We report on the effect of compressive stress on the optical properties of graphene oxide using a wet ball milling technique. For this purpose, graphene oxide was prepared using the modified Hummer's method and subsequently processed with wet ball milling. X-ray diffraction infers a peak at 9.655˚ which is the allowed reflection for the graphene oxide. The Williamson-Hall method is used to quantify the strain on the 10 hrs and 20 hrs ball milled graphene oxide samples and is found to be 4.2% and 4.8% respectively. Although we applied strain on the graphene oxide, it actually helped to reduce the defects which are confirmed by the intensity drop-off of D-peak in Raman spectroscopy. Indeed there exists a band gap alteration of 0.14 eV for an applied compressive strain of ~4.8%, hinting that the reduction in oxygen functional groups and the same is confirmed with the Fourier Transform Infrared Spectroscopy (FTIR). The present results would be helpful in developing graphene oxide based flexible memories and optoelectronic devices.

Abstract:In this manuscript, we propose a method to prepare small flakes of DyCu 2 . On top of that we also report on the magnetocaloric effect and nature of magnetic transition of a strongly anisotropic DyCu 2 in its low dimension. Magnetization measurements were carried out in the temperature range of 5 -100 K and up to the maximum magnetic field strength of 50 kOe.Magnetic entropy change (ΔS M ) is estimated using the well-known Maxwell's equations and is found to be -4.31 J/kg -K. Indeed, the ΔS M peak broadened marginally compared with its bulk DyCu 2 and such a broadening can be attributed to significant increase in the total grain boundary volume. As these small flakes consists larger ΔS M values at temperatures higher than the Nѐel temperature (T N ), one can use them as a magnetic refrigerant material in a broad temperature range. We also plotted the M 2 vs. H/M (which are called as the Arrott plots) in order to find the nature of magnetic transition. Arrott plots infer that indeed there exists nonlinearity in M 2 vs.H/M behavior and such nonlinear behavior is ascribed to the random anisotropy or a random field that is present in the system.

No abstract

Abstract:We demonstrate the evidenced exchange bias properties of graphene nanoribbons (GNRs) with the negative magnetic field cooling. Upon the negative field cooling from 300 K to 5 K, the hysteresis loop shifts along the negative magnetic field axis, that coincides with the cooling field direction. This observation indicates that there exists a positive exchange bias in GNRs. Furthermore, enhanced exchange bias was observed when the polarity of field cooling is negative as compared with positive field cooling, hinting that there might be complex interplay between orbital and spin degrees of freedom. In addition, the variation of exchange bias and the coercive field as a function of negative cooling field is also studied.

No abstract