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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
16 Feb 1996-Science
TL;DR: In this article, the authors focus on the properties of quantum dots and their ability to join the dots into complex assemblies creates many opportunities for scientific discovery, such as the ability of joining the dots to complex assemblies.
Abstract: Current research into semiconductor clusters is focused on the properties of quantum dots-fragments of semiconductor consisting of hundreds to many thousands of atoms-with the bulk bonding geometry and with surface states eliminated by enclosure in a material that has a larger band gap. Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability to join the dots into complex assemblies creates many opportunities for scientific discovery.

10,737 citations

Journal ArticleDOI
TL;DR: A review of the metal-insulator transition can be found in this article, where a pedagogical introduction to the subject is given, as well as a comparison between experimental results and theoretical achievements.
Abstract: Metal-insulator transitions are accompanied by huge resistivity changes, even over tens of orders of magnitude, and are widely observed in condensed-matter systems. This article presents the observations and current understanding of the metal-insulator transition with a pedagogical introduction to the subject. Especially important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is categorized as the Mott Insulator. Near the transition point the metallic state shows fluctuations and orderings in the spin, charge, and orbital degrees of freedom. The properties of these metals are frequently quite different from those of ordinary metals, as measured by transport, optical, and magnetic probes. The review first describes theoretical approaches to the unusual metallic states and to the metal-insulator transition. The Fermi-liquid theory treats the correlations that can be adiabatically connected with the noninteracting picture. Strong-coupling models that do not require Fermi-liquid behavior have also been developed. Much work has also been done on the scaling theory of the transition. A central issue for this review is the evaluation of these approaches in simple theoretical systems such as the Hubbard model and $t\ensuremath{-}J$ models. Another key issue is strong competition among various orderings as in the interplay of spin and orbital fluctuations. Experimentally, the unusual properties of the metallic state near the insulating transition have been most extensively studied in $d$-electron systems. In particular, there is revived interest in transition-metal oxides, motivated by the epoch-making findings of high-temperature superconductivity in cuprates and colossal magnetoresistance in manganites. The article reviews the rich phenomena of anomalous metallicity, taking as examples Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ru compounds. The diverse phenomena include strong spin and orbital fluctuations, mass renormalization effects, incoherence of charge dynamics, and phase transitions under control of key parameters such as band filling, bandwidth, and dimensionality. These parameters are experimentally varied by doping, pressure, chemical composition, and magnetic fields. Much of the observed behavior can be described by the current theory. Open questions and future problems are also extracted from comparison between experimental results and theoretical achievements.

5,781 citations

Journal ArticleDOI
TL;DR: It is proposed that in addition to double-exchange physics a strong electron-phonon interaction arising from the Jahn-Teller splitting of the outer Mn $d$ level plays a crucial role.
Abstract: The ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ system with $02\ensuremath{\lesssim}x\ensuremath{\lesssim}04$ has traditionally been modeled with a ``double-exchange'' Hamiltonian in which it is assumed that the only relevant physics is the tendency of carrier hopping to line up neighboring spins We present a solution of the double-exchange model, show it is incompatible with many aspects of the data, and propose that in addition to double-exchange physics a strong electron-phonon interaction arising from the Jahn-Teller splitting of the outer Mn $d$ level plays a crucial role

2,302 citations

Journal ArticleDOI
TL;DR: In this article, the authors considered the case in which the electronic-overlap term of the total Hamiltonian is a small perturbation, and showed that the probability of off-diagonal transitions goes up exponentially with increasing temperature.

2,246 citations

Journal ArticleDOI
TL;DR: The fundamental physical properties of doped oxides and their underlying physics were known more than 40 years ago as mentioned in this paper, and the concept of double exchange in particular, and points out the missing elements that have led to a massive resurgence of interest in these and related materials.
Abstract: The fundamental physical properties of doped ${\mathrm{LaMnO}}_{3},$ generically termed ``manganites,'' and much of the underlying physics, were known more than 40 years ago. This article first reviews progress made at that time, the concept of double exchange in particular, and points out the missing elements that have led to a massive resurgence of interest in these and related materials. More recent research is then described, treating first the ground states that emerge as divalent atoms are substituted for trivalent La. A wide range of ground states appear, including ferromagnetic metals, orbital- and charge-ordered antiferromagnets, and more complex stripe and spin-glass states. Because of the interest in so-called colossal magnetoresistance that occurs in the ferromagnetic/metallic composition range, a section is devoted to reviewing the atypical properties of that phase. Next the high-temperature phase is examined, in particular, evidence for the formation of self-trapped small polarons and the importance of Jahn-Teller coupling in this process. The transitions between the high-temperature polaronic phase and the ferromagnetic and charge-ordered states are treated in a fourth section. In each section, the authors stress the competition among charge, spin, and lattice coupling and review the current state of theoretical understanding. They conclude with some comments on the impact that research on these materials has on our understanding of doped oxides and other strongly correlated electronic materials.

2,060 citations