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We report the development of a high-temperature Seebeck coefficient Standard Reference Material (SRM) for use in instrument validation and interlaboratory data comparison in the temperature range of 295–900 K to support the research, development, and production of materials and devices related to thermoelectric-based energy conversion applications. We describe the synthesis, anneal–quench procedure, and physical characterization of a p-type boron-doped polycrystalline silicon–germanium alloy with a nominal composition of Si80Ge20. For the certification measurements, we describe the measurement protocols, statistical analysis, the certified Seebeck coefficient values, comprehensive uncertainty budgets, and metrological traceability. Our extensive efforts to identify, reduce, and quantify measurement uncertainties will be emphasized. This new SRM complements SRM 3451 Low-Temperature Seebeck Coefficient Standard (10–390 K) to provide certified reference materials traceable to the International System of Units (SI) for Seebeck coefficient measurements within the temperature range 10–900 K.

We have successfully developed a Seebeck coefficient Standard Reference Material (SRM™), Bi2Te3, that is essential for interlaboratory data comparison and for instrument calibration. Certification measurements were performed using a differential steady-state technique on 10 samples (15 measurements) randomly selected from a batch of 390 bars. The certified Seebeck coefficient values are provided from 10 to 390 K, and they are further supported by transient measurements. The availability of this SRM will validate measurement results, leading to a better understanding of the structure/property relationships and underlying physics of potential high-efficiency thermoelectric materials.

A numerical model based on Navier-Stokes equation is developed to simulate the interface evolution of flooding flows. The two-dimensional fluid domain is discretised by structured rectangular elements according to finite volume method (FVM). The interface between air and liquid is captured through compressive interface capturing scheme for arbitrary meshes (CICSAM) based on the idea of volume of fluid (VOF). semiimplicit method for pressure linked equations (SIMPLE) scheme is used for the pressure-velocity coupling. A second order upwind discretization scheme is applied for the momentum equations. Both laminar flow model and turbulent flow model have been studied and the results have been compared. Previous experiments and other numerical solutions are employed to verify the present results on a single flooding liquid body. Then the simulation is extended to two colliding flooding liquid bodies. The impacting force of the flooding flow on an obstacle has been also analyzed. The present results show a favourable agreement with those by previous simulations and experiments.

The exchange anisotropy in NiFe/NiMn bilayers was studied by using the planar Hall effect. The sputtered NiFe/NiMn films were patterned into strips of 1 mm in length and 200 μm in width and with six terminals for anisotropy magnetoresistance and planar Hall voltage measurements by a photolithographic process. It is shown that the planar Hall effect is an effective method to characterize the exchange anisotropy in ferromagnetic/antiferromagnetic (AF) systems. It can be used to accurately determine the exchange field and describe the magnetization reversal processes. The effective uniaxial anisotropy field HK eff, the effective unidirectional anisotropy field Hud, and AF domain wall energy Hw can be obtained by fitting the experimental results. We found that in the NiFe/NiMn bilayer system, the parameters HK eff, Hud, and Hw have the same values in reversible and irreversible measurements, and the domain wall energy in AF layer is larger than interfacial unidirectional anisotropy.

Spin valve multilayers exhibiting enhanced giant magnetoresistive (GMR) effect and weak interlayer coupling as well as strong exchange biasing were fabricated by a two-step deposition procedure. The down sublayers (i.e., buffer layer Ta/free layer NiFe/interlayer Cu) were deposited at a lower argon pressure, then the upper sublayers (i.e., pinned layer NiFe/pinning layer FeMn/cover layer Ta) were deposited at a higher argon pressure. The former promoted formation of the strong (111) textures, smooth interfaces, and dense Cu film, resulting in a weak interlayer coupling. The latter promoted small domains and less diffusive interfaces, resulting in a strong exchange biasing and an enhanced GMR ratio. This shows that independent control of magnetoresistance, interlayer coupling, and exchange biasing is possible.

Synthetic spin-filter spin valves with spin-engineered biasing scheme “sub/Ta/NiFe/IrMn/NiFe/NOL/Cu1/CoFe/Cu2/CoFe/Ru/CoFe/IrMn/Ta” were developed. In the structure, the orthogonal magnetic configuration for biasing and pinning field was obtained by one-step magnetic annealing process by means of spin flop, which eliminated the need for two antiferromagnetic materials with distinctively different blocking temperatures and two-step magnetic annealing as in conventional exchange biasing scheme. The longitudinal domain biasing of spin valves was achieved by using interlayer coupling field through Cu1 spacer. By adjusting the thickness of the Cu1 layer, the interlayer coupling biasing field can provide domain stabilization and was sufficiently strong to constrain the magnetization in coherent rotation. This can prevent Barkhausen noises associated with magnetization reversal. We report here a proof of concept study of such a domain-biasing scheme, which has its important technological applications in nanoscale spin valve and magnetic tunneling junction read heads and other spintronic devices.

Spin valves with structure of sub/Ta/NiFe/FeMn/NiFe/Mo/NiFe/Cu/NiFe/CrMnPt/Ta were developed. In this configuration, a longitudinal-biasing field from interlayer coupling stabilized the magnetic domains of the free layer. Planar Hall effect was used to study the magnetization reversal process of the free layer. It was shown that by adjusting the thickness of Mo layer, the interlayer coupling biasing field can provide domain stabilization and was sufficiently strong to constrain the magnetization in coherent rotation. This can prevent Barkhausen noises associated with magnetization reversal. Such a spin valve sensor structure is particularly attractive for high density read heads.

Spin valves with a canted pinning field were studied. Magnetoresistance (MR) and planar Hall effect (PHE) in the spin valves were simultaneously measured in fields applied in the film plane at different angles (α) with respect to the easy axis of the free layer. The Boltzmann transport equation was used to simulate MR and PHE curves, and to determine the magnetization orientation of the free layer at different α. Results showed that in the magnetization configuration in which the pinning field was perpendicular to the easy axis of the free layer, there existed two distinct magnetization reversal modes when the applied field angle α was near 90°. The magnetization reversal was an incoherent rotation when α 90°. However, in the configuration in which the angle between the pinning field and the easy axis of the free layer was about 45°, there was only one magnetization reversal mode. The interlayer coupling kept the free layer in a...

Both a thin free layer and high magnetoresistance (MR) ratio are required in spin valves for high magnetic density recording heads. In traditional spin valve structures, reducing the free layer normally results in a reduction in MR. We report here on a spin-filter specular spin valve with structure Ta 3.5 nm/NiFe 2 nm/IrMn 6 nm/CoFe 1.5 nm/Nol/CoFe 2 nm/Cu 2.2 nm/CoFe tF/Cu tSF/Nol2/Ta 3 nm, which is demonstrated to maintain MR ratio higher than 12% even when the CoFe free layer is reduced to 1 nm. The semiclassical Boltzmann transport equation was used to simulate MR ratio. An optimized MR ratio of ∼14.5% was obtained when tF was about 1.5 nm and tSF about 1.0 nm as a result of the balance between the increase in electron mean free path difference and current shunting through conducting layer. It is found that the Cu enhancing layer not only enhances the MR ratio but also improves soft magnetic properties of CoFe free layer due to the low atomic intermixing observed between Co and Cu. The CoFe free layer...