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X-ray diffraction curves of oxidized Si nanowires with a strain distribution having a trapezoidal cross-section are analyzed using an X-ray kinematical treatment. The analysis is carried out assuming a strain distribution and cross-sectional shape to calculate a diffraction curve, followed by comparing it to the experimental one. The calculated diffraction curves reproduce the experimental ones over the whole measured range. Particularly, the calculated intensities as well as positions of fringe maxima and minima agree with the experimental curves. Also, the calculation indicates that the strain on a plane parallel to the bases becomes larger, as the plane becomes far from the longer base. This is demonstrated only by calculating X-ray diffraction curves assuming both strain distributions and cross-sectional shapes.

In this paper we propose a MEMS fabrication process that enables a polydimethylsiloxane (PDMS) diaphragm to be integrated with a sputtered thin film permanent magnet (TFPM), which can be used for micro pumps, energy harvesters, tactile display devices and so on. The magnetic performance of the 14.8 μm thick TFPM, consisting of multilayers of 300 nm thick NdFeB and 10 nm thick Ta deposited sequentially, is as high as a conventional bulk NdFeB magnet. However, the high sputtering temperature makes it impossible to deposit the TFPM directly onto the PDMS diaphragm without damaging the PDMS material. The process proposed here involves, firstly, sputtering the TFPM onto a silicon substrate, then coating this with PDMS, and finally etching silicon using XeF2 gas. The high substrate temperature during the XeF2 etching process degraded the magnetic performance of the TFPM and also caused part of the TFPM to become detached from the PDMS layer. The variation in temperature of the substrate during the XeF2 etching process with respect to etching pressure, and the magnetic properties of the TFPM as well as the mechanical ones of the PDMS diaphragm were evaluated experimentally. The substrate temperature can be decreased by reducing the XeF2 etching pressure, thus avoiding both degradation of the magnetic performance of the TFPM and delamination of the TFPM. The results of the evaluation show that the PDMS diaphragm and the TFPM not only remained attached, but also retained their mechanical and magnetic properties.

Structure, lattice parameters, spontaneous magnetization (I s ), and the Curie temperature (T C ) of MnAlGe and MnGaGe compounds with the Cu 2 Sb-type structure and their substituted compounds were investigated. Cr substitution for Mn enhanced I s and T C , whereas Fe substitution for Mn degraded them. These behaviors are in accord with the previously reported results, and are also common to the MnGaGe compound series. For MnAlGe, lattice parameter a increases by 0.2% and 0.4% for Cr and Fe substitution, while c changes by +0.1% and -1.3%, respectively. For MnGaGe, a decreases by 0.08% for Cr and increases by 0.2% for Fe substitution, while c changes by +0.5% and -1.0%, respectively. T C tended to increase with increasing length of c, suggesting that the interlayer distance between Mn layers is a key factor related to the height of T C , i.e., the strength of the magnetic exchange interaction.

The effect of the annealing temperature on the magnetostrictive properties of Fe­Co alloy thin films on quartz glass was systematically investigated. The saturation magnetostriction was 56ppm for the Fe32Co68-sputtered thin film quenched from 673K, and it increased to 159ppm with increasing annealing temperature up to 1073K. The magnetostriction above 1093K significantly decreased with the emerging fcc phase in the Fe­Co alloy. SEM images showed that the crystal grains present in the fcc phase aggregated to form a discontinuous surface, which resulted in a decrease in the effective magnetostriction. Measurements of the magnetic properties by vibrating sample magnetometer and magnetic force microscopy revealed the enhancement of the magnetization at the crystal grain boundaries of Fe­Co alloy thin films with large magnetostriction. Thus, the heterogeneity of the magnetization can play a key role in inducing the large magnetostrictive effect. [doi:10.2320/matertrans.MBW201315]

We conducted an experiment on the fabrication of fluidic devices for producing fine droplets. In our proposed method, multiple channels were fabricated by using a focused ion beam (FIB) system. The minimum feature top width was found to be approximately 56 nm. When both the target width and depth of one channel were set to 500 nm, the resultant top width was 750–780 nm, the bottom width was 250–320 nm, and the depth was 560 nm, almost achieving the target size for the channel depth.

Comparisons of the experimental and calculated X-ray diffraction profiles have been made for Si nanowires with trapezoidal cross-sections. Examined samples are periodically arranged nanowires prepared on a silicon-on-insulator wafer by electron-beam lithography, so that they are isolated from Si substrate. The nanowire periodicity gives rise to diffractions at additional reciprocal lattice points, which we employ to avoid the mixture of the diffraction from the Si substrate. The experimental diffraction profiles are found to be in good agreement with the square modulus of the Fourier transform of the trapezoidal cross-sections determined from transmission electron micrographs.

Reduction-resistant lead-free (Ba,Ca)(Ti,Sn)O3 piezoceramics with high piezoelectric constants were fabricated by optimizing the amount of Li2CO3 added. Oxygen partial pressure was controlled during the sintering of (Ba,Ca)(Ti,Sn)O3 ceramics in a reducing atmosphere using H2–CO2 gas. Enhanced grain growth and a high-polarization state after poling treatment were achieved by adding Li2CO3. Optimizing the amount of Li2CO3 added to (Ba0.95Ca0.05)(Ti0.95Sn0.05)O3 ceramics sintered under a low oxygen partial pressure resulted in improved piezoelectric properties while maintaining the high sintered density. The prepared Li2CO3-added ceramic samples had homogeneous microstructures with a uniform dispersion of each major constituent element. However, the residual Li content in the 3 mol % Li2CO3-added (Ba0.95Ca0.05)(Ti0.95Sn0.05)O3 ceramics after sintering was less than 0.3 mol %. Sintered bodies of this ceramic prepared in a CO2 (1.5%)–H2 (0.3%)/Ar reducing atmosphere (PO2 = 10−8 atm at 1350 °C), exhibited sufficient electrical resistivity and a piezoelectric constant (d 33) exceeding 500 pC/N. The piezoelectric properties of this nonreducible ceramic were comparable or superior to those of the same ceramic sintered in air.

We formed optical switches in which a mirror is driven by a magnetostrictive cantilever, and measured their properties. The cantilever has a cross-sectional structure of Al (10 nm)/SmFe (6μm)/Al (10 nm)/Cr (1.2μm)/glass (20μm) and the dimensions are 12 mm ×0.8 mm. A cantilever with a gold mirror on the surface is installed in the gap of a magnetic circuit. The gap field is 1.5 kOe for an electric current of 200 mA. At this current the deflection of a cantilever is 230μm. These components are combined with optical fibers with a lens and a 1 × 2 optical switch is formed. The insertion loss and the crosstalk are 0.23 dB and −64.4 dB, respectively. The power consumption is 120 mW, which is expected to be decreased by improving the magnetostrictve properties. The switching time is 15 ms, which is determined by a vibration of the cantilever. Damping techniques for the vibration can reduce the switching time.

BiFeO3 and Ag nanoparticle-embedded BiFeO3 thin films were prepared on Pt/TiO x /SiO2/Si and MgO(100) substrates using colloidal silver and BiFeO3 metal–organic precursor solutions. Colloidal silver solution was prepared by a chemical reductive method using NaBH4 as a reductant. The prepared Ag nanoparticles exhibited characteristic optical absorption properties based on their surface plasmon resonance related to particle size. The synthesized BiFeO3 and Ag nanoparticle/BiFeO3 thin films demonstrated rapid on/off responses of photocurrent to visible light. The Ag nanoparticle-incorporated BiFeO3 film exhibited a 2–4-fold higher photocurrent than the BiFeO3 film. Optical and ferroelectric properties did not change markedly even when Ag nanoparticles were embedded in the BiFeO3 thin film within the quantities of this study. Furthermore, in the Ag nanoparticle/BiFeO3 composite structure, Ag nanoparticles were introduced in the near-metallic state with maintained their nanometer size. In the Ag nanoparticle-embedded BiFeO3 film, photoinduced charge separation and transport of photoexcited carriers were enhanced by the surface plasmon effect of nanosized Ag particles as well as the internal bias electric field existed in the narrow-bandgap BiFeO3 thin film.

Highly c-axis oriented, single crystal films of Co/sub 1-x/Cr/sub x/ have been grown epitaxially on mica substrates by e-beam evaporation. The method, using a Ru underlayer, is simple and applicable to similar c-axis oriented, large area growth of the wide range of Co alloys suitable for perpendicular recording. The films show narrow peak widths in X-ray diffraction (/spl Delta//spl Theta//sub 00.2//spl sim/1.0-1.5/spl deg/) and their magnetic properties are composition dependent. Moreover, for any given Cr concentration, these single crystal films exhibit the largest saturation magnetization when compared with either sputtered/evaporated samples or films grown under identical conditions on glass/silicon substrates. It is shown that this enhanced M/sub s/ is directly correlated with the dispersion of the c-axis about the film normal and their narrowest values are observed for these epitaxially grown films. X-ray microanalysis shows some inter/intra-granular variation in Cr content, but systematic segregation trends appropriate for explaining these results have not yet been observed. >

Microstructure and magnetic properties of Mn‐Al multilayered films are studied by high‐resolution transmission electron microscopy (TEM), x‐ray diffraction, and vibrating sample magnetometry to investigate the origin of ferromagnetism. High‐resolution TEM images show that the Mn‐Al interface is sharp and that the crystal lattice is continuous across the interface. The possibility of ferromagnetic alloy formation is ruled out for explaining the origin of ferromagnetism. The magnetic measurements are made on films with various layer thicknesses and numbers of layers. The saturation magnetization increased as the number of interfaces increased. Magnetic anisotropy differs between films with odd and even numbers of layers. These results suggest that the ferromagnetic regions are located around the Mn‐Al interfaces, where large strain and/or stress exists.

A junction has been developed for hybrid bubble memory devices using ion-implanted tracks for high density data storage and Permalloy tracks for write and read functions. An 18- mu m diameter Permalloy corner pattern is used. Both the tapered ion-implanted edges and the operating bias field adjustment boundary at the junctions are located under the Permalloy corner pattern edges. Improved junction properties and analysis by visual inspection are reported. The bubble potentials and the phase of the rotating field, when a bubble reaches the junction boundary, were compared for the conventional and the corner-type junctions. Replicate gate performance for the corner-type junction was investigated. The replicate phase margin was greatly improved for the enlarged Permalloy corner pattern. The temperature dependences of the junction performance were measured between 0 and 80 degrees C. In this temperature range, the margins of the junctions were improved, making them suitable for hybrid bubble memory devices. >

On-track signal and noise characteristics of CoCr-alloy single-layer perpendicular recording media have been investigated by using three types of ring-shaped heads for writing and an MR head for reading. The output signal is improved with decreasing the write-gap length of ring-shaped head. The D/sub 50/ and the S/N ratio at 200 kFCI are respectively improved by 59 kFCI and 5.7 dB, when the write-gap length is decreased from 0.40 to 0.22 /spl mu/m. When the recording characteristics of CoCrTa, CoCrPt and CoCrPtTa media are compared by using narrow-gap write head, it is clarify that the CoCrTa medium indicates the S/N ratio higher than 29 dB at 400 kFCI, and that the CoCrPt and the CoCrPtTa media shows the D/sub 50/ value higher than 235 kFCI. The medium noise of the CoCrPt or the CoCrPtTa at high recording density should be reduced by improving the recording layer.

Ferromagnetism at room temperature has been found in Mn/C/Si films prepared by sequential deposition of these elements at a substrate temperature about 360 °C by vacuum evaporation. The saturation magnetization increases rapidly with the carbon quantity, and it is about 250 emu/cc for a film with a nominal structure of Mn(6 nm)/C(0.5 nm)/Si(6 nm). The magnetization measurements at low temperatures show that the magnetic moment per ferromagnetic Mn atom corresponds to more than 1.2 Bohr magnetons.

Magnetic recording will face very serious problems beyond Tera bit/in/sup 2/, such as: recorded bit thermal stability in a size range of less than 20 nm×30 nm; very strong magnetic field necessary to write on a high coercive media, estimated over 15 kOe; write frequency limited to a few GHz, depending on the natural resonance of the magnetic material. In a hybrid recording scheme, writing is done at a high temperature around 150-230 °C, while archiving at room temperature. Such a simple concept brings solutions to solve the above difficulties. This paper outlines various hybrid recording device configurations and checks out the applicability of several materials for this type of application.

Advantages of Hybrid recording and material candidates like CoCrPt,TbFeCo.Pd/Co and FePt are discussed targeting the recording density beyond Tera bit/in2.

c‐axis oriented, single‐crystal, Co films were grown on mica using either Ti or Ru underlayers and exhibited the following crystallographic orientation relationship (00.1)mica ∥ (00.1)underlayer ∥ (00.1)Co, and [11.0]mica ∥ [10.0]underlayer ∥ [10.0]Co. Fundamental magnetic properties of the films were measured: Hc∼4 kA/m, Bs∼1.95 T, and Ku∼5×105 J/m3. The as‐grown magnetization structure of thinner (t≤30 nm) films shows mainly 180° domain walls with a uniform distribution of crossties, while thicker (t=60 nm) samples show stripe domains with a width of 75 nm. In spite of their excellent c‐axis orientation (FWHMCo(002)∼1.5°), the effective anisotropy of these films is in‐plane but with a small perpendicular magnetization component. These features in the hysteresis behavior are consistent with a simple noninteracting particle model incorporating the shape anisotropy of the small sized grains. For thinner samples the validity of this model has been verified by annealing experiments.

Ferromagnetic Mn-Si films with Curie temperature of 120 degrees C are obtained, although no Mn-Si compound ferromagnetic at room temperature is reported. Ferromagnetism at room temperature appears when the films are prepared by alternate deposition at a substrate temperature around 360 degrees C. The saturation magnetization is enhanced when polyimide is used as the substrate or placed on other substrate surfaces. The ferromagnetic regions are localized near the interfaces between Mn and Si layers, judging from cross-sectional transmission electron micrographs and the stacking period dependence of the saturation magnetization. >

Relationships between the magnetic properties and the film structure of Mn/Al multilayers are examined by changing the thicknesses of Mn and Al layers. X‐ray diffractions show that the Mn lattice spacing measured vertical to the substrate becomes smaller by increasing the Mn layer thickness or by decreasing the Al layer thickness. Saturation magnetization and magnetic anisotropy vary depending on the change of the Mn lattice spacing. Ferromagnetism and magnetic anisotropy of Mn/Al multilayers are closely related to the strain in the Mn lattice.

Correlation between the structure and the magnetic properties of Mn‐Al multilayered films prepared by vacuum evaporation have been investigated. Films on MgO(100) substrates with layer thicknesses of 100 A or more were found to have structures with flat layers and (100) orientation of α‐Mn, while a film on a glass substrate and a film with a layer thickness of 50 A on a MgO(100) substrate were seen to have variations in layer thicknesses and no crystal orientation of α‐Mn. Saturation magnetizations for the former two films are more than several times greater than those for the latter two films. From these properties, it is judged that stacking of α‐Mn layers with (100) surfaces and Al layers is an important factor for the evolution of ferromagnetic properties in Mn‐Al multilayered films.

The magnetization reversal process has been studied in a series of four TbFeCo films over the temperature range 300–460 K. The films were characterized by time decay, dynamic coercivity, Kerr imaging, and torque measurements. For a film with a sputter-etched SiN underlayer, the reversal process at low temperatures was dominated by nucleation followed by rapid domain wall motion. The low temperature relaxation curves for this sample were analyzed using a Fatuzzo model. At high temperatures, the Fatuzzo model did not apply. For the other films, with no etching, relaxation curves were logarithmic at all temperatures. All activation volumes increased with increasing temperature and decreased with increasing sputtering pressure. The magnetic anisotropy direction changed from perpendicular to in-plane as the argon sputtering pressure was increased.

The magnetic properties have been investigated in MnAl multilayer films on the different number of layers. The easy magnetization directions and the symmetry of torque curves are found to alternate with each additional layer.

Highly c-axis oriented, single crystal films of Co{sub 1-x}Cr{sub x} (0{le} {times} {le} 0.3) have been grown epitaxially on mica substrates by e-beam evaporation. Films grown on Ru underlayers have an average grain size of 50--80nm, negligibe fcc content and very narrow c-axis dispersions. For Co films (x=0), the as-grown magnetization structure are mainly 180{degree} domain walls with a uniform distribution of cross-ties for thinner samples ({le} 300{Angstrom}), whilst thicker (>400{Angstrom}) ones show stripe domains. These images were analysed in detail to measure that wall widths and associated energy densities for as-grown, remanent and ac- magnetised samples. As expected, the magnetic properties of these films are composition dependent. However, for any Cr concentration, these films exhibit the largest saturation magnetisation when compared with either sputtered or evaporated samples. This enhancement can be attributed to a nanometer-scale segregation of Cr, which in these samples, which in these samples, could be particularly aided by the diffusion on the close-packed planes of the films with very narrow c-axis dispersions. Preliminary X-ray microanalysis and NMR data support this interpretation.

Magnetic torque curves are measured for Mn-Al multilayered films, while changing the number of layers or the layer thickness, to investigate the magnetic anisotropy. A seven-layer film with layer thickness of 10 nm shows two-fold symmetry, while the eight-layer film shows a unique four-fold symmetry in the torque curves measured with the magnetic field rotated in the normal plane. The torque amplitude of four-fold symmetry component decreases as the layer thickness increases. The results suggest that the four-fold symmetry in the torque curves of the Mn-Al multilayered films is due to the magnetic interactions between the ferromagnetic regions near the Mn-Al interfaces.

In ion-implanted and Permalloy hybrid bubble memory devices, the operating bias field region of ion-implanted tracks is lower than that of Permalloy tracks when the cell size is less than 4μm × 4μm. This reduces the overall bias field margin. The operating bias field region of Permalloy tracks has been shifted using the garnet film thickness dependence of a bubble collapse field. Thickness of a garnet film under Permalloy tracks is reduced using the ion-milling technique. The ion-milled region has a low coercive field and shows a good bias field margin. It has been confirmed in hybrid bubble memory devices with a 3.5μm × 3.5μm cell size that the operating bias field adjustment made by thinning a garnet film can improve the overall bias field margin.

Hybrid bubble memory devices have been proposed and operated with the memory density of 4 Mbit/cm2. In the hybrid bubble memory devices, minor loops are composed of ion-implanted tracks with 4-µm period, and major lines and functional parts including block-replicate and swap gates are composed of Permalloy tracks with a longer period of 12 µm. Passive junctions between ion-implanted and Permalloy tracks have been developed, introducing the tapered ion-implantation technique. Improving the characteristics of the functional parts composed of Permalloy tracks, the hybrid bubble memory devices with block-replicate and swap gates have been operated, and the feasibility of the devices has been confirmed. In addition, the possibility of higher memory density has been shown.

The thickness dependence of the magnetization and the Curie temperature has been calculated for (111)‐oriented Y3Fe5O12 films using the molecular field theory to compare with the experimental results. It is found that the sublattice magnetization for a layer, i.e., the local magnetization, changes with depth. The local magnetization changes only four layers from surfaces and is constant for layers inside at room temperature. The average value of the local magnetization with respect to depth, i.e., the magnetization of the film decreases monotonically with decreasing thickness. The Curie temperature is constant down to about 30 A; below that it decreases. The calculated results explain the experimental thickness dependence of Curie temperature and effective anisotropy field within the error.

X‐ray dynamical theory has been applied to determine strain distributions caused by ion implantation into magnetic bubble garnets. Experimental rocking curves obtained by a double‐crystal x‐ray diffractometer were compared with theoretical curves for assumed strain distributions, and after several trials, good fittings were obtained. It is shown that slight change in the assumed strain distribution leads to appreciable change in the theoretical rocking curve. Comparison between dynamical and kinematical treatments shows that dynamical treatment is more accurate. Applying the method, it was confirmed that strain by multiple ion implantation was basically the sum of those by single ion implantation.

The characteristics of junctions between ion-implanted and Permalloy tracks are described for hybrid bubble memory devices. It has been found that the junctions which have a sharply formed edge of the ion-implanted layer have a problem in reproducibility of bias field margins. It is caused by the potential barrier due to the stress change and free poles which appear at the edge as well as the attractive poles in the ion-implanted tracks which tend to keep the bubbles in the ion-implanted tracks. To reduce their influence, we have introduced the tapered edge. A good bias field margin has been obtained for the tapered junctions with the modified pickax Permalloy pattern from the ion-implanted to Permalloy tracks. In the junctions from the Permalloy to ion-implanted tracks, the bias field margin strongly depends on the orientation of the edge of the ion-implanted layer with respect to the easy magnetization directions of the garnet. The edge should not be parallel to the easy magnetization direction, and the Permalloy pattern should be made larger near the edge. The improved junctions have a good bias field margin with reproducibility.

The origin of effective anisotropy field change induced by ion implantation in magnetic garnet films has been investigated using films with uniform strains. Uniform strains were produced by ion implantation into very thin (600 A) garnet films. Using such ion-implanted samples, strain, saturation induction 4πMs, magnetostriction coefficient λ 111 and effective anisotropy field change Δ(Hk-4πMs) were measured. It was found that Δ(Hk-4πMs) is mainly brought about by the magnetostriction effect for both H 2 + and Ne+ implantations. Different dependences of Δ(Hk-4πMs) on strain between H 2 + and Ne+ implantations are attributed to different dependences of λ 111 and 4πMs. A large value of Δ(Hk-4πMs) for H 2 + implantation originates from a large magnitude of λ 111 .

Reductions in cell size of ion-implanted Permalloy hybrid magnetic bubble memory devices give rise to large differences in operating bias field regions of ion-implanted and Permalloy propagation tracks. Attempting to utilize the dependence of the operating bias field on the thickness of the bubble garnet film, the authors ion-milled films to reduce their thicknesses, thereby lowering the bubble collapse field (H o ). The ion milling was found not to change the film coercivity. In this way, by shifting the permalloy track section field margin downward by 10 Oe, the bias field regions were matched, for a larger overall (common) bias field margin.

Curie temperature T c and effective anisotropy field H k - 4 π M s have been measured for epitaxial magnetic garnet films with thicknesses ranging from 20 A to 2.8 μm. It was found that T c and H k - 4π M s were unchanged down to 60 A for mixed garnet.

Attempts to use 0.8 μm diameter bubble material to obtain ion-implanted propagation tracks with a 3 × 3 μm cell size were described. Two track shapes ("CD" and "snake" types) were used, and the period in bubble propagation direction λb and period between adjacent tracks λ l were varied. For a 3 × 3 μm cell size, snake type tracks resulted in broader operating margins, but CD type tracks were found to yield better performance for smaller cell sizes. It was concluded that by varying track parameters, ion-implanted propagation tracks of cell size 3 × 3 μm and using 0.8 μm diameter bubbles may be realized.

To study start/stop operations in ion-implanted magnetic bubble propagation tracks, H 2 was implanted at 35 keV and 1 × 1016/cm 2 and at 80 keV and 4.4 × 1016/cm 2 , and set four stop directions both parallel and normal to the linear propagation track. The characteristics were then measured at 100 kHz. From the DC in-plane magnetic field H dc dependence of the start/stop operating bias field margin, nonnegative H dc values resulted in a start/stop bias field margin equal to the continuous operation margin. In most experiments, start/stop bias field margins of 8 percent or more were obtained.

The magnetic properties of Mn-Al multilayered films prepared by alternate deposition of Mn and Al in a vacuum evaporation system are investigated. Such films are found to show ferromagnetic properties when the substrate temperature during deposition is around 300°C. The saturation magnetization is seen to depend on the kind of substrate: the values for MgO(100) substrates are greater than those for MgO(111) and glass substrates. The obtained saturation magnetization of 50 emu/cm3 is expected to increase.

A method of implanting a magnetic garnet film with ions is disclosed in which a covering film is provided on a monocrystalline magnetic garnet film for magnetic bubbles, and hydrogen ions are implanted in a desired portion of a surface region in the magnetic garnet film through the covering film. According to this method, it is possible to form an ion-implanted layer in which the ion concentration distribution in the direction of depth is uniform, and moreover the inplane anisotropy field in the ion-implanted layer decreases only a little with time in an annealing process.

Hybrid bubble memory devices using ion‐implanted and Permalloy bubble propagation tracks have been proposed and developed. In this paper, the reduction of the cell size from 4 to 3 μm will be discussed. In the hybrid devices, the minor loops are composed of ion‐implanted tracks and the functions are composed of Permalloy tracks. To reduce the cell size, therefore, both of the tracks should be improved. For the 3‐μm‐period ion‐implanted tracks, the bubble diameter is reduced from 1 to 0.8 μm. According to the reduction of a bubble diameter, magnetostrictive anisotropy Δλ=λ100−λ111 is increased from 5 to 8×10−6 because the Sm content is increased to increase the anisotropy field Hk. The large Δλ affects the characteristics of inside and outside turns in the ion‐implanted tracks. To get a good margin for the turns, the anisotropy field change induced by ion implantation ΔHk should be larger than in 4‐μm‐period tracks. There is a new problem in 3‐μm‐period hybrid devices. In the hybrid devices, there is no de...