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The magnetic and electronic transport properties of the lightly doped SrRu1-x Fex O3 (x ≤ 0.15) have been studied. All the samples show a paramagnetic-ferromagnetic phase transition and hysteresis effect. With the increase of Fe, the temperature of magnetic phase transition decreases but coercive field increases indicting the existence of antiferromagnetic interaction and magnetic-crystalline anisotropy. In low temperature, all the doping samples exhibit an insulating behavior while metal feature appears only at x ≤ 0.10 samples. The induced disorder suppresses the itinerant property of Ru 4d electron due to Fe random occupation. As a result, the ferromagnetism is weakened and metal-insulator transition is suppressed. [ABSTRACT FROM AUTHOR]

An electrochemically active nanostructured silver copper fluoride (SCF) perovskite, AgCuF 3 , was synthesized via a mechanochemical reaction between AgF and CuF 2 precursors. Phase composition and electrochemical properties of the SCF perovskites produced under various synthetic parameters were studied. The optimum SCF perovskite sample exhibited an appreciable electrochemical performance through the use of conductive carbon matrix in a primary lithium half cell. A high specific capacity of 270 mAh g −1 was achieved at a cutoff voltage of 2 V with 190 mAh g −1 above 3 V, leading to a total volumetric energy density of 3666 Wh L −1 at >3 V and 4848 Wh L −1 at >2 V. [ABSTRACT FROM AUTHOR]

The perovskite La0.8Sr0.2Ga0.83Mg0.17O2.815 (LSGM) fuel cell electrolyte was prepared by a polymeric method using poly(vinyl alcohol) (PVA). The LSGM precursor powder was examined by thermogravimetric and differential thermal analysis (TG/DTA) and Fourier transform infrared (FTIR) spectroscopy. It was found that thermal decomposition of the LSGM precursor powder occurs in a number of different stages, and complete decomposition of the precursor is obtained at 1000 °C. X-ray diffraction (XRD) showed that calcined powder contains three secondary phases, namely La4Ga2O9, LaSrGa3O7, and LaSrGaO4, even after calcination at 1100 °C. Furthermore, the fraction of secondary phases decreases with increasing calcination temperature. Single phase perovskite LSGM pellets with a relative density of 97% were obtained after sintering at 1450 °C for 10 h. It was therefore shown that the powder prepared by the simple PVA method is fine, highly reactive, and sinterable. The electrical properties of LSGM pellets were characterised by impedance spectroscopy. The conductivity of the LSGM pellets sintered at 1450 °C for 10 h was 8.24?10-2 S/cm at 800 °C. [ABSTRACT FROM AUTHOR]

In this paper, we present the investigations of electron paramagnetic resonance on perovskite manganite PrSrMnO and Ga-doped PrSrMnGaO. The temperature dependent paramagnetic resonance spectra parameters (effective g-factor, peak-to-peak linewidth Δ H and double integrated intensities) have been used to study the paramagnetic spin correlations and spin dynamics. The gradual increase of effective g-factor is attributed to the presence of orbital ordering above T. The model fittings of temperature dependent double integrated intensities reveal Arrhenius law is appropriate for describing PrSrMnGaO instead of PrSrMnO system. As for PrSrMnO, the broadening of linewidth with the temperature increase origins from the contribution of small polaron hopping in the PM regime. However, as for PrSrMnGaO, the broadening of EPR linewidth can be understood with the spin-lattice relaxation mechanism. [ABSTRACT FROM AUTHOR]

We have studied the magnetotransport properties of the La[sub l.4]Sr[sub l.6-y]Ba[sub y]Mn[sub 2]O[sub 7] (y≤0.50) samples with a bilayered perovskite structure. For lightly doped samples, the metal-insulator transition accompanying a three-dimensional ferromagnetic transition can be understood commonly in terms of the double-exchange interaction. For heavier doped samples, the metal-insulator transition remains without a ferromagnetic transition and shifts to higher temperature with increasing Ba doping level. On account of the coexistence of short-range ferromagnetic ordering and paramagnetic state, the results can be explained by a recent percolation model based on phase separation. The percolative metal-insulator transition is consistent with the relative ferromagnetic metallic fraction change with temperature and doping level. [ABSTRACT FROM AUTHOR]

We have studied the effects of Cr substitution in the perovskite La[sub 0.67]Sr[sub 0.33]MnO[sub 3] on the magnetic, electrical transport, and magnetoresistance properties. Cluster glass behaviors have been observed in the La[sub 0.67]Sr[sub 0.33]Mn[sub 1-x]Cr[sub x]O[sub 3] system. The most interesting feature is that extraordinary transport and colossal magnetoresistance (CMR) behaviors, characterized by double peaks, were observed with Cr substitution. When 0.1≤x≤0.2, the temperature range of CMR response is greatly broadened, from the lowest temperature to above room temperature. These results suggest that Cr substitution can be a potent way in tuning CMR response and also imply a ferromagnetic interaction similar to double exchange occurs between Mn and Cr. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

For ferromagnets, varying from simple metals to strongly correlated oxides,the critical behaviors near the Curie temperature (TC) can be grouped into several universal classes. In this paper, we report an unusual critical behavior in manganese nitrides Cu1-xNMn3+x (0.1 ≤ x ≤ 0.4). Although the critical behavior below TC can be well described by mean field (MF) theory, robust critical fluctuations beyond the expectations of any universal classes are observed above TC in x = 0.1. The critical fluctuations become weaker when x increases, and the MF-like critical behavior is finally restored at x = 0.4. In addition, the paramagnetic susceptibility of all the samples deviates from the Curie-Weiss (CW) law just above TC. This deviation is gradually smeared as x increases. The short-range antiferromagnetic ordering above TC revealed by our electron spin resonance measurement explains both the unusual critical behavior and the breakdown of the CW law. [ABSTRACT FROM AUTHOR]

We have studied the magnetic and magnetotransport properties of the perovskite LaMn[sub 1-x]Cu[sub x]O[sub 3] (x≤0.3). All of these compounds show ferromagnetism and cluster glass behavior at low temperatures. Though no metallic-insulating transition associated with the ferromagnetic-paramagnetic transition appears, a large magnetoresistance was observed in the ferromagnetic phase. Due to the fact that the Cu ion in these compounds is divalent, the ferromagnetism in LaMn[sub 1-x]Cu[sub x]O[sub 3] is believed to be consistent with the Mn[sup 3+]-O-Mn[sup 4+] double-exchange mechanism. These results suggest that double exchange and large magnetoresistance can be obtained by direct Mn-site doping. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) was applied extensively to probe the phase separation and spin relaxation mechanism in the perovskite manganites. In this study, we conducted the measurement of EPR for the perovskite manganites (La 0.5 Pr 0.5 ) 0.67 Ca 0.33 MnO 3 . We found that both paramagnetic and ferromagnetic resonance peaks simultaneously emerged on resonance spectrum near below T C , exhibiting a typical characteristic of phase separation. The linewidth of EPR spectrum progressively enlarged upon the rising of temperature in the temperature range of T > T C and a quasilinear variation of peak-peak width was observed at T C < T < 500 K. In contrast to the usual beliefs that the variation of peak-peak linewidth can be understood either by spin-lattice relaxation or by spin-spin relaxation, however, the linewidth behavior observed here shows a coexistence of two spin relaxation mechanisms. We proposed that the inhomogeneous electronic phases due to the intrinsic self-organizing growth were responsible for the appearance of multiple spin exchange interactions and variational relaxation mechanism. This finding would be possible to pave a new way for further investigating magnetic correlations and spin dynamics in the paramagnetic hole-doped manganites. [ABSTRACT FROM AUTHOR]

In this study, we investigated the structural, magnetic phase transition, and magnetocaloric properties of bilayer perovskite manganite La 1.38 Sr 1.62 Mn 2 O 7 based on X-ray diffraction, electron paramagnetic resonance, and temperature-/magnetic field-dependent magnetization measurements. The structural characterization results showed the prepared sample had a tetragonal structure with the space group I 4/ mmm . The Curie temperature was determined as 114 K in the magnetization studies and a second-order paramagnetic-ferromagnetic transition was confirmed by the Arrott plot, which showed that the slopes were positive for all the curves. According to the variation in the electron paramagnetic resonance spectrum, we detected obvious electronic phase separation across a broad temperature range from 220 to 80 K in this magnetic material, thereby indicating that the paramagnetic and ferromagnetic phases coexist above as well as below the Curie temperature. Based on a plot of the isothermal magnetization versus the magnetic applied field, we deduced the maximum magnetic entropy change, which only reached 1.89 J/kg.K under an applied magnetic field of 7.0 T. These theoretical investigations indicated that in addition to the magnetoelastic couplings and electron interaction, electronic phase separation and anisotropic exchange interactions also affect the magnetic entropy changes in this bilayer manganite. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we have studied the magnetic and magnetocaloric properties of the perovskite manganite Pr0.55Sr0.45MnO3. It shows a sharp paramagnetic–ferromagnetic phase transition at 291K and possesses a moderate magnetic entropy change near room temperature. In addition, a large relative cooling power (143.64J/kg) and a wide temperature range (84K) have been found in this material. Compare with the Landau model, we find that the itinerant electrons mainly contribute the larger magnetic entropy change at paramagnetic region. [Copyright &y& Elsevier]

Abstract: In the present work, the magnetic entropy change of the half-doped Nd0.5Ca0.25Sr0.25MnO3 manganite has been investigated. The measurement of isothermal magnetization around Curie temperature reveals the maximum isothermal magnetic entropy change of 1.85 and 0.77J/kgK for and 1.0T magnetic field variation, respectively. In addition, from the data of heat capacity, we find the adiabatic temperature change of 0.88K for a magnetic field variation of 3.0T. Though only a moderate magnetic entropy change and a small adiabatic temperature change were obtained, a considerable large relative cooling power (140J/kg as ) and a wide temperature range (74K as ) were found in this sample, this ensure it to be a promising candidate for the actual magnetic refrigerant materials. [Copyright &y& Elsevier]