Dynamic Phase Transitions Of Bimetallic Oxalates Under An Oscillating Magnetic Field

In recent years, coordination chemists have acquired higher control and expertise in the design of molecule-based magnets, and the investigation of molecule-based magnets have become a fascinating subject in the field of material and coordination chemistry for their important properties and potential application. On the other hand, the Ising model is a representative model for exploring the properties of magnetic materials. In particular, this model can be used to explain the phase transition of magnetic films far from the equilibrium state, so great interest has been aroused for Ising model, which is driven by an oscillating magnetic field.In this paper, the properties of the phase transitions in the Blume-Capel model (BC model) under an oscillating magnetic field are studied through the correlated effective-field theory. This model can be used to describe the ultra magnetic films with ions in the high spin state and crystal field. The results show that the behavior of the system strongly depends on the value of the crystal-field constant. When the crystal-field constant is large enough but negative, a new coexistence region appears at low values of temperature and magnetic field. The more spin-spin fluctuations to be considered, the narrower the range of the coexistence region is. The first-order-order phase transition has been found in S=3/2 BC model, but there is no first-order-order phase transition in S=1 BC model. Spin state strongly affects the phase transition behaviors of the magnetic films.On the basis of the results of the BC model, a mixed spin ferrimagnetic Ising model on a honeycomb lattice was built to describe bimetallic oxalates. The magnetic properties of the compounds under the oscillating magnetic field have been investigated. AVâ…¡Vâ…¢(C2O4)3 compounds show that including the interlayer interactions between Vâ…¢ ions is considered to be one of the causes for the dynamical compensation phenomenon in the compounds. If the interlayer interaction between Vâ…¢ ions is zero, no compensation behaviors occur in the compounds. There is a critical value of the crystal-field constant, above which the compensation point can be found. The compensation temperature decreases as the crystal-field constant increases. When the crystal-field constant becomes large, the compensation temperatures seem to become insensitive to the change of the crystal-field constant. The ferrimagnetic ordering temperature increases as the interlayer interaction increases, and the temperature increases as the crystal-field constant increases, and the temperature increases as the magnetic field decreases.AFeâ…¡Feâ…¢(C2O4)3 compounds show that the interlayer interaction is not the primarily responsible for the compensation behaviors in the low value of the magnetic field. The system may exhibit a dynamic compensation point for large enough crystal field, even if interlayer interactions are zero. The results support the existence other longer-range interactions in this system. The ferrimagnetic ordering temperatures depend on the values of the interlayer interactions and the crystal-field constant. And both values are sensitive to the constituents of the organic cation. If the size of the organic cation is large, the interlayer interaction decreases due to the increase of the layer separation, so the critical temperature decreases; if the structure of the organic cation is complex, the critical temperature increases due to the increase of the crystal-field constant. The organic cation affects the ferrimagneic ordering temperature strongly. Comparing AVâ…¡Vâ…¢(C2O4)3 with AFeâ…¡Feâ…¢(C2O4)3, we find that replacing V with Fe the ferrimagnetic ordering temperature increases in the same condition.