Journal of Alloys and Compounds 509 (2011) 2833–2837 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Exchange bias behaviour in magnetron sputtered Ni 49.8 Mn 36.1 Sn 13.9 ferromagnetic shape memory alloy thin film Ritu Vishnoi, Davinder Kaur ∗ Functional Nanomaterials Research Laboratory, Department of Physics and Center of Nanotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India article info Article history: Received 27 June 2010 Received in revised form 12 November 2010 Accepted 19 November 2010 Available online 3 December 2010 Keywords: Exchange bias FSMA thin film DC magnetron sputtering abstract In the present study we report the observation of exchange bias effect in Ni 49.8 Mn 36.1 Sn 13.9 ferromagnetic shape memory alloy thin film, grown on Si (1 0 0) substrate at 550 ◦ C by dc magnetron sputtering. The shift in hysteresis loop up to 41 Oe from the origin was observed at 5 K when film was cooled under a magnetic field of 2 T. Above 55 K, the exchange bias field disappears and the coercivity gets significantly reduced due to the fact that the pinning between an antiferromagnet and ferromagnet becomes weak with increase in temperature. The observed exchange bias behaviour in Ni 49.8 Mn 36.1 Sn 13.9 film is attributed to the presence of AFM–FM interactions that result from the coexistence of antiferromagnetic and ferromagnetic phases in the martensite phase of the film at low temperature. This behaviour is an additional property of the Ni–Mn–Sn thin films apart from various other multifunctional properties. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Since the discovery of the exchange bias (EB) in 1956 by Meikle- john and Bean in Co particles embedded in antiferromagnetic CoO [1], the materials exhibiting EB effect have been studied exten- sively for their potential applications in spin-electronic devices, ultra-high density magnetic recording media [2], sensors, perma- nent magnets [3,4], giant magnetoresistance and many others. This effect is described as the shift in magnetic hysteresis loop of the material from the origin when it is cooled in the presence of an applied magnetic field. The shift is due to the unidirec- tional anisotropy produced by the coupling of ferromagnet (FM) to antiferromagnet (AFM) at the interface. Therefore, EB has been observed in systems containing FM/AFM interface, such as AFM–FM bilayers, magnetic nanoparticles [4,5], spin glass systems [3] and thin films [6,7]. One of the promising materials exhibiting EB effect that have attracted increasing attention in recent years are the ferromagnetic shape memory alloys (FSMAs). FSMAs are the interesting materials exhibiting shape memory effect and magnetism simultaneously. They show magnetic field-induced strains at room temperature greater than any magnetostrictive, piezoelectric or electrostrictive material, and faster frequency response than temperature driven shape memory alloys [8]. Among various FSMA materials, Ni–Mn–X ∗ Corresponding author at: Department of Physics and Center of Nanotechnology, Indian Institute of Technology Roorkee, Roorkee, India. Tel.: +91 1332 2285407; fax: +91 1332 273560. E-mail address: dkaurfph@iitr.ernet.in (D. Kaur). (X = In, Sn, Sb) have gained considerable interest due to their multi- functional properties such as shape memory effect, magnetocaloric effect, magnetoresistance, etc., associated with first order marten- site to austenite structural transition [9]. Detailed studies on the magnetic and structural properties and EB behaviour of these bulk FSMA materials have been reported [10–16]. However, limited studies have been reported on the growth and magnetic properties of FSMA thin films [17,18]. Thin films of FSMA are important for the applications of these materials in emerging micro-devices such as magnetically driven microelectromechanical systems (MEMS) which require a high quality of FSMA thin films grown on semi- conductor substrates [19,20]. To the best of our knowledge, there are no reports on the observation of EB effect in thin films of FSMA, particularly for Ni–Mn–X (X = In, Sn, Sb) system, which is keenly required since most of the device applications based on EB are in thin film form. In the present study, we report for the first time, as far as we know, the observation of EB effect associated with phase separation in Ni 49.8 Mn 36.1 Sn 13.9 FSMA thin film grown on Si (1 0 0) substrate. It can be useful in technological devices such as read-heads, magnetic sensors or magnetoresistive memories. Precise control of sputter- ing parameters was done to obtain high quality film. The influence of EB on magnetic properties of the film is investigated in detail. 2. Experimental plan Ni–Mn–Sn thin film was deposited on (1 0 0) silicon substrate by dc magnetron sputtering system using Ni–Mn–Sn sputtering target of 1 in. diameter and 3 mm thickness. The details of process set up have been described elsewhere [21,22]. The substrates were initially cleaned thoroughly in an ultrasonic bath with a mixture of distilled water and trichloroethylene in 4:1 ratio and then washed with boiled 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.11.133