arXiv subjects

Ashok Kumar

Publications and source records attributed to Ashok Kumar.

93 records · Page 6Linked to original sources

arXiv2010

Magnetic Effects on Dielectric and Polarization Behavior of Multiferroic Hetrostructures

PbZr0.52Ti0.48O3/La0.67Sr0.33MnO3(PZT/LSMO) bilayer with surface roughness ~ 1.8 nm thin films have been grown by pulsed laser deposition on LaAlO3(LAO) substrates. High remnant polarization (30-54 micro C/cm2), dielectric constant(400-1700), and well saturated magnetization were observed depending upon the deposition temperature of the ferromagnetic layer and applied frequencies. Giant frequency-dependent change in dielectric constant and loss were observed above the ferromagnetic-paramagnetic temperature. The frequency dependent dielectric anomalies are attributed to the change in metallic and magnetic nature of LSMO and also the interfacial effect across the bilayer; an enhanced magnetoelectric interaction may be due to the Parish-Littlewood mechanism of inhomogeneity near the metal-dielectric interface.

cond-mat.mtrl-sci↗

arXiv2010

Processing and Characterization of Multiferroic Bi-relaxors

We compare chemical solution deposition (CSD), and pulsed-laser-deposition (PLD), specimens of the new room-temperature, single-phase, multiferroic magnetoelectric, [PbFe2/3W1/3O3]x[PbZr0.53Ti0.47O3]1-x (PZTFWx ~ 0.40<x<0.20) with polarization, loss (<1%), and resistivity (typically 108 ohm.cm) equal to or superior to BiFeO3. Single phase polycrystalline multiferroics PZTFWx thin films were fabricated on platinized silicon substrate by CSD and as epitaxial single-crystal films on MgO substrate by PLD. High dielectric constants (1200- 3000), high polarization (30 - 60 micro C/cm2), weak saturation magnetization (0.48 - 4.53 emu/cm3), a broad dielectric temperature peak, high-frequency dispersion, low dielectric loss and low leakage current were observed in these materials, suggesting the family as candidates for room-temperature multiferroic devices. The ferroelectric switching in these materials can be suppressed or quenched with applied magnetic field.

cond-mat.mtrl-sci↗

arXiv2009

Magnetic control of large room-temperature polarization

Numerous authors have referred to room-temperature magnetic switching of large electric polarizations as The Holy Grail of magnetoelectricity.We report this long-sought effect using a new physical process of coupling between magnetic and ferroelectric relaxor nano-regions. Here we report magnetic switching between the normal ferroelectric state and the ferroelectric relaxor state. This gives both a new room-temperature, single-phase, multiferroic magnetoelectric, PbZr0.46Ti0.34Fe0.13W0.07O3, with polarization, loss (<4%), and resistivity (typically 108 -109 ohm.cm) equal to or superior to BiFeO3, and also a new and very large magnetoelectric effect: switching not from +Pr to negative Pr with applied H, but from Pr to zero with applied H of less than a Tesla. This switching of the polarization occurs not because of a conventional magnetically induced phase transition, but because of dynamic effects: Increasing H lengthens the relaxation time by x500 from <200 ns to >100 ?s, and it couples strongly the polarization relaxation and spin relaxations. The diverging polarization relaxation time accurately fits a modified Vogel-Fulcher Equation in which the freezing temperature Tf is replaced by a critical freezing field Hf that is 0.92 positive/negative 0.07 Tesla. This field dependence and the critical field Hc are derived analytically from the spherical random bond random field (SRBRF) model with no adjustable parameters and an E2H2 coupling. This device permits 3-state logic (+Pr,0,negative Pr) and a condenser with >5000% magnetic field change in its capacitance.

cond-mat.mtrl-sci↗