Spin-flop and spin-Peierls transition in doped CuGeO3.

Ni++ ions doped inorganic CuGeO3 sample has been studied by using electron spin resonance (ESR) technique in the temperature range of 3-300 K. The ESR spectrum of Cu++ ion has been observed to be strongly temperature dependent for inorganic spin-Peierls (SP) Cu0.96Ni0.04GeO3 samples. The ESR line width and ESR amplitude exponentially vanishes below a critical temperature, Tsp=14 K. The one-dimensional (1D) antiferromagnetic (AF) spin chain formed of Cu++ is broken by Ni++ (spin-1) ion, giving uncoupled spins at the end of the chains that give extra contribution to the spectra at lower temperature and stabilizes a Néel state. The g-factor is much smaller than the expected value for isolated Cu++ and Ni++ ions and is much more anisotropic than for undoped samples [O. Yalçin, B. Aktaş, J. Magn. Magn. Mater. 258/259 (2003) 137 (reference therein)]. It is shown that the ground state of dimerized spins is singlet. The spin-flop (SF) phenomenon is obtained from AF state mixed condition and then ferromagnetic (FM) state. The spin-flop field slightly increases when increasing temperature in the temperature range 100-300 K. The SF transition is showed almost AF order for Cu0.96Ni0.04GeO3.