Magnetic Force Microscopy using Quartz Tuning Fork Yongho

Magnetic Force Microscopy using Quartz Tuning Fork Yongho Seo Center for Near-field Atom-photon technology, Seoul Nation University, Rep. of Korea & Department of Physics, University of Virginia Kyungho Kim, Hyunjun Jang, Wonho Jhe School of Physics and Center for Near-field Atom-photon technology, Seoul Nation University, Rep. of Korea

Quartz Tuning Fork as a Force Sensor Micro-machined Cantilever - optical deflection - laser diode - photo diode - optical alignment - addition actuator Quartz Crystal Tuning fork - Self actuating - Self sensing - No light - No alignment

Force Sensitivity of Quartz Tuning Fork Cantilever Tuning Fork f ~ 10 - 100 k. Hz k ~ 1 - 100 N/m f ~ 32 - 100 k. Hz k ~ 103 - 105 N/m Q ~ 102 ~ 10 nm dithering Q ~ 104 (106 in vacuum) < 1 nm dithering Force sensitivity (Qf/k) 1/2 • Low force sensitivity • Low thermal noise due to high stiffness • High resolution by small dithering amplitude

Previous works : MFM using tuning fork Hal Edwards, et. al. (1997) Todorovic and Schultz (1998)

Tuning Fork based Electrostatic force microscopy -Ferroelectrics -surface charge in Semiconductor f = 32. 768 KHz k = 1300 N/m Q = 1300 L = 2. 2 mm, t = 190 mm, w = 100 mm

EFM images using Tuning Fork Surface polarization images of PZT film poling 7 x 7 mm 2 Line drawing 0. 9 x 0. 9 mm 2 7 x 7 mm 2 Y. Seo, et al, Appl. Phys. Lett. 80 4324, (2002). dot 4 x 4 mm 2

Tuning Fork Based Magnetic Force Microscopy MFM contrast - magnetic force gradient between tip and sample Force gradient Frequency shift Phase shift Magnetic force - very weak force (~p. N) Lift mode - keep constant gap between tip and sample (~10 nm) - to avoid the strong short range topographic contrast

Approach Curve of MFM Approach Withdraw Shear force Attractive force f = 0. 1 Hz 0. 01 Hz 1 m. Hz high S/N ratio high frequency Sensitivity < 3 m. Hz

Tip Manufacture Electrochemical Etching - Co or Ni wire H 3 PO 4 Pt Co, Ni H 3 PO 4 D = 100 mm 10 mm

Tip Attachment -Attach the wire to the tuning fork and make a tip -Use home-made micromanipulator Pt Co, Ni Silver paint H 3 PO 4 Tuning fork

Tip & Tuning Fork epoxy Co or Ni tip L = 2. 2 mm, t = 190 mm, w = 100 mm spring constant, k = 1300 N/m

Shear Mode MFM Advantage of the shear mode MFM - Perpendicularly recorded sample -longitudinally polarized tip - monopole approximation

Magnetic Force Microscopy Images (a) shear mode, Co tip, perpendicular 100 Mbit / Inch 2 hard disk (b) shear mode, Co tip, parallel dithering (c) shear mode, Ni tip (d) tapping mode 30 x 30 mm 2

Lift Height & Dithering Amplitude Height (h) dependency Amplitude (a) dependency Tip h a Sample 13 x 3 mm 2 3 x 1 mm 2

High Resolution Tuning Fork Based MFM 1 Gbit/inch 2 hard disk Dithering Amplitude : 20 nm lift height : 50 nm Spatial resolution : 50 nm 2 x 2 mm 2

Summary • MFM using Tuning Fork • High resolution. • low power dissipation at low temperature. • No laser : dark environment. • Cryogenic experiment (Vortex in superconductor).