VFM2™ Variable Field Module for Magnetic AFM Applications
The Variable Field Module (VFM2) is an ideal option for researchers who want to apply high magnetic fields to their atomic force microscopy experiments.
Asylum Research has developed a second generation Variable Field Module (Figure 1) for the MFP-3D™ Atomic Force Microscopes (AFM). This module is useful for magnetic force microscopy (MFM), conductive AFM (C-AFM), and other applications where the sample’s properties are magnetic field dependent. The VFM2 can apply static magnetic fields up to ±0.8 Tesla (~1G resolution), parallel to the sample plane.
How it Works
The VFM2 has a unique design incorporating a motor driven permanent magnet. Figure 2 shows how the rotation of a powerful rare earth magnet translates into a variable field at the sample. Once a field value is reached, the motor is turned off and the field is maintained without residual heat, thermal drift, or mechanical vibration.
The VFM2 attaches to the MFP-3D XY sample scanner by means of the included quick release plate. Adjustable pole pieces allow for optimal choice between maximum required field, sample placement and minimum field gradients. Field intensity is software controllable. An integrated Hall sensor provides a quantitative measure of the applied magnetic field and closed loop feedback control between motor and sensor allow for linear field ramps. A beryllium copper non-magnetic cantilever clip that minimizes field distortion is included.
The image sequence in Figure 3 shows the application of an increasing magnetic field to a piece of PMR (Perpendicular Magnetic Recording) hard disk. The written bits are progressively degaussed as the in-plane magnetic field is increased from zero to >0.7 Tesla.
Figure 3 presents MFM phase images of a Terfenol-D disk with and without fields applied perpendicular to the magnetization. Figure 3(a) and 3(b) show the MFM phase signal with an applied 2000G field and after the field is removed, respectively. Figures 2(c) and 2(d) similarly show phase images with and without a -2000G field.
Optional High Voltage Tip Bias
For experiments where combined magnetic field and a high tip-sample voltage bias are required, such as for studies of ferroelectric and piezoelectric materials, the VFM2 HV Kit can be attached to the module with a few screws (Figure 5).
The VFM2 HV Kit also requires an MFP-3D AFM upgraded with the High Voltage Option, which includes:
MFP-3D and VFM2 are trademarks of Asylum Research.
Figure 1: The VFM2 Variable Field Module.
Figure 2: The strength and sign of the magnetic field applied to the sample depends on the rotation angle of the rare earth magnet. At 0° or 180°, the magnetic flux is shunted away from the sample by the soft iron armature and pole pieces. As the magnet rotates, more and more flux is channeled instead through the sample. At 90°, the field is maximized.
Figure 3: Five frames showing a piece of PMR hard disk degaussed with an in-plane ~0.7 Tesla magnetic field using the VFM2. Click to enlarge image.
Figure 4: MFM phase images of the Terfenol-D disk under a series of in-plane fields perpendicular to the magnetization. (a) MFM phase images taken at 2000G and (b) after field removal; (c) MFM phase images taken at -2000G and (d) after field removal. The direction of the magnetic field is indicated by the arrow. 10μm scan. Image courtesy of Shuhong Xie, Xiangtan University, China and JiangYu Li, University of Washington.
Figure 5: VFM2 with High Voltage Unit attached.