Murali Krishnan | National Aerospace Laboratories (original) (raw)
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Papers by Murali Krishnan
The magnetic electrodes with perpendicular magnetic anisotropy (PMA) have gained a great deal of ... more The magnetic electrodes with perpendicular magnetic anisotropy (PMA) have gained a great deal of attention in magnetic information storage technology. The use of perpendicular magnetic tunnel junctions (p-MTJs) enhances the storage density due to the reduction in area required for a unit bit. Among two electrodes in a MTJ structure (ferromagnetic/insulator/ferromagnetic), one electrode should be fixed or pinned to a specific direction of magnetization in order to have a unidirectional magnetic anisotropy with higher exchange field 1 . This can be achieved by a phenomenon of exchange bias observed between the ferromagnetic (FM) and the anti-ferromagnetic (AFM) materials as a shift in the hysteresis loop when they are deposited in the presence of an external applied field 2 .
Journal of Magnetism and Magnetic Materials, 2013
ABSTRACT We investigated the structural and magnetic properties o fSmCo5/Co exchange coupled nano... more ABSTRACT We investigated the structural and magnetic properties o fSmCo5/Co exchange coupled nanocomposite thin films grown by magnetron sputtering from Sm and Co multitarget ssuccessively.The growth of the films was carried out at elevated substrate temperature followed by insitu annealing. On Si(100) substrate, X-ray diffraction confirms the formation of texture d (110) SmCo5 hard phase,whereas on MgO (110) substrate,the diffraction pattern shows the epitaxial growth of SmCo5 phase with crystalline orientation along[100] direction.Secondary Ion Mass Spectroscopy reveals the structural transformation from multilayered (Sm/Co) to SmCo5/Co nano-composite films due to high reactivity of Sm at elevated temperature.Transmission electron microscopy indicates the existence of nanocrystalline phase of SmCo5 along with unreacted Co.Observed single phase behavior in magnetic hysteresis measurements indicates well exchange coupling between the soft and the hard phases in these nano-composite films. For samples with samarium layer thickness, tSm = 3.2 nm and cobalt layer thickness, tCo=11.4nm, the valuesof of BHmax were obtained as 20.1MGOe and 12.38MGOe with Hc value ∼3:0 kOe grown on MgO and Si substrates,respectively.
Journal of Applied Physics, 2013
ABSTRACT The angular dependence of magnetic properties was investigated in Co nanowire (NW) array... more ABSTRACT The angular dependence of magnetic properties was investigated in Co nanowire (NW) array with varying length grown by pulse electrochemical route. In these investigations, three different NW lengths, 200, 400, and 1000 nm were considered. Detail structural investigation revealed the formation of hcp (002) texture for NW of length 200 nm. However, the existence of both hcp (002) and hcp (100) oriented texture was observed in longer NW of length 1000 nm. It was established that these two phases were well separated along the axis of the NW with lower segment having hcp (002) and upper segment with hcp (100) oriented texture. Micromagnetic simulation was carried out to correlate the experimentally obtained angular dependent magnetization reversal results with simulated data considering the different crystallographic structures as a function of NW length, and with the variation of angle between the applied magnetic field and NW axis. Inference was drawn from these correlations that the magnetization reversal occurs by coherent rotation in case of NW with sole hcp (002) structure, whereas vortex state formation plays an important role for hcp (100) structure. In case of bilayer structure, the interaction between these two states leads to a gradual crossover from a coherent state to a vortex one along the NW axis. Effort has also been made to explain the angular dependence of coercive field by micromagnetic simulation irrespective of the NW length.
Bulletin of Materials Science, 2011
Applied Physics Letters, 2013
ABSTRACT Cobalt nanowire arrays with varying length were grown by pulse electrochemical route int... more ABSTRACT Cobalt nanowire arrays with varying length were grown by pulse electrochemical route into the pores of alumina template. The structural investigation reveals that at the bottom of the nanowire, it grows with hcp (002) structure up to few hundred nanometer in length and then changes its crystal orientation to hcp (100) phase as it further grows along the wire axis. The variation of measured coercivity and the remanent ratio as a function of nanowire length indicate that each nanowire in array grows with three different segments. The micromagnetic simulations carried out on these structures are then correlated with experimental observations.
... Raghuvaran, K and Krishnan, M and Shivakumara, C and Barshilia, Harish C and Rajam, KS (2010)... more ... Raghuvaran, K and Krishnan, M and Shivakumara, C and Barshilia, Harish C and Rajam, KS (2010) Anodic alumina template assisted growth of Co nano-wires. In: International Conference on Nanomaterials and Nanotechnology, 13-16 Dec 2010, KS Rangasamy College of ...
Advanced Science Letters, 2012
![Research paper thumbnail of High coercivity through texture formation in SmCo[sub 5]/Co multilayers](https://attachments.academia-assets.com/66706855/thumbnails/1.jpg)
](First-principles studies of interlayer exchange coupling in (Ga, Cr)N-based diluted magnetic semi... more First-principles studies of interlayer exchange coupling in (Ga, Cr)N-based diluted magnetic semiconductor multilayers J. Appl. Phys. 113, 054302 (2013) What does a first-order reversal curve diagram really mean? A study case: Array of ferromagnetic nanowires J. Appl. Phys. 113, 043928 Interaction effects and transport properties of Pt capped Co nanoparticles J. Appl. Phys. 113, 043917 Exchange coupling and coercivity enhancement in cuprate/manganite bilayers Appl. Phys. Lett. 102, 032401 Cation and magnetic orders in MnFe2O4 from density functional calculations Abstract. We have shown that high coercivity in SmCo 5 /Co multilayer exchange spring magnet can be obtained on silicon substrates as well. This is achieved by annealing the as-grown sample at an optimum temperature that favors texture formation. This compares well with multilayers grown on MgO substrates and post-annealed at the same temperature.
The magnetic electrodes with perpendicular magnetic anisotropy (PMA) have gained a great deal of ... more The magnetic electrodes with perpendicular magnetic anisotropy (PMA) have gained a great deal of attention in magnetic information storage technology. The use of perpendicular magnetic tunnel junctions (p-MTJs) enhances the storage density due to the reduction in area required for a unit bit. Among two electrodes in a MTJ structure (ferromagnetic/insulator/ferromagnetic), one electrode should be fixed or pinned to a specific direction of magnetization in order to have a unidirectional magnetic anisotropy with higher exchange field 1 . This can be achieved by a phenomenon of exchange bias observed between the ferromagnetic (FM) and the anti-ferromagnetic (AFM) materials as a shift in the hysteresis loop when they are deposited in the presence of an external applied field 2 .
Journal of Magnetism and Magnetic Materials, 2013
ABSTRACT We investigated the structural and magnetic properties o fSmCo5/Co exchange coupled nano... more ABSTRACT We investigated the structural and magnetic properties o fSmCo5/Co exchange coupled nanocomposite thin films grown by magnetron sputtering from Sm and Co multitarget ssuccessively.The growth of the films was carried out at elevated substrate temperature followed by insitu annealing. On Si(100) substrate, X-ray diffraction confirms the formation of texture d (110) SmCo5 hard phase,whereas on MgO (110) substrate,the diffraction pattern shows the epitaxial growth of SmCo5 phase with crystalline orientation along[100] direction.Secondary Ion Mass Spectroscopy reveals the structural transformation from multilayered (Sm/Co) to SmCo5/Co nano-composite films due to high reactivity of Sm at elevated temperature.Transmission electron microscopy indicates the existence of nanocrystalline phase of SmCo5 along with unreacted Co.Observed single phase behavior in magnetic hysteresis measurements indicates well exchange coupling between the soft and the hard phases in these nano-composite films. For samples with samarium layer thickness, tSm = 3.2 nm and cobalt layer thickness, tCo=11.4nm, the valuesof of BHmax were obtained as 20.1MGOe and 12.38MGOe with Hc value ∼3:0 kOe grown on MgO and Si substrates,respectively.
Journal of Applied Physics, 2013
ABSTRACT The angular dependence of magnetic properties was investigated in Co nanowire (NW) array... more ABSTRACT The angular dependence of magnetic properties was investigated in Co nanowire (NW) array with varying length grown by pulse electrochemical route. In these investigations, three different NW lengths, 200, 400, and 1000 nm were considered. Detail structural investigation revealed the formation of hcp (002) texture for NW of length 200 nm. However, the existence of both hcp (002) and hcp (100) oriented texture was observed in longer NW of length 1000 nm. It was established that these two phases were well separated along the axis of the NW with lower segment having hcp (002) and upper segment with hcp (100) oriented texture. Micromagnetic simulation was carried out to correlate the experimentally obtained angular dependent magnetization reversal results with simulated data considering the different crystallographic structures as a function of NW length, and with the variation of angle between the applied magnetic field and NW axis. Inference was drawn from these correlations that the magnetization reversal occurs by coherent rotation in case of NW with sole hcp (002) structure, whereas vortex state formation plays an important role for hcp (100) structure. In case of bilayer structure, the interaction between these two states leads to a gradual crossover from a coherent state to a vortex one along the NW axis. Effort has also been made to explain the angular dependence of coercive field by micromagnetic simulation irrespective of the NW length.
Bulletin of Materials Science, 2011
Applied Physics Letters, 2013
ABSTRACT Cobalt nanowire arrays with varying length were grown by pulse electrochemical route int... more ABSTRACT Cobalt nanowire arrays with varying length were grown by pulse electrochemical route into the pores of alumina template. The structural investigation reveals that at the bottom of the nanowire, it grows with hcp (002) structure up to few hundred nanometer in length and then changes its crystal orientation to hcp (100) phase as it further grows along the wire axis. The variation of measured coercivity and the remanent ratio as a function of nanowire length indicate that each nanowire in array grows with three different segments. The micromagnetic simulations carried out on these structures are then correlated with experimental observations.
... Raghuvaran, K and Krishnan, M and Shivakumara, C and Barshilia, Harish C and Rajam, KS (2010)... more ... Raghuvaran, K and Krishnan, M and Shivakumara, C and Barshilia, Harish C and Rajam, KS (2010) Anodic alumina template assisted growth of Co nano-wires. In: International Conference on Nanomaterials and Nanotechnology, 13-16 Dec 2010, KS Rangasamy College of ...
Advanced Science Letters, 2012
First-principles studies of interlayer exchange coupling in (Ga, Cr)N-based diluted magnetic semi... more First-principles studies of interlayer exchange coupling in (Ga, Cr)N-based diluted magnetic semiconductor multilayers J. Appl. Phys. 113, 054302 (2013) What does a first-order reversal curve diagram really mean? A study case: Array of ferromagnetic nanowires J. Appl. Phys. 113, 043928 Interaction effects and transport properties of Pt capped Co nanoparticles J. Appl. Phys. 113, 043917 Exchange coupling and coercivity enhancement in cuprate/manganite bilayers Appl. Phys. Lett. 102, 032401 Cation and magnetic orders in MnFe2O4 from density functional calculations Abstract. We have shown that high coercivity in SmCo 5 /Co multilayer exchange spring magnet can be obtained on silicon substrates as well. This is achieved by annealing the as-grown sample at an optimum temperature that favors texture formation. This compares well with multilayers grown on MgO substrates and post-annealed at the same temperature.