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Determining the Phase Boundary of Circle and Square Nanomagnets

Determining the Phase Boundary of Circle and Square Nanomagnets. Tim Morgan Scott Whittenburg AMRI. Abstract.

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Determining the Phase Boundary of Circle and Square Nanomagnets

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  1. Determining the Phase Boundary of Circle and Square Nanomagnets Tim Morgan Scott Whittenburg AMRI

  2. Abstract In the disk storage industry, there is a desire to have a higher capacity storage device. Magnets are used to read and write information in these disk storage devices. The shape of the magnet has been shown to highly affect the storage capacity. We have investigated the magnetic properties of circle and square nanomagnets to determine the equilibrium states. We examined different sizes and thicknesses for each shape to verify these phase domain lines. For circles, the single domain and vortex states are most stable; for squares, we see that the flower and leaf states are the ground states. We used the NIST code, OOMMF, to perform our micromagnetic calculations.

  3. Why Find Phase Boundary? • Semiconductor Industry: • Important to know stable states at different sizes and thickness for different shapes • Shape Anisotropy • Shape determines storage capacity • Product: High Capacity Storage Devices • Hard-drives • Memory

  4. Micromagnetic Calculations • Computational Methods • Create virtual nanomagnets • Computer calculates magnetic properties • OOMMF (NIST) • Object Oriented MicroMagnetic Framework • Java Programming • Created program to calculate phase boundary line for circles

  5. Circles • Calculated boundary where exchange energy equals demagnetization energy for different values of Q, a unit less anisotropy variable • Verified boundary with Micro Magnetic calculations • Found single domain state to be most stable underneath the phase boundary and vortex to be most stable above phase boundary

  6. Insert Graph of Circle Phase Boundary

  7. Squares • Determined boundary between stable states for different values of Q using Micro Magnetic calculations • Stable states varied for different values of Q • Q = 0 Above: Leaf | Below: Flower • Q = 0.01  Above: PseudoLeaf | Below: Flower • Q = 0.1  Above: Vortex | Below: Flower

  8. Insert Squares Chart Here

  9. References & Acknowledgements • H. Hoffmann and F. Steinbauer, J. Appl. Phys. 92, 5463 (2002) • R P Cowburn, J. Phys. D: Appl. Phys. 33, R1 (2000) • R. P. Cowburn and M. E. Welland, Physical Review B 58, 9217 (1998) • Scott L. Whittenburg, Magnetic Nanostructures, 425 (2002) • National Science Foundation (DMR-0243977) • Patrick Nichols

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