| Compared with the traditional compressing refrigeration with Freon, the technology of magnetic refrigeration with many advantages in efficiency and pollution-free has received much attention recently. One of the key to developing the room-temperature of magnetic refrigeration is enhancing the temperature, where the working substances achieve the biggest value of magnetic entropy change (MEC), and the other is making the magnetic density of the materials large enough. The standard Monte Carlo simulation is used to study the magnetic properties and MEC of the magnetic materials described by Ising model. The main conclusions are as follows:In the ferromagnetic and antiferromagnetic systems with different spin quantum numbers, it is no hard to find that, as the absolute value of anisotropic constant is lower than spin exchange effect constant, the phase transition temperature decreases with anisotropy effect increasing, while the ground-energy increases. In the vicinity of phase transition point of ferromagnetic system, the internal energy shows a critical point, and specific heat and magnetic susceptibility have the biggest value, what’s more, MEC has a negative value. When anisotropic constant achieves to a critical value (-2.871) in spin-1ferromagnetic system, the competition between anisotropy and interaction effect becoming balance, so that the saturated magnetization decreases to zero suddenly, namely first-order ferro-para phase transition takes place. In the systems with a higher spin quantum numbers, the curves of temperature dependence of magnetization of ferromagnetic systems show a step behavior, and the curves of magnetic specific heat and susceptibility performance double-peak structures. While MEC presents an obvious phenomenon in the ferromagnetic system with spin-2near the transition temperature in low temperature region. In the other hand, the phenomenon is similar with ferromagnetic system in respect to internal energy and specific heat in antiferromagnetic system, but the phenomenon of magnetic susceptibility is different, it presents a gentle and small peak. The abnormal MEC can be found in the antiferromagnetic system, namely the system presents positive value at low temperature region. As the temperature increases, the positive number vanishes, and the positive MEC presents extreme value about the critical anisotropic constant.Furthermore, study on the impact of the concentration of magnetic atom on thermodynamic properties and MEC. It is found that, the saturated magnetization, phase transition temperature, the peaks of specific heat and magnetic susceptibility fall as the concentration of magnetic atom decreases. In addition, the alloys have the biggest negative MEC near the transition temperature, and the value decreases with the magnetic atom decreases in ferromagnetic alloys. While mixed some nonmagnetic atom in antiferromagnetic alloy, MEC increases. When the concentration of non-magnetic atom gets to0.25, the value of MEC is the biggest one. Moreover, the value of ferromagnetic system is apparently bigger than that in the antiferromagnetic system.In the end, study on the strict solution of one-dimensional Ising model with negative anisotropic constant by transfer matrix. It is found that, the curves of magnetic susceptibility are always diverging in spin-3/2systems. In the other hand, as the absolute value of anisotropic constant increasing, the diverging curves of magnetic susceptibility turn to limited peak in the systems with spin-2. The ferromagnetic system has the biggest negative values near the transformation temperature with the critical anisotropic constant. While in the antiferromagnetic alloys, the curves of magnetic susceptibility present gentle peak, and the positive MEC have the biggest value in low temperature region under the critical anisotropic constant. |
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