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.
44 citations
References
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01 Sep 1997
TL;DR: In this paper, the authors review recent experimental work falling under the broad classification of colossal magnetoresistance (CMR), which is magnetoreduction associated with a ferromagnetic-toparamagnetic phase transition.
Abstract: We review recent experimental work falling under the broad classification of colossal magnetoresistance (CMR), which is magnetoresistance associated with a ferromagnetic-toparamagnetic phase transition. The prototypical CMR compound is derived from the parent compound, perovskite LaMnO 3. When hole doped at a concentration of 20–40% holes/Mn ion, for instance by Ca or Sr substitution for La, the material displays a transition from a high-temperature paramagnetic insulator to a low-temperature ferromagnetic metal. Near the phase transition temperature, which can exceed room temperature in some compositions, large magnetoresistance is observed and its possible application in magnetic recording has revived interest in these materials. In addition, unusual magneto-elastic effects and charge ordering have focused attention on strong electron–phonon coupling. This coupling, which is a type of dynamic extended-system version of the Jahn–Teller effect, in conjunction with the double-exchange interaction, is also viewed as essential for a microscopic description of CMR in the manganite perovskites. Large magnetoresistance is also seen in other systems, namely Tl 2Mn2O7 and some Cr chalcogenide spinels, compounds which differ greatly from the manganite perovskites. We describe the relevant points of contrast between the various CMR materials.
1,336 citations
TL;DR: Mott and Davis as mentioned in this paper proposed the theory of electrons in a non-crystalline medium and its application to liquid metals, amorphous semimetals and semiconductors.
Abstract: N F Mott and E A Davis London: Oxford University Press 1971 pp xiii + 437 price £750 It is hard to think of a physicist other than Professor Mott who would be able to attempt successfully a book of such a broad compass and in Dr Davis, a specialist in the field of amorphous semiconductors, he has found an ideal co-author. The book is divided into two parts: the first deals with the theory of electrons in a noncrystalline medium and its application to liquid metals, amorphous semimetals and semiconductors.
1,062 citations
30 May 2000
TL;DR: In this paper, the fundamental features of CMR Manganites have been discussed, including Spin Dynamics and Electronic Structures, Materials Systematics and Lattice Effects, and Tunnelling Magnetoresistance.
Abstract: 1. Fundamental Features of CMR Manganites 2. Spin Dynamics and Electronic Structures 3. Materials Systematics and Lattice Effects 4. Tunnelling Magnetoresistance.
982 citations
814 citations
TL;DR: In this paper, it was shown that the observed temperature dependence of low-field conductivity in granular metals can be attributed to a relationship between the separation of neighboring metal grains and the electrostatic energy required to create a positive-negative charged pair of grains.
Abstract: We present evidence that in granular metals the observed temperature dependence of the low-field conductivity, $\mathrm{exp}(\ensuremath{-}\frac{b}{{T}^{\ensuremath{\alpha}}})$ with $\ensuremath{\alpha}=\frac{1}{2}$, can be ascribed to a relationship $s{E}_{c}=\mathrm{const}$ between $s$, the separation of neighboring metal grains, and ${E}_{c}$, the electrostatic energy required to create a positive-negative charged pair of grains. This relationship results from simple considerations of the structure of granular metals. The predictions of the theory, for both the high- and the low-field electrical conductivity, are in excellent accord with experimental results in granular Ni-Si${\mathrm{O}}_{2}$ films.
765 citations