Detection of hydrogen by the extraordinary Hall effect in CoPd alloys

Abstract

Aviv, 69978 Tel Aviv, Israel 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 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 20%  x  50% with the strongest response near the EHE polarity reversal point 0~3 8%. Depending on the film composition and field of operation the EHE response of CoPd to low concentration hydrogen can reach hundreds percent, which makes the method and the material attractive for hydrogen sensing. 2 Introduction. Hydrogen is a combustible gas present in practically every chemical process. The detection and concentration measurement of hydrogen is of a paramount importance in limitless cases of human activity from chemical, metallurgical, semiconductor and nuclear power industry to the emerging hydrogen energy economy. Many types of hydrogen sensors are commercially available or are in development. Following the classification by Hübert et al 1 they can be divided in eight groups as: catalytic, thermal conductivity; electrochemical, resistance based, work function based, mechanical, optical and acoustic.Yet, there is a continued need for faster, more accurate and more selective detection of hydrogen gas. It was suggested recently 2 that accuracy and selectivity of gas detection in general and hydrogen in particular, could be improved by measuring two or more independent gas-dependent parameters, e.g. resistance and magnetization. To execute a sensitive magnetic measurement in a compact and handy apparatus it was proposed to use the extraordinary Hall effect (EHE), which is an electric replica of magnetization compatible with a standard four-probe resistance measurement. Successful implementation of the technique would enrich the gas detection arsenal by magnetic type of sensors using the spintronics effect. In this paper, we present a systematic study of hydrogen detection using the extraordinary Hall effect in thin CoPd films. Experimental.Polycrystalline CoxPd(100-x) films with Co atomic concentration x (at. %) varying over an entire range 0  x  100 were deposited by rf co-sputtering from Co and Pd targets onto room temperature glass and GaAs substrates. The base pressure prior to deposition was 5 × 10 -7 mbar. Sputtering was carried out at Ar-pressure of 5 × 10 -3 mbar. Composition of samples was controlled by rf-power of the respective sputtering sources. Co and Pd are

Resistivity Testing of Palladium Dilution Limits in CoPd Alloys for Hydrogen Storage

“…Co and Pd are soluble and form an equilibrium fcc solid solution phase at all compositions at room temperature [ 41 ]. Ferromagnetic CoPd alloys were used recently for magnetic and spintronics detection of hydrogen [ 42 , 43 , 44 , 45 ]. 15-nanometer-thick polycrystalline Co x Pd 100-x films were grown by rf-magnetron sputtering onto room-temperature glass substrates from two separate targets (99.99%) Co and Pd in the custom made deposition system., Co atomic concentrations covered the entire range 0 100.…”

Magneto-electronic hydrogen gas sensors: a critical review

“…It was found in [90] that thinner film samples would be more suitable for sensing applications because of their higher surface-to-volume ratio and since the absolute value of the measured signal increases when the film thickness is decreased. This proposed concept has been followed [14,70,[108][109][110][111][112][113] and its feasibility was further confirmed by demonstrations of detection of low concentration of H 2 using thin Pd/Co films as the sensor material [70,90,109,114,115]. In particular, it was shown that the EHE sensitivity of optimised samples could exceed 240% per 104 ppm at H 2 concentrations below 0.5% in the N 2 /H 2 atmosphere [90], thus providing a more than two orders of magnitude higher sensitivity compared with the competing resistivity-based sensor architectures.…”

Magnetic gas sensing: working principles and recent developments

“…Extra-ordinary Hall phenomena (EHE, eqn (6)-( 9)) are employed in ferromagnetic Co/Pd lms for hydrogen gas sensing applications. 15,49 Due to the high solubility of hydrogen in Pd, it is usually chosen to make stacked layers of Pd with the transition metal for H 2 sensing. The palladium lattice expands signicantly with the absorption of H 2 (0.15% for a-phase and 3.4% for b-phase), which leads to the formation of palladium hydride; this phenomenon is usually employed for the fabrication of H 2 sensors based on Co-Pd alloys and multi-layered lms.…”

“…From the detailed H 2 sensing studies, it was demonstrated that depending on the lm composition, thickness, and eld of operation, enhanced EHE response of the Co/Pd lms could be achieved and these types of materials emerge as an attractive candidate for magnetic gas sensing. 15,49 Hall effect-based sensors depend on the operating temperature, p-or n-type conductivity of the material, as well as on the lm composition, thickness, and eld of operation.…”