H. K. Singh

Supercooling transition in phase separated manganite thin films: An electrical transport study

The impact of variation in the relative fractions of the ferromagnetic metallic and antiferromagnetic/charge ordered insulator phases on the supercooling/superheating transition in strongly phase separated system, La5/8−yPryCa3/8MnO3 (y ≈ 0.4), has been studied employing magnetotransport measurements. Our study clearly shows that the supercooling transition temperature is non-unique and strongly depends on the magneto-thermodynamic path through which the low temperature state is accessed. In contrast, the superheating transition temperature remains constant. The thermo-magnetic hysteresis, the separation of the two transitions and the associated resistivity, all are functions of the relative fraction of the coexisting phases.

Comparative study of magnetic and magnetotransport properties of Sm0.55Sr0.45MnO3 thin films grown on different substrates

Highly oriented polycrystalline Sm0.55Sr0.45MnO3 thin films (thickness ∼100 nm) deposited on LaAlO3 (LAO, (001)), SrTiO3 (STO, (001)) and (La0.18Sr0.82) (Al0.59Ta0.41)O3 (LSAT, (001)) single crystal substrates by ultrasonic nebulized spray pyrolysis have been studied. The out of plane lattice parameter (OPLP) of the film on LAO is slightly larger than that of the corresponding bulk. In contrast, the OPLP of the films on STO and LSAT are slightly smaller than the corresponding bulk value. This suggests that the film on LAO is under compressive strain while LSAT and STO are under tensile strain. The films on LAO and LSAT show simultaneous paramagnetic-ferromagnetic (PM–FM) and insulator-metal transition (IMT) temperature at TC/TIM ∼ 165 K and 130 K, respectively. The PM–FM and IM transition occur at TC ∼ 120 K and TIM ∼ 105 K, respectively in the film on STO substrate. At T < TC, the zero field cooled–field cooled (ZFC–FC) magnetization of all the films shows strong bifurcation. This suggests the presence o...

Effect of phase separation induced supercooling on magnetotransport properties of epitaxial La5/8−yPryCa3/8MnO3 (y≈0.4) thin film

Thin films of La5/8−yPryCa3/8MnO3 (y≈0.4) have been grown on single crystal SrTiO3 (001) by RF sputtering. The structural and surface characterizations confirm the epitaxial nature of these film. However, the difference between the ω-scan of the (002) and (110) peaks and the presence of pits/holes in the step-terrace type surface morphology suggests high density of defect in these films. Pronounced hysteresis between the field cooled cooling (FCC) and field cooled warming (FCW) magnetization measurements suggest towards the non-ergodic magnetic state. The origin of this nonergodicity could be traced to the magnetic liquid like state arising from the delicacy of the coexisting magnetic phases, viz., ferromagnetic and antiferromagnetic-charge ordered (FM/AFM-CO). The large difference between the insulator metal transitions during cooling and warming cycles (TIMC ∼ 64 K and TIMW ∼ 123 K) could be regarded as a manifestation of the nonergodicity leading to supercooling of the magnetic liquid while cooling. Th...

Magnetotransport and thermal properties characterization of 55 K superconductor SmFeAsO0.85F0.15

This report fairly underlines the magneto-transport, thermal properties characterization and bulk superconductivity in the FeAs-based SmFeAsO0.85F0.1. The phase formation and structure are confirmed by Rietveld analysis of room temperature powder X-ray diffraction (XRD) data. Electron microscopy was employed to unravel the micro structural details, such as perfection of the lattice and the grain morphology including size and boundaries. The electrical and magnetic measurements have been carried out to confirm the bulk superconductivity and understand the nature of electrical transport in the normal and superconducting state. The intra-grain critical current density (J c ) with applied magnetic field is calculated from isothermal DC magnetization (MH) plots using conventional Bean critical state model. Superconductivity is observed at transition temperature (Tc) above 55 K without HPHT (high pressure high temperature) synthesis route. The value of J c is found to be around 5.26 × 104 A/cm2 at 5 K in zero field. The dependence of thermally activated flux flow energy (U/kB) on the applied magnetic field has been observed. AC susceptibility measurements were performed for 55 K superconducting SmFeAsO0.85F0.15 sample at various amplitude of applied AC drive field and its granular nature is confirmed. The parent compound SmFeAsO is found to be magnetic with Fe spin density wave ( SDW ) like order below 150 K, on the other hand the F doped SmFeAsO0.85F0.15 sample is bulk superconducting at below 55 K. Both Fe ( SDW ) at 150 K for SmFeAsO and 55 K superconductivity in case of SmFeAsO0.85F0.15 sample has confirmed by Specific heat [C p (T)] measurement too. Further Sm orders anti-ferro-magnetically at 4.5 K for non-superconducting and at 3.5 K for superconducting samples, also the entropy change is reduced significantly for the later than the former. Summarily complete physical property characterization for both non-superconducting SmFeAsO and 55 K superconductor SmFeAsO0.85F0.15 samples is provided and discussed in the current article.

Structure, magnetism and electrical transport in epitaxial La0.23Pr0.41Ca0.36MnO3 thin films: Consequences of film thickness

A systematic study of the consequences of in-plane tensile strain on the correlation between structure/microstructure and magneto-electrical properties of La0.23Pr0.41Ca0.36MnO3/SrTiO3 (001) thin f...

Role of oxygen annealing on charge order and insulator metal transition in Pr[sub 0.58]Ca[sub 0.42]MnO[sub 3] thin films

We investigate the role of oxygen in the electronic phase coexistence in polycrystalline Pr0.58Ca0.42MnO3 (PCMO) thin filmsspray pyrolysis on single crystal SrTiO3 (001) substrates. All films are single phase and have good crystallographic orientation. Our results demonstrate that the ground state of oxygen deficient PCMO is a phase separated cluster glass in which both charge ordered-antiferromagnetic insulating (COI-AF) and ferromagnetic metallic (FMM) clusters coexist. Oxygen annealing is observed to (i) favour the COI phase, (ii) reduce the FMM fraction and (iii) weaken the cluster glass state.

Role of oxygen annealing on charge order and insulator metal transition in Pr0.58Ca0.42MnO3thin films

We investigate the role of oxygen in the electronic phase coexistence in polycrystalline Pr0.58Ca0.42MnO3 (PCMO) thin filmsspray pyrolysis on single crystal SrTiO3 (001) substrates. All films are single phase and have good crystallographic orientation. Our results demonstrate that the ground state of oxygen deficient PCMO is a phase separated cluster glass in which both charge ordered-antiferromagnetic insulating (COI-AF) and ferromagnetic metallic (FMM) clusters coexist. Oxygen annealing is observed to (i) favour the COI phase, (ii) reduce the FMM fraction and (iii) weaken the cluster glass state.

Impact of quenched disorder on magnetotransport properties in Nd0.55-xSmxSr0.45MnO3 thin films

The effect of size mismatch induced quenched disorder on magnetotransport properties has been studied in polycrystalline Nd0.55-xSmxSr0.45MnO3 (x=0.00, 0.05, 0.15, 0.25, 0.35, and 0.45) thin films (thickness ∼300nm) prepared on LaAlO3 [LAO (001)] single crystal substrates by chemical spray pyrolysis. X-ray diffraction (XRD) data reveals that the films have oriented growth along out-of-plane (OP) direction. The OP lattice parameter decreases on substitution of Sm3+ ions for Nd3+. The insulator-metal/PM-FM transition temperatures (TIM/TC) for all the compositions decrease systematically and the transitions get sharpened as the variance σ2 that measures the quenched disorder due to size mismatch. The in-plane and out-of-plane low field magnetoresistance (LFMR) are enhanced appreciably with increasing quenched disorder (σ2). The variation in peak magnetoresistance (maximum MR around TIM) with σ2 shows drastic change above σ2 = 0.008469A2(x = 0.25). The small polaron activation energy also increases appreciabl...

Role of oxygen annealing on charge order and insulator metal transition in Pr0.58Ca0.42MnO3 thin films

We investigate the role of oxygen in the electronic phase coexistence in polycrystalline Pr0.58Ca0.42MnO3 (PCMO) thin filmsspray pyrolysis on single crystal SrTiO3 (001) substrates. All films are single phase and have good crystallographic orientation. Our results demonstrate that the ground state of oxygen deficient PCMO is a phase separated cluster glass in which both charge ordered-antiferromagnetic insulating (COI-AF) and ferromagnetic metallic (FMM) clusters coexist. Oxygen annealing is observed to (i) favour the COI phase, (ii) reduce the FMM fraction and (iii) weaken the cluster glass state.

First order phase transition in Sm0.53Sr0.47MnO3 films

In the present work Sm0.53Sr0.47MnO3 thin films were deposited on single crystal LAO (LaAlO3/(100)) substrates by DC magnetron sputtering. The θ-2 and ω-2θ scans show that these films are epitaxially grown and are under small compressive strain. The paramagnetic-ferromagnetic (insulator-metal) transition was found at TC∼126 K (at TIM∼128 K). The magnetic state at T<TC is akin to cluster glass, which is formed by the presence of charge ordered-antiferromagnetic clusters in the ferromagnetic matrix. The nature of the magnetic phase transition was investigated by applying the Banerjee criterion. The negative slope of the M2 – H/M curves and hysteresis in resistivity measured in the cooling and warming cycle establishes the first order nature of the phase transition.