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We measured the magnetic hysteresis and coercivity of individual Co and Co0.8Fe0.2 bilayer nano-sized island structures formed on Cu (111) substrate using spin-polarized scanning tunneling microscopy. From the hysteresis taken on various sizes of islands, we found that the alloyed islands are ferromagnetic with out-of-plane magnetic anisotropy, same as the pure islands. Coercivity of the alloy islands, which is dependent on their size, was significantly reduced to ≈40% of that of the pure islands. Based on the Stoner–Wohlfarth model, we evaluated the amount of magnetic anisotropic energy and anisotropy constant for both pure and alloy islands. Since tunneling spectra taken on the alloy islands show upward shifts of the valence electronic states as compared to the pure ones, fewer electrons populated in the valence band of the alloy islands are presumably responsible for the reduction in the magnetic anisotropic energy.

${\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}$ bilayer nanomagnets formed on a Cu(111) substrate with the alloy composition of $x=0$, 0.2, 0.5, 0.8, and 1 were investigated using scanning tunneling microscopy (STM). The islands with $x=0$, 0.2, and 0.5 were further studied using spin-polarized STM. With $x=0.2$, the nanoislands exhibit triangular shapes similar to the pure Co islands with an upward shift in the peak energy of the minority $d$ state. On the other hand, at $x=0.5$, the appearance of the nanoislands evolve to a round shape, and the peak energy is distributed irregularly within the islands. A hexagonal shape and inhomogeneous electronic states similar to pure Fe islands are observed on the $x=0.8$ islands. The magnetic field dependence of the spin-sensitive signal revealed that the perpendicular anisotropy of the ${\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}$ alloy islands is persistent up to half of the Fe alloy composition.

CoPd alloy nanostructures and thin films were deposited on MoS2 flakes through e-beam evaporation at a high temperature (HT) (500 K) and at room temperature (RT) (300 K). In HT growth, CoPd nanoparticles assembled at the edge of the MoS2 flake. The nanoparticles formed parallel chains at the edge of each layer in multilayered MoS2. As indicated by the quenched photoluminescence, HT deposition resulted in a flat CoPd coverage with a roughness of ≤ ± 0.5 nm on a MoS2 terrace. By contrast, RT growth led to a relatively rough CoPd thin film on MoS2 (roughness ≤ ± 2 nm). The film comprised a merged nanoparticle assembly. The MoS2/SiO2 step edge played a crucial role in magnetic domain pinning such that the magnetic coercivity (Hc) of Pd/Co/MoS2 was smaller than that of Pd/Co/SiO2. Similarly, RT CoPd (8 nm)/MoS2 exhibited a parallelogram-shaped hysteresis loop with a relatively small Hc value compared with that of the square hysteresis loops of RT CoPd (8 nm)/SiO2. The hydrogenation of RT CoPd (8 nm)/MoS2 resulted in reversible Hc enhancement.

Because of the expected long spin-transport length of organic materials, the magnetic metal/organic interface is crucial to the application of organic spintronics. In this study, [Fe/C

The combination of yttrium iron garnet (Y3Fe2(FeO4)3, YIG) and ferromagnetic materials or antiferromagnetic materials has attracted much attention because of its potential in applications such as spin pumping. In this study, a high-temperature and oxygen-poor environment was used to deposit a CoOx top layer on YIG for the observation of magnetic modulation. The temperature- and saturation-field-dependent bias shift of the YIG hysteresis loop was observed. The complex modulation of the magnetic behavior originated from the magnetic coupling of the antiferromagnetic CoO and an additional interfacial coupling of the ferromagnetic CoOx. Depth-profiling X-ray photoemission spectroscopy revealed the nonuniform stoichiometric distribution in the 20-nm CoOx layer, which confirmed the origin of the various magnetic coupling effects on the bottom YIG layer. The comparative ferromagnetic resonance measurements also demonstrated the considerable magnetic coupling effect on the dynamic magnetism of the YIG.

In this study, 6-nm CoxPd1−x alloy films were deposited on MoS2 flakes at a high temperature (HT) of 200 °C. The morphology and magnetic properties of these flakes was studied. In contrast to the nanoparticle assembly fabricated through room-temperature deposition, HT growth led to a relatively uniform coverage on MoS2 flakes with a roughness of less than 1 nm. The flat CoxPd1−x alloy films form magnetic single domains on individual MoS2 flakes. For 6-nm Co0.5Pd0.5 and Co0.35Pd0.65, the magnetic coercivity (Hc) was approximately 50 Oe. Co0.5Pd0.5/MoS2 exhibited more distinct azimuthal angle-dependent magnetic behavior than that of Co0.35Pd0.65/MoS2. The different angle-dependent Hc variation for various MoS2 flakes could be attributed to the shape and demagnetization effect at the edge. After hydrogen exposure, the Hc of Co0.5Pd0.5/MoS2 was enhanced by 30% ± 10% and the magnetic domains extended over the MoS2 flakes, which indicated that H absorption in Co0.5Pd0.5 bridges magnetic coupling across the MoS2 edge.

Recent studies have shown promising results regarding the power conversion efficiency, band-gap tunability, and interfacial charge carrier ability of organic lead halide perovskites. In light of these fundamental abilities, we fabricated a heterostructure: MAPbBr 3 spin-coated on an FePd alloy layer, consisting of both magnetic and optical capabilities. The perovskite’s discrete coverage across the FePd underlayer was confirmed by atomic force microscope, as made up of separate disc-like nanostructures that stand at ∼ 400 nm in height and a size width of up to ∼ 2 µm. We studied the thermal endurance and the inter-facial diffusion stability between MAPbBr 3 and FePd alloy by post-annealing it to temperatures ranging 100–170 ∘ C. The instable interfacial effects of perovskite/FePd was observed at 120 ∘ C, as indicated by the drastic reduction in magnetic coercivity of FePd and the photoluminescence of MAPbBr 3 . This interfacial diffusion behavior between perovskite and FePd advances as the post-annealing temperature reaches 170 ∘ C, supported by the enhanced noise to Kerr signal ratio.

In this study, the self-assembly of surface nanoclusters on 10–20-nm-thick Co 50 Pd 50 (Co–Pd) alloy thin films deposited on the Al 2 O 3 (0001) substrate was systematically investigated. The time-dependent evolution of the nanocluster size and magnetic properties was monitored using an atomic force microscope (AFM) and the magneto-optical Kerr effect. When the Co–Pd alloy films were stored in an ambient environment, small nanodots gradually gathered to form large nanoclusters. Approximately 30 days after growth, a nanocluster array formed with an average lateral size of 100 ± 20 nm and average height of 10 ± 3 nm. After 100 days, the average lateral size and average height had increased to 140 ± 20 and 25 ± 5 nm, respectively. The AFM phase image exhibited a structured contrast on the nanocluster surface, indicating the nonuniform stiffness distribution of the nanoclusters. A microscopic Auger spectroscopy measurement suggested that in contrast to the Pd-rich signal in the flat area, the nanoclusters were cobalt- and oxygen-rich areas. Cross-sectional investigation through transmission electron microscopy coupled with energy dispersive spectroscopy showed that the nanoclusters were mostly composed of Co oxide. A uniform Pd-rich underlayer had been maintained underneath the self-assembled Co-oxide nanoclusters. With the formation of a Co-oxide nanocluster array and Pd-rich underlayer, the magnetic easy axis of the Co–Pd film gradually altered its direction from the pristine perpendicular to in-plane direction. Because of the change in the magnetic easy axis, the hydrogenation-induced spin-reorientation transition was suppressed with the evolution of the surface Co-oxide nanoclusters.

Because of the Pd-catalyzed hydrogen dissociation and absorption, magnetic Pd-alloys provide a model system for the investigation of the critical hydrogenation effect on magnetism. In this study, Co 50 Pd 50 (CoPd) alloy thin films were fabricated by e-beam-heated co-evaporation on Al 2 O 3 (0001) substrates. These films exhibited a thickness-dependent spin reorientation transition (SRT) from perpendicular direction to in-plane direction with increase of thickness. For 10-30 nm-thick CoPd alloy films with perpendicular magnetic anisotropy (PMA), hydrogenation triggered a SRT to an in-plane anisotropy. The reversibility of SRT was demonstrated by cyclicly changing the hydrogen gas pressure. Furthermore, hydrogenation-induced SRT randomized the magnetic domain orientation. The surface morphology of the CoPd thin films was composed of nanoclusters, which may play a crucial role in hydrogen dissociation and affect PMA. In comparison with a bare CoPd film, a stronger PMA and a less pronounced hydrogenation-induced SRT were observed in a Pd-capped CoPd film. These observations suggest that the hydrogen content in CoPd alloy films can drastically and reversibly modify PMA, inferring the possible hydrogenation-induced charge transfer and modulation of electronic structure in CoPd.

Electric field control of magnetism has many potential applications in magnetic memory storage, sensors and spintronics. Epitaxial heterostructure involving ferroelectric (FE), ferromagnetic (FM) materials is one of the possible routes towards the realization of devices exploiting sizable magnetoelectric effects. In this study, we prepared multiferroic composite ferromagnet/ferrite/ferroelectric thin films on SrTiO3(1 1 1) substrate by electron beam evaporation and pulsed laser deposition. This system represents a prototypical example of interface between body-centered-cubic Fe, spinel NCZF (Ni0.25Cu0.05Zn0.7Fe1.96O3.96) and perovskite PZT (PbZr0.52Ti0.48O3), respectively. Magnetoelectric effects measured as a function of bias voltage on these heterostructures have been investigated via magneto-optical Kerr effect (MOKE). The magnetic coercivity ( H c ) considerably decreased as a voltage was applied. The H c values exhibited the similar variation whether the applied voltage was positive or negative and the reversibility was demonstrated. The strain coupling-mediated magnetoelectric effect and local heating effect are supposed to be the possible origins of H c variation.

In this study, CoxPd1−x alloy thin films and microstructures were grown through an e-beam heated co-evaporation method on Al2 O3(0001) substrates. The Fourier transformation analysis of high-resolution transmission electron microscopy images revealed a structural transition from a partial crystalline structure in the bottom layer region to a well-ordered crystalline structure in the top layer region. Increasing the Pd content in the CoxPd1−x thin films shifted the magnetic anisotropy toward the perpendicular direction. Correspondingly, magnetic force microscopy revealed submicrometer-scale magnetic domain structures for CoxPd1−x thin films, where x = 37%–50%. By combining oblique deposition and a grid mask, this study fabricated a 1-dimensional (1-D) microstructured Co50 Pd50 thin film that exhibited uniaxial magnetic anisotropy (UMA). Hydrogenation exerted a more sensitive effect on the magnetic properties of this structured thin film than it did on those of a continuous thin film. After hydrogen absorption, the magnetic coercivity was enhanced by approximately 50% and squareness by more than 100%. The reversibility of the hydrogenation effect on the UMA was also demonstrated. These observations suggest that the 1-D microstructured Co Pd film is sensitive and suitable for applications related to sensing hydrogen gas.

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.

In this study, we examined the growth of Au over monolayer MoS2 flakes on SiO2/Si(001) substrates at a temperature range of 25–230 °C. Based on atomic force microscopy (AFM) images, a height reversal phenomenon was observed after deposition of 2–8 nm Au. Depending on the growth temperature and Au coverage, the height difference between the MoS2 flake and the SiO2 area reversed from a single layer height of MoS2 (∼+0.7 nm) to a range –1.0 to –3.5 nm. This indicates that, based on AFM data, the apparent height of Au/MoS2 is significantly lower than that of Au/SiO2. Scanning electron microscopy results indicate the different lateral nucleation size and shapes of Au coverage on the MoS2 and SiO2 surfaces. In addition, transmission electron microscopy images confirmed the two dimensional and three dimensional growth of Au on the MoS2 and SiO2 surfaces, respectively. The different growth modes of Au on the MoS2 and SiO2 surfaces led to significant changes in the apparent height and thus blocked electrical conduction. These results provide information about nucleation and morphology of Au coverage on MoS2/SiO2 and will be valuable for future applications.

The metal/oxide hetero-structure has attracted much attention in recent decades because of its potential in various applications such as heterogeneous catalysis. In particular, the combination of magnetic metal with an oxide thin film, e.g., the magneto-tunneling junction, has been widely studied and applied in data storage and spintronics. ZnO is one of the important semiconducting materials, not only for photoluminescence but also more importantly for its promising applications in spintronics. Transition metal-doped ZnO is predicted to be useful as a magnetic semiconductor for room-temperature (RT) application. Furthermore, ZnO exhibits the largest electromechanical response, among the known tetrahedral semiconductors, which makes it suitable for devices in microelectromechanical and communication systems.

In this study, we deposited Fe films on MoS2 flakes, and investigated the microscopic magnetic behavior on individual flakes. The MoS2 flakes were fabricated on SiO2/Si(1 0 0) substrates using chemical vapor deposition. Fe coverage was deposited on the MoS2 flakes by e-beam evaporation with a thin Pd capping for protection. Investigations by atomic force microscope and Raman spectroscopy confirmed that the MoS2 flakes had a mean lateral size of 10–20 μ m and mostly single layer thick. After depositing 3.6 and 7.0 nm Fe on MoS2/SiO2, clear hysteresis loops were observable with the in-plane magnetic field. From the investigation using a magneto-optical Kerr microscope, we measured the hysteresis curves within individual MoS2 flakes. Although the Fe coverage was much thicker than the MoS2 atomic step height (~0.66 nm) and the direct connection and strong ferromagnetic coupling between Fe/MoS2 and Fe/SiO2 were expected, a magnetic decoupling between the magnetic domains of Fe/MoS2 and Fe/SiO2 was surprisingly observed. For 3.6 nm Fe/MoS2, the magnetic coercivity (H c ) was 28 ± 5 Oe, while in contrast, the H c of 3.6 nm Fe/SiO2 ranged 58 ± 5 Oe. With a thicker Fe coverage of 7.0 nm, the H c of Fe/MoS2 and Fe/SiO2 converged and the magnetic decoupling became too weak to observe. The distinct interface magnetic anisotropy of Fe on different substrates was held responsible for the observed magnetic decoupling across the MoS2 atomic step between Fe/MoS2 and Fe/SiO2 domains. These observations will be valuable in combining a magnetic coverage with a single layer MoS2 for future spintronic applications.

In this study, the application of bias voltage to 4–8 nm Co/275 nm ZnO heterostructures changed the magnetic behavior reversibly or irreversibly, depending on the different voltage-induced mechanisms. The magnetic coercivity (Hc) monotonically decreased 20% when the small voltages of 0–8 V were applied. The Hc reduction was symmetric with the voltage polarity, and the reversibility was demonstrated by cyclically switching the bias voltage between 0 and 7 V. While a large voltage up to 40 V was applied to the Co/ZnO junction, the current heating effect became considerable and the Co-oxide was formed, as confirmed by depth-profiling X-ray photoemission spectroscopy analysis. The presence of Co-oxide in the Co films induced the irreversible reduction of the Kerr signal and Hc at room temperature. The considerable Hc enhancement at 130 K also indicates the exchange bias coupling effect from the antiferromagnetic Co-oxide.