Detection of hydrogen by the extraordinary Hall effect in CoPd alloys

The effect of hydrogen adsorption on the extraordinary Hall phenomenon (EHE) in ferromagnetic CoPd films is studied as a function of composition, thickness, substrate, and hydrogen concentration in the atmosphere. Adsorption of hydrogen adds a positive term in the extraordinary Hall effect coefficient and modifies the perpendicular magnetic anisotropy with the respective changes in coercivity and remanence of hysteresis loops. Hydrogen sensitive compositions are within the Co concentration range of 20% ≤ x ≤ 50% with the strongest response near the EHE polarity reversal point x0∼ 38%. Depending on the film composition and field of operation, the EHE response of CoPd to low concentration hydrogen can reach hundreds of percent, which makes the method and the material attractive for hydrogen sensing.