The evolution of the Griffiths phase (GP) with a ferromagnetic metal (FMM) cluster above the Curie temperature (T_C) and its effect on the magnetic properties, electrical transport, magnetoresistance (MR), and magnetocaloric effect (MCE) is studied comprehensively, using bulk compounds of La_1−xBa_xMnO₃ (0.15 ≤ x ≤ 0.25) with different lattice distortions but with the same structural symmetry and space group. These La_1−xBa_xMnO₃ samples show ferromagnetic transition at T_C increasing from 229 K for x = 0.15–300 K for x = 0.25, in addition to the presence of GP with FMM clusters in the paramagnetic (PM) region, which have been confirmed by the combination of magnetization (susceptibility) measurements, the GP theory, and electron paramagnetic resonance technology. With increasing the Ba²⁺ ion doping, GP temperature (T_G) and T_C of La_1−xBa_xMnO₃ are increased, and the GP regime is strengthened. The GP ratio in the PM region reached 27.7% for the sample with x = 0.20. The resistivity decreases and the FMM phase increases with increasing x from 0.15 to 0.25, which can be explained by the decrease in the bandgap (E_g) and the enhancement of the double-exchange effect. Remarkably, large room-temperature MR (∼44.7%) can be observed in the sample with x = 0.25 under 60 kOe, which is related to the presence of the GP regime. Furthermore, the MCE is also affected by the GP regime, and it is deduced that the magnetic transition is of second order. The value of magnetic entropy change ($|\mathrm{\Delta }{S}_M|$ ) reaches 3.04 J/kg K near room temperature for the sample with x = 0.25 under 50 kOe. This value is associated with a relative cooling power (RCP) of 248.1 J/kg. For the sample with x = 0.15, the value of RCP reaches 307.6 J/kg under 50 kOe. The discovery of the MR and MCE near room temperature is of great significance from the practical application of perovskite manganites in magnetic sensors and magnetic refrigerants.

Magnetic characteristics, magnetocaloric effect, and critical behavior of Nd1−xSrxMnO3 compounds by Sr doping (x = 0.2, 0.3, 0.4, 0.5) were studied. All samples maintained orthorhombic structures, but the space group changed from Pnma (No. 62) for x = 0.2, 0.3 to Imma (No. 74) for x = 0.4, 0.5. As Sr doping increased, the Curie temperature (TC), Curie–Weiss temperature (TCW), and magnetization increased, attributed to the double exchange (DE) interaction. A discrepancy between TCW and TC was observed due to the competition between polarons and DE interaction. The critical behavior was investigated systematically using the self-consistent (modified Arrott plots, MAP) method and the Kouvel–Fisher (KF) relation. The KF relation was suitable for the samples with x = 0.2 and 0.5, while the MAP method was suitable for the samples with x = 0.3 and 0.4. Among the Ising, XY, Heisenberg, and mean-field models, the samples with x = 0.2, 0.3, and 0.4 aligned more closely with the mean-field model, except for the x = 0.5 sample. Entropy change (−ΔSM) of Nd1−xSrxMnO3 (0.2 ≤ x ≤ 0.5) increased with the applied field, with the maximum value observed around TC. For the sample with x = 0.3, (−ΔSM) reached 4.315 J/kg K at μ0ΔH = 50 kOe, corresponding to a relative cooling power (RCP) of 280.48 J/kg. Remarkably, the x = 0.4 sample displayed (−ΔSM) of 3.298 J/kg K at μ0ΔH = 50 kOe near room temperature, with the RCP of 283.64 J/kg. These findings underscore the role of Sr doping in tuning the magnetic properties, critical behavior, and magnetocaloric effect of NdMnO3.

The magnetic properties, critical behavior, and magnetocaloric effect of perovskite NdMnO₃ are studied. The Nd ordering is induced by the Mn ferromagnetic component with antiferromagnetic coupling with each other and then magnetization reversal occurs due to Mn moments reorientation induced by the ordering Nd moments, which explains the phenomenon of negative magnetization at low temperatures. The critical behavior of NdMnO₃ is studied using Kouvel–Fisher and self-consistent methods. The results show that the Kouvel–Fisher method is reliable and critical exponents are coming out as β = 0.462 for T_C = 11.15 K, γ = 1.041 for T_C = 11.42 K, δ = 3.252 by critical isotherm analysis. Magnetic exchange distance may decay as $J(r)\approx r^{-4.563}$ , that is, somewhere between the three-dimensional Heisenberg model and the mean field model. Remarkably, three temperature transitions and the corresponding three extremum values including positive and negative entropy change are observed in NdMnO₃, which is different from previous reports on NdMnO₃. A positive entropy change as 3.82 J/kg K at 10–15 K for μ₀ΔH = 50 kOe and a negative entropy change as −0.557 J/kg K at around 8 K for μ₀ΔH = 5 kOe are found, which can be put down to a fast magnetization change of NdMnO₃ because of the Nd moments ordering and Mn moments reorientation. Besides, an entropy change of 1.22 J/kg K is found for μ₀ΔH = 50 kOe at 80–85 K, which is corresponding to the Mn ferromagnetic ordering temperature. The relative cooling power of NdMnO₃ reaches 105.9 J/kg, making it a promising candidate in the field of magnetic refrigeration.

Emergent phenomena at interfaces have been investigated intensely in pursuit of the next generation spintronics. In this work, we have integrated heterostructure consisting of paramagnetic (PM) metallic Pt and antiferromagnetic (AFM) insulator LaMnO ₃ (LMO). High-quality Pt (3 nm)/LMO (100 nm) heterostructure has been obtained by pulsed laser deposition. The structure, lattice strain and magnetic properties of epitaxial Pt/LMO heterostructure are fully studied. Due to the high sensitivity of synchrotron radiation and the high quality of epitaxial layer, the reflection intensity of the 3 nm-thick ultrathin Pt layer and LMO layer can be detected, and then lattice strain can be calculated. The LMO layer is under relative large tensile strain (2.13%), while the Pt layer is under relative small compressive strain (−0.46%). Magnetization measurements suggest that unexpected ferromagnetic behavior is observed clearly in the PM-Pt/AFM-LMO heterostructure. Moreover, spin glass (SG) state and exchange bias (EB) is also observed in this heterostructure. SG state is observed as a result of competing magnetic orders and spin frustration at the Pt/LMO interface. The heterostructure shows the EB effect below blocking temperature ( T _B ), which is much lower than the Néel temperature ( T _N ) of LMO, suggesting that the EB is strongly related to the SG state. The EB originates from the coupling between the SG and AFM phases.