P. K. Siwach

Thickness dependent transport properties of compressively strained La0.88Sr0.12MnO3 ultrathin films

Thickness dependent magnetic and transport properties of compressively strained La0.88Sr0.12MnO3 thin films grown on single crystalline SrTiO3 (100) substrates have been studied. All films exhibit a large enhancement of ∼130 K in TC/TIM as compared to that of the bulk target (TC∼175 K). This has been explained in terms of suppression of the cooperative Jahn–Teller distortion due to in-plane compressive strain. The TC/TIM of the 5 nm film is 315 K/318 K and slightly increases for film thicknesses ≤25 nm. At higher film thicknesses, ∼60 nm, the TC/TIM starts decreasing. At T>TIM, the electrical transport is due to thermally activated hopping of small polarons. The activation energy is found to be sensitive to film thickness and shows a minimum at around L∼15–25 nm, which corresponds to the maximum of TC/TIM. All films possess large magnetoresistances (MRs) in the vicinity of room temperature. Low as well as high field MRs are observed to nearly double as the film thickness increases from 5 nm (MR∼28%/3 T) to 60 nm (MR%∼50%/3 T). Thicker films (L≥25 nm) are found to exhibit sufficiently large temperature coefficients of resistivities, ∼4%–5%/K, which could be suitable for bolometric applications.

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...

Impact of magnetic phase coexistence on magnetotransport in polycrystalline Nd0.51Sr0.49MnO3 thin film

We report the magnetic and transport properties of Nd0.51Sr0.49MnO3 polycrystalline thin films (thickness ~ 100?nm) prepared by dc magnetron sputtering on single crystal Y-stabilized ZrO2(1?0?0) substrates. The paramagnetic (PM) to ferromagnetic (FM) transition at TC = 260?K is followed by A-type antiferromagnetic (AFM) ordering at and charge ordered (CO) phase having the CE type spin order at . The strong CO-AFM transition observed at TCO ~ 150?K at half doping is softened by a small increase in the Nd concentration and the disorder due to the polycrystalline nature of these films. The multiple magnetic transitions are suggestive of strong phase coexistence. In this study the insulator-like to metal-like transition temperature TIM ~ 140?K is considerably lower than the TC and remains independent of the external magnetic field up to 70?kOe. This suggests that electrical transport is dominated by grain boundaries and has percolation type characteristics due to the existence of metallic (FM + A-AFM) and insulating (CO-AFM + GB) paths. The films show large magnetoresistance at low as well as high magnetic fields.

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...

Microstructure, magnetism and magnetotransport of epitaxial Sm0.45Nd0.08Sr0.47MnO3 thin films

The growth of low bandwidth manganite thin films having optical magnetic and transport properties has been found to be extremely difficult. In the present study we have prepared thin films of a low bandwidth manganite Sm0.45Nd0.08Sr0.47MnO3 and carried out detailed study of microstructural and magnetotransport properties. Thin films (thickness ~36 nm and ~80 nm) of Sm0.45Nd0.08Sr0.47MnO3 were grown by dc magnetron sputtering on (001) oriented LaAlO3 single-crystal substrate and post-annealed in oxygen. The x-ray diffraction (θ–2θ) shows that the as grown films, irrespective of the thickness are under extremely high compressive strain, which is only partially relaxed by post deposition annealing in oxygen. High resolution x-ray diffraction (ω–2θ scans) shows the occurrence of Pendellosung fringes in the ~36 nm film, which appear to get disordered in the thicker ~80 nm film. This shows that the films have grown epitaxially at lower thickness and at higher thickness the microstructural degradation destroys its global nature. The epitaxial growth is confirmed by occurrence of step-terrace morphology in the 36 nm film, which, however, appears to be less prominent at higher film thickness of ~80 nm. The as-grown films do not show any insulator metal transition and only weak paramagnetic-to-ferromagnetic transition is observed. The O2 annealed 36 nm film shows a broad paramagnetic to ferromagnetic transition at ≈100 K but no insulator–metal transition is seen. Magnetic field (H) produces insulator metal transition and colossal decrement in the resistivity (ρ) in the 36 nm film. At T < T C, ρ–H curves show strong hysteresis, which is a signature of a first-order phase transition. In the 80 nm a paramagnetic insulator to ferromagnetic metal transition occurs at T C ≈ 145 K but magnetic field induced colossal decrease in resistivity and the ρ–H hysteresis is reduced considerably. Our results clearly show that the electrical transport is strongly influenced by the phase separation in these films. The differences in the magnetic properties and magnetic field dependent electrical transport behaviours are attributed to the modulation of the phase separated state due to the strain induced variation in the fraction of the competing ferromagnetic metallic and antiferromagnetic-charge ordered insulating phases.