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, an investigation of Griffiths singularity in La 0.5 Sr0.5 MnO3 nanocrystalline by means of magnetic susceptibility and electron paramagnetic resonance (EPR) was conducted, and an unusual platform was found in paramagnetic region.
11 citations
TL;DR: The effect of Ni2+ substitution on the magneto-transport properties and the concomitant relationship with the magnetocaloric function of nano-sized La07Ca03Mn1−xNixO3 (x = 0, 002, 007, and 010) perovskite manganites are reported in this article.
11 citations
TL;DR: In this article, the influence of partial substitution of La by Dy on the magnetocaloric response of (La1−xDyx)0.33Mn0.25 is studied.
10 citations
TL;DR: In this article, electrical, magnetic and Mossbauer measurements have been carried out on La0.67−xEuxCa0.33MnO3 (x=0.21 and 0.29) for a comparative study of different grain size materials.
Abstract: Electrical, magnetic and Mossbauer measurements have been carried out on La0.67−xEuxCa0.33MnO3 (x=0.21 and 0.29) for a comparative study of different grain size materials. The samples have been prepared through sol–gel method and sintered at 700, 800, and 900 °C to achieve nanosized materials. All the prepared samples are found to be single phase having orthorhombic structure. The particle sizes are estimated through x-ray diffraction (XRD) by using the Debye–Scherrer’s formulae and these sizes are further confirmed by transmission electron microscopy (TEM) images. E151u Mossbauer studies reveal that Eu is in 3+ charge state. The isomer shift and full width at half maximum (FWHM) of the Mossbauer peak decrease with the increase in particle size. Reduction in the grain size leads to drastic increase in electrical resistivity in all the samples. The typical metal–insulator transition (MIT) observed in x=0.21 bulk sample disappears with decrease in grain size while an external magnetic field of 8T restores t...
9 citations
TL;DR: In this paper, high pressure and high temperature treatment (HPT) results in significant changes of the crystallochemical parameters of polycrystalline Nd 0.7 Sr 0.3 MnO 3 samples after it had been subjected to a high quasihydrostatic pressure of 9 GPa.
Abstract: Polycrystalline Nd 0.7 Sr 0.3 MnO 3 was quenched from 1300 K to 300 K and 80 K after it had been subjected to a high quasihydrostatic pressure of 9 GPa. Such high pressure and high temperature treatment (HPT) results in significant changes of the crystallochemical parameters—Mn–O lengths and Mn–O–Mn angles within unchanged lattice symmetry of the Pnma-type. A strong increase of the resistivity and a large decrease of the FM–PI transition temperature were detected for the Nd 0.7 Sr 0.3 MnO 3 HPT treated samples. The intrinsic characteristic T MI ( T C ) ( T MI is the metal–insulator and T C is the ferromagnetic–paramagnetic transition temperature) correlates with the change of the Mn–O(1)–Mn angle, which is consistent with the double exchange model of the ferromagnetic metallic state in manganites. Remarkable electroresistive (ER) and magnetoresistive (MR) effects appear after HPT treatment, which were not present in the starting Nd 0.7 Sr 0.3 MnO 3 sample. The structure sensitive properties such as resistivity, MR and ER effects correlate with the change of the nanograin sizes after HPT treatment. Nonlinear current–voltage characteristics showing a hysteresis appear for HPT treated samples at low temperatures. The transport in granular Nd 0.7 Sr 0.3 MnO 3 samples is likely defined by spin-dependent scattering of charge carriers inside the ferromagnetic metallic grains with embedded small charged isolating islands and by jumping over charged insulating barriers at the intergrain boundaries, which can be strongly affected by the external electric and magnetic fields.
7 citations
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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
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
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
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
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