Phase Diagram of Magnetic Nanodisks measured by SEMPA


S.-H. Chung1,2, R. D. McMichael1, D. T. Pierce1, and J. Unguris1                                                                       
1Center for Nanoscale Science and Technology, NIST, Gaithersburg, MD 20899
2Maryland NanoCenter, University of Maryland, College Park, MD 20742



The magnetic behavior of ferromagnetic nanodisks is technologically important due to the applications of these disks in magnetic data storage and magnetic memory devices. However, most previous experimental studies have measured the average properties of nanodisk arrays, or have imaged the magnetic domain structure of perpendicularly magnetized nanodisks using magnetic force microscopy (MFM). Determining the phase diagram of magnetic nanodisks has been a challenge for magnetic microscopy since it requires a non-invasive measurement of both the in-plane and out-of-plane magnetization components with high resolution. In this study, we use Scanning Electron Microscopy with Polarization Analysis (SEMPA) to image the magnetic domain structures of individual ferromagnetic nanodisks, and thereby determine the phase diagram of the magnetic ground states yielding a phase diagram as a function of diameter and thickness. A Permalloy wedge film was grown on a resist template patterned by electron beam lithography, followed by lift-off to create disks with diameters that range from 35 nm to 190 nm and with thicknesses that range from 10 nm to 65 nm. Depending on the nanodisk dimensions, we observe one of three distinct ground state magnetic configurations: a single domain in-plane, a single domain out-of-plane, or a vortex state. By systematically imaging Permalloy nanodisks with various diameters and thicknesses, we are able to locate phase boundaries and the triple point between the three phases, and to observe a mixture of the different phases near the phase boundaries and triple point. Furthermore, a magnetic phase diagram calculated by using the OOMMF micromagnetic simulator agrees well with the phase diagram determined by the SEMPA measurements. This work has been supported by the NIST-CNST/UMD-NanoCenter Cooperative Agreement.









Mentors Name: John Unguris

Division, Laboratory: CNST

Room, Building Mail stop: A247, Bldg. 216, Stop 6202

Tel: 301-975-3768

Fax: 301-926-2746



                                                                       Is your mentor a Sigma Xi Member?     No