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Soumik Mukhopadhyay

Publications and source records attributed to Soumik Mukhopadhyay.

46 records · Page 3Linked to original sources
arXiv2014

Direct experimental evidence of multiferroicity in a nanocrystalline Zener polaron ordered manganite

We discuss the particle size driven tunability of the coexistence of ferromagnetism and ferroelectricity in Pr0.67Ca0.33MnO3(PCMO) with the help of x ray diffraction, magnetization, impedance spectroscopy, and remanent polarization measurements. The remanent polarization measurements using the positive up negative down method clearly prove the existence of ferroelectricity in PCMO with phase separation between Zener polaron(ZP) ordered P21nm and disordered Pbnm structures. We also find that the ferroelectric response is enhanced in nanocrystalline samples so long as ZP ordering is not destroyed while the long-range antiferromagnetic ordering at low temperature in bulk system is replaced by ferromagnetic correlations in nanoparticles. The conclusion that by reducing the crystallite size it might be possible to make ferromagnetism and ferroelectricity coexist near room temperature should be generally applicable to all ZP ordered manganites.

cond-mat.str-el↗
arXiv2010

Field-tunable stochasticity in the magnetization reversal of a cylindrical nanomagnet

The nature of magnetization reversal in an isolated cylindrical nanomagnet has been studied employing time-resolved magnetoresistance measurement. We find that the reversal mode is highly stochastic, occurring either by multimode or single-step switching. Intriguingly, the stochasticity was found to depend on the alignment of the driving magnetic field to the long axis of the nanowires, where predominantly multimode switching gives way to single-step switching behavior as the field direction is rotated from parallel to transverse with respect to the nanowire axis.

cond-mat.mes-hall↗
arXiv2010

Tracking random walk of individual domain walls in cylindrical nanomagnets with resistance noise

The stochasticity of domain wall (DW) motion in magnetic nanowires has been probed by measuring slow fluctuations, or noise, in electrical resistance at small magnetic fields. By controlled injection of DWs into isolated cylindrical nanowires of nickel, we have been able to track the motion of the DWs between the electrical leads by discrete steps in the resistance. Closer inspection of the time-dependence of noise reveals a diffusive random walk of the DWs with an universal kinetic exponent. Our experiments outline a method with which electrical resistance is able to detect the kinetic state of the DWs inside the nanowires, which can be useful in DW-based memory designs.

cond-mat.mes-hall↗
arXiv2010

Colossal enhancement of magnetoresistance in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ / Pr$_{0.67}$Ca$_{0.33}$MnO$_{3}$ multilayers: reproducing the phase-separation scenario

Colossal enhancement of magnetoresistance has been achieved over a broad temperature range which extends upto the room temperature, in ferromagnetic metal-charge ordered insulator manganite multi-layers. The artificially created phase coexistence in the multilayers reproduce the characteristic signatures of metastability in the magnetotransport properties commonly observed in electronically phase-separated manganites.

cond-mat.mes-hall↗
arXiv2006

Pinhole and tunneling conduction channels superimposed in magnetic tunnel junction: results and inferences

The influence of ballistic channels superimposed on tunneling conduction channels in magnetic tunnel junctions has been studied in a manganese oxide based tunneling device. Inversion of magnetoresistance has been observed in magnetic tunnel junctions with pinhole nanocontacts over a broad temperature range. The tunnel magnetoresistance undergoes a change of sign at higher bias and temperature. This phenomenon is attributed to the parallel conduction channels consisting of spin conserved ballistic transport through the pinhole contact where the transmission probability is close to unity and spin polarized tunneling across the insulating spacer with weak transmittivity. The results seem to resolve a controversy regarding ballistic magnetoresistance in ferromagnetic nanocontacts and establishes that ballistic magnetoresistance do exist even if the previous results are attributed to magnetostriction and magnetostatic force related artifacts.

cond-mat.mes-hall↗
arXiv2006

Giant enhancement of room temperature magnetoresistance in La_{0.67}Sr_{0.33}MnO_{3}/Nd_{0.67}Sr_{0.33}MnO_{3} multilayers

The metal-insulator transition temperature in CMR manganites has been altered and brought close to the room temperature by preparing La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO)/ Nd$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (NSMO) multilayers with ultra thin individual layers of LSMO and NSMO. The LSMO/NSMO multilayers with ultra thin individual layers of thickness of about $10Å$ exhibits 150% magnetoresistance at 270 K whereas LSMO/NSMO multilayers with moderate individual layer thickness of about $40Å$ each exhibits a mere 15% magnetoresistance at the same temperature. We have shown that the reduction in thickness of the individual layers leads to increased spin fluctuation which results in the enhancement of magnetoresistance.

cond-mat.mes-hall↗
arXiv2006

Inversion of magnetoresistance in magnetic tunnel junctions : effect of pinhole nanocontacts

Inverse magnetoresistance has been observed in magnetic tunnel junctions with pinhole nanocontacts over a broad temperature range. The tunnel magnetoresistance undergoes a change of sign at higher bias and temperature. This phenomenon is attributed to the competition between the spin conserved ballistic transport through the pinhole contact where the transmission probability is close to unity and spin polarized tunneling across the insulating spacer with weak transmittivity.

cond-mat.mes-hall↗
arXiv2005

Enhancement of low field magnetoresistance at room temperature in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Al$_{2}$O$_{3}$ nanocomposite

Magnetotransport properties in a nanocrystalline La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/micron sized Al$_{2}$O$_{3}$ granular composite with different concentrations of Al$_{2}$O$_{3}$ have been studied. The resistivity curves in absence of magnetic field and the various transport mechanisms which might account for the upturn in resistivity at low temperature, has been discussed. Enhancement of low field magnetoresistance at room temperature with the introduction of Al$_{2}$O$_{3}$ has been observed.

cond-mat.mtrl-sci↗
arXiv2005

Anomalous bias dependence of tunnel magnetoresistance in a magnetic tunnel junction

We have fabricated a spin-polarized tunneling device based on half metallic manganites incorporating $Ba_{2}LaNbO_{6}$ as insulating barrier. An anomalous bias dependence of tunnel magnetoresistance (TMR) has been observed, the first of its kind in a symmetric electrode tunnel junction with single insulating barrier. The bias dependence of TMR shows an extremely sharp zero bias anomaly, which can be considered as a demonstration of the drastic density of states variation around the Fermi level of the half metal. This serves as a strong evidence for the existence of minority spin tunneling states at the half-metal insulator interface.

cond-mat.mtrl-sci↗