Anomalous Hall effect of PdCo alloy thin films to detect low hydrogen concentration in air

The anomalous Hall effect of thin PdCo films (Pd_0.8Co_0.2 alloy films; 5, 15, and 30 nm thick) subjected to various hydrogen concentrations in the gas phase was investigated. The Hall voltage of the 15 and 30 nm thick PdCo films against an external magnetic field exhibited hysteresis, indicating the anomalous Hall effect of PdCo. The hydrogen absorption in the 5 nm PdCo film decreased the Hall voltage in all considered magnetic fields. Moreover, the slope of the Hall voltage around a zero magnetic field decreased. When N₂ was used as the carrier gas, the slope was proportional to the logarithm of the hydrogen concentration. For dry air, the slope differed from and was similar to that for N₂ below and above hydrogen concentrations of 0.5% and 1.0%, respectively. The adsorbed oxygen on the PdCo surface disturbed the dissolved hydrogen in PdCo at low hydrogen concentrations in dry air.