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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 article, the effect of nanometric grain sizes on microstructural, electrical-, magneto-transport and magnetic behaviors in nanocrystalline Nd0.67Sr0.33MnO3 CMR manganites was investigated.
Abstract: We have investigated the effect of nanometric grain sizes on Microstructural, electrical-, magneto-transport and magnetic behaviors in nanocrystalline Nd0.67Sr0.33MnO3 CMR manganites. Three nanocrystalline powders of Nd0.67Sr0.33MnO3 were synthesized through chemical route “Pyrophoric Reaction Process” and calcined for 5 hrs at calcinations temperature (TCal = 650o C, 750o C, and 850o C). XRD patterns indicate that all the synthesized powders have pseudo-cubic perovskite structure without any secondary impurity phase. Using Debye Scherrer formula we calculated the crystallites size for three nanocrystalline Nd0.67Sr0.33MnO3 powders (~ 30, 40, and 54 nm for TCal = 650o C, 750o C, and 850o C respectively). TEM micrographs show that the average particle sizes are in nanometric regime (φ ~ 30-50 nm). In AC susceptibility and resistivity measurement we observed that there is an almost constant Curie temperature (TC) has value around 240 K and gradual decrease of metal-insulator transition temperature (TP) (from 200-129 K) with decrease of TCal. The magneto resistance of ultra fine nanoparticles increases with grain sizes. Highest magnetoresistance observed ~ 24 for Nd0.67Sr0.33MnO3 with TCal = 850o C. Experimental results revels, the effect of nanometric grain sizes has an important impact in magnetic properties and magneto-transport behaviors.

3 citations

Book ChapterDOI
01 Jan 2019
TL;DR: Ferroic and spin glasses are a broad class of magnetic materials that exhibit varying degrees of disorder and magnetic frustration, resulting in characteristic glassy relaxation behavior including frequency-dependent susceptibility, aging, and memory as discussed by the authors.
Abstract: Spin glasses are a broad class of magnetic materials that exhibit varying degrees of disorder and magnetic frustration, resulting in characteristic glassy relaxation behavior including frequency-dependent susceptibility, aging, and memory. Ferroic glasses include spin glasses and also relaxor ferroelectrics and strain glasses, which exhibit glassy dynamics in polarization and strain respectively, in similar ways to spin glasses. This chapter introduces ferroic and spin glasses, their phenomenological classification, and some parallels with structural (amorphous) glasses. A brief theoretical treatment is given, including modeling of the relaxation phenomena in ferroic glasses. Strain glasses and relaxors are discussed, followed by a detailed taxonomy of spin glasses and comparison with collectively behaving particle systems and structurally amorphous magnetic materials. Finally, some characteristic experimental methods are discussed, and an outlook for the future involvement of glass scientists in the study of spin glasses is offered.

2 citations

Journal ArticleDOI
TL;DR: In this article, the structural properties of La0.8Ag0.2MnO3 nanoparticles have been characterized by X-ray diffraction using Rietveld refinement and transmission electron microscopy.
Abstract: In thisresearch,nanoparticlesof La0.8Ag0.2MnO3 with mean particle sizes d of 16 and 22 nm have been prepared by sol-gel method. Dynamic magnetic properties of the samples have been carried out by AC magnetic susceptibility and electron spin resonance techniques. The structural properties of the samples have been characterized by X-ray diffraction using Rietveld refinement and transmission electron microscopy. The analysis of the AC magnetic susceptibility by phenomenological models reveals the interacting superparamagnetic behaviors in La0.8Ag0.2MnO3 nanoparticles. From the Vogel-Fulcher model, the values of 1.3 × 104 and 2.8 × 104 erg/cm3 are obtained for the effective magnetic anisotropy constant for d= 16 and 21 nm, respectively. Electron spin resonance signals of the samples are well described by double Lorentzian line shapes which suggest the presence of ferromagnetic clusters in the paramagnetic phase and possible phase separation at room temperature.

2 citations

Journal ArticleDOI
TL;DR: In this article, the effect of particle size reduction on the magnetic correlations of Pr0.4Bi0.2Sr0.3 nanoparticles prepared by top-down approach has been studied in detail.
Abstract: The effect of particle size reduction on the magnetic correlations of Pr0.4Bi0.2Sr0.4MnO3 nanoparticles prepared by top-down approach has been studied in detail. It was observed that as the milling time increases from 0 to 240 min, particle size decreases from 160 to 12 nm. Correspondingly it was observed that the ferromagnetic transition temperature (TC) drops (264 to 213 K) and saturation magnetization (MS) decreases (2.12–0.41 $${\upmu }_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.$$ ) while coercivity (HC) shows a monotonous increase (0.18–1.5 kOe) as the particle size decreases due to increase in milling. The magnetic entropy change (ΔS) also decreases (2.41–0.24 J/kg-K) as particle size decreases indicating a strong correlation between magnetism and particle size. The metamagnetic M–H response of the bulk sample, which signifies the magnetic phase coexistence, is suppressed, and the nature of magnetic interactions demonstrates a transition from long range to short range. The observed characteristics emphasizes that with particle size reduction there is an increase in the surface disorder which can be explained by considering the core–shell model for the nanoparticles.

2 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