We study the magnetic properties of single crystals of rutile TiO2 implanted with cobalt for various fluences. The temperature variation of zero field cooled(ZFC) and field cooled (FC) magnetization shows a much higher blocking temperature (TB) along [1-10]. Similarly the scaling of magnetization isotherms above TB is seen only when the field is parallel to [1-10] direction. With field along this direction, the magnetization shows near saturation at a much smaller field compared to that of[001] direction. The Co nanoclusters possess an "easy" and "hard axis" of magnetization coupled by the magneto crystalline anisotropy of secondary phases of cobalt with TiO2. In addition, at T=2 K we observe a crossover in the magnetization vs field isotherms between the two field directions in the samples which has been attributed to the anisotropic paramagnetism arising from cobalt present in 2+ ionic state with S = 3/2.
@article{arxiv.1703.04965,
title = {Anisotropic super-paramagnetism in cobalt implanted rutile-TiO2 single crystals},
author = {Shalik Ram Joshi and B. Padmanabhan and Anupama Chanda and N. Shukla and Vivek Malik and D. Kanjilal and Shikha Varma},
journal= {arXiv preprint arXiv:1703.04965},
year = {2017}
}