Stable antiparallel domains in 3D corrugated magnetic thin films

Area of Science:

• Materials Science
• Nanotechnology
• Magnetism

Background:

• 3D magnetic textures in nanostructured materials are crucial for applications like non-conventional computing and magnetic field sensing.
• Characterizing these complex magnetic structures is challenging due to optical phenomena induced by nanostructure geometry.

Purpose of the Study:

• To investigate the magnetization and magneto-optical properties of a ferromagnetic thin film deposited on a silicon nanograting.
• To understand how the nanograting's topography influences magnetic texture and magneto-optical Kerr effect (MOKE) signals.
• To develop a method for characterizing sub-wavelength magnetic features in 3D corrugated materials.

Main Methods:

• Deposition of a continuous permalloy thin film onto a triangular silicon nanograting with 250 nm periodicity and 180 nm amplitude.
• Magneto-optical Kerr effect (MOKE) measurements using red (subwavelength) and violet (diffraction) light regimes.
• Optical modeling and micromagnetic simulations.
• Magnetic force microscopy (MFM) for experimental verification.

Main Results:

• The nanograting induces an unusual magnetic texture with features smaller than the light wavelength.
• Violet light, exciting surface plasmon polaritons, enhances the transverse Kerr signal by an order of magnitude and reverses the longitudinal Kerr signal compared to red light.
• Optical modeling reveals spatially non-uniform MOKE, localized at different grating regions depending on the light regime.
• Surface-MOKE measurements show a single easy axis and vanishing coercive fields symmetrically about the hard axis, consistent with antiparallel magnetic domains.
• Magnetic force microscopy confirms the nanoperiodic magnetic domain pattern.

Conclusions:

• The interplay between nanostructure geometry and light interaction significantly impacts MOKE measurements.
• Utilizing different optical regimes (red vs. violet light) allows for disentangling and characterizing complex 3D magnetic textures and domain reversals.
• This approach offers a novel pathway for detailed magnetic characterization of corrugated nanostructured materials.