Specific Heat of the Tb1−xLaxNi2Tb_{1-x}La_xNi_2 Solid Solutions

Specific heat measurements have been performed on the polycrystalline $TbNi_2, LaNi_2$ and their solid solutions $Tb_{1-x}La_xNi_2$ (x=0.2, 0.3). The Debye temperatures, phonon and conduction electron contributions as well as the magnetic part of the heat capacity were determined and discussed. The magnetocaloric effect was estimated from measurements performed in a magnetic field of 0.42 T for $TbNi_2,$ $Tb_{0.8}La_{0.2}Ni_2$ and $Tb_{0.7}La_{0.3}Ni_2$

Specific heat and magnetocaloric effect in Ho-Er-Co solid solutions

Specific heat measurements have been performed on polycrystalline HoCo2, ErCo2 and their solid solutions Ho1−x Er x Co2 (0.1≤x≤0.5). These compounds were synthesized using high-purity rare-earth metals and cobalt. X-ray diffraction patterns taken at room temperature reveal that all compounds have the C15 cubic Laves phase structure. Heat capacity measurements have been performed in the temperature range of 2–300 K without magnetic field and in a magnetic field of 1 and 2 T. The magnetocaloric effect has been estimated in terms of isothermal magnetic entropy change for all solid solutions in magnetic fields up to 2 T. The effect of increasing Er amount in Ho1−x Er x Co2 on the magnetic and magnetocaloric properties will be discussed

Piezoresistive properties of boron-doped silicon whiskers at cryogenic temperatures

Piezoresistive properties of boron-doped p-type silicon whiskers in temperature range of 1.7 to 300 K were studied. The giant piezoresistance was observed in p-Si whiskers in the vicinity of metal-insulator transition at helium temperatures. The gauge factor dependence on impurity concentration and temperature has been investigated. The extremely high gauge factor 5.7-105 at 4.2 K has been found in moderately doped silicon microcrystals with boron concentration 3-1018 cm-3 in the vicinity of metal-insulator transition at the insulating side. The possibility of application of giant piezoresistance to develop high-sensitive mechanical sensors operating, at cryogenic temperatures is discussed.Исследованы пьезорезистивные свойства нитевидных кристаллов кремния, легированных бором, в диапазоне температур 1,7-300 К. Гигантский пьезорезистивный эффект в нитевидных кристаллах p-Si наблюдался вблизи перехода металл-изолятор при гелиевых температурах. Исследовалась зависимость коэффициента тензочуствительнос-ти от концентрации примеси и температуры. Экстремально высокий коэффициент тен-зочувствительности 5,7-105 при 4,2 К был обнаружен в микрокристаллах кремния с промежуточным уровнем легирования с концентрацией бора 3-1018 cм-3 вблизи перехода металл-изолятор со стороны изолятора. Обсуждается возможность использования гигантского пьезосопротивления для создания высокочувствительных сенсоров механических величин, работоспособных при криогенных температурах.Досліджєно п’єзорєзистивні властивості ниткоподібних кристалів крємнію, легованих бором, в діапазоні температур 1,7-300 К. Гігантський п’єзорезистивний ефект у ниткоподібних кристалах p-Si спостерігався поблизу переходу метал-ізолятор при гелієвих температурах. Досліджено залежність коефіцієнту тензочутливості від концетрації домішок і температури. Екстремально високий коефіцієнт тензочутливості 5,7-105 при 4,2 К був знайдений у мікрокристалах кремнію з проміжним рівнем легування з концентрацією бору 3-1018 cм-3 поблизу переходу метал-ізолятор з боку ізолятора. Обговорюється можливість використання гігантського п’єзоопору для створення високочутливих сенсорів механічних величин, працездатних при кріогенних температурах

Strain induced effects in p-type silicon whiskers at low temperatures

Complex studies of strain induced effects in boron doped p-type silicon whiskers with [111] crystallographic direction in the wide temperature range 4.2 - 300 K at magnetic fields up to 14 T and under high-energy electron irradiation were carried out. The peculiarities of piezomagnetoresistance of Si whiskers heavily boron doped and with boron concentration in the vicinity of metal-insulator transition were determined. The influence of electron irradiation with energy 10 MeV and fluence Φ = 5*10¹⁷ el/cm ² on the gauge factor of boron doped Si whiskers at low temperatures have been also studied. High-sensitive piezoresistive sensor to measure pressure of liquid helium on the basis of silicon whiskers with a giant gauge factor was developed. Heavily doped Si whiskers with classic piezoresistance have been successfully used in mechanical sensors operating in the wide temperature range 4.2 - 300 K

Semiconductor microcrystals with ultra-high sensitivity to mechanical strain at cryogenic temperatures

Results of the studies of the low-temperature piezoresistance for p-type silicon microcrystals doped with boron up to $N=7\times 10^{17}-1\times 10^{19}$ cm$^{-3}$ are presented. The dependence of piezoresistance on impurity concentration and temperature was studied. The extremely high piezoresistance was found at the lowest temperatures 4.2-20 K in samples with boron concentration corresponding to the insulating side of the metal-insulator transition in the vicinity of it. A practical application of such a giant piezoresistance in mechanical sensors for cryogenic temperatures is discussed.

Microminiature Hall probes for applications at pulsed magnetic fields up to 87 Tesla

Microminiature Hall probes (MHP) may be used as magnetic field transducers, with virtually no change of sensitivity with temperature, for applications at room and cryogenic temperatures. The probes have a nominal active sensing area from 90x90 mu m down to 20x20 mu m and are based on Sn-doped n-InSb/i-GaAs MBE-grown heterostructures. MHPs were intensively tested in static (up to 14 T) and pulsed magnetic fields and shown to be appropriate for various applications in the temperature range 2-300 K and in pulsed magnetic fields up to 87 T. The latest version of these probes, with overall cross-section thickness-width dimensions of 150x750 mu m, are the smallest encapsulated Hall probes currently available and can be placed in areas not previously accessible to commercial packaged or unpackaged sensors