Azah Jaafar - Academia.edu (original) (raw)

Papers by Azah Jaafar

Effect of Fe Doping on the Structural, Electrical and Magnetic Properties of Perovskite La0.7Ca0.3Mn1-xFexO 3 (X = 0, 0.01, 0.03 and 0.05)

Solid State Phenomena, 2021

The effect of Fe-substitution at the Mn-site in La0.7Ca0.3Mn1-xFexO3 (x = 0, 0.01, 0.03 and 0.05)... more The effect of Fe-substitution at the Mn-site in La0.7Ca0.3Mn1-xFexO3 (x = 0, 0.01, 0.03 and 0.05) on its structure, electrical and magnetic properties has been studied. These properties were investigated via X-ray diffraction (XRD) analysis, temperature-dependent resistance measurements and temperature-dependent AC magnetic susceptibility measurements. XRD analysis showed all samples are single phase materials. Temperature dependent resistance measurements between 30–300 K showed all samples to undergo insulator-metal transition as temperature decreases. Increase in Fe doping for x = 0, 0.01, 0.03 and 0.05 caused the transition temperature TIM to decrease from 257 K, 244 K, 205 K and 162 K respectively. The magnetic susceptibility measurements showed the samples to exhibit paramagnetic to ferromagnetic transition as temperature decreased. Increase in Fe substitution x at the Mn-site progressively decreased the Curie temperature TC from 250 K at x = 0 to 170 K at x = 0.05.

The Effect of Sr-substitution on the Electrical and Structural Properties in Colossal Magnetoresistive La1-x Sr x MnO3 with x = 0.05, 0.12, 0.18, 0.30 and 0.40

Journal of Physics: Conference Series, 2018

Sains Malaysiana, 2018

The effects of mixed-valence Mn substitution at the Cu site on the superconducting and elastic pr... more The effects of mixed-valence Mn substitution at the Cu site on the superconducting and elastic properties of La 1.85-1.5x Sr 0.15+1.5x Cu 1-x Mn x O 4 (x = 0, 0.02 and 0.04) were studied. The samples were characterized by X-ray diffraction (XRD) method, temperature-dependent resistance measurements, scanning electron microscopy (SEM) and sound velocity measurements at room temperature. An elastic softening and a decrease in the critical temperature T c was observed as Mn was substituted for Cu. The Debye temperature θ D for x = 0 and 0.02 void free samples were calculated to be 459 K and 430 K, respectively. Internal lattice strain which is related to lattice parameter ratio a/c did not correlate with T c. The electron-phonon coupling estimated using the conventional Bardeen-Cooper-Schrieffer (BCS) theory was λ = 0.367 (x = 0) and 0.368 (x = 0.02). The electron-phonon coupling in two-dimensional van Hove scenario was calculated to be λ vH = 0.0148 (x = 0) and 0.0149 (x = 0.02). These results were compared with other cuprates and related superconductors. The comparison showed that other than electron-phonon coupling, the elastic moduli might play an important role in the mechanism of superconductivity in these materials.

Journal of Materials Science-materials in Electronics, 1999

The derivatives of Tl-1212 type phase superconductors with nominal starting compositions Tl0.85Cr... more The derivatives of Tl-1212 type phase superconductors with nominal starting compositions Tl0.85Cr0.15)Sr2(Ca1-xRx)Cu2O7 where R = Pr or Nd (Ca series) together with Tl0.85Cr0.15)Sr2(Ca1-xRx)Cu2O7 (Sr series) for x = 0 - 0.5 have been prepared and investigated by d.c. electrical resistance and powder X-ray diffraction analyses. Partial substitution of Ca with Pr or Nd has the advantage of stabilizing the tetragonal

Effect of Pr-Substitution in Eu_1-xPr_xBaSrCu₃O_7-δ on the Superconductivity and Transport Properties

Advanced Materials Research, 2014

The effect of Pr-substitution at the Eu-site on the superconductivity and transport properties in... more The effect of Pr-substitution at the Eu-site on the superconductivity and transport properties in Eu1-xPrxBaSrCu3O7-d (x = 0.0, 0.1, 0.2, 0.4, 0.5) has been investigated. Tc onset for x = 0.0, 0.1, 0.2, 0.4, 0.5 are 86 K, 75 K, 65 K, 38 K, 27 K, respectively. The critical temperature (Tc) decreased linearly with increase in Pr concentration x indicating a magnetic pair-breaking mechanism. The transport critical current density (Jc) decreased with increasing x. Analysis of the structure of the samples via X-ray powder diffraction (XRD) technique showed transformation from orthorhombic to pseudo-tetragonal structure at x = 0.2. Scanning electron microscope (SEM) showed no variation in the microstructure.

Sound velocity and ultrasonic attenuation in RuSr 2 GdCu 2 O 8

Superconductor Science and Technology, 2005

... Malaysia, 43600 Bangi, Selangor, Malaysia E-mail: ras@pkrisc.cc.ukm.my Received 21 June 2005,... more ... Malaysia, 43600 Bangi, Selangor, Malaysia E-mail: ras@pkrisc.cc.ukm.my Received 21 June 2005, in final form 9 August 2005 Published 25 August 2005 Online at stacks.iop.org/SUST/18/1365 Abstract The temperature dependent ...

Physics Letters A, 2001

Ultrasonic longitudinal and shear wave velocities were measured for superconducting and non-super... more Ultrasonic longitudinal and shear wave velocities were measured for superconducting and non-superconducting DyBaSr Cu 3 O 7−δ (Dy-1113) at 10 MHz between 80 and 270 K. The superconducting sample exhibits a step-like elastic anomaly between 190 and 230 K. No elastic anomaly was observed in the non-superconducting Dy-1113. The anomaly observed in the superconducting sample is attributed to structural phase transition caused by oxygen orderings.

Physica B: Condensed Matter, 2003

The colossal magnetoresistive material La 1Àx Ca x MnO 3 with x ¼ 0:25; 0.33, and 0.45, was inves... more The colossal magnetoresistive material La 1Àx Ca x MnO 3 with x ¼ 0:25; 0.33, and 0.45, was investigated through sound velocity and ultrasonic attenuation measurements. Lattice hardening was observed below T c (paramagneticferromagnetic transition) in x ¼ 0:25 and 0:33 samples, indicating the prominent role of lattice vibrations in the physical properties of this material. The x ¼ 0:45 sample also showed lattice hardening together with velocity hysteresis which is suggested to be caused by simultaneous occurrence of conducting ferromagnetic state and charge-ordered region.

Current Applied Physics, 2003

Pr-substituted (Dy 1Àx Pr x)BaSrCu 3 O 7Àd (x ¼ 0:0, 0.1, 0.2, 0.4 and 0.7) has been investigated... more Pr-substituted (Dy 1Àx Pr x)BaSrCu 3 O 7Àd (x ¼ 0:0, 0.1, 0.2, 0.4 and 0.7) has been investigated for its superconducting and elastic properties. Structural transition from orthorhombic to tetragonal symmetry is observed at x ¼ 0:1. Temperaturedependent sound velocity was measured using the pulse-echo overlap method. Elastic anomalies in the form of lattice stiffening with decreasing temperature were observed above 200 K. These anomalies were attributed to oxygen vacancy orderings in the Cu(1)O plane and also depended on the configurational state of oxygen orderings which is strongly influenced by Prdoping.

Elastic Properties of MgB2 and SiC-doped MgB2 Superconductors

ABSTRACT