Visualizing hydrogen diffusion in magnetic film through magneto-optical Kerr effect

Abstract

The kinematics of hydrogen diffusion in nontransparent metallic materials is crucial to the hydrogen-sensing and-storage technology and remains a challenge. Alongside the conventional optical investigations, the hydrogen absorption-induced reversible changes of magnetic properties in ferromagnetic thin films provides a new method for visualization of hydrogen in solids. Here we monitor real-time hydrogen diffusion in a cobalt-palladium alloy (Co 25 Pd 75) film using a magneto-optical Kerr microscope. The spatially resolved magneto-optical contrasted images provide a noninvasive method of monitoring hydrogen movement. Hydrogen diffusion follows Fick's diffusion law, and a diffusion coefficient of 3 ± 2 × 10 −12 m 2 /s is obtained. The diffusion velocity of the 2-4% hydrogen concentration fronts reaches 30 ± 15 nm/s in the uniform film area and increases to 50 ± 20 nm/s near a defect site. These results can be applied in detecting hydrogen diffusion in other spintronic materials, such as magnetic palladium-alloy thin films.

Hydrogen tunes magnetic anisotropy by affecting local hybridization at the interface of a ferromagnet with nonmagnetic metals

“…At ambient conditions, these films show an easy magnetization axis that is perpendicular to the film plane, while after hydrogen insertion, magnetization undergoes a 90 • rotation to become in-plane. The applicability of a Co/Pd heterostructure as low-pressure hydrogen sensors has also been recently demonstrated based on the H 2 -dependent variation of magnetic anisotropy observed through ferromagnetic resonance [18,19] or magneto-optic Kerr effect measurements [20]. In addition to magnetic anisotropy, hydrogenation of magnetic structures was employed to manipulate noncollinear magnetic states by reversibly tuning the Dzyaloshinskii-Moriya interaction [21,22] and stabilizing the formation of skyrmions (e.g., at the Fe/Ir interface [23,24]).…”

Exchange-bias dependent diffusion rate of hydrogen discovered from evolution of hydrogen-induced noncollinear magnetic anisotropy in FePd thin films

“…The FePd thin film is investigated using longitudinal MOKE microscopy with the Kerr sensitivity along the magnetic field to capture the images of the magnetic domains during measurements of its hysteresis loops [13].…”

“…As hydrogenation is found to be able to manipulate noncollinear magnetic states by reversibly tuning the Dzyaloshinskii-Moriya interaction [7][8][9][10], related research is drawing more attention for possible applications. The applicability of CoPd heterostructures or alloys as hydrogen sensors has recently been demonstrated through hydrogen-dependent variation of the magnetic anisotropy observed via ferromagnetic resonance [11,12] or magneto-optic Kerr effect (MOKE) microscopy [13].…”

“…Reversible changes of magnetic properties of ferromagnetic thin films such as magnetic Pd alloy films induced by hydrogenation are therefore being intensively investigated for the study of hydrogen diffusion. Among the measurement techniques of magnetic properties, MOKE microscopy has long been broadly applied in probing nanoscale structures because of its high sensitivity and feasibility in monitoring the evolutions of the magnetic domains, and therefore becomes a powerful tool to track hydrogen diffusion [13].…”

Magneto-electronic hydrogen gas sensors: a critical review

“…The burgeoning interests in thin films and nanotechnologies have motivated the development of a number of innovative spectroscopy and microscopy tools, some of which exploit the magneto-optical effects [27][28][29][30] to investigate physical properties of magnetic materials [54][55][56][57]. For example, the magneto-optical Kerr effect (MOKE) represents a change in the polarisation and intensity of light that is reflected from the surface of a magnetic material.…”