Specific Heat of Four Rare-Earth Compounds Between 0.4° and 5°K
We have measured the specific heat of lanthanum and holmium ethylsulfate (LaES and HoES) and of lutetium and gadolinium iron garnet (LuIG and GdIG) by means of a cryostat using liquid 3He or 4He. The sample, in the form of single crystals or a sintered block, is attached to a support which is made up of a quartz frame and thin copper strips in order to have a low specific heat. This support can be brought in contact with the helium refrigerator by means of a heat switch. Two carbon resistors are used: a Speer 450-Ω resistor covers the region from 0.35° to 0.9 °K, and a 40-Ω (math)W Allen-Bradley is used at higher temperatures. The resistor operating below 0.9°K is calibrated by means of the vapor pressure of liquid 3He and the susceptibility of three single crystals of cerium magnesium nitrate which obeys Curie’s law in this temperature region. The samples are cooled from room temperature entirely by means of the heat switch and without any helium exchange gas. This is to prevent adsorption of the gas on the specimen, in particular on the sintered samples, which have been found to be porous.
KeywordsHeat Switch Helium Refrigerator Cerium Magnesium Nitrate Total Specific Heat Gadolinium Iron
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