Synthesis and characterization of Ni incorporated titanium dioxide thin films

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ARTICLE Synthesis and characterization of Ni incorporated titanium dioxide thin ﬁlms Deepak Kumar Department of Physics, Graphic Era Hill University, Dehradun 248002, India

Prasanta Mandal Department of Physics, University of Petroleum and Energy Studies, Dehradun 248007, India

Anil Singh Department of Physics, Graphic Era Hill University, Dehradun 248002, India

Charu Pant Centre for Nanotechnology, University of Petroleum and Energy Studies, Dehradun 248007, India

Sudesh Sharmaa) Department of Physics, University of Petroleum and Energy Studies, Dehradun 248007, India (Received 14 June 2018; accepted 19 September 2018)

Thin ﬁlms of insulating Ti1xNixO2 (x 5 0.00, 0.05, 0.10, and 0.15) are synthesized by the spray pyrolysis technique. All the ﬁlms are seen to crystallize into polycrystalline anatase phase of TiO2. However, weak signature of the NiTiO3 phase is also observed for the ﬁlms having higher Ni ion concentration. Optical absorption analysis suggests nonmonotonous band gap decrease from 3.67 to 3.59 eV with respect to added concentration of Ni ions unto ‘x’ 5 0.10 in the TiO2 matrix. The presence of ferromagnetic ordering at room temperature in Ni incorporated TiO2 ﬁlms is revealed by M–H measurements. Calculated values of saturation magnetization indicate that the observed ferromagnetism is not due to the presence of Ni clusters or segregation of other ferromagnetic phase. Electrically insulating nature of the ﬁlms suggests that the observed FM ordering is most probably due to the ferromagnetic interaction between bound magnetic polarons which formed due to the creation of oxygen vacancies or defects.

I. INTRODUCTION

In last few years, much attention has been paid globally to the emerging ﬁeld of spintronics because of rapidly increasing demands of huge data storage capacity and relatively faster data processing. Semiconductors containing very tiny amount of magnetic impurities substituted at the cationic site of host semiconducting lattice, also called dilute magnetic semiconductors (DMSs), exhibit room temperature ferromagnetism (RTFM) and are hence potential candidates for spintronics. After the theoretical report of ferromagnetism in Mn-doped GaAs,1 extensive research has been carried out on DMSs to explore their possibility as potential application in spin-based electronic devices such as spin ﬁlter and spin transport media.2 The efﬁcient control of both charge ﬂow and spin of carriers in DMSs turns the development of spintronic devices with all its new functionalities attainable. The elementary requirement for a DMS is that it should exhibit ferromagnetic Curie temperature (TC) at/above a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.377 J. Mater. Res., 2018

room temperature. The discovery of ferromagnetic ordering in Co-doped TiO2 by Matsumato et al.3 has led focused experimental and theoretical research on the presence of ferromagnetism and potentially applicable mechanisms of ferromagnetism in oxide-based DMS (such as transition metal (TM

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