Kranti Kumar

UGC-DAE Consortium for Scientific Research, Indaur, Madhya Pradesh, India

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Publications (19)22.95 Total impact

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    ABSTRACT: We report the effect of field, temperature and thermal history on the time dependence in resistivity and magnetization in the phase separated state of Al doped Pr(0.5)Ca(0.5)MnO(3). The rate of time dependence in resistivity is much higher than that of magnetization and it exhibits a different cooling field dependence due to percolation effects. Our analysis shows that the time dependence in physical properties depends on the phase transition dynamics, which can be effectively tuned by variation of temperature, cooling field and metastable phase fraction. The phase transition dynamics can be broadly divided into the arrested and unarrested regimes, and in the arrested regime this dynamics is mainly determined by time taken in the growth of critical nuclei. An increase in cooling field and/or temperature shifts this dynamics from the arrested to unarrested regime, and in this regime, this dynamics is determined by the thermodynamically allowed rate of formation of critical nuclei, which in turn depends on the cooling field and available metastable phase fraction. At a given temperature, a decrease in metastable phase fraction shifts the crossover from arrested to unarrested regimes towards lower cooling field. It is rather significant that in spite of the metastable phase fraction calculated from resistivity being somewhat off that of magnetization, their cooling field dependence exhibits a striking similarity, which indicates that the dynamics in arrested and unarrested regimes are so different that it comes out vividly provided that the measurements are performed around the percolation threshold.
    Journal of Physics Condensed Matter 08/2012; 24(38):386001. · 2.36 Impact Factor
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    ABSTRACT: We study through the time evolution of magnetization the low temperature (T) dynamics of the metastable coexisting phases created by traversing different paths in magnetic field (H) and T space in a shape memory alloy system, Ni$_{45}$Co$_{5}$Mn$_{38}$Sn$_{12}$. It is shown that these coexisting phases consisting of a fraction of kinetically arrested austenite phase and remaining fraction of low-T equilibrium martensitic phase undergo a slow relaxation to low magnetization (martensitic) state but with very different thermomagnetic history-dependent rates at the same T and H. We discovered that, when the nucleation of martensitic phase is initiated at much lower T through the de-arrest of the glass like arrested state contrasted with the respective first order transformation (through supercooling at much higher T), then the long time relaxation rate scales with the non-equilibrium phase fraction but has a very weak dependence on T. This is explained on the basis of the H-T path dependent size of the critical radii of the nuclei and the subsequent growth of the equilibrium phase through the motion of the interface.
    09/2011;
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    ABSTRACT: We study through the time evolution of magnetization the low-temperature (T) dynamics of the metastable coexisting phases created by traversing different paths in magnetic field H and T space in a shape memory alloy system, Ni45Co5Mn38Sn12. It is shown that these coexisting phases consisting of a fraction of kinetically arrested austenite phase and a remaining fraction of low-T equilibrium martensitic phase undergo a slow relaxation to low magnetization (martensitic) state but with very different thermomagnetic history-dependent rates at the same T and H. We discovered that, when the nucleation of the martensitic phase is initiated at much lower T through the de-arrest of the glasslike arrested state contrasted with the respective first-order transformation (through supercooling at much higher T), the long-time relaxation rate scales with the nonequilibrium phase fraction but has a very weak dependence on T. This is explained on the basis of the H-T path dependent size of the critical radii of the nuclei and the subsequent growth of the equilibrium phase through the motion of the interface.
    Physical review. B, Condensed matter 01/2011; 84.
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    P. Chaddah, S. Dash, Kranti Kumar, A Banerjee
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    ABSTRACT: A system initially far from equilibrium is expected to take more time to reach equilibrium than a system that was initially closer to equilibrium. The old puzzling observation (also called Mpemba effect) that when a sample of hot water and another sample of cold water are put in a freezer to equilibrate, the hot water sometimes overtakes as they cool, has been highlighted recently. In the extensively studied colossal magnetoresistance manganites, cooling in a magnetic field (H) often results in an inhomogeneous mixture of transformed equilibrium phase and a kinetically arrested non-equilibrium phase which relaxes slowly towards equilibrium at fixed H and temperature (T). Here we show that the magnetization decay rate at the same H and T is larger for the state that was initially farther from equilibrium, and it continues to relax faster even after these have become equal. Our result should help propose an explanation, for Mpemba effect, that does not attribute it to any artifact.
    11/2010;
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    S. Dash, Kranti Kumar, A. Banerjee, P. Chaddah
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    ABSTRACT: We study combined effect of hydrostatic pressure and magnetic field on the magnetization of La0.5Ca0.5MnO3. We do not observe any significant effect of pressure on the paramagnetic to ferromagnetic transition. However, pressure asymmetrically affects the thermal hysteresis across the ferromagnetic-antiferromagnetic first-order transition, which has strong field dependence. Though the supercooling (T∗) and superheating (T∗∗) temperatures decrease and the value of magnetization at 5 K (M5 K) increases with pressure, T∗ and M5 K shows abrupt changes in tiny pressure of 0.68 kbar. These anomalies enhance with field. In 7 T field, transition to antiferromagnetic phase disappears in 0.68 kbar and M5 K show significant increase. Thereafter, increase in pressure up to ∼10 kbar has no noticeable effect on the magnetization.
    Physical review. B, Condensed matter 07/2010; 82(17).
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    ABSTRACT: It is shown that variation of the third order ac-susceptibility as a function of measuring field and frequency lead to distinguish between superparamagnetic and spin glass like ordering in the rare earth substituted magnetic ferrofluids. We observe the divergent behavior of the peak values of the third order susceptibility, as a function of measuring field and frequency, tends to zero is consistent with theoretical prediction for the ground state for a spin glass like system. This behavior is further substantiated by a linear dependence of log-log plots of peak of the third order susceptibility as a function of the measuring field and frequency.
    Physics Procedia 01/2010; 9:32.
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    ABSTRACT: Glass-like arrest has recently been reported in various magnetic materials. As in structural glasses, the kinetics of a first order transformation is arrested while retaining the higher entropy phase as a non-ergodic state. We show visual mesoscopic evidence of the irreversible transformation of the arrested antiferromagnetic-insulating phase in Pr(0.5)Ca(0.5)Mn(0.975)Al(0.025)O(3) to its equilibrium ferromagnetic-metallic phase with an isothermal increase of magnetic field, similar to its iso-field transformation on warming. The magnetic field dependence of the non-equilibrium to equilibrium transformation temperature is shown to be governed by Le Chatelier's principle.
    Journal of Physics Condensed Matter 01/2010; 22(3):032101. · 2.36 Impact Factor
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    ABSTRACT: Glass-like arrest has recently been reported in various magnetic materials. As in structural glasses, the kinetics of a first-order transformation is arrested while retaining the higher-entropy phase as a non-ergodic state. We show visual mesoscopic evidence of the irreversible devitrification of the arrested antiferromagnetic-insulating phase in $Pr_{0.5}Ca_{0.5}Mn_{0.975}Al_{0.025}O_3$ to its equilibrium ferromagnetic-metallic phase with isothermal increase of magnetic field, similar to its iso-field devitrification on warming. The slope of $T_g$ vs magnetic field in half-doped manganites is shown to have a sign governed by Le Chatelier's Principle.
    05/2009;
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    A Banerjee, Kranti Kumar, P Chaddah
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    ABSTRACT: We show that Pr(0.5)Ca(0.5)MnO(3) with 2.5% Al substitution and La(0.5)Ca(0.5)MnO(3) (LCMO) exhibit qualitatively similar and visibly anomalous M-H curves at low temperature. Magnetic field causes a broad first order but irreversible antiferromagnetic (AF)-insulating (I) to ferromagnetic (FM)-metallic (M) transition in both and gives rise to a soft FM state. However, the low temperature equilibrium state of Pr(0.5)Ca(0.5)Mn(0.975)Al(0.025)O(3) (PCMAO) is FM-M whereas that of LCMO is AF-I. In both systems the respective equilibrium phase coexists with the other phase with contrasting order, which is not in equilibrium, and the cooling field can tune the fractions of the coexisting phases. It is shown earlier that the coexisting FM-M phase behaves like 'magnetic glass' in LCMO. Here we show from specially designed measurement protocols that the AF-I phase of PCMAO has all the characteristics of magnetic glassy states. It devitrifies on heating and also recrystallizes to an equilibrium FM-M phase after annealing. This glass-like AF-I phase also shows a similar intriguing feature observed in FM-M magnetic glassy state of LCMO, that when the starting coexisting fraction of glass is larger, successive annealing results in a larger fraction of the equilibrium phase. This similarity between two manganite systems with contrasting magnetic orders of respective glassy and equilibrium phases points to a possible universality.
    Journal of Physics Condensed Matter 01/2009; 21(2):026002. · 2.36 Impact Factor
  • A Banerjee, Kranti Kumar, P Chaddah
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    ABSTRACT: The nature of the coexisting ferromagnetic–metallic (FMM) and antiferromagnetic–insulating (AFI) phases in a La0.5Ca0.5MnO3 sample is explored through magnetization and resistivity studies. Like many first-order magnetic transitions, in this case also the FMM–AFI transformation is interrupted by glass-like arrest of kinetics. As a result, a fraction of the high-temperature FMM phase persists in a glassy state to the lowest temperature. We show that this glassy FMM phase devitrifies to equilibrium AFI phase on heating. Significantly, it can be 'recrystallized' to AFI state by annealing and more easily by successive annealing, presumably by heterogeneous nucleation. We show that the recrystallization is easier when the starting glass fraction is larger.
    Journal of Physics Condensed Matter 05/2008; 20(25):255245. · 2.36 Impact Factor
  • P. Chaddah, Kranti Kumar, A. Banerjee
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    ABSTRACT: We report studies on a magnetic glass formed by the arrest of the ferromagnetic-metallic to antiferromagnetic-insulating transition in a manganite around half doping, La0.5Ca0.5MnO3. The observed glass-to-crystal conversion rate varies drastically and nonmonotonically with temperature; this variation is qualitatively consistent with what we predict by phenomenology. We also show that both homogeneous and heterogeneous nucleation can be obtained in the same sample under different annealing conditions. This gives rise to a gigantic change in resistivity without application of any magnetic field.
    Physical Review B 01/2008; 77(10). · 3.77 Impact Factor
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    A Banerjee, Kranti Kumar, P. Chaddah
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    ABSTRACT: We probe through magnetization and resistivity measurements a kinetically arrested glass-like but long-range ordered magnetic state. The transformation kinetics of the magnetic field-temperature induced broad first-order transition from ferromagnetic-metallic (FMM) to antiferromagnetic-insulating (AFI) state gets hindered at low temperature in a La(0.5)Ca(0.5)MnO3 sample. A fraction of high-temperature FMM phase persists to the lowest temperature, albeit as a non-ergodic state. We present a phenomenology for this glass-like but long-range order FMM phase which devitrifies on heating and converts to equilibrium AFI phase. The residual kinetically arrested FMM phase can be `recrystallized' to AFI state by annealing and more efficiently by successive annealing, presumably by heterogeneous nucleation. This glass-like state shows a stimulating feature that when the fraction of glass is larger the `recrystallization' is easier.
    12/2007;
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    A Banerjee, Kranti Kumar, P. Chaddah
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    ABSTRACT: Magnetization measurements in La0.5Ca0.5MnO3 manganite show that the high-temperature long-range ferromagnetic-metallic phase transforms to antiferromagnetic-insulating phase, although a fraction of ferromagnetic-metallic phase undergoes glass-like kinetic arrest and coexists at low temperature with the equilibrium antiferromagnetic-insulating phase. We show here through resistivity measurements that the residual arrested ferromagnetic-metallic fraction can be converted to the equilibrium antiferromagnetic-insulating phase by successive annealing at higher temperatures, possibly through heterogeneous nucleation of equilibrium phase. Significantly, larger fractions of this glassy ferromagnetic-metallic phase can be obtained by cooling in higher fields and larger conversion to equilibrium antiferromagnetic-insulating phase results.
    11/2007;
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    P. Chaddah, Kranti Kumar, A Banerjee
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    ABSTRACT: Glass-like arrest of kinetics has been observed across many magnetic first-order transitions. By traversing the two control variable H-T space, tunable coexisting fractions of arrested and equilibrium phases have been observed. We report here a fortuitous situation in a half-doped manganite sample, where these features occur by varying only temperature (T) along the H=0 line. The resistivity at 5 K rises by more than a factor of three provided second cool-down is effected from a specified intermediate T. This significant enhancement results from heterogeneous nucleation during second cool-down of regions that were kinetically arrested during first cool-down.
    11/2007;
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    ABSTRACT: A detailed investigation of the first-order antiferromagnetic insulator (AFI) to ferromagnetic metal (FMM) transition in Nd0.5Sr0.5MnO3 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 cannot be explained in terms of the supercooling effect alone and the H–T diagram based on isothermal M–H or R–H measurements alone does not reflect the 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 anticorrelated, i.e. regions which are arrested at low temperature have higher supercooling temperature and vice versa.
    Journal of Physics Condensed Matter 06/2007; 19(25):256211. · 2.36 Impact Factor
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    ABSTRACT: We show that minimal disturbance to the robust charge-ordered Pr0.5Ca0.5MnO3 by 2.5% Al substitution on the Mn site drives the system toward a ferromagnetic ground state. The history-dependent coexisting phases observed are explained as the outcome of a hindered first-order transition with glasslike arrest of kinetics resulting in irreversibility. Consistent with a simple phase diagram having a ferromagnetic ground state, it is experimentally shown that these coexisting phases are far from equilibrium.
    Physical Review B 12/2006; 74(22). · 3.77 Impact Factor
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    ABSTRACT: Coexisting ferromagnetic and antiferromagnetic phases over a range of temperature as well as magnetic field have been reported in many materials of current interest, showing disorder-broadened first-order transitions. Anomalous history effects observed in magnetization and resistivity are being explained invoking the concepts of kinetic arrest akin to glass transitions. From magnetization measurements traversing unusual paths in field-temperature space, we obtain the intriguing result that the regions of the sample which can be supercooled to lower temperatures undergo kinetic-arrest at higher temperatures, and vice versa. Our results are for two diverse systems viz., the inter-metallic doped CeFe2 which has an antiferromagnetic ground state, and the oxide La-Pr-Ca-Mn-O which has a ferromagnetic ground state, indicating the possible universality of this effect of disorder on the widely encountered phenomenon of glass-like arrest of kinetics.
    Physical review. B, Condensed matter 02/2006; 73(18).
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    ABSTRACT: Antiferromagnetic-insulating (AF-I) and ferromagnetic-metallic (FM-M) phases coexist in various half-doped manganites over a range of temperature and magnetic field, and this is often believed to be an essential ingredient of their colossal magnetoresistance. We present magnetization and resistivity measurements on Pr0.5Ca0.5Mn0.975Al0.025O3 and Pr0.5Sr0.5MnO3 showing that the fraction of the two coexisting phases at low temperature in any specified measuring field, H, can be continuously controlled by following designed protocols traversing field-temperature space; for both materials the FM-M fraction rises under similar cooling paths. Constant-field temperature variations, however, show that the former sample undergoes a first-order transition from AF-I to FM-M with decreasing T, while the latter undergoes the reverse transition. We suggest that the observed path-dependent phase-separated states result from the low-T equilibrium phase coexisting with supercooled glass-like high-temperature phase, where the low-T equilibrium phases are actually homogeneous FM-M and AF-I phases respectively for the two materials.
    Journal of Physics Condensed Matter 01/2006; 18(49). · 2.36 Impact Factor
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    ABSTRACT: We report a quantitative investigation of the magnetic field-temperature phase diagram by taking into account a simple phenomenological model arising out of the interplay of kinetic arrest and thermodynamic transitions in a magnetic glass Pr0.5Ca0.5Mn0.975Al0.025O3, through magnetization measurements. Such studies are necessary as kinetic arrest plays an important role in the formation of “magnetic glasses”, which has been observed in systems undergoing first order magnetic phase transitions. It has been shown that disorder in a system results in the formation kinetic arrest (H K ,T K ) band, like supercooling (H *,T *) and superheating (H **,T **) band. Quantitative proofs are given to show that (H K ,T K ) band is anticorrelated with (H *,T *) and (H **,T **) bands, while the later two are correlated among themselves. Analysis of time dependence of magnetization at different temperatures is carried out to establish the fact that the kinetic arrested state is different from the supercooled state.
    Physics of Condensed Matter 86(1). · 1.28 Impact Factor