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Journal ArticleDOI

Electrical transport properties and magnetic cluster glass behavior of Nd0.7Sr0.3MnO3 nanoparticles

28 Nov 2006-Journal of Applied Physics (American Institute of Physics)-Vol. 100, Iss: 10, pp 104318
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
Citations
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Journal ArticleDOI
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

Journal ArticleDOI
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

Journal ArticleDOI
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

Book ChapterDOI
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

Journal ArticleDOI
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.

44 citations

References
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Journal ArticleDOI
TL;DR: In this article, the temperature dependent resistivity and thermoelectric power of monovalent (Ag) doped La07Sr03−xAgxMnO3 polycrystalline pellets (x = 005,010,020,025) between 20 and 450 K are reported.
Abstract: The temperature dependent resistivity and thermoelectric power of monovalent (Ag) doped La07Sr03−xAgxMnO3 polycrystalline pellets (x = 005,010,020,025) between 20 and 450 K are reported Ag substitution enhances the conductivity of this system The Curie temperature (TC) also increases from 303 to 364 K with increasing Ag content In the paramagnetic region (T>TC), the electrical resistivity is well represented by adiabatic polaron hopping, while in the ferromagnetic region (T TC and in the high temperature limit for the thermoelectric power is primarily defined by the spin contribution At low temperatures (T

17 citations

Journal ArticleDOI
TL;DR: In this article, the activation energy for the amorphous phase is calculated to be about + 1.25 kJ g-1. And the characterization of resistivity (T ) for La 0.7 Ca 0.3 MnO3 perovskites has also been investigated.
Abstract: Nanocrystalline ferromagnetic La0.7 Ca0.3 MnO3 perovskites with magnetoresistance effect have been successfully prepared by mechanical alloying. Thermal transformation of the amorphous phase, resulting from ball milling, to perovskite structure was studied by differential scanning calorimetry. Following the law of mass action, we discuss the crystallization dynamics of the amorphous phase. The activation energy for crystallization transformation is calculated to be about + 1.25 kJ g-1 . The characterization of resistivity (T ) for La0.7 Ca0.3 MnO3 perovskites has also been investigated. At low temperature T , (T ) has a direct-proportion dependence on T 2 . With increasing annealing temperature, the slope of the -T 2 curve decreases. The temperature dependent magnetoresistance effect at temperature far below the Curie temperature can be well expressed as the equation / 0 = p 1 - p 2 T 3/2 - p 3 T 5/2 .

7 citations