Palash Nath

Defect induced magnetism in planar silicene: a first principles study

We study here the magnetic properties of two dimensional silicene using spin polarized density functional theory. The magnetic properties were studied by introducing monovacancy and di-vacancy, as well as by doping phosphorous and aluminium into the pristine silicene. It is observed that there is no magnetism in the monovacancy system, while there is large significant magnetic moment present for the di-vacancy system. Besides, the numerical computation reveals that the magnitude of the magnetic moment is more when the system is doped with aluminium than phosphorous. All these theoretical predictions in this two dimensional system may shed light to open a new route to design silicon based nano-structures in spintronics.

Ab initio calculation of magnetic properties of p-block element doped ZnO

Recently, extensive calculations based on density functional theory (DFT) have been carried out to understand the origin of magnetism by doping ZnO, as observed experimentally. Theoretically, it has been understood that the main source of the magnetic moment arises from the unpaired 2p electrons at O sites surrounding the Zn vacancy. In the present work, we try to understand the reason for induced magnetic moment in ZnO by replacing O, using different p-block elements. We have studied the effective magnetic moments of the Zn54O53X (X = B, C, N, Al, Si, P, Ga, Ge, As) system in the framework of density functional theory. Our calculations suggest that partial substitution of the oxygen atom by a foreign element can induce magnetism in ZnO, and the amount of induced magnetic moment depends upon the electronegativity and the size of the doping element with respect to the oxygen atom.

Room temperature ferromagnetic ordering in 4?MeV Ar5+ irradiated TiO2

Room temperature ferromagnetic ordering has been observed in a rutile TiO2 polycrystalline sample after 4 MeV Ar5+ ion irradiation. The sheet resistance of the irradiated sample decreases from 107 to 3 × 103 Ω cm−2. Ab initio calculation in the density-functional theory indicates that both oxygen vacancy (VO) and titanium vacancy (VTi) can lead to ferromagnetism. However, the drastic lowering of resistance and change of colour (from white to black) indicate the formation of VO. Experimental results along with the theoretical calculation suggest that presence of VO in the irradiated sample plays the main role in inducing ferromagnetism.

Defect driven ferromagnetism in SnO2: a combined study using density functional theory and positron annihilation spectroscopy

Room temperature ferromagnetic ordering has been observed in a high purity polycrystalline SnO2 sample due to irradiation of 96 MeV oxygen ions. Ab initio density functional theory calculation indicates that tin vacancies are mainly responsible for inducing the magnetic moment in SnO2 whereas oxygen vacancies in SnO2 do not contribute any magnetic moment. Positron annihilation spectroscopy has been employed to characterize the chemical identity of irradiation generated defects in SnO2. Results indicate the dominant presence of Sn vacancies in O ion irradiated SnO2. The irradiated sample turns out to be ferromagnetic at room temperature.

Kardar–Parisi–Zhang universality class of a discrete erosion model

We investigate a novel (d + 1)-dimensional discrete erosion model for d = 1, 2 and 3. The dynamics of the model is controlled by the physically motivated erosion mechanism. The coarse grained nature of this erosion process has been well compared with the Kardar–Parisi–Zhang (KPZ) equation. The kinetic roughening of the discrete model shows the same scaling behavior as that of the KPZ equation in the dimensions d = 1, 2. Moreover, in this present discrete model in (3 + 1)-dimension almost smooth interface has been obtained with vanishingly small roughness exponent, indicating the model belongs to the weak coupling regime of KPZ universality class.

Observation of nonuniversal scaling exponent in a novel erosion model

In this present numerical work, we report a discrete erosion kind of model in (1 + 1)-dimension. Erosion and re-deposition phenomena with probabilities p and q(= 1 - p) are considered as two tunable parameters, which control the overall kinetic roughening behavior of the interface. Redeposition or diffusion dominated erosion like kinetic roughening model gives rise to nonuniversal growth exponent, which varies continuously with respect to erosion probability. However, universal character is restored for the roughness exponent with the value of 0.5 in (1 + 1)-dimension with respect to p. Due to nonuniversal nature of growth exponent, we observe a significant modification to the scaling behavior of surface width with respect to erosion probability. For low erosion probability (≲ 0.1) a power law like divergence has been observed of the correlation growth time. This can be argued as limiting behavior of a generalized functional behavior of crossover time with erosion probability.