Effect of sputtering parameters on the structural and
magnetic properties of Tb-Fe thin film
Himalay Basumatary*†, J Arout Chelvane, S V Kamat and Rajeev Ranjan†
*
†
Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad
Department of Materials Engineering, Indian Institute of Science, Bangalore
Email: himab4@gmail.com
Key words: Magnetostriction, micro-actuators, micro-sensors, sputter deposition, super-paramagnetism
Abstract: Structural and magnetic properties of Tb-Fe thin
films deposited at varying sputtering power were studied.
The films exhibit granular morphology whose size increases
with increasing sputtering power. Thermo-magnetic
measurements show superparamagnetic behaviour for the
film deposited at 50W and 100W sputtering power and the
film deposited at 150W sputtering power display
ferrimagnetism.
1. Introduction:
Magnetostrictive
material
exhibit
dimensional change under the application of magnetic
field and are of great research interest today due to the
wide application of these materials in actuators and
acoustic devices. Rare earth-iron based alloys occupy
a prime position in this area due to the large
magnetostriction displayed by them at room
temperature. Thin films of these materials have
potential applications in MEMS devices such as
micro-sensors and micro-actuators [1]. The magnetic
properties of such films are largely controlled by the
grain sizes of the films which largely depend on
deposition parameters. This paper reports the microstructural and magnetic properties of Tb-Fe thin films
deposited on Si<100> substrate with varying
sputtering power.
2. Experimental details:
Tb-Fe thin films were deposited on Si <100>
substrate using sputtering technique with varying
sputtering power viz., 50, 100 and 150W.
Microstructural studies were carried out using Field
Emission Gun SEM (FEG-SEM) and Transmission
Electron Microscopy. Low temperature and room
temperature magnetization measurements were carried
out using a SQUID – VSM.
50 W
50
W
100 W
100
W
150 W
150
W
Fig.1: FEG-SEM micrograph of Tb-Fe films deposited
at sputtering power of 50W, 100W and 150W
3. Results and discussions:
The increase in sputtering power is found to
increase the thickness of the film without changing the
composition. A granular surface morphology is
observed for all the films (Fig.1) and the size of the
granules (island size) is found to increase with
increasing sputtering power.
Thermo-magnetic
and
magnetization
measurement show that the films deposited at lower
sputtering power (i,e) 50W and 100W display superparamagnetic behaviour and this may be corroborated
with the fine granules observed in the microstructure
of these films. A small cusp observed around 20 K
from the ZFC & FC plot for the film deposited at
100W corresponds to the spin freezing/ blocking
temperature (Tb) [Fig. 2]. However, such a cusp is not
observed for the film grown at 50 W even up to 4 K
owing to the presence of very fine globules. Assuming
the films consisting of
continuous
distribution of fine
granules, the thermomagnetic ZFC & FC
plots can be well
described
by
the
characteristic
relaxation time ()
given by:
 = o exp(KV/kT) [2].
As the granule size
(V) increases with
Fig.2: FC and ZFC Plots of
sputtering power, the
Tb-Fe films deposited with
relaxation
time
different sputtering power
becomes longer and
of 50W, 100W and 150W
the spins are blocked
to relatively higher
temperature. Therefore, an increase in the spin
freezing/blocking temperature could be observed for
the films grown at higher sputtering power. The ZFC
& FC plot for the film deposited at 150W, shows
ferrimagnetic nature with Curie temperature (Tc)
around 220K. The large irreversibility in the ZFC and
FC curves correspond to the large anisotropy
associated with the film and is also corroborated with
the magnetization behaviour measured at different
temperatures.
Acknowledgement: DRDO for the financial support.
References:
1. E. Quandt, K. Seemann, Sensonr and Actuators
A 50 (1995) 105 – 109.
2. Dunlop, and Ö. Özdemir, Rock Magnetism:Fundamentals
and Frontiers, Cambridge University Press, New York,
573 pp., 1997.