Magnetic Properties and Magnetocaloric in Double Perovskite Oxides

The study uses Monte Carlo analysis to look into the magnetic properties and magnetocaloric effect of the Sr2FeMoO6 combination. It looks into magnetic entropy, adiabatic temperature, thermal magnetisation, transition temperature, and lock-in transition temperatures for different magnetic fields. The study also finds out how relative cooling power and the magnetic hysteresis cycle change with magnetic field and temperature. Based on the results, Sr2FeMoO6 might be a good starting point for making new magnetic refrigerants for magnetic refrigeration technology.

The double perovskite Sr2FeMoO6 is very magnetic and resistant, which means it can be used in spintronics and magnetoresistance. The substance is a double perovskite (ABB’O6). The alkaline-earth ion A is Sr, and the transition metal ions B and B’ are Fe and Mo grouped in a rock-salt pattern. The magnetism test results show that the Sr2FeMoO6 sample is ferromagnetic, and its magnetic transition temperature is around 380K. The double perovskite crystal structure is made up of two face-centered cubic sublattices that fit inside each other. The Fe3+ (3d5) and S = 5/2 magnetic moments are arranged in a way that makes them antiferromagnetically coupled to the Mo5+ and S = 1/2 moments. This creates a total saturation magnetic moment of 4¼B at low temperatures.

The ordered double-perovskite Sr2FeMoO6 has amazing magneto-resistivity and transport features at room temperature and low field. These are caused by structure and magnetic instabilities that cause a cubic-tetragonal phase shift around 420K. A pair of M2+ and Mo6+ ions can be made when other 3d metals are used instead of Fe3+.

Two types of Sr2FeMoO6 ceramics were compared in terms of their magnetic properties: those made by the sol–gel and solid-state reaction methods and sintering in the traditional way; and those made by the same two methods but sintering in the spark plasma method. Neutron diffraction and magnetic susceptibility were also used to look into Sr2FeMoO6’s crystal and magnetic structures.

Ising Model and Monte Carlo Simulations

If you use the Ising model to look at the Sr2FeMoO6 molecule, the Hamiltonian includes interactions between nearest neighbours, an external magnetic field (h), and a crystal field (). The number of spins in the system is N = NS + Nπ, where NS = 2331 and Nπ = 2310. Monte Carlo simulation is used to make a copy of the Hamiltonian in Equation (1).

It is thought that the Sr2FeMoO6 compound lives in unit cells, and the system is made up of N spins, where NS = 2331 and Nπ = 2310. To do the Monte Carlo update, random spins were picked out and then flipped using Boltzmann’s chance method. If (∂ S∂h) T=(∂ M∂T) h, then S and M are thermodynamically related.

You can find a material’s magnetic entropy by its S(T, h) = ∫ T0 Cm T dT, where Cm is the material’s magnetic specific heat. ΔSm(T, h) = Sm(T, h) − Sm(T, 0) = ∫ hmax0(∂ M∂T)hi dh shows how the magnetic entropy changes when h is not zero and when h is zero.

¥Tad = −TΔSm Cp,h gives you the adiabatic temperature from Equation (6). The relative cooling power (RCP) is shown as the area under the curve where ΔSm(T) changes with temperature. This is the best balance between the size of the change in magnetic entropy and the width of the peak. It is written as B = h + 4πM, where M is the magnetic field strength.

Finally, the Ising model and Monte Carlo simulations are used to study the Sr2FeMoO6 compound’s properties and its magnetocaloric properties.

Results and Discussion of Magnetic Properties
and Magnetocaloric in Double Perovskite Oxides

Using Monte Carlo models, the study looks into the magnetic properties and magnetocaloric effect of the Sr2FeMoO6 molecule. Previous research had found the Curie temperature (TC) to be between 358 K and 420 K. This study’s results show that it is 460 K. This low TC value is because of anti-site defects, oxygen vacancies, and the presence of the nonmagnetic SrMoO4 secondary phase. The secondary phase raises the Fe content in the sample, which causes antiferromagnetic Fe–O–Fe interactions and anti-site defects.

It is shown how the magnetic entropy change of the Sr2FeMoO6 compound changes with temperature for different magnetic fields (h = 2, 4, 8, and 12 T). The Curie temperature (TC) can be found by looking at the highest value of −ΔS (T, h), which shows a second-order magnetic phase shift.

The adiabatic temperature change of the Sr2FeMoO6 compound is also seen for different magnetic fields (h = 2, 4, 8, and 12 T), and the Curie temperature is found to be similar to what has been done before. The Sr2FeMoO6 compound’s relative cooling power (RCP) also goes up as the external magnetic field strength goes up.

The Sr2FeMoO6 compound’s magnetic hysteresis cycle shows that as the temperature rises, the magnetic coercive field weakens. Around the transition temperature (TC), superparamagnetic behaviour is seen. The relationship between the magnetic excitation B and the external magnetic field h at different temperatures (0.1, 0.5, 1, and 2 K) also shows that the material is superparamagnetic when it is cold.

Conclusions

Using Monte Carlo models, the study looks into the magnetic properties and magnetocaloric effect of the Sr2FeMoO6 molecule. At the ferromagnetic transition, the results show a big increase in both magnetic entropy change and adiabatic temperature change. This is a common feature of second-order transitions. The ΥSmax goes up as the external magnetic field gets stronger, and different temperatures show magnetic hysteresis cycles. As the temperature rises, the coercive fields weaken. This makes Sr2FeMoO6 a possible material for ferromagnetic cooling. Around the Curie temperature and at low temperatures, the system acts in a superparamagnetic way. The study also shows that the Sr2FeMoO6 compound’s relative cooling power (RCP) changes with the magnetic field and doesn’t show any hysteresis. This makes it a possible material for ferromagnetic refrigeration.