arXiv subjects

R. Rawat

Publications and source records attributed to R. Rawat.

45 records · Page 3Linked to original sources

arXiv2007

Effect of Hetrovalent substitution at Mn site on the Magnetic and Transport Properties of La$_{0.67}$Sr$_{0.33}$MnO$_3$

Magnetic and transport properties of Ti substituted La$_{0.67}$Sr$_{0.33}$MnO$_3$ are drastically affected with a change in preparation conditions. Low temperature infra-red absorption measurements reveal that this is perhaps due to inhomogeniety in substitution of Ti$^{4+}$ on Mn sites. It is found that, in the high temperature annealed samples, the substitution of Ti supresses the double exchange interaction due to the formation of Mn$^{3+}$-O-Ti$^{4+}$ chains. While in the low temperature annealed case substitution of Ti causes formation of isolated ferromagnetic clusters linked to each other by a variable range hopping polaron.

cond-mat.str-el↗

arXiv2007

Anomalous First Order Transition in $Nd{_{0.5}}Sr{_{0.5}}MnO{_{3}}$: An interplay between kinetic arrest and thermodynamic transitions

A detailed investigation of the first order antiferromagnetic insulator (AFI) to ferromagnetic metal (FMM) transition in $Nd{_{0.5}}Sr{_{0.5}}MnO{_{3}}$ is carried out by resistivity and magnetization measurements. These studies reveal several anomalous features of thermomagnetic irreversibility across the first order transition. We show that these anomalous features can not be explained in terms of supercooling effect alone and H-T diagram based on isothermal MH or RH measurement alone do not reflect true nature of the first order transition in this compound. Our investigations reveal glass-like arrest of kinetics at low temperature which plays a dominant role in the anomalous thermomagnetic irreversibility observed in this system. The interplay between kinetic arrest and supercooling is investigated by following novel paths in the H-T space. It is shown that coexisting FMM and AFI phases can be tuned in a number of ways at low temperature. These measurements also show that kinetic arrest temperature and supercooling temperature are anti-correlated i.e. regions which are arrested at low temperature have higher supercooling temperature and vice versa.

cond-mat.str-el↗

arXiv2005

Double metal-insulator transitions and magnetoresistance:An intrinsic feature of Ru substituted La(0.67)Ca(0.33)MnO(3)

In this paper, we examine the possible influence of extrinsic factors on the electrical and magnetotransport of La(0.67)Ca(0.33)Mn(1-x)Ru(x)O(3) (x < 0.10). These results not only exclude the extrinsic factors, but establishes the fact that the metal transitions both exhibiting MR is intrinsic to Ru substituted La(0.67)Ca(0.33)MnO(3) and the system. These results substantiate our hypothesis that Ru substituted system undergoes a magnetic phase separation involving the co-existence of two ferromagnetic-metallic phases in its ground state.

cond-mat.mtrl-sci↗

arXiv2005

Ti substituted La(0.67)Ca(0.33)MnO(3) ortho-perovskites: Dominant role of local structure on the electrical transport and magnetic properties

We discuss the effects of local structure on the electrical transport and magnetic properties of La(0.67)Ca(0.33)Mn(1-x)Ti(x)O(3) system.Based on the intercomparison of the structure, transport and magnetic properties of the Mn site substituted La(0.67)Ca(0.33)MnO(3) with isovalent diamagnetic and paramagnetic ions, we argue that local structural effects have a decisive role to play, compared to the local spin coupling effects, in the ferromagnetic-metallic ground state of the CMR manganites

cond-mat.str-el↗

arXiv2005

Effect of Mn substitution on the delicate balance between structure and properties of Gd1.4Ce0.6Sr2RuCu2O10

Some new members of a Ruthenocuprate (2212) series have been synthesized by Mn substitution for Ru in Gd1.4Ce0.6Sr2RuCu2O10 . Characterisation by XRD phase analysis followed by Rietveld refinement has been carried out. IR spectroscopy studies and Rietveld refinements are consistent with substitution of Mn at Ru site. XRD studies indicate changes in structural features on substitution including a significant change in lattice parameter for a very low substitution level (1mole% of Ru). The pristine compound shows coexistence of superconductivity and magnetism. Four probe resistivity studies indicate a semiconductor like upturn in resistivity and absence of superconductivity even for Mn substitution levels as low as 1 mole%. a. c. susceptibility measurements show a progressive suppression of the magnetic transition temperature as well as a smearing of the magnetic transition as a function of Mn substitution. Possible reasons for absence of superconductivity have been discussed.

cond-mat.supr-con↗

arXiv2005

Large negative magnetoresistance in a ferromagnetic shape memory alloy : Ni_{2+x}Mn_{1-x}Ga

5% negative magnetoresistance (MR) at room temperature has been observed in bulk Ni_{2+x}Mn_{1-x}Ga. This indicates the possibility of using Ni_{2+x}Mn_{1-x}Ga as magnetic sensors. We have measured MR in the ferromagnetic state for different compositions (x=0-0.2) in the austenitic, pre-martensitic and martensitic phases. MR is found to increase with x. While MR for x=0 varies almost linearly in the austenitic and pre-martensitic phases, in the martensitic phase it shows a cusp-like shape. This has been explained by the changes in twin and domain structures in the martensitic phase. In the austenitic phase, which does not have twin structure, MR agrees with theory based on s-d scattering model.

cond-mat.mtrl-sci↗

arXiv2001

Thermal relaxation in charge ordered Pr$_{0.63}$ Ca$_{0.37}$ MnO$_3$ in presence of a magnetic field

We report observation of substantial thermal relaxation in single crystal of charge ordered system Pr$_{0.63}$Ca$_{0.37}$MnO$_3$ in an applied magnetic field of H = 8T. The relaxation is observed when the temperature is scanned in presence of a magnetic field in the temperature interval $T_{MH}<T<T_{CO}$ where $T_{CO}$ is the charge ordering temperature and $T_{MH}$ is charge melting temperature in a field. In this temperature range the system has coexisting charged ordered insulator (COI) and ferromagnetic metallic (FMM) phases. No such relaxation is observed in the COI state in H = 0T or in the FMM phase at $T < T_{MH}$ in presence of a magnetic field. We conclude that the thermal relaxation is due to two coexisting phases with nearly same free energies but separated by a potential barrier. This barrier makes the transformation from one phase to the other time-dependent in the scale of the specific heat experiment and gives rise to the thermal relaxation.

cond-mat.str-el↗

arXiv2001

Specific heat study of single crystalline Pr$_{0.63}$ Ca$_{0.37}$ MnO$_{3}$ in presence of a magnetic field

We present the results of a study of specific heat on a single crystal of Pr$_{0.63}$Ca$_{0.37}$MnO$_3$ performed over a temperature range 3K-300K in presence of 0 and 8T magnetic fields. An estimate of the entropy and latent heat in a magnetic field at the first order charge ordering (CO) transition is presented. The total entropy change at the CO transition which is $\approx$ 1.8 J/mol K at 0T, decreases to $\sim$ 1.5 J/mol K in presence of 8T magnetic field. Our measurements enable us to estimate the latent heat $L_{CO}$ $\approx$ 235 J/mol involved in the CO transition. Since the entropy of the ferromagnetic metallic (FMM) state is comparable to that of the charge-ordered insulating (COI) state, a subtle change in entropy stabilises either of these two states. Our low temperature specific heat measurements reveal that the linear term is absent in 0T and surprisingly not seen even in the metallic FMM state.

cond-mat.str-el↗

arXiv2000

Magneto-Transport properties in the thin films of Charge ordered thin films

Thin films of Pr0.7Ca 0.3MnO3, Nd-0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3 have been fabricated. by pulse laser deposition. Magnetic and electrical transport properties of these films were compared with their bulk solids. All the films grow in (101) direction on LaAlO3(100). Electrical transport measurements carried out with and without magnetic field has shown dr/dT<0 in these thin films. Application of magnetic field has shown dilution of the insulating behavior. The magnetization studies of Nd-0.5Sr0.5MnO3 exhibited ferromagnetic behavior at 260K and showed antiferomagnetic feature below 130K. This is close to the bulk magnetic behavior of Nd-0.5Sr0.5MnO3. Pr0.7Ca0.3MnO3 showed ferromagnetic transition below 130K and becomes antiferromagnetic at 90K. Nd-0.5Ca0.5MnO3 showed paramagnetic behavior down to low temperatures. Deviation in the properties of the thin films from the bulk solids is attributed to the growth of the films in more symmetric structure.

cond-mat.mtrl-sci↗