Electrical transport properties and magnetic cluster glass behavior of Nd0.7Sr0.3MnO3 nanoparticles
TL;DR: In this article, the transport and magnetic properties of Nd07Sr03MnO3 nanoparticles were investigated by the sol-gel method and the results showed that resistivity increases with the decrease of the particle size due to the enhancement of the grain boundary effect.
Abstract: The transport and magnetic properties have been investigated in Nd07Sr03MnO3 nanoparticles prepared by the sol-gel method The resistivity (ρ) increases with the decrease of the particle size due to the enhancement of the grain boundary effect ρ(T) shows two distinct transitions for all the samples such as metal-insulator transition and transition due to the barrier caused by the grain boundary effect The thermopower (S) is found to be negative and at high temperature S follows the adiabatic small polaron hopping theory In the metallic region the spin wave contribution is found to be dominant in the temperature dependence of the thermopower The magnetoresistance (MR) of the ultrafine particles increases with the decrease of particle size indicating substantial contribution from the grain boundaries Spin polarized intergrain tunneling effect plays an important role in the MR of a smaller size particle, whereas in the case of samples of higher dimension spin fluctuation contributes predominantly The
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TL;DR: In this paper, the temperature dependence of the ac magnetic susceptibility was measured at different frequencies and ac magnetic fields in the selected ranges of 40-1000-Hz and 80-800-A/m, respectively.
96 citations
TL;DR: In this article, the magnetic properties of compacted La0.8Ca0.2MnO3 manganite nanoparticles with average particle size of 18 and 70 nm and Curie temperatures TC 231 K and TC 261 K, respectively, have been investigated.
Abstract: Magnetic properties of compacted La0.8Ca0.2MnO3 manganite nanoparticles with average particle size of 18 and 70 nm and Curie temperatures TC 231 K and TC 261 K, respectively, have been investigated. The relative volume of the ferromagnetic phase has been estimated to be 52% for ensembles of 18 nm particles and 92% for 70 nm particles. It was found that applied hydrostatic pressure enhances TC of La0.8Ca0.2MnO3 nanoparticles at a rate dTC /dP 1.8– 1.9 K / kbar, independently on the average particle size. Pronounced irreversibility of magnetization below Tirr 208 K and strong frequency dependent ac susceptibility below TC for smaller 18 nm particles have been observed. 18 nm particles have also shown aging and memory effects in zero-field-cooled ZFC and field-cooled magnetization. These features indicate the appearance of spin-glasslike state, partially reminiscent the behavior of La1�xCaxMnO3 crystals, doped below the percolation threshold xxC = 0.225. In contrast, ensembles of larger 70 nm particles have shown insignificant irreversibility of magnetization only and no frequency dependence of ac susceptibility, similarly to the behavior of La1�xCaxMnO3 crystals with xxC. The temperature of the ZFC magnetization maximum for 18 nm particles decreases with increasing magnetic field and forms a critical line with an exponent 1.89 0.56. The results suggest that superspin-glass features in ensembles of interacting 18 nm particles appear along with superferromagnetic-like features.
86 citations
TL;DR: In this article, structural, magnetic, and electrical properties of the La0.8−xSmxSr0.2MnO3 manganites prepared by a solid-state reaction technique was studied systematically.
58 citations
TL;DR: In this article, the authors systematically outline some fundamentals and key experimental results concerning magnetic properties of perovskite manganites, focusing on magnetocaloric properties, pressure effect on magnetic properties, and magnetism of manganite nanoparticles.
Abstract: This chapter attempts to systematically outline some fundamentals and key experimental results concerning magnetic properties of perovskite manganites, focusing on (i) magnetocaloric properties, (ii) pressure effect on magnetic properties, and (iii) magnetism of manganite nanoparticles. Each family of manganites has unique properties that can be used as a way of tuning the optimum magnetocaloric response. The relatively easy possibility of tuning the Curie temperature of manganites is a key point in developing efficient magnetocaloric materials. The most interesting effects of applied external pressure observed for various classes of manganite systems, such as hole-doped manganites; parent, single-valent, and self-doped manganites; hexagonal manganites, near-half-doped manganites, electron-doped manganites, and manganite nanoparticles are reviewed. Some of the most relevant finite-size and surface effects on the magnetic properties of ferromagnetic and antiferromagnetic manganite nanoparticles are also discussed. New phenomena such as a suppression of charge/orbital ordering with decreasing particle size, collective states, and nonequilibrium dynamics in ensembles of antiferromagnetic manganite nanoparticles are presented.
57 citations
TL;DR: In this article, the authors determined the values of critical exponents of two polycrystalline samples (Nd1−xYx)0.7Sr0.3MnO3 (x = 0 and 0.07) from the magnetization data versus temperature and magnetic field, M(H, T), to learn about their magnetic and magnetocaloric (MC) properties.
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TL;DR: In this paper, the grain-size-dependent transport properties in granular perovskite have been investigated and a resistivity formula originating from interfacial tunneling is obtained and the theoretical calculation is found to be in good agreement with the experimental results.
Abstract: The grain-size-dependent transport properties in the granular perovskite ${\mathrm{La}}_{0.85}{\mathrm{Sr}}_{0.15}{\mathrm{MnO}}_{3}$ have been investigated. A giant magnetoresistance (GMR) effect, similar to that observed in granular transition metals, and a crystal intrinsic colossal magnetoresistance (CMR) have been simultaneously observed. With grain growth, the GMR effect gradually weakens and the intrinsic CMR effect becomes prominent in the present granular system. A resistivity formula originating from interfacial tunneling is obtained and the theoretical calculation is found to be in good agreement with our experimental results.
327 citations
TL;DR: In this article, the authors investigated the low-field and high-field magnetoresistance response of LMO samples with grain sizes ranging from 10 to 20 nm and revealed a clear relationship between the thickness, the intergranular resistance, and the height of the surface energy barrier.
Abstract: The low-field (LFMR) and high field (HFMR) magnetoresistance response of ceramic ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3}$ (LSMO) samples having grain sizes diameters \ensuremath{\emptyset} ranging from 10 \ensuremath{\mu}m to 20 nm have been investigated. A limiting LFMR of about \ensuremath{\approx}30% is obtained for the \ensuremath{\emptyset} \ensuremath{\approx}0.5 \ensuremath{\mu}m but no larger values are obtained by further reduction of the grain size down to the nanometric range. On the contrary, the HFMR progressively rises when reducing the grain size. Magnetic and transport measurements suggest that HFMR originates from the existence of a noncollinear surface layer, having a thickness t that increases when reducing \ensuremath{\emptyset}. We have disclosed a clear relationship between the thickness, the intergranular resistance, and the height of the surface energy barrier. In addition, we show that in samples with submicronic grains, there is an intergranular Coulomb gap.
288 citations
TL;DR: In this paper, a large, nearly field-independent difference between the activation energies for resistivity and thermopower S, a characteristic of Holstein polarons, is observed, and ln\ensuremath{\rho} ceases to scale with the magnetization.
Abstract: Thermoelectric power, electrical resistivity, and magnetization experiments, performed in the paramagnetic phase of ${\mathrm{La}}_{2/3}$${\mathrm{Ca}}_{1/3}$${\mathrm{MnO}}_{3}$, provide evidence for polaron-dominated conduction in colossal magnetoresistance materials. At high temperatures, a large, nearly-field-independent difference between the activation energies for resistivity \ensuremath{\rho} and thermopower S, a characteristic of Holstein polarons, is observed, and ln\ensuremath{\rho} ceases to scale with the magnetization. On approaching ${\mathit{T}}_{\mathit{c}}$, both energies become field dependent, indicating that the polarons are magnetically polarized. Below ${\mathit{T}}_{\mathit{c}}$, the thermopower follows a law S(H)\ensuremath{\sim}1/\ensuremath{\rho}(H) as in nonsaturated ferromagnetic metals. \textcopyright{} 1996 The American Physical Society.
283 citations
TL;DR: In this paper, the magnetoresistance of epitaxial Nd0.7Sr0.3MnOδ thin films has been studied and a large GMR ratio with −ΔR/RH≳3000% was obtained at ∼60 K and a magnetic field of 8 T.
Abstract: The magnetoresistance of epitaxial Nd0.7Sr0.3MnOδ thin films has been studied. A giant magnetoresistance, with more than 4 orders of magnitude change in resistance (−ΔR/RH≳106%), was obtained at ∼60 K and a magnetic field of 8 T. This giant magnetoresistance (GMR) ratio is about one order of magnitude larger than the highest value reported previously which was observed in La–Ca–Mn–O film. We have also obtained a large GMR ratio with −ΔR/RH≳3000% for H=5 T in an in situ Nd0.7Sr0.3MnOδ thin film, a much larger effect than the previous results in doped manganese oxide films in which a large GMR ratio was obtained only in postannealed samples. Our results also show that the GMR effect in these films can be strongly influenced by the thin‐film preparation conditions.
259 citations