Exchange bias and magnetic memory effect in hole doped Nd0.78Sr0.22CoO3 nanoparticles.

Nd0.78Sr0.22CoO3 nanoparticles having 89 nm average particle size are synthesized by standard sol-gel techniques. Structural and morphological characterization is performed by X-ray diffraction and FESEM images. DC magnetization studies in the range 1.6 K to 300 K reveal the disordered magnetic phase below 36 K. Existence of this disordered magnetic phase is substantiated by the magnetic memory effect. A significant upturn in the ZFC magnetization below 4.5 K, which is a signature of a dominant ferromagnetic (FM) component, is observed. This FM component may be attributed to the uncompensated (UC) spins at the surface of Nd0.78Sr0.22CoO3 nanoparticles. The presence of the interface of these two magnetic components with significantly different anisotropy results in the exchange bias effect.

Unraveling the Charge Transport Mechanism in Mechanochemically Processed Hybrid Perovskite Solar Cell.

The long-term operation of organic-inorganic hybrid perovskite solar cells is hampered by the microscopic strain introduced by the multiple thermal cycles during the synthesis of the material via a solution process route. This setback can be eliminated by a room temperature synthesis scheme. In this work, a mechanochemical synthesis technique at room temperature is employed to process CH3NH3PbI2Br films for fabricating perovskite solar cell devices. The solar cell device has produced a 957 mV Voc, a 16.92 mA/cm2 short circuit current density, and a 10.5% efficiency. These values are higher than the published values on mechanochemically synthesized CH3NH3PbI3. The charge transport properties of the devices are studied using DC conductivity and AC impedance spectroscopy, which show a multichannel transport mechanism having both ionic and electronic contributions. A much smaller defect density in the mechanochemically synthesized hybrid perovskite material is confirmed. A polarization assisted recombination mechanism is observed to have a dominant effect on the overall charge transport mechanism. However, no obvious grain boundary and intralayer lattice defect related responses are found in the perovskite layer. Interfacial charge transport and recombination are found to show major effects on both the temperature dependent and illumination dependent impedance spectra.