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Thanks for visiting my home page!
My
present research is mainly focusing on Ferromagnetic nanostructures such as
nanorings, nanowires
and thin films for higher efficient, high density data storage, MRAM,
sensors and other potential electronic applications. We fabricate high
quality of nanostructures ranges from few nanometers to few hundreds of
nanometer by using Top-down approach.
Ferromagnetic Nanoring: Ferromagnetic nanoring
exhibit unique magnetic configurations which does not seen in other
geometries. Nanoring exhibit onion state (where
two domain in the nanoring separated by two 1800DWs,
H-H and T-T magnetic spin configurations), vortex states (where no net
magnetization exist in a perfect symmetric ring, with magnetic moments
rotates either CW or CCW direction) and twisted state with partial
magnetization. More interestingly circular nanodisc
has some extra ordinary characteristic than the nanoring,
which forms vortex state in which magnetization forms closure structure
with a central magnetic core pointing either up or down possess 4-fold
degeneracy. The most recent research work is focused on investing new
magnetic states and controlling them by externally applied field such as
magnetic field, electric field/current and temperature. Magnetic states
possessed by particular ring structures depend upon their geometries. We
are working on ferromagnetic nanorings made of permalloy (NiFe) and Cobalt
materials, fabricated by Electron-Beam Lithography technique. We able to
fabricate high density (>15Giga rings/inch2) nanorings with different diameters ranges from 200-1000nm
outer diameter structures to study the dynamics of novel states exhibit in nanorings.
Symmetric nanoring
shows onion-vortex-onion switching or onion-onion switching via rotation of
DWs process with in-plane applied field. The local circular field given us opportunity to manipulate the DWs in each
individual ring geometry more precisely. We can control the vortex chirality directly from one CW-Vortex state to
CCW-Vortex state without following all the way along the hysteresis loop.
The local circular field we apply on the each ring structure generated by
passing current through a conducting AFM tip in contact mode. Micromagnetic study reveals formation of ±3600DW
by applying circular field (2π DW bit storage devices). We were able to verify this proposed
simulation study in experimentally. In the other hand asymmetric ring can
be tuned to 100% vortex switching by choosing the direction of
externally applied field.
The experimental technique that we developed make
possible to investigate most
reliable way to control the switching of magnetic states in ferromagnetic nanorings with different geometries by externally
applied azimuthal filed. Click here FOR
MORE ABOUT THIS RESEARCH
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Nihar R Pradhan
Postdoctoral Research Associate
Department of Physics, UMass
Amherst
Email: nihar@physics.umass.edu
, npradhan@mtholyoke.edu
Website: http://people.umass.edu/nihar/
Ph.D.
(2006-2009) Worcester Polytechnic Institute,
Worcester, MA, USA
Title
of Thesis: Thermal
Conductivity of Nanowires, Nanotubes and Polymer- Nanotube
Composites (Adviser:
Germano S Iannacchione)
Masters
(2005-2006), Worcester Polytechnic Institute, Worcester, MA, USA
My
research focuses on controlling magnetic states of Ferromagnetic nanorings and nanowires
for high density data storage and MRAM devices. The high sensitive
asylum MFP3D scanning probe microscope used to manipulate magnetic
states of individual nanorings of sizes
ranges from 500 - 1000nm diameters and 10 - 30nm thickness.
Excellence clean
room
facilities available at UMass Amherst used to fabricate high
quality nanoring and nanowire
sample.
Office Address
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University
of Massachusetts:
217 Hasbrouck Laboratory
Department of Physics
Prof. Mark Tuominen
Group
UMass Amherst
666 North Plesant
Street
Amherst, MA-01003
USA
Email: nihar@physics.umass.edu
Cell: 508-410-3551
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Mount
Holyoke College:
213 Kendade Hall
Department of Physics
Prof. Katherine Aidala
Group
Mount Holyoke College
50 College Street
South Hadley, MA-01075
USA
Email: npradhan@mtholyoke.edu
Ph: 413-538-3523
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