In the present article the recent developing process on the new application of high entropy magnetic materials in the He temperature range will be shown. First, the theoretical basis of these applications will be explained briefly and the necessary condition for selection of the magnetic materials will be discussed. Then, the several experimental results, such as the temperature dependences of the specific heat, in some promising Er compounds, Er3Ni, ErNi, ErNi2-DyNi2 etc., will be shown. In order to show clearly the present stage of the magnetic regenerator material investigation, we will show several results which verify the effectiveness of the magnetic regenerator materials obtained from refrigeration experiment using the GM refrigerator. Moreover, it has been made clear that the regenerator characteristics depends largely on the structure of the regenerator which contains several kinds of magnetic regenerator materials. Therefore, as an example, the experimental result of regenerator characteristics in the double layer type magnetic regenerator, in which Er3Ni powders are piled up on the ErNi powders, will be shown. Lastly, on the basis of the above experimental results, the development of the magnetic material application to regenerator in future will be discussed.
Procedures to measure critical parameters such as the critical temperature, Tc, the upper critical field, Hc2, the critical current, Ic, and the AC loss in practical superconductors are described. The criteria and factors which influence the evaluation of the parameters are briefly discussed. The importance of the holder in the 4 probe method which supports the sample against the Lorentz force is emphasized from the view point of strain effect. The magnetization method to measure the AC loss of a multifilamentary wire is described in detail.
Discussed are energy conversion and energy flux accompanied to oscillations of viscous fluid. The energy conversion per unit volume is shown to be ρm(∂T/∂p)S«p⋅dS/dt»+«u⋅∇p» for a small cycle, for which variations of pressure p and entropy S are small. ρm is time average of the density, u is the velocity and ∇p is the pressure gradient. « » indicates double operations of spatial average over crosssectional area of flow-channel and time average. «u⋅∇p» is a negative quantity corresponding to dissipation due to viscosity of fluid. The average of energy flux is shown to be enthalpy flux ρm«H⋅u» approximately, in the case that the velocity u and the mass flux «ρ⋅u» are small and the wave length is long. ρ and H are variations of the density and the enthalpy respectively. The enthalpy flux for small cycle is shown to be summation of heat flux and work flux: ρm«H⋅u»=ρmTm«S⋅u»+«p⋅u» where «p⋅u» is the work flux and ρmTm«S⋅u» is the heat flux. Final discussions are on the energy conversion, the work flux and the heat flux of adiabatic reversible small-cycle, isothermal small-cycle, polytropic small-cycle, isobaric small-cycle and isochoric small-cycle.