4
͒
2
͑77.8ϫ77.5
ϫ36.4 mm
3
͒ is prepared by solid-state reaction. In brief,
high--purity Na
2
CO
3
,WO
3
͑4N͒, and Tb
4
O
7
͑5N͒ are mixed
stoichiometrically, are pressed into tablets. The tablets are
sintered at 900 ° C for 10 h in air. A seed with orientation
͓001͔ is used for the growth of NaTb͑WO
4
͒
2
crystal. The
pulling and rotation rates are 1.5 mm/h and 10–15 rpm, re-
spectively, during the crystal growth.
8
The all-optical magnetic switching is measured using a
pump-probe technique,
3–5
both control and signal beams are
delivered from a Ti:sapphire laser ͑Spectra-physics, Spitfire
Pro.͒ with a pulse width of 120 fs and a repetition rate of
1 kHz at a photon energy of 1.55 eV. The control beam is
varied from linearly to a circularly polarized state by a
quarter-wave plate, and the signal beam remains linearly po-
larized. The both beams are focused on the crystal with a
spot diameter of about 200
m for the control and some-
what smaller for the signal beam. With the control beam
blocked, a broadband half-wave plate is used to rotate the
polarization of the transmitted signal beam to 45° with re-
spect to the optical axis of a Glan polarization beam splitter,
which gives equal intensities in both arms of a photodiode
pair bridge. The small control-induced deviations are mea-
sured by a lock-in amplifier. In this geometry, the rotation is
detected. Instead of the half-wave plate, a quarter-wave plate
is placed in front of the bridge detector to measure the ellip-
ticity signal.
For strongly absorbing media such as metals and metal
alloys, the main triggering mechanism of light-matter inter-
action is due to absorption of light energy by the electronic
system followed by its redistribution between spin and pho-
non systems. However, in our case, magneto-optical crystal
NaTb͑WO
4
͒
2
shows very low optical absorption and large
a͒
Electronic mail: ghma@staff.shu.edu.cn.
APPLIED PHYSICS LETTERS 96, 201108 ͑2010͒
0003-6951/2010/96͑20͒/201108/3/$30.00 © 2010 American Institute of Physics96, 201108-1