Studies on the local structures and spin Hamiltonian parameters for the rhombic Nb4+ centers in MO2 (M = Sn, Ti and Ge) crystalsZ.-H. Zhang, S.-Y. Wu, P. Xu, L.-L. Li and S.-X. ZhangEur. Phys. J. Appl. Phys., 53 2 (2011) 20902DOI: https://doi.org/10.1051/epjap/2010100161