Syed Rizwan

Giant electrical modulation of magnetization in Co40Fe40B20/Pb(Mg1/3Nb2/3)0.7Ti0.3O3(011) heterostructure

We report a giant electric-field control of magnetization (M) as well as magnetic anisotropy in a Co40Fe40B20(CoFeB)/Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) structure at room temperature, in which a maximum relative magnetization change (ΔM/M) up to 83% with a 90° rotation of the easy axis under electric fields were observed by different magnetic measurement systems with in-situ electric fields. The mechanism for this giant magnetoelectric (ME) coupling can be understood as the combination of the ultra-high value of anisotropic in-plane piezoelectric coefficients of (011)-cut PMN-PT due to ferroelectric polarization reorientation and the perfect soft ferromagnetism without magnetocrystalline anisotropy of CoFeB film. Besides the giant electric-field control of magnetization and magnetic anisotropy, this work has also demonstrated the feasibility of reversible and deterministic magnetization reversal controlled by pulsed electric fields with the assistance of a weak magnetic field, which is important for realizing strain-mediated magnetoelectric random access memories.

One Dimensional Graphitic Carbon Nitrides as Effective Metal-Free Oxygen Reduction Catalysts

To explore the effect of morphology on catalytic properties of graphitic carbon nitride (GCN), we have studied oxygen reduction reaction (ORR) performance of two different morphologies of GCN in alkaline media. Among both, tubular GCN react with dissolved oxygen in the ORR with an onset potential close to commercial Pt/C. Furthermore, the higher stability and excellent methanol tolerance of tubular GCN compared to Pt/C emphasizes its suitability for fuel cells.

The Gadolinium (Gd 3+ ) and Tin (Sn 4+ ) Co-doped BiFeO 3 Nanoparticles as New Solar Light Active Photocatalyst

The process of photocatalysis is appealing to huge interest motivated by the great promise of addressing current energy and environmental issues through converting solar light directly into chemical energy. However, an efficient solar energy harvesting for photocatalysis remains a critical challenge. Here, we reported a new full solar spectrum driven photocatalyst by co-doping of Gd3+ and Sn4+ into A and B-sites of BiFeO3 simultaneously. The co-doping of Gd3+ and Sn4+ played a key role in hampering the recombination of electron-hole pairs and shifted the band-gap of BiFeO3 from 2.10 eV to 2.03 eV. The Brunauer-Emmett-Teller (BET) measurement confirmed that the co-doping of Gd3+ and Sn4+ into BiFeO3 increased the surface area and porosity, and thus the photocatalytic activity of the Bi0.90Gd0.10Fe0.95Sn0.05O3 system was significantly improved. Our work proposed a new photocatalyst that could degrade various organic dyes like Congo red, Methylene blue, and Methyl violet under irradiation with different light wavelengths and gave guidance for designing more efficient photocatalysts.

Magnetoresistance effect in antiferromagnet/nonmagnet/antiferromagnet multilayers

The magnetoresistance (MR) effect between two antiferromagnetic layers separated by a nonmagnetic Cu layer was investigated. The MR ratio of 0.5% was observed in the structure of IrMn(8)/Cu(2.8)/IrMn(0.5)/CoFe(8) (in nanometers), where IrMn stands for Ir22Mn78 and CoFe for Co90Fe10. The study of different structures with and without top IrMn layer indicates that the MR effect originates from the giant magnetoresistance effect between the uncompensated magnetic moments at the IrMn interfaces across nonmagnetic Cu spacer.

Exchange-bias like hysteretic magnetoelectric-coupling of as-grown synthetic antiferromagnetic structures

The magnetoelectric (ME) coupling of CoFeB/Ru/CoFeB synthetic antiferromagnetic (SAF) structure is studied at room-temperature when the SAF structure was deposited on the (011)-Pb(Mg1/3Nb2/3)O3-PbTiO3 piezoelectric substrate. It was found that the magnetoelectric coupling showed butterfly like curve when measured in the absence of magnetic field but it showed hysteresis loop-like behavior as well as the exchange-bias like shift of the ME hysteresis under fixed magnetic fields of +250 Oe and +500 Oe. This exchange-bias like hysteretic ME coupling is attributed to the direct coupling of CoFeB layer with the substrate ferroelectric domain, the absence of magnetocrystalline anisotropy and the switching of 109° ferroelastic domains of the substrate. We have also measured the magnetoelectric coupling of CoFe/Ru/CoFe SAF structure but observed no exchange-bias like hysteresis behavior. Our results establish another way of obtaining the non-volatile memory devices based on magnetoelectric systems.

Ferroelectric-domain-controlled magnetic anisotropy in Co40Fe40B20/YMnO3 multiferroic heterostructure

We report on the magnetic properties of Co40Fe40B20/YMnO3 multiferroic heterostructures in which Co40Fe40B20 shows an in-plane uniaxial magnetic anisotropy with the magnetic easy axis along the ferroelectric polarization direction of YMnO3. The coercive field (Hc) of Co40Fe40B20 shows an interesting non-monotonic change from the easy axis to hard axis with a maximum at a certain angle. It was demonstrated that the magnetic property of Co40Fe40B20 was dominated by the FE domain induced strain and the angular dependence of Hc can be understood by the two phase model. This work is helpful for understanding the coupling between ferromagnetic and ferroelectric materials.

The high photocatalytic activity and reduced band gap energy of La and Mn co-doped BiFeO3/graphene nanoplatelet (GNP) nanohybrids

Recently, bismuth ferrites have attracted great interest in the field of photocatalysis due to their magnetic nature and narrow band gap. Herein, nanohybrids of lanthanum (La) and manganese (Mn) co-doped BiFeO3 (BLFMO)/graphene nanoplatelets (GNPs) have been synthesized. The hybrids were prepared by two different but simple and low-cost synthesis routes: (i) co-precipitation (namely the C-series), and (ii) hydrothermal (namely the H-series) methods. This article details a comparison of the C-series and H-series BLFMO/GNP nanohybrids based on their photocatalytic activity and band gap. The H-series nanohybrids showed a more crystalline structure, reduced band gap and less dye removal compared to the C-series nanohybrids. The enhanced dye removal (92%) of the C-series nanohybrids is attributed to their high surface area (55 m2 g−1) due to GNP incorporation inside the BLFMO/GNP nanohybrids. The higher surface area enables more adsorption of dye molecules over the catalyst surface under dark conditions. In addition, the band gap of the BLFMO/GNP nanohybrids was reduced from 2.04 eV (pure BiFeO3) to 1.40 eV (BLFMO/GNPs) because of the presence of new donor energy levels with Mn loading. The calculated particle sizes from Scherrer’s formula were 19.3–23.5 nm (C-series) and 22.5–26 nm (H-series). The estimated particle size calculated via transmission electron microscopy (TEM) is approximately 31 nm for the C-series nanohybrids. The graphene based nanohybrids significantly enhanced dye removal compared to pure BiFeO3 (44%) under visible light irradiation. The low cost, easy preparation and higher catalytic activity of the BLFMO/GNP nanohybrids reported here make nanohybrids suitable candidates for practical applications.

Mesoporous template-free gyroid-like nanostructures based on La and Mn co-doped bismuth ferrites with improved photocatalytic activity

Template-free and gyroid-like mesoporous nanostructures of La and Mn co-doped bismuth ferrites were fabricated using a simple and low-cost double solvent sol–gel technique. By carefully controlling the amount of precursors and precisely optimizing the calcination process, a well-ordered and crystalline La and Mn co-doped BiFeO3 gyroid-like mesoporous nanostructures network was obtained for photo-degradation applications. The substitution of Mn ions into the Fe sites resulted in a well-ordered mesoporous nanostructure with a flexibility for optical band-gap tuning up to a large extent. Catalytic photo-degradation of Congo red under visible light irradiation occurred at a much higher rate using the mesoporous nanostructures compared to pure BiFeO3 nanoparticles. Thus, large tunability of the band gap, high activity of the mesoporous nanostructure and stability were successfully achieved. The new fabrication method presented here is the first evidence to suggest that such a well-ordered, template-free, gyroid-like mesoporous nanostructure network can be fabricated for low-cost commercial applications.

Piezoelectric enhancement of giant magnetoresistance in spin-valves with different magnetic anisotropies

The phenomenon of giant magnetoresistance (GMR) in spin-valves under applied magnetic field is well established. We present piezoelectric control of the GMR ratio at room temperature for standard multilayered spin-valve structure fabricated on (011)-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) piezoelectric substrate. Four samples namely, S1, S2, S3, and S4 were, respectively, fabricated such that the magnetic easy axis makes an initial angle of 0°, 30°, 45°, and 60° with magnetic field applied during measurement. For S1, the GMR ratio decreases under electric field whereas it increases for the samples making progressively larger initial magnetization angles with the external field. We suggest that for S1, magnetic alignment between the two magnetic layers decreases due to the rotation of bottom free layer magnetization resulting in the decrease of antiparallel resistance as well as the GMR ratio under applied electric field whereas for the other samples, the antiparallel resistance increases due to improvement in an...

ELECTRIC-FIELD CONTROL OF GIANT MAGNETORESISTANCE IN SPIN-VALVES

It has been known that magnetic properties of a ferromagnet grown on piezoelectric substrates can be altered by the electric field-induced strain. We consider spin-valve CoFe/Cu/CoFe/IrMn grown on (011)-cut piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) substrate and investigate the effect of the electric field on the giant magnetoresistance (GMR) of the spin valve. We found that the electric field induced strain on PMN–PT substrate enhances the coercivity of the magnetic layers. The transport measurement shows that the GMR ratio of the spin valve could be altered as much as 50% for an electric field of -8 kV/cm. The change of GMR is attributed to the reduced maximum degree of the antiparallel alignment between the magnetization directions of the free and pinned layers. The present studies establish a prototype electrically tunable magnetic memory device such that the electric field can reversibly tune spin valve magnetoresistance without deteriorating electric and magnetic properties.