Panda S.,Trident Academy of Technology |
Kar J.K.,Orissa Engineering College, Bhubaneswar |
Rout G.C.,Condensed Matter Physics Group
Materials Research Express | Year: 2016
Weaddress the interplay of charge and magnetic orderings in colossal magnetoresistive material manganese oxides.Wepropose here on-site double exchange spin-spin interaction in the presence of Heisenberg-type spin-spin interaction in localized t2g core electrons.Weconsider charge-density wave (CDW) interaction in the crystal lattice as an extra mechanism in the itinerant eg band, to take into account of colossal magnetoresistance (CMR) in the system.Wecalculate electron Green's functions by Zubarev's Green's function technique and hence calculate the charge-ordering gap and magnetic gap in the conduction band as well as core electron states. These orders are solved selfconsistently for different model parameters of the system.Weobserve that the induced magnetic gap in the conduction band exists near the antiferromagnetic Néel temperature, which accounts for the CMRin the system. For all values of temperature, theCDWcoupling lies in the range of g=0.04 to 0.06, where the induced magnetic gap exists. The temperature-dependent specific heat exhibits anomalous jumps near charge-ordering and magnetic-ordering temperatures. The eg electron density of states exhibits a two-gap structure which explains tunneling conductance spectra measurements. © 2016 IOP Publishing Ltd.
Sahu S.,KIIT University |
Rout G.C.,Condensed Matter Physics Group
Journal of Magnetism and Magnetic Materials | Year: 2016
We present here a tight-binding model study of generation of magnetism and pseudo-spin polarization in monolayer graphene arising due to substrate, impurity and Coulomb correlation effects. The model Hamiltonian contains the first-, second- and third-nearest-neighbor hopping integrals for π electrons of graphene besides substrate induced gap, impurity interactions and Coulomb correlation of electrons. The Hubbard type Coulomb interactions present in both the sub-lattices A and B are treated within the mean-field approximation. The electronic Green's functions are calculated by using Zubarev's technique and hence the electron occupancies of both sub-lattices are calculated for up and down spins separately. These four temperature dependent occupancies are calculated numerically and self-consistently. Then we have calculated the temperature dependent pseudo-spin polarization, ferromagnetic and anti-ferromagnetic magnetizations. We observe that there exists pseudo-spin polarization for lower Coulomb energy, u<2.2t1 and pseudo-spin polarization is enhanced with substrate induced gap and impurity effect. For larger Coulomb energy u>2.5t1, there exists pseudo-spin polarization (p); while ferromagnetic (m) and antiferromagnetic (p m) magnetizations exhibit oscillatory behavior. With increase of the substrate induced gap, the ferromagnetic and antiferromagnetic transition temperatures are enhanced with increase of the substrate induced gap; while polarization (p) is enhanced in magnitude only. © 2016 Elsevier B.V.
Fahd C.,Condensed Matter Physics Group |
Anas H.,National School of Technology |
Otman A.,Electronics and Microwaves Group |
Mounia C.,Condensed Matter Physics Group |
Mounir E.Y.,Condensed Matter Physics Group
International Journal of Microwave and Optical Technology | Year: 2015
In this paper, Chirped Fiber Bragg Grating (FBG) has been introduced as a dispersion compensator in dense Wavelength Division Multiplexing (WDM) for optical long-haul network. The new model has been compared with a previous work proposed by other authors having DCF as dispersion compensator. Both configurations have been modeled and simulated using the same initial setting so as to prove the efficiency of our model. For this purpose, different parameters of the Chirped FBG which include chirp parameter, apodization function and grating length, have been investigated in order to get the most suitable settings of the proposed model. The WDM transmission system is simulated using the advanced tools of Optisystem 7.0. The simulation results have been examined and validated by analyzing the eye diagram for short and long channel lengths, the Q-factor, the BER analysis and nonlinear effects at WDM network. © 2015 IAMOT.