The authors are obliged to Maharshi Dayanand University, Rohtak, for providing the necessary facilities and support. The authors also thank SAIF, Panjab University, Chandigarh, India, for their instrumentation support. J Rasgania and N Sahu acknowledge the Council of Scientific and Industrial Research for granting senior and junior research fellowships, respectively. R Gavadia acknowledges the University Grants Commission for providing senior research fellowship.