arXiv subjects

M. Mahesh Kumar

Publications and source records attributed to M. Mahesh Kumar.

4 recordsLinked to original sources

arXiv2005

Deviations from the Summerfield scaling in the piezoelectric PbZr0.57Ti0.43O3

Extending our earlier observations of the deviations from Summerfield scaling in a crystalline ferroelectric system of SBCT, we have studied the scaling of conductivity in another ferro/piezoelectric perovskite crystalline oxide, PZT. The deviations from Summerfield scaling are found at T greater than TC. Correction to the Summerfield scaling is achieved by the application of the Random Barrier Model and master cures are constructed with a value of the scaling function alpha 3.2. As in the case of SBCT, deviations still occur at T greater TC. The master curves are constructed from the conductivity data sigma prime fitted to a modified Jonscher law in the frequency range 10 to 1e5 Hz over the temperature region 30 to 480 degrees C. The positive values of alpha indicate coulomb exchange between the interacting particles. This work provides an additional example which allows us to believe that crystalline systems as well may follow the scaling laws, not only amorphous glasses, as was previously believed.

cond-mat.mtrl-sci↗

arXiv2005

Magnetization and magnetoresistance in insulating phases of SrFeO3-d

We report the synthesis and properties of two new insulating phases of SrFeO3-d with introduction of oxygen deficiencies in metallic SrFeO3 ; one with 0.15 < d < 0.19 (sample A)and the other above d = 0.19 (sample B). Sample A shows large negative magnetoresistance around the charged ordering (CO) temperature with magnetic anomalies seen in the temperature dependent resistivity,magnetization and M-H hysteresis loops. Sample B shows a smooth insulating behavior with no thermal hysteresis in the resistivity and with a small positive magnetoresistance. cac and cdc show multiple features associated with a frustrated magnetic order (helical) due to competing ferro- and antiferromagnetic interactions. The competing effects of ferro- and antiferromagnetic phases extend up to T ~ 230 K revealing a new high temperature scale in this system. These observations are discussed in the context of magnetic interactions associated with the varying Fe4+/Fe3+ ratio.

cond-mat.mtrl-sci↗

arXiv2000

Magnetic and electrical resistance behaviour of the oxides, Ca$_{3-x}$Y$_x$LiRuO$_6$ (x= 0.0, 0.5 and 1.0)

We have investigated the magnetic and electrical resistance behaviour of Ca$_{3-x}$Y$_x$LiRuO$_6$. The parent compound exhibits magnetic ordering from Ru sublattice at a rather high temperature, 113 K. Though the paramagnetic Curie temperature ($θ$$_p$) is negative indicative of antiferromagnetic ordering, the large magnitude (-250 K) of $θ$$_p$ reveals complex nature of the magnetism in this compound. Ru ions appear to be in the pentavalent state. We note that the Néel temperature undergoes only a marginal reduction by Y substitution. All these compositions are found to be insulators and thus the electron doping does not result in metallicity. Thus the overall magnetic and transport behaviour are found to be essentially insensitive to Y substitution for Ca, a finding which may favour the idea of quasi-one-dimensional magnetism in these compounds.

cond-mat.mtrl-sci↗

arXiv1999

La substitution induced linear temperature dependence of electrical resistivity and Kondo behavior in the alloys, Ce_{2-x}La_{x}CoSi_{3}

The results of electrical resistivity, heat capacity and magnetic susceptibility behavior of new class of alloys, Ce_{2-x}La_{x}CoSi_{3}, are reported. The x= 0.0 alloy is mixed valent and La substitution for Ce (x= 0.25) induces linear temperature dependence of resistivity at low temperatures, an observation of relevance to the topic of non-Fermi liquid behavior. The modifications of Kondo effect for all the alloys are also presented.

cond-mat.str-el↗