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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. [ABSTRACT FROM AUTHOR]

The microstructure and magnetotransport of LaMnO3 manganite have been studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) at room temperature show that the LaMnO3 sample has a single-phase orthorhombic structure, and the sample particles and elements are densely and evenly distributed. By studying the temperature dependence of resistivity and magnetoresistance (MR), and the magnetic filed dependence of resistivity, it is found that the resistivity versus temperature curves of LaMnO3 show three extreme values in the temperature range of 10–390 K. Firstly, the minimum resistivity at about 70 K comes from the spin polarization tunneling effect. Secondly, there is a maximum resistivity near 189 K due to the inhomogeneity of the polycrystalline sample. Finally, the traditional metal to insulator (MI) transition leads to another maximum resistivity near 241 K, where the corresponding temperature is MI transition temperature (TMI). Moreover, the resistivity of LaMnO3 exhibits a decline as the external magnetic field being increased, implying the presence of MR. In the region of low temperature (close to the TMI), the negative MR reaches 14.68 and 45.28% under 1 T and 4 T applied fields, respectively. The coexistence of two kinds of MR mechanisms in LaMnO3 induced by spin polarization tunneling and Jahn–Teller distortion leads to the enhanced MR within the wide temperature range (10–265 K). [ABSTRACT FROM AUTHOR]

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 TC = 11.15 K, γ = 1.041 for TC = 11.42 K, δ = 3.252 by critical isotherm analysis. Magnetic exchange distance may decay as J (r) ≈ 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. [ABSTRACT FROM AUTHOR]

Magnetoresistance and temperature coefficient of resistance (TCR) of manganites with ferromagnetism have been reported extensively, but the magnetoresistance and TCR of antiferromagnetic manganites are scarce. The transport properties, TCR, and magnetoresistance effect of antiferromagnetic NdMnO3 have been studied in this work. NdMnO3 samples exhibit semiconductor conductivity, and with the different applied magnetic fields, they still maintain semiconductor characteristics and have considerable stability. Under an applied magnetic field of 6 T, a small negative magnetoresistance of 8% appears near 150 K. Moreover, the conduction mechanism and TCR of NdMnO3 are studied. Three models, thermal activation (TA) model, small polaron (SP) model, and variable range jump (VRH) model, are used to analyze the electrical transport of NdMnO3 samples. The results show that the transport behavior of NdMnO3 samples is more consistent with the TA model. The maximum TCR is 9.4% K−1 within the low temperature region (above liquid nitrogen temperature). The TCR decreases with increasing temperature and it remains 2.5% K−1 near room temperature. Antiferromagnetic NdMnO3 has good TCR performance, which can be applied to temperature sensing field and has good application prospect in antiferromagnetic insulating electronic devices. [ABSTRACT FROM AUTHOR]

The evolution of the Griffiths phase (GP) with a ferromagnetic metal (FMM) cluster above the Curie temperature (TC) and its effect on the magnetic properties, electrical transport, magnetoresistance (MR), and magnetocaloric effect (MCE) is studied comprehensively, using bulk compounds of La1−xBaxMnO3 (0.15 ≤ x ≤ 0.25) with different lattice distortions but with the same structural symmetry and space group. These La1−xBaxMnO3 samples show ferromagnetic transition at TC 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 (TG) and TC of La1−xBaxMnO3 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 (Eg) 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 (| Δ 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. [ABSTRACT FROM AUTHOR]

The structure, magnetic, transport and magnetoresistance properties of SrMnO3 sample have been investigated. The SrMnO3 sample has single-phase structure with hexagonal symmetry, which is obtained by the X-ray diffraction. The scanning electron microscope reveals the particles of the sample are evenly distributed. The composition of the SrMnO3 sample is detected using the energy dispersive spectrometer, indicating the element ratio of Sr:Mn:O = 19.25:20.35:60.40. The magnetic, electrical transport and the magnetoresistance effect are studied via the temperature dependences of the magnetization, the resistivity and the magnetoresistance. An antiferromagnetic phase transition near 300 K appears in the SrMnO3 sample, and no significant entropy change can be found in the antiferromagnetic sample. The sample shows the insulator state since the resistance increases gradually with the decrease of temperature. Therefore, SrMnO3 is an antiferromagnetic insulator material. Moreover, the resistivity reduces significantly with the applied magnetic field, indicating an existence of magnetoresistance. Remarkably, the room-temperature magnetoresistance of the antiferromagnetic insulator SrMnO3 reaches 16.68% under 60 kOe field. This work opens our understanding of magneto-transport and magnetic properties of the antiferromagnetic SrMnO3. The discovery of magnetoresistance near room temperature in the antiferromagnetic insulator (SrMnO3) is of great significance for the development of antiferromagnetic spintronics. [ABSTRACT FROM AUTHOR]

The magnetocaloric and ferromagnetic properties of Pr0.7Sr0.3MnO3 film grown on (001) Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) using pulsed laser deposition technology have been investigated in this work. The X-ray diffraction measurement shows that the (001)-oriented film has been successfully deposited on PMN-PT substrate. The ferromagnetic properties and magnetocaloric effect resulted from ferromagnetic transition are explored via using the magnetic moment versus temperature plots, hysteresis loops, and the magnetic moment versus magnetic field curves. The magnetic moment versus temperature plots (M-T curves) show that with the decrease of temperature, the Pr0.7Sr0.3MnO3 film undergoes a transition from paramagnetic to ferromagnetic phase at temperature close to Curie–Weiss temperature (TCW). TCW (approximately 133 K) is determined by the Curie–Weiss law. The Pr0.7Sr0.3MnO3 film reveals the ferromagnetic feature below TCW, while the film exhibits the paramagnetic state at temperature higher than TCW. Hysteresis loops also confirm that the film reveals ferromagnetic feature at temperature lower than TCW (e.g. ferromagnetic behaviors at 10 and 100 K). The result of hysteresis loops is in accordance with the M-T curves. Besides, entropy change has been investigated in our work. The maximum entropy change of Pr0.7Sr0.3MnO3 film reaches about 2.4 J/kg·K at around TCW under 10 kOe field change, that is close to the entropy change of reference sample Gd (approximately 2.8 J/kg·K within the field change of 10 kOe), suggesting that the Pr0.7Sr0.3MnO3 film on PMN-PT has a great application prospect in magnetic refrigeration. [ABSTRACT FROM AUTHOR]

The magnetic behaviors and magnetocaloric effect (MCE) of Pr0.7Sr0.3MnO3 (PSMO-7) film grown on a (001) SrTiO3 single-crystal substrate by a pulsed laser deposition (PLD) were studied in this paper. X-ray diffraction with a high resolution (HRXRD) measurement shows that PSMO-7 film is grown with a (001) single orientation. The magnetic properties and the MCE related to the ferromagnetic (FM) phase transition of the PSMO-7 film are investigated using the temperature dependence of magnetization M(T) and the magnetic field dependence of magnetization M(H). The M(T) data suggest that with decreasing temperatures, the PSMO-7 film goes through the transition from the paramagnetic (PM) state to the FM state at around the Curie temperature (TC). The TC (about 193 K) can be obtained by the linear fit of the Curie law. Magnetic hysteresis loop measurements show that the PSMO-7 film exhibits the FM feature at temperatures of 10, 100, and 150 K (low magnetic hysteresis can be found), while the film reveals the PM feature with the temperature increased up to 200 and/or 300 K. The research results of M(H) data are consistent with the M(T) data. Furthermore, the magnetic entropy change ( − Δ S M ) of the PSMO-7 film was studied. It was found that the maximum value of ( − Δ S M ) near TC reaches about 4.7 J/kg·K under the applied field change of 20 kOe, which is comparable to that of metal Gd ( − Δ S M of 2.8 J/kg K under 10 kOe), indicating the potential applications of PSMO-7 film in the field of magnetic refrigeration. [ABSTRACT FROM AUTHOR]

The transport properties and magnetoresistance (MR) effect of Pr0.7Sr0.3MnO3 (PSMO) film on SrTiO3 (STO) substrate are investigated in this work. The PSMO film is grown on (001) STO substrate by pulsed laser deposition (PLD). The high-resolution X-ray diffraction (XRD) pattern suggests that the Pr0.7Sr0.3MnO3 film shows the out-of-plane single orientation. Atomic force microscopy (AFM) image shows that the surface of the film is smooth. In addition, the significant interference peaks can be found in the XRD. All these confirm the high quality of the PSMO film grown on STO substrate to some extent. The magnetotransport properties and the MR associated to the double exchange (DE) interactions of the Pr0.7Sr0.3MnO3 film have been studied by the resistivity versus temperature and resistivity versus magnetic field data. The temperature dependence of resistivity shows that the film sample undergoes a metal-to-insulator (MI) transition at MI temperature TMI. The TMI gradually increases with the increase of applied magnetic field. Under different fields of 1 T, 2 T, 4 T and 6 T, the maximum values of negative MR (MR = [ρ-ρ0/ρ0] × 100%) reveal about 47.16%, 53.16%, 86.59% and 92.22%, respectively. Compared with other reports on bulk polycrystalline PSMO compounds and polycrystalline PSMO films, the PSMO film on STO in our work has relatively large MR, which is related to the single-oriented growth of PSMO/STO film. The large MR is conducive to the practical applications in magneto-electronic devices. The applied magnetic field dependence of resistivity shows that near TMI, the resistance changes significantly with the change of the applied field. This also implies that there is a large MR at around TMI, which can be explained by the traditional DE mechanism. [ABSTRACT FROM AUTHOR]

Samples of (110), (100), and (111) MgO single crystals were implanted with 70 keV N ions at room temperature. All as-implanted samples showed room temperature hysteresis in magnetization loops. The observed saturation magnetization (Ms) was 0.79 × 10−4 emu/g, 1.28 × 10−4 emu/g, and 1.5 × 10−4 emu/g for (110), (100) and (111) orientation implanted-MgO and follows the relation Ms(111) > Ms(100) > Ms(110), indicative of crystalline orientation-dependent ferromagnetism in N-implanted MgO. The samples were characterized by X-ray photoelectron spectroscopy (XPS), high resolution X-ray diffraction (HRXRD), reciprocal space mapping (RSM), and photoluminescence (PL). The results indicated that the amount of N-substitute-O and N-interstitial defects in these three N-implanted MgO samples showed the same changing tendency as compared with Ms data. Thus, we conclude that the N-substitute-O and N-interstitial defects may play a crucial role in controlling the N+-implanted-induced ferromagnetism. [ABSTRACT FROM AUTHOR]

The magnetic properties and exchange bias (EB) effect of perovskite NdMnO3 ceramic are studied in this work. In A-type antiferromagnetic (AFM) NdMnO3, the ordering of Nd3+ is caused by Mn3+ ferromagnetic component with antiferromagnetic coupling with each other. Interestingly, the Nd3+ ordering induces the Mn3+ spin reorientation, which explains the phenomenon of the negative magnetization at low temperature. The magnetic ordering of Nd3+ and Mn3+ ions is decisive to the EB effect. Remarkably, the positive EB effect is observed at 40 and 25 K, and both positive and negative EB effects are found at 5 K. These EB effects are relied on the cooling fields. The EB can be determined by the initial states and the coupling of Nd3+ ordering and Mn3+ ordering. The present work shows the role of magnetic ordering of Nd3+ and Mn3+ ions in regulating the EB and magnetic properties of perovskite NdMnO3. [ABSTRACT FROM AUTHOR]

The nanostructures usually possess plenty of surface traps owing to their large surface-ratio comparing with the corresponding bulk materials. Hence understanding the carrier transport related to the traps is critical to enhance the performance of the nanostructures. Here, based on the studies to Meyer–Neldel relationship, a phenomenon closely related to the traps and widely observed in various materials, we reveal the broad distribution nature of the trap in the nested nano-networks of Bi2S3, and accordingly design the improved strategy to enhance its switching performances based on trapping/detrapping of the charge carriers in Bi2S3 nested nano-networks. It achieves improved optical switching time from few hundred seconds to few seconds by using only the shallow traps. While thanks for their deep traps, it could produce multi-level resistive switching with optimal on/off ratio better than 50. [ABSTRACT FROM AUTHOR]