Renormalization of magnetic chains in a field: Isothermal magnetocaloric effect

Motivated by the recently developed [T. Plackowski , Rev. Sci. Instrum. 73, 2755 (2002)] technique for measuring isothermal magnetocaloric coefficient (M-T), we revisit the thermodynamic properties of coupled spin chains in a field. The coupled Ising antiferromagnetic chains in two and three dimensions, quantum XY chain in a transverse field, and Heisenberg chain are considered. For the Ising model the shift of the critical temperature under magnetic field and dependence of M-T on interchain coupling are found. The field dependence of M-T for several models is presented. It is demonstrated that in the disordered phase in the presence of antiferromagnetic fluctuations, M-T changes sign at some value of the magnetic field. Generally, M-T is negative if magnetic field competes with a short-range order, and consequently it can be an indicator of the change in the short-range correlation.