EFFECT OF MEAN ION SIZE AND SPATIAL SPIN DISORDERS FOR (La1-xYx)2/3Ca1/3MnO3 MANGANITES

2004 ◽  
Vol 18 (26) ◽  
pp. 3451-3464 ◽  
Author(s):  
JINCANG ZHANG ◽  
YUFENG ZHANG ◽  
SHIXUN CAO ◽  
CHAO JING
Keyword(s):  
Single Phase ◽  
Bond Angle ◽  
Gradual Increase ◽  
High Concentration ◽  
Magnetic Studies ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Average Ionic Radius ◽  
Lower Temperature ◽  
Ion Size

The structure and transport properties of perovskite ( La 1-x Y x)2/3 Ca 1/3 MnO 3 (0≤x≤0.3) systems are systematically investigated. It is found that all the specimens show a single-phase structure and reveal a direct relationship between the Curie temperature Tc and the average ionic radius <rA> of La site. With increasing Y 3+ doped content, the metal-insulator transition temperature T MI (M-I) shifts to lower temperature. While the relevant resistivity peak ρp is sharp increased, for the specimens with large doping content, x=0.3, it has enhanced eight orders of magnitudes larger than the non-doped samples (x=0.0). At high concentration area, that is to say, when x>0.1, magnetic studies show a gradual increase of antiferromagnetic interaction with an increase of x, ultimately leading to a spatial-spin disorders, that is, spin-glass-like state for x=0.2 and x=0.3 compounds at about 35 K. The results show that it has connected a reduction of Tc and an increase in magnetoresistance with a decrease in the microstructural Mn - O - Mn bond angle.

scholarly journals Study of Microstructural, Electrical and Dielectric Properties of La0.9Pb0.1MnO3 and La0.8Y0.1Pb0.1MnO3 Ceramics

2019 ◽  
pp. 33-44 ◽  
Keyword(s):  
Transition Temperature ◽  
Frequency Dispersion ◽  
Insulator Transition ◽  
X Ray Diffraction ◽  
Phonon Modes ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Solid State Route ◽  
Distorted Structure ◽  
Lower Temperature

The present work studies the microstructural and electrical properties of La0.9Pb0.1MnO3 and La0.8Y0.1Pb0.1MnO3 ceramics synthesized by solid-state route method. Microstructure and elemental analysis of both samples were carried out by field emission scanning electron microscope (FESEM) and energy dispersive spectroscopy (EDS) method, respectively. Phase analysis by X-ray diffraction (XRD) indicated formation of single phase distorted structure. The XRD data were further analyzed by Rietveld refinement technique. Raman analysis reveals that Y atom substitutes La site into the LPMO with shifting of phonon modes. The temperature variation of resistivity of undoped and Y-doped La0.9Pb0.1MnO3 samples have been investigated. The electrical resistivity as a function of temperature showed that all samples undergo an metal-insulator (M-I) transition having a peak at transition temperature TMI. Y-doping increases the resistivity and the metal-insulator transition temperature (TMI) shifts to lower temperature. The temperature-dependent resistivity for temperatures less than metal-insulator transition is explained in terms the quadratic temperature dependence and for T > TMI, thermally activated conduction (TAC) is appropriate. Variation of frequency dispersion in permittivity and loss pattern due to La-site substitution in LPMO was observed in the dielectric response curve.

Magnetic studies of the metal–insulator transition in CuIr2S4−xSex (x=0, 0.1, and 4)

1996 ◽  
Vol 79 (8) ◽  
pp. 5401 ◽  
Author(s):  
P. Somasundaram ◽  
J. M. Honig ◽  
T. M. Pekarek ◽  
B. C. Crooker
Keyword(s):  
Insulator Transition ◽  
Magnetic Studies ◽  
Metal Insulator Transition ◽  
Metal Insulator

STUDY OF STRUCTURAL, ELECTRICAL TRANSPORT AND MAGNETIC PROPERTIES IN La1-xAgxMnO3 COMPOUNDS

2004 ◽  
Vol 18 (05n06) ◽  
pp. 221-231 ◽  
Author(s):  
MANORANJAN KAR ◽  
S. RAVI
Keyword(s):  
Magnetic Field ◽  
Electrical Transport ◽  
Single Phase ◽  
Ac Susceptibility ◽  
X Ray Diffraction ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Phase Form ◽  
X Ray ◽  
Maximum Value

X-ray diffraction, electrical resistivity and ac susceptibility measurements have been carried out on La 1-x Ag x MnO 3 compounds for x=0.05 to 0.30. These samples are found to be in single phase form with [Formula: see text] space group and with typical lattice parameters a=b=5.524Å and c=13.349Å for x=0.05 sample. The Mn–O–Mn bond angles and variance, σ2 are found to increase with doping. Metal-insulator transitions in the temperature range 254 to 259 K have been observed. These materials exhibit paramagnetic to ferromagnetic transitions in the vicinity of metal-insulator transition temperatures. The paramagnetic susceptibility could be analyzed using Curie–Weiss law. All the above samples exhibit colossal magneto-resistivity and its maximum value is found to be 73% for x=0.15 sample at 50 kOe magnetic field.

Structural and Magnetic Studies of Metal-Insulator Transition in Thiospinel CuIr2S4

1994 ◽  
Vol 63 (9) ◽  
pp. 3333-3339 ◽  
Author(s):  
Takao Furubayashi ◽  
Takehiko Matsumoto ◽  
Takatsugu Hagino ◽  
Shoichi Nagata
Keyword(s):  
Insulator Transition ◽  
Magnetic Studies ◽  
Metal Insulator Transition ◽  
Metal Insulator

MAGNETIC STUDIES OF METAL–INSULATOR TRANSITION IN A QUANTUM WELL SYSTEM

2008 ◽  
Vol 07 (04n05) ◽  
pp. 207-213 ◽  
Author(s):  
A. JOHN PETER ◽  
L. CAROLINE SUGIRTHAM
Keyword(s):  
Magnetic Field ◽  
Quantum Well ◽  
Effective Mass ◽  
Diamagnetic Susceptibility ◽  
Insulator Transition ◽  
Magnetic Studies ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Intense Magnetic Field ◽  
Mass Approximation

Metal–insulator transition in doped semiconductors is investigated in the presence of intense magnetic fields. A variational procedure within the effective mass approximation is employed using the Thomas–Fermi screening function and the exact quasi-Q2D Lindhard dielectric function. The Hubbard model results are justified using an effective mass that depends on interimpurity separation. The nonparabolicity of the subband is included using an energy-dependent effective mass. Though an increase of ionization energy with a magnetic field is observed for isolated donor models, the metallization occurs with an intense magnetic field at a higher concentration for a particular well width. The diamagnetic susceptibility of a hydrogenic donor impurity in GaAs / Ga 1 - x Al x As quantum well systems is discovered in the observation of metal–insulator transition. It is shown that the diamagnetic susceptibility diverges for all critical concentrations for a given well width. The large diamagnetic susceptibility (> 6) is observed at the transition. All the calculations are carried out for infinite and finite barriers, and the results are compared with the existing literature.

scholarly journals Hysteresis and the single-phase metal-insulator transition in switchableYHxfilms

2000 ◽  
Vol 62 (15) ◽  
pp. 10088-10100 ◽  
Author(s):  
E. S. Kooij ◽  
A. T. M. van Gogh ◽  
D. G. Nagengast ◽  
N. J. Koeman ◽  
R. Griessen
Keyword(s):  
Single Phase ◽  
Insulator Transition ◽  
Metal Insulator Transition ◽  
Metal Insulator

scholarly journals Effect of The Calcination Process On The Magnetotransport Properties in Co-Precipitation Derived La0.67Ca0.33MnO3 Ceramics

2021 ◽  
Author(s):  
Yule Li ◽  
Ping Yu ◽  
Xiaojin Wang ◽  
Fuxin Ling ◽  
Qingming Chen ◽  
...  
Keyword(s):  
Colossal Magnetoresistance ◽  
Sol Gel ◽  
Insulator Transition ◽  
Precipitation Method ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Calcination Process ◽  
Temperature Ranges ◽  
Lower Temperature ◽  
Co Precipitation

Abstract La0.67Ca0.33MnO3 (LCMO) attracts considerable attention as a quintessential example for colossal magnetoresistance (CMR), metal-insulator transition and related temperature coefficient of resistance (TCR) studies. Here, co-precipitation method was utilized to prepare the LCMO ceramics, whose magnetotransport properties as a function of calcination temperature (Tcal) and calcination time (tcal) were investigated. The magnetotransport properties of these LCMO ceramics were significantly enhanced compared with LCMO derived by sol-gel methods. The TCR of LCMO increased firstly and then decreased as the Tcal increased, whereas the metal-insulator transition temperature (TMIT) shifted towards to the lower temperature. Magnetoresistance (MR) increased as Tcal rose and reached 82.4 % at Tcal = 800 ℃. The mechanism of such magnetotransport properties with different temperature ranges was discussed. The optimal TCR of 32.3%·K-1 in LCMO was prepared with Tcal = 500 ℃ and tcal = 8 h, showing that co-precipitation method would facilitate the potential application of LCMO in infrared detecting and magnetoresistive switching.

scholarly journals Metal-insulator transition in a semiconductor nanocrystal network

2019 ◽  
Vol 5 (8) ◽  
pp. eaaw1462 ◽  
Author(s):  
Benjamin L. Greenberg ◽  
Zachary L. Robinson ◽  
Yilikal Ayino ◽  
Jacob T. Held ◽  
Timothy A. Peterson ◽  
...  
Keyword(s):  
Semiconductor Nanocrystals ◽  
Insulator Transition ◽  
Transparent Conductors ◽  
Contact Radius ◽  
Interparticle Contact ◽  
Metal Insulator Transition ◽  
Free Electron Density ◽  
Metal Insulator ◽  
Semiconductor Nanocrystal ◽  
Lower Temperature

Many envisioned applications of semiconductor nanocrystals (NCs), such as thermoelectric generators and transparent conductors, require metallic (nonactivated) charge transport across an NC network. Although encouraging signs of metallic or near-metallic transport have been reported, a thorough demonstration of nonzero conductivity, σ, in the 0 K limit has been elusive. Here, we examine the temperature dependence of σ of ZnO NC networks. Attaining both higher σ and lower temperature than in previous studies of ZnO NCs (T as low as 50 mK), we observe a clear transition from the variable-range hopping regime to the metallic regime. The critical point of the transition is distinctly marked by an unusual power law close to σ ∝ T1/5. We analyze the critical conductivity data within a quantum critical scaling framework and estimate the metal-insulator transition (MIT) criterion in terms of the free electron density, n, and interparticle contact radius, ρ.

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