Magnetic properties of spinels GeNi2-xCoxO4 systems: Green's function and high-temperature series expansions

摘要

The Green's function theory and high-temperature series expansions technical have been developed for magnetic systems GeNi2-xCoxO4. We have applied the Green's function theory to evaluate thermal magnetization and magnetic susceptibility for different values of magnetic field and dilution x, considering all components of the magnetization when an external magnetic field is applied in (x,z)-plane. The second theory combined with the Pade approximants method for a randomly diluted Heisenberg magnet is used to deduce the magnetic phase diagram of GeNi2-xCoxO4 systems. The critical exponents and associated with the magnetic susceptibility and the correlation length , respectively, have been deduced. The theoretical results are compared with those given by magnetic measurements.