Structural and magnetic characterization of the incommensurate phase in TiOCl

D. MASTROGIUSEPPE; M. E. TORIO; C. GAZZA; A. DOBRY

Buenos Aires, Argentina

Workshop; At the Frontiers of Condensed Matter IV; 2008

Comisión Nacional de Energía Atómica

Going beyond a recently proposed microscopic model for the incommensurate transition in the spin-Peierls TiOX (X=Cl, Br) compounds, in the present work we start by studying the thermodynamics of the model with XY spins and adiabatic phonons. We find that the system enters in an incommensurate phase by a first order transition at a low temperature Tc1. At a higher temperature Tc2 a continuous transition to a uniform phase is found. Furthermore, we study the magnetism in the incommensurate phase by Density Matrix Renormalization Group (DMRG) calculations on a 1D Heisenberg model where the exchange is modulated by the incommensurate atomic position pattern. Whenthe wave vector q of the modulation is near pi, we find local magnetized zones (LMZ) in which spins get free from their singlets as a result of the domain walls induced by the modulated distortion. When q moves away enough from pi, the LMZ disappear and the system develops incommensurate magnetic correlations induced by the structure. We discuss the relevance of this result regarding to previous and future experiments in TiOCl.