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Helium-3-free cooling, explained
Most routes below one kelvin depend on helium-3, an isotope in short supply. Magnetic cooling gets there with a magnet, a paramagnetic material and a cryocooler.
Why helium-3 is the problem
A pulse-tube or Gifford-McMahon cryocooler takes an experiment to a few kelvin with nothing more than electricity and cooling water. Below that, the classic tools are helium-3 sorption coolers and dilution refrigerators, and both need helium-3.
Helium-3 is rare. It is recovered mainly from the decay of tritium, demand from research, security screening and quantum technology competes for it, and its price and availability have been a long-standing concern for low-temperature laboratories. A cooling method that does not use it removes that dependency entirely.
How it works
How magnetic cooling works
Adiabatic demagnetization refrigeration (ADR) uses a paramagnetic material whose disorder, its entropy, depends on the magnetic field applied to it.
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01
Magnetise
A superconducting magnet applies a strong field to the paramagnetic material while it is thermally connected to the cryocooler stage. The magnetic moments line up, and the heat this releases flows to the cryocooler.
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02
Isolate
A heat switch disconnects the material from the cryocooler stage, so no heat can flow in or out.
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03
Demagnetise
The field is ramped down. With the material isolated, its total entropy is fixed, so as the moments are free to disorder again, the temperature of the material falls, far below that of the cryocooler stage.
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04
Hold, or cycle again
The material now absorbs heat from the experiment until it warms. In a single-shot system the cycle is then repeated; in a continuous system two or more stages take turns, so the experiment stays cold without interruption.
What this changes in the lab
No helium-3 supply risk
The cooling medium is a solid paramagnetic material that stays in the cryostat. Nothing is consumed and nothing has to be sourced.
Cryogen-free
With a closed-cycle cryocooler as the first stage, there is no liquid helium to order, transfer or recover.
Automated operation
The cycle is a sequence of current ramps and switch states, so it can be run by software rather than by hand.
Where Kiutra fits
Kiutra, a company based in Munich, builds cryostats on this principle, including continuous ADR, so that experiments can stay at sub-kelvin temperature for as long as they need to. Paeonia Bloch distributes Kiutra cryostats in ASEAN. See the Kiutra cryostats, or read how ADR compares with a dilution refrigerator.
Common questions
Is magnetic cooling the same as a dilution refrigerator?
No. A dilution refrigerator cools by moving helium-3 across a phase boundary in a helium-3/helium-4 mixture. Magnetic cooling (ADR) cools a paramagnetic material by lowering a magnetic field while the material is thermally isolated. No helium-3 is involved.
Does the magnetic field affect my sample?
The cooling magnet is part of the cryostat design, and manufacturers shield or position it relative to the sample space. Whether the residual field matters depends on your experiment; ask us and we will get the figures for the system you are considering.
Can a magnetic cooler run continuously?
Yes. Continuous ADR uses two or more cooling stages that alternate, so one is always holding the experiment at temperature while the other recycles.
Would helium-3-free cooling work for your experiment?
Tell us the temperature, hold time and sample. We will tell you which Kiutra configuration fits, or that it does not.