Investigation of magnetocaloric effect in Holmium substituted Dysprosium iron garnet for magnetic refrigeration applications

The (Dy1-xHox)3Fe5O12(Ho-DyIG) with x = 0.0 to 1.0 garnet samples are prepared by solid-state reaction route by sintering them at 1200 degrees C for 24 hours followed by calcination. The samples have simple cubic structure with Ia3d space group. The lattice constant is obtained from the Rietveld refinement technique and is found to be decreased from 12.4181A to 12.3858A with Ho doping. All the samples exhibit ferrimagnetic behavior below their transition temperature of 555K(x = 0.0) to 545K(x = 1.0). This drop in transition temperature is attributed to the dilution of Fe(a) -O -Fe(d) networks. All the samples show magnetic compensation because of the strong anisotropy induced at lower temperatures. In addition, we have also observed spin reorientation in all the samples of Ho-DyIG series. We have performed magnetocaloric measurements for x = 0.4 and 0.8 samples and observed that the magnetic entropy is improved from 3.92 to 4.30J/kgK when measured at a maximum applied field of 5T around their respective Belov tranistion temperature i.e. TB. We have seen both normal and inverse magnetocaloric effects in these samples. To test the extent of magnetic refrigeration capacity, we have calculated the Relative Cooling Power, which comes out to be 364.6J/kg for x = 0.4 and 313.0J/kg for x = 0.8 samples at 5T magnetic field. The Arrott plots are also investigated and they have positive slope suggesting the presence of second-order phase transition in our samples.