Influence of substrate temperature on structural and
magnetic properties of Ni-Mn-Ga thin films
S. Vinodh Kumar1, R.K. Singh2, M. Manivel Raja2, S. Seenithurai1, and M. Mahendran1*
Smart Materials Lab, Department of Physics, Thiagarajar College of Engineering, Madurai – 625 015, India
2
Advanced Magnetics Group, Defence Metallurgical Research Laboratory, Hyderabad – 500 058, India
*Corresponding author’s e-mail: manickam-mahendran@tce.edu, Tel.: +914522482430; Fax: +91-4522483427
1
Abstract
Polycrystalline Ni-Mn-Ga thin films were deposited on
pre-heated Si (001) substrates with substrate temperatures
(Ts) varying from room temperature to 873K. The asdeposited films showed crystalline and ferro-magnetic
behavior at Ts greater than 573K. A strong dependence of
magnetic properties on microstructure and atomic
ordering was observed.
was studied using SEM. The grain size and morphology
was found to change significantly with increase in the
substrate temperature (Fig. 1a).
Keywords: Ferromagnetic shape memory alloy, Thin film,
Substrate temperature, Grain growth, Magnetization.
Introduction
Ni-Mn-Ga ferromagnetic shape memory thin
films possess large potential in micro-electro
mechanical systems. The films sputtered deposited at
room temperature are normally in amorphous or quasiamorphous state with poor magnetic properties [1]. In
order to fully crystallize, these films require a thermal
treatment either in the form of substrate heating while
deposition or in the form of post-deposition annealing to
optimize their properties. In order to study the effect of
substrate temperature on microstructural and magnetic
behavior of Ni-Mn-Ga films, the films were prepared at
different substrate temperatures and no post annealing
was performed on these films.
Experimental Procedure
Polycrystalline Ni-Mn-Ga thin film was
deposited using ultra high vacuum d.c. magnetron
sputtering unit on Si (001) substrate at different
substrate temperatures (RT–873 K). To examine the
crystallinity of the film structure X-ray diffraction
(XRD) was carried out at room temperature. The
surface morphology of the films was observed using
atomic force microscopy and scanning electron
microscopy. The magnetic properties of the films were
analyzed using vibrating sample magnetometer
(SQUID-VSM).
Results and discussions
The films deposited at substrate temperature
(Ts < 473 K) were amorphous in nature while the films
deposited at Ts greater than 573K showed crystalline
peaks in XRD corresponding to the (220) plane of the
parent austenite phase. The microstructure of these films
Fig. 1: (a) SEM image of Ni-Mn-Ga thin film deposited
at Ts of 573 K, (b) M-H curves of films deposited at
various Ts measured at room temperature.
In-plane M – H curves were measured for all
the films at 4 and 300 K. The films deposited at Ts <
473 K showed paramagnetic behavior up to 4 K.
However, the films deposited at Ts of 573-873 K
displayed ferromagnetic behavior (Fig.1b) with Curie
temperature similar to that observed in bulk state. It is
known that ferromagnetism in Ni-Mn-Ga is very
sensitive to atomic ordering. The observed difference in
magnetic properties of these films can be attributed to
the change in atomic ordering and microstructure with
substrate temperature.
Conclusions
Effect of substrate temperature on structural
and magnetic properties of Ni-Mn-Ga thin film was
studied. It is concluded that substrate temperatures have
a great impact on surface morphology, crystallite size
and magnetic properties of these films.
Acknowledgment
The author (S.V.K) would like to thank the
CSIR, New Delhi for their financial support (CSIRSRF) and DMRL for facilities to carry out this work.
References
[1] C. Liu, Z. Y.Gao, X. An, H. B.Wang, L. X. Gao,
W. Cai, Appl. Surf. Sci. 254, (2008) 2861-2865.