Abstract
In this study, the microscopic origin of the hydrogen effect on magnetic materials was explored through the characterization of time-dependent magnetic domain evolution. We prepared 25-nm Co30Pd70 alloy films with canted magnetic moment on SiO2/Si(001) substrates. From macroscopic Kerr hysteresis loops, considerable hydrogen-induced reduction of magnetic coercivity by a factor of 1/5 in a longitudinal direction and enhancement of magnetic remanence to saturation ratio from 60% to 100% were observed. The magnetic reversal behavior of the Co30Pd70 alloy films gradually transformed from nucleation- to domain-wall-motion dominance when H2 pressure was increased from a vacuum of 1 × 10−5 mbar to 0.8 bar. Domain size also increased considerably with H2 pressure. When H2 pressure was above 0.4 bar, the domain wall (DW) motion was clear to observe and the DW velocity was approximately 10−6–10−5 m/s. Greater hydrogen content in the Co30Pd70 alloy films promoted DW motion that was closer to the behavior of a thermally activated model. The hydrogen effects on magnetism were observed to be reversible and could have valuable future application in spintronic devices for hydrogen sensing.
Highlights
Owing to the strength of the interaction between Pd and hydrogen atoms, Pd has been used as an efficient catalyst for the dissociation of hydrogen molecules into individual hydrogen atoms[1,2,3,4]
When the Co30Pd70 alloy film was exposed to an environment filled with 0.2 bar H2 gas, the magnetic hysteresis loops became square, in which the remanence magnetization sustained the same value as the saturation value and magnetization reversal switched sharply as the magnetic field was close to the Hc
With the increase in H2 pressure from 0.2 to 0.8 bar, the magnetic hysteresis loops remained in a square-like shape and the Hc monotonically increased from 140 Oe to 194 Oe and from 200 Oe to 435 Oe for the longitudinal and polar geometry, respectively
Summary
Owing to the strength of the interaction between Pd and hydrogen atoms, Pd has been used as an efficient catalyst for the dissociation of hydrogen molecules into individual hydrogen atoms[1,2,3,4]. Lueng et al reported that nanopatterned Pd/Co films were candidates for future hydrogen gas sensing devices based upon their hydrogen-absorption-modified ferromagnetic resonance[16]. Their qualitative analysis demonstrated that the magnetoelastic contribution to hydrogen-induced change in perpendicular magnetic anisotropy (PMA) was negligible[17]. All the aforementioned research reported the effect of hydrogen on macroscopic magnetic properties, such as collective magnetic hysteresis loops, averaged magnetic moment, and ferromagnetic resonance. These results demonstrated the potential of using spintronic materials in hydrogen-related technologies. The experimental results fitted with theoretical models and the transition of domain reversal behavior are discussed in this paper
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