Helium is a rare gas found in limited quantities worldwide. Numerous problems will appear regarding production and distribution arising from the various circumstances confronting helium in recent years. This article analyzes the current status of helium for industrial use and based on this shows the difficulties faced by helium for use.
In this article, we describe the method attaining low temperatures below 1 K using a commercial compact GM refrigerator. The main part of this system consists of 4 K plate attached to the second cooling stage of GM refrigerator, 1 K pot and 3He pot, which are covered with three radiation shields attached to the first stage of GM refrigerator, 4 K pot and 1 K pot. The required time to reach temperatures below 1 K is within 6 hours, and temperatures below 0.5 K can be maintained for more than one day by one-shot operation. This system can be applied to terahertz industry as well as low temperature physics.
We describe our recent progress in high-pressure nuclear magnetic resonance (NMR) technique, which extends the range of practical NMR experiments to 10 GPa-class. The new opposed-anvil type cell has significantly large sample space, though the whole clamp cell size is small enough to put within superconducting magnets or fridges. We also show other new techniques on loading of argon pressure transmitting medium, pressure determination, and wiring of electrodes. The application on a pressure-induced superconductivity of SrFe2As2 has demonstrated a remarkable advantage brought by the combination of the clean crystal, pressure control, and spectroscopy.
In this article, we report recent development of miniature high-pressure apparatus for bulk measurements at low temperature and in magnetic field. The new compact multi-anvil type “Palm cubic anvil cell” extends the temperature range down to ∼0.45 K by using a 3He refrigerator. We also present a technique for measuring the specific heat under pressure and magnetic field using newly developed miniature piston cylinder cell made of Ag-Pd-Cu alloy. Its application to the heavy fermion compound YbCo2Zn20 is presented.
We review an indenter-type pressure cell, which possesses a maximum pressure of 5 GPa and a sample space of φ1.6×1.6 mm. This pressure cell is available not only for transport measurements but also for ac-susceptibility and NMR measurements. An advantage is the small size being able to change the direction of the pressure cell in the conventional superconducting magnet, which makes it possible to measure the anisotropy against magnetic field.
In high-pressure study, the crystal structures of materials are a very important factor at low temperature. X-ray diffraction measurement is the most frequent and useful method techniqe to determine the crystal structure under pressure. In this article, our recent progresses of high-pressure and low-temperature X-ray diffraction system are reviewed. We also describe the recent researches in our laboratory.
In general high-pressure experiments, solid pressure medium causes complicated stress condition. Examining cylindrical samples by the deformation-DIA (D-DIA) module, which simplifies stress condition, we have tried to address such non-hydrostaticity issue. Our results reveal that lattice strain, from which physical quantities such as “pressure” or “volume” are calculated, may vary depending on the amount of deformation, referred to as total axial strain, even at a steady pressure and temperature condition. Understanding the relation between lattice strain and total axial strain is therefore of fundamental importance for precise in situ strain measurements. High-pressure studies have not monitored total axial strain so far, but the total strain could be the reason why strain measurements have varied from one study to another. In addition to precise strain measurement, total axial strain also controls plastic deformation. Plastic deformation develops texture, which is observed as an intensity variation in the diffraction Debye ring; thus we can now observe texture development as a function of total strain. Flow mechanism during plastic deformation can be inferred from the texture development. Controlling and monitoring total axial strain is not only essential for precise strain measurement of conventional high-pressure study, but crucial for discussion in plastic property in the next decade of in situ observation.