Skip to comments.Molecular fridge can reach millikelvin
Posted on 04/08/2011 4:27:22 PM PDT by neverdem
Scientists have laid the foundations for a high-performance 'molecular fridge' capable of reaching temperatures within a few thousandths of a degree of absolute zero (0K) with a high degree of efficiency. Such ultracoolers could have applications in areas such as ultra-low temperature physics, where alternative technologies such as those that rely on expensive and rare helium-3 could be unsuitable or too costly.
The system relies on a phenomenon called the magneto-caloric effect, where the removal of a magnetic field from a ferromagnetic material causes a drop in temperature. The key to achieving a high magneto-caloric effect is to have a material with many unpaired electrons, all of whose spin states are aligned.
Euan Brechin from the University of Edinburgh in the UK, Keith Murray from Monash University in Australia and Marco Evangelisti from the University of Zaragoza in Spain and their colleagues designed a molecule based on gadolinium and copper, which can be cooled to a few millikelvin.
Molecular structure of the gadolinium and copper complex
'But once you start joining these individual ions together into a large molecule, there is a problem,' says Brechin. 'Ninety-five per cent of all metal-metal interactions are antiferromagnetic - their magnetic moments cancel each other out.'
So the challenge was to retain the electronic and magnetic integrity of the individual ions while incorporating them into a molecule capable of being processed. 'The key is to use organic connector ligands,' says Brechin. 'We use a polyalkoxide - when it is deprotonated the oxygens can bridge the metals. We are almost making a metal oxide but are stopping growth by encapsulating the metal centres in an organic shell.' This produces a crystalline material consisting of discrete molecules, each retaining its important characteristics. When a magnetic field is removed, significant temperature reductions can be achieved at the molecular level and hence in the whole material.
'When we change the magnetic field by 1 tesla the temperature falls by 2 kelvin,' says Brechin. 'This is a very big drop. So if you take the sample material down to 4K by conventional means, you can then take it to very close to absolute zero extremely efficiently.'
Commenting on the research Eric McInnes, an expert in low-temperature magnetic refrigerants at the University of Manchester in the UK, says, 'This new material adds to the growing family of magnetic cluster compounds that show considerable promise for low-temperature cooling applications, but it raises the bar for the potential level of performance.'
Molecular coolers: The case for [CuII5GdIII4]
Stuart K. Langley, Nicholas F. Chilton, Boujemaa Moubaraki, Thomas Hooper, Euan K. Brechin, Marco Evangelisti and Keith S. Murray, Chem. Sci., 2011
seems like the kind of thing you would find interesting
finally.....a cold beer.
This could have huge ramifications but the 'conventional means' statement is probably a deal killer for most of them. I assume that means liquid helium and perhaps liquid nitrogen as well. Or maybe there are some neat coolers now in use. It's been a long, long time since I paid any attention to this technology.
But getting to absolute zero by affordable means is a laudable goal. Lots of applications.
As I understand it, getting to absolute zero isn’t possible as the atoms that hold the cooler together would no longer be cohesive. Is this correct?
Yes, especially those gladiolas. Pretty flower. ;-)
Thanks for the ping. The article doesn't spell out any potential real-world applications but I suppose someone will find some.
Millie Kelvin was delighted to finally have been reached.
Hellloooooo.....did you see the post about COLD BEER? (although, i'm more of a margarita girl, myself...and i'm sure I can adjust accordingly)
Idunno. The prez seems to be awfully close.
Hah! They laughed at me when I proposed changing the magnetic field by 1, maybe 2 teslas. Who's laughing now! Ha ha!
Yeah, but I try not to think about drunk physicists.
[Molecular fridge can reach millikelvin]
Almost as fridgid as my ex!
although....how else are we ever going to come up with a unified theory? eh? *that* will definitely involve some kind of alcohol, I'd be willing to bet. ;)
I haven't heard that but I can't dispute it. As a practical matter you cannot actually make it although getting below 4 degrees Kelvin should certainly be possible.
When I was involved in cryogenics we were using a liquid nitrogen vessel to house a liquid helium vessel. This combination was used to cool a liquid helium maser (not laser) to 4.2 degrees Kelvin for use in radio astronomy telescopes and (probably -I'll never know) military satellite ulta low noise communications.
At these low temperatures a maser could deliver noise temperatures of under 10 degrees K, certainly state of the art in those days and equivalent to Noise Figures of something like 0.1 db. I assume there is something better now, probably helium cooled solid-state amplifiers of some sort.
And all along I thought the closest we got to absolute Zero was at 1600 Pennsylvania Avenue.
A liquid helium vessel within a larger liquid nitrogen vessel is the standard for cooling the superconducting magnets used in commerical nuclear magnetic resonance spectrometers employed in chemical analysis - refilling the liquid helium as it slowly evaporates is a real drag, since doing it wrong causes the magnet coils to warm, with a very rapid (and mildly scary) evaporation of the liquid helium.
Sounds like there hasn't been much progress in this area in decades. Sad to say.
For those who have never seen liquid nitrogen it is really something - a shimmering clear liquid. It rapidly boils off in an open container but not so fast that you can't stick your finger in it. I don't recommend this but it is possible if you are really quick. The boiling nitrogen around your finger will temporarily insult it. Leave in in for a few seconds and lose a finger. Those were the days.
If you're hoping to see liquid helium I wish you luck. It boils off essentially instantly when exposed to room temperature.
same old. same old.
Just another implementation of the Giauque cycle, many decades old. Look it up.
But again many Freepers are not that knowledgeable of past technologies. So the post is worthwhile for the present audience.
Apparently the journalist/(science writers) have a shallow science background and can do a much better job in giving proper background to new scientific/engineering developments.
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