Improved Scaling of the Magnetic Heat Capacity in La 0.85 Ag 0.15 MnO 3 Manganite

The heat capacity in a La0.8 Ag0.15 MnO3 manganite has been measured near the Curie temperature T C in applied magnetic fields up to 26 kOe to study the scaling critical behavior and to obtain the universality class. The conventional scaling fails in application to the manganites with a hysteresis and the strong sensitivity of T C to a magnetic field. However, the application of the improved scaling procedure designed by us allows yielding the good scaling the magnetic heat =0.23 capacity in La0.85Ag0.15MnO3, which may belong to a new universality class for systems with the strong spin-orbital coupling of t 2g -electrons, namely, double -Heisenberg with the critical exponent of the heat capacity α = −0.23 and the critical exponent of the correlation radius v=0.7433. This new universality class is consistent with the crystal, magnetic and orbital symmetries for the La0.85Ag0.15MnO3. Scaling failure in the vicinity of T C in the range of t/H 1/2ν ≈ [−0.033;0.024] is understood by finite-size and other disordering effects when T →T C. It is remarkable that finite-size effect is consistent with grain size, L ≈ 50 μm, in the La0.85Ag0.15MnO3. The correlation radius, Lt ν ≈ 30.28 A, estimated from the finite-size effect is of the same order of magnitude with the sizes of the ferromagnetic fluctuations and drops in manganites.