Influence of Permanent Magnetic Properties on Laser-Assisted Heating Magnetization for Magnetic MEMS

When magnetic microelectromechanical systems (MEMS) devices utilize thin- or thick-film permanent magnets, the uniform magnetization of these magnets, owing to their flat-shape, generate a strong antimagnetic field and weak surface magnetic flux density. This study proposes a laser-assisted micro multi-pole magnetization method that reduces the antimagnetic field and generates a high surface magnetic flux density. The proposed method involves locally reducing the coercivity through laser-assisted heating and an external reverse magnetic field to selectively reverse the magnetization in heated areas, thereby generating fine and different magnetic patterns on permanent magnets. This study experimentally investigates the relationship between the magnetic properties of twelve NdFeB magnet samples (residual flux density (
$\text{B}_{\mathrm {r}}$
):1.20-1.39 T and intrinsic coercivity (
$\text{H}_{\mathrm {cj}}$
):955-2388 kA/m) magnetized using the proposed method and the resulting surface magnetic flux densities. Here, the magnetization ratio is introduced as the ratio of the measured to the analyzed surface magnetic flux density. The experimental results reveal that the magnetization ratio increases with an increase in
$\text{H}_{\mathrm {cj}}$
. The highest achieved surface magnetic flux density was 391 mTp-p with a
$\text{B}_{\mathrm {r}}$
of 1.3 T and
$\text{H}_{\mathrm {cj}}$
of 2388 kA/m. The magnetization ratio was 78.5%. Hence, a higher
$\text{H}_{\mathrm {cj}}$
suppressed the demagnetization. The magnetization ratio peaks around
$\text{B}_{\mathrm {r}}=1.29$
T. A higher
$\text{B}_{\mathrm {r}}$
promotes magnetization reversal, thereby making demagnetization easier. To increase the magnetization ratio and surface magnetic flux density, a permanent magnet with the highest possible
$\text{H}_{\mathrm {cj}}$
and optimal
$\text{B}_{\mathrm {r}}$
for the magnetization state must be selected. This study has great potential for the development of magnetic MEMS devices.