line decor


Current Research Projects

Past Research Projects



Events and News

Fabrication images




Nanotechnology will let us build computers that are incredibly powerful.

We'll have more power in the volume of a sugar cube than exists in the entire world today - Ralph Merkle


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 occur 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


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




University of Massachusetts:

217 Hasbrouck Laboratory

Department of Physics

Prof. Mark Tuominen Group

UMass Amherst

666 North Plesant Street

Amherst, MA-01003


Email: nihar@physics.umass.edu

Cell: 508-410-3551

Mount Holyoke College:

213 Kendade Hall

Department of Physics

Prof. Katherine Aidala Group

Mount Holyoke College

50 College Street

South Hadley, MA-01075


Email: npradhan@mtholyoke.edu

Ph: 413-538-3523