adiabatic demagnetization
- adiabatic demagnetization
-
process by which the removal of a
magnetic field from certain materials serves to lower their temperature. This procedure, proposed by chemists Peter Debye (
Debye, Peter) (1926) and William Francis Giauque (
Giauque, William Francis) (
independently, 1927), provides a means for cooling (
cryogenics) an already cold material (at about 1 K) to a small fraction of 1 K.
The mechanism involves a material in which some aspect of disorder of its constituent particles exists at 4 K or below (liquid helium temperatures). Magnetic dipoles—
i.e., atoms that have poles like bar magnets—in a crystal of paramagnetic salt (
e.g., gadolinium sulfate, Gd
2(
SO4)
3·8H
2O) have this property of disorder in that the spacing of the energy levels of the magnetic dipoles is small compared with the thermal energy. Under these conditions the dipoles occupy these levels equally, corresponding to being randomly oriented in space. When a magnetic field is applied, these levels become separated sharply;
i.e., the corresponding energies are widely different, with the lowest levels occupied by dipoles most closely aligned with the applied field. If the magnetic field is applied while the paramagnetic salt is in contact with the liquid helium bath (an isothermal process in which a constant temperature is maintained), many more dipoles will become aligned, with a resultant transfer of thermal energy to the bath. If the magnetic field is decreased after contact with the bath has been removed, no heat can flow back in (an adiabatic process), and the sample will cool. Such cooling corresponds to the dipoles remaining trapped in the lower energy states (
i.e., aligned). Temperatures from 0.3 K to as low as 0.0015 K can be reached in this way.
Much lower temperatures can be attained by an analogous means called adiabatic nuclear demagnetization. This process relies on ordering (aligning) nuclear dipoles (arising from nuclear spins), which are at least 1,000 times smaller than those of atoms. With this process, temperatures of the ordered nuclei as low as 16 microdegrees (0.000016 degree) absolute have been reached.
* * *
Universalium.
2010.
Look at other dictionaries:
adiabatic demagnetization — adiabatinis išmagnetinimas statusas T sritis fizika atitikmenys: angl. adiabatic demagnetization vok. adiabatische Entmagnetisierung, f rus. адиабатическое размагничивание, n pranc. démagnétisation adiabatique, f; désaimantation adiabatique, f … Fizikos terminų žodynas
adiabatic demagnetization — adiabatinis išsimagnetinimas statusas T sritis fizika atitikmenys: angl. adiabatic demagnetization vok. adiabatische Entmagnetisierung, f rus. адиабатическое размагничивание, n pranc. démagnétisation adiabatique, f; désaimantation adiabatique, f … Fizikos terminų žodynas
Magnetic refrigeration — Gadolinium alloy heats up inside the magnetic field and loses thermal energy to the environment, so it exits the field cooler than when it entered. Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique… … Wikipedia
Entropy (order and disorder) — Boltzmann s molecules (1896) shown at a rest position in a solid In thermodynamics, entropy is commonly associated with the amount of order, disorder, and/or chaos in a thermodynamic system. This stems from Rudolf Clausius 1862 assertion that any … Wikipedia
Coldest temperature recorded on Earth — The coldest natural temperature ever recorded on Earth was −89 °C (−128°F) at the Russian Vostok Station in Antarctica July 21, 1983. [http://www.globe.gov/fsl/html/templ.cgi?archive atmos10271999 lang=en nav=6] Lower temperatures have been… … Wikipedia
air conditioning — Synonyms and related words: adiabatic absorption, adiabatic demagnetization, adiabatic expansion, aerage, aeration, air cooling, airing, blast freezing, chilling, congealment, congelation, cooling, cross ventilation, cryogenics, deep freezing,… … Moby Thesaurus
chilling — Synonyms and related words: ache, aching, adiabatic absorption, adiabatic demagnetization, adiabatic expansion, air conditioning, air cooling, alarming, algific, awing, blast freezing, blast freezing, chilblains, chill, chilliness, cold creeps,… … Moby Thesaurus
cryogenics — Synonyms and related words: Newtonian physics, absolute zero, acoustics, adiabatic absorption, adiabatic demagnetization, adiabatic expansion, aerophysics, air conditioning, air cooling, algidity, applied physics, astrophysics, basic conductor… … Moby Thesaurus
freezing — Synonyms and related words: Siberian, adiabatic absorption, adiabatic demagnetization, adiabatic expansion, air conditioning, air cooling, algid, algific, anhydration, arctic, below zero, biting, bitter, bitterly cold, blast freezing, blast… … Moby Thesaurus
Orders of magnitude (temperature) — Temperature in °C compared to the thermodynamic scale in electron volts, which are also used as a unit of temperature. List of orders of magnitude for temperature Factor Multiple Item 10−∞ 0 K … Wikipedia
