The magnetic interactions are governed by the Tri-Critical Mean Field model with emphasis on the coexistence of long-range and short-range interactions. Nearly 100–500 percent increases in magnetic entropy change was realised over existing parent compounds and the entropy changes are greater than the prototype, Gd of active magnetic refrigeration. Phenomenal improvement in magnetic sensitivity at low magnetic fields was achieved with T C close to room temperature. The sample has a soft ferromagnetic nature with a single magnetic transition occurring at 275 K. The chemical additive Bi 2O 3 has assisted in grain growth to form densified specimens even at low sintering temperatures. In a chemical reaction, the change in entropy can also be attributed to the rearrangement of atoms or ions from one pattern to another.

The only'' is important it means without any other changes occurring. So if the system (aka rubber band) heat is positive, heat must go into the strands of polymer. For this change the entropy increases, which means the heat is positive. The second law thus tells us that we cannot get work from a single reservoir only. Entropy is related to heat as the amount of heat transferred (in a reversible fashion) at constant Temperature divided by the temperature: S q r e v T > 0. The total entropy change in the proposed process is thus less than zero, which is not possible. In the products, if the molecules are very much disordered in comparison to the reactants, there will be a resultant increase in entropy during the reaction. Figure 5.5: Work from a single heat reservoir. If the entropy of a system increases, S is positive. The symbol for entropy is S, and a change in entropy is shown as delta S or S. It can often help to understand it as a measure of the possible arrangements of the atoms, ions, or molecules in a substance. A 10% Bi ion substitution at the La site has led to the relatively higher symmetry R c rhombohedral structure showing improvement in Mn–O–Mn bond angles. In a chemical reaction, the change in entropy can also be attributed to the rearrangement of atoms or ions from one pattern to another. Entropy is a mathematically defined property in thermodynamics. Change in states of reactants and products Change in number of moles As gases have high entropy and solids have low entropy. There are two rules to identify the change in entropy. The bismuth (Bi)-substituted La 0.85− xBi xNa 0.15MnO 3 ( x = 0 and x = 0.1) manganites have been investigated for achieving room temperature magnetic entropy change at low magnetizing intensities. Entropy changes in reactions In a chemical reaction, by comparing the entropies of reactants and products we can determine whether the entropy increase or decreases.