• Demagnus – Magnetic Cooling physics T-shirt
  • Demagnus – Magnetic Cooling physics T-shirt
  • Demagnus – Magnetic Cooling physics T-shirt
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DemagnusAdiabatic Demagnetisation

Demagnus – Adiabatic Demagnetisation Physics T-Shirt

$29.99 USD
$29.99 USD
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S–5XL
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How do you get colder than liquid helium? Align the spins of a paramagnetic salt with a strong field, let the heat drain away, then isolate it and slowly turn the field off. The spins disorder by taking energy from the lattice, so the salt cools. Giauque and MacDougall reached below 1 K this way in 1933. Pixel-art unisex tee; equation, symbols and sources in the physics panel below.

Color
Size

Size guideS–5XL · inches

Details

Size & fitS–5XL

Unisex heavy cotton (Gildan 5000), classic fit.

SizeWidthLengthSleeve
S182815.1
M202916.5
L223018
XL243119.5
2XL263221
3XL283322.4
4XL303423.7
5XL323525

Measurements in inches, ±1.5 in tolerance.

ShippingFree US

Free US shipping · $10 flat shipping outside the US. Printed to order for you.

Delivery times & where we ship

Returns & replacements21 days

Every item is printed to order, so we can’t accept returns or exchanges for change of mind, or if you ordered the wrong size or colour.

Print defect, misprint, damage or the wrong item? We’ll send a free replacement, or a refund if you prefer. Report it within 21 days of delivery with a photo; no need to send it back.

Full refund & replacement policy

The physics

Line up the spins of a paramagnetic salt with a strong field while it sits in liquid helium, and let the heat of magnetising escape. Then isolate it and slowly turn the field down.

For an ideal paramagnet the spin entropy depends only on B/T, so if no heat flows in, temperature must fall with the field. Peter Debye and William Giauque proposed it in 1926; Giauque and MacDougall reached 0.25 K in 1933.

Demagnus relaxes the field. Freeze.

Equations

\[S = S\!\left(\frac{B}{T}\right)\;\Rightarrow\; \frac{T_f}{T_i} = \frac{B_f}{B_i}\quad\text{(ideal paramagnet, adiabatic)}\]
\[T_f = T_i\sqrt{\frac{B_f^{2}+b^{2}}{B_i^{2}+b^{2}}}\quad\text{(with internal field } b\text{)}\]
SymbolMeaningUnit
\(S\) entropy of the spin system \(\mathrm{J/K}\)
\(B\) applied magnetic field \(\mathrm{T}\)
\(T\) temperature \(\mathrm{K}\)
\(T_i, T_f\) temperature before and after demagnetising \(\mathrm{K}\)
\(B_i, B_f\) field before and after demagnetising \(\mathrm{T}\)
\(b\) effective internal field from spin–spin interactions \(\mathrm{T}\)

Sources

  1. Giauque & MacDougall (1933) Attainment of Temperatures Below 1° Absolute by Demagnetization of Gd2(SO4)3·8H2O, Phys. Rev. 43, 768
  2. NobelPrize.org — William F. Giauque, Nobel Prize in Chemistry 1949
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