Frustrated magnets

Scientists sometimes take magnetism for granted. But some materials behave badly and scientists funded by the UK’s Engineering and Physical Sciences Research Council (EPSRC) are trying to find out why. They are looking at the conventional wisdom of modern theories and finding it does not always stick to exotic magnets.

Scientists from archaeologists to zoologists are attracted to magnetic measurements. Archaeologists use magnetic artefacts to date sites, while a zoologist might be investigating the effects of magnetism on bird brains. Magnetism is fundamental to science, but despite their ubiquity scientists still cannot fully explain magnetic materials.

Professor of Solid State Chemistry at Edinburgh University, Andrew Harrison hopes with the help of EPSRC funding to get inside some exotic magnets, which could provide insight into more common magnetic materials and ultimately help in the design of computer memory and electrical devices. “The study of the fundamental properties of magnets gives us valuable insights into the principles that govern the structure of solids,” he explains, “This has implications that stretch beyond magnetism and into superconductivity.”

The conventional picture of a magnet says each atom in a material acts like a tiny magnet. The magnetic moment, or direction of the North-South divide on the atoms line up parallel (in permanent ferromagnets like iron) or anti-parallel in an up-down arrangement in antiferromagnetic materials, such as manganese oxide. “The reason why such materials behave this way,” says Professor Harrison, “is that below a certain critical temperature the magnetic moments ‘freeze’, or become locked in position.” For an iron magnet this critical temperature is well above room temperature but for other materials they have to be cooled near to absolute zero before they become magnetic. The picture was fairly simple until high-temperature cuprate superconductors were discovered and started throwing up strange results. For instance, some of these materials, at first sight seemed not to have frozen magnetic moments. Such findings inspired researchers to seek new understanding of magnetic materials.

Because the magnetic moments in some superconducting magnets were very small, quantum fluctuations in their orientation overpower the usual forces that normally lock the magnetic moments in place. In the case of lanthanum cuprate, this is not quite enough to upset the conventional picture but a new ingredient – frustration – changes completely the conventional picture. Frustration is found in materials where the magnetic moments are on a triangular rather than a square lattice. “You cannot physically align all the moments antiparallel with their neighbours!” says Harrison. In such a ‘frustrated’ lattice, the conventional forces between magnetic moments are much reduced and the quantum fluctuations are more influential. This kind of magnet may never freeze and the material fluctuates between different states with the moments twitching between the sides of the triangles. The result is that the material exists as a “spin fluid” and such materials could help explain magnetism and possibly superconductivity.
According to Harrison, however, materials that have a small magnetic moment in a frustrated lattice are very rare and have proved difficult to synthesize. “Such a material is one of the Holy Grails in this area of science” he muses There are many materials with triangular lattices, such as vanadium(II) chloride, but they have conventional magnetism. “The challenge is to swap the elements such as vanadium, which have relatively large atomic moments, for magnetic copper ions, which have small atomic moments, while retaining a triangular lattice. So far the wrong lattice forms,” adds Harrison, “It’s as if nature doesn’t want to produce such a material with this kind of unstable ground state, what happens is that the magnet distorts to some other form as it cools down.”
Harrison and collaborators have tried an alternative material type over the last few years. A material of chemical formula ABO2 (A and B are two different metals, O2 is oxygen) can crystallize with the rock salt, sodium chloride NaCl, structure but instead of Na-Cl-Na-Cl? it would contain A-O-B-O-A-O? making a triangular lattice. If A is magnetic and B non-magnetic, as in NaTiO2, one might be able to make a frustrated magnet. Making this material was a huge challenge but eventually Harrison’s collaborators Matt Rosseinsky (Liverpool University) and Simon Clarke (Oxford University) succeeded. Unfortunately, on cooling below its critical temperature, the atoms in the initially triangular lattice layers, jostled each other and the structure distorted. “The strategy of simply knowing which materials might produce the right lattice structure does not always produce a positive result,” says Harrison.
“With our EPSRC grant we are setting our own agenda as chemists, so instead of saying, ‘right nature gives us these materials to work with’, we could try and direct the lattice’s architecture by choosing chemical groups, or ligands, to join the metal ions.” One approach was to build a template that would bind to three metal ions, but not only that it would have to allow the magnetic moments of the metal atoms to couple with each to produce a magnetic material despite their being locked in a triangular lattice.

Working with chemist Neil Robertson the team is trying to design a ligand for the job. They are exploring hexathiabenzene – six-carbon rings with sulfur atoms attached to each carbon. Pairs of sulfur atoms can grab metal ions like pincers, so each hexathiabenzene links three metals together giving a triangular building block for the lattice. Smearing of the electrons – delocalization – through the benzene ring then provides the machinery for magnetic coupling between building blocks. “Although there is an element of design in this, there is also an element of luck,” says Harrison. The team is now investigating what happens when hexathiabenzene templates a copper or cobalt structure, but he admits, “We are still just finding our way around what works, designing a material is a black art.”

 

The team has a couple of likely products – magnetic materials with what they hope is a triangular, frustrated lattice, which will make them behave as spin fluids. The problem remains that these materials form only fine powders, which means no conclusive crystal structure. The other problem they are yet to overcome is that for their materials that critical temperature is a rather chilly five degrees above absolute zero. “The long-term challenge of building molecular magnets that might have technological applications remains a distant target,” explains Harrison. But, while that remains so, they are developing interesting structures that are helping them probe the inner mysteries of magnetism. “Our and other studies might conceivably lead to new generations of functional magnetic materials, for computing and other applications, but I’d be wary of saying it’s just around the corner because it isn’t!”

Nature is not entirely mean. The magnetic jarosite minerals used as rich orange-red pigments and cosmetics for millennia contain iron. Harrison spotted the parent compound, potassium hydroxy iron sulfate, as containing a frustrated crystal lattice while still a post-doctoral researcher in Canada.
He and Andrew Wills of the Laue-Langevin Institute and colleagues, have since studied natural and synthetic jarosites from hundreds of rock samples. “We’ve also adapted the ‘natural preparation’ to include ions not commonly found in nature,” says Harrison. The resulting “spin glasses” are providing insights into magnetic phenomena.

By the way, if you want an answer to the question, “is there a material that blocks magnetic forces?”, check out the SciObs blog, the succinct answer is no.

Alternative Germans

A federal health report by the Robert-Koch-Institute in Berlin, Germany, has revealed that three quarters of Germans use, or have used, complementary medicine and so-called alternative remedies and 90% would recommend such treatments to others. Since 1995, health insurance companies in Germany have had discretion in including or excluding complementary medicine from the treatments they cover. A lack of definitive medical research could be said to assist the companies in reaching their decisions over certain treatments. Stats source: BMJ.

Telesales taken to task

A paper in a recent issue of the journal 雷竞技王者荣耀 Of Otolaryngology – Head & Neck Surgery (2002, Vol 128, Issue 5, pp 571-577) discusses the problems facing telesales people, particularly with regard to voice problems. Telesales staff, the study, led by Katherine Jones of the University of Nebraska found, were twice as likely to report one or more symptoms of vocal “attrition” compared with controls, after adjusting for age, sex, and whether they were smokers or not. Apparently, voice problems and “occupational vocal load” can adversely affect productivity and “are associated with modifiable risk factors.”

We hung-up before finding out what these factors are but was left wondering whether the researchers cold-called the people and whether those interviewed were in the middle of dinner or had had to get out of the bath to answer the phone. In a more malicious moment we’d like to think so.

Cancer mismatch

UK scientists believe a map of how cancer research funding is distributed might help streamline the R&D process and spot underfunding in particular areas. The National Cancer Research Institute has produced the first map of its kind to analyze the distribution of some $390m of cancer research funding from charities and government in the UK. The map revealed that most of the money is spent on the biggest cancers but some rare disorders are being funded disproportionately. (Brit Med Journal)

Wireless power

Cambridge start up Splashpower hopes to commercialize wireless power technology for recharging all your rechargeable devices, cellphones, mp3 players etc, without having to worry about plugging different chargers into power outlets.

Their approach has two parts: the first is a sub-millimeter thin receiver module that can be customized to just about any size, shape or curve of a device. The second part is a thin pad (less than 6 mm) that acts as a universal wireless charging platform and is plugged into the power outlet. Any device fitted with a SplashModule instantly begins to recharge when placed anywhere on the pad.Several devices can be charged at the same time.

Major benefit cited by the company include:

  1. Contactless, efficient, wire-free power
  2. Fast and safe charging rates
  3. Low-cost technology
  4. Low profile

Nothing new under the sun

For those who think the revelation that carcinogens are formed in the nonenzymic browning reaction known as the Maillard reaction is something new, take a look at the following item by 雷竞技官网 from a 1990 issue of New Scientist. Science: Cooking up carcinogens – The chemicals generated in our food, New Scientist vol 127 issue 1729 – 11 August 1990).

Chemical reactions that take place during cooking, baking and preserving generate products that are very important in giving different foods their distinctive aromas and colour. Recently, researchers have discovered that many of these products can reduce the food’s nutritional value, and some can actually be poisonous.

Franze Ledl of Stuttgart University and Erwin Schleicher of the academic hospital Munich-Schwabing in West Germany have studied many of the reactions involved, which are known collectively as the Maillard reaction. They believe that the reaction products could cause some diseases, including certain forms of cancer (Angewandte Chemie, International Edition in English, 1990, vol 29, p 565). If you are an NS subscriber you can read 雷竞技官网 ’s article in the archive. It seems that the potential for carcinogens, such as acrylamide.

Dead parrot sketch

woman brought a very limp parrot into a veterinary surgery. As she lay her pet on the table, the vet pulled out his stethoscope and listened to the bird’s chest. After a moment or two, the vet shook his head sadly and said, “I’m so sorry, Polly has passed away.”

The distressed owner wailed, “Are you sure? I mean, you haven’t done any testing on him or anything. He might just be in a coma or something.”

The vet rolled his eyes, shrugged, turned and left the room, returning a few moments later with a beautiful black labrador. As the bird’s owner looked on in amazement, the dog stood on his hind legs, put his front paws on the examination table and sniffed the dead parrot from top to bottom. He then looked at the vet with sad eyes and shook his head.

The vet fussed the dog and took it out, but returned a few moments later with a cat. The cat jumped up and also sniffed delicately at the ex-bird. The cat sat back, shook its head, meowed and ran out of the room. The vet looked at the woman and said, “I’m sorry, but like I said, your parrot is most definitely 100% certifiably…dead.” He then turned to his computer terminal, hit a few keys and produced a bill which he handed to the woman. The parrot’s owner, still in shock, took the bill.

“£150!,” she cried, “£150 just to tell me my bird is dead!” The vet shrugged. “If you’d taken my word for it the bill would only have been £20, but what with the Lab report and the Cat scan…”

Interesting Beer Supply

A recent spam email was offering me the rather desirable possibility of “firmer, lager breasts”. Perhaps the next one will offer a “bigger beer belly” to go with them? Although too much of the old hop juice often leads to brewer’s droop, so the next spam after that will inevitably be for herbal Viagara (sic) or verbal hiagra.

UPDATE for 4th July 2008: did you take part in the Sciencebase Beer or Wine poll yet? Or, read about the beer vs wine debate (apologies for using the same picture of lager breasts on both posts, by the way).

Silly molecule of the month

As if to prove chemists have a sense of humour, Bristol University’s Paul May has added a list of unusual, but genuine, chemical names to his Molecule of the Month web site. Among the chemical delicacies are the super-tough compound ‘adamantane’ and its chemical cousin ‘bastardane’ (more formally known as ethano-bridged noradamantane.

Then there’s the soccer-ball shaped ‘buckminsterfullerene’ and the natural product ‘megaphone’ from the roots of the plant Aniba megaphylla. There is even a mineral with the enticing name of ‘cummingtonite’ while the stuttering ‘unununium’ makes an elemental appearance too. But, the choice that May puts at the top of his list is…for the sake of decency…best left to visitors to find for themselves. Suffice to say, it involves the arsenic version of the molecule pyrrole and it’s ring shaped: sillymols.htm.

Planetary poop

I just got a software planetarium to review…very nice program allows you to put in your city or coordinates and then shows you the night sky as it would appear if there were no clouds. There’s the water carrier (Aquarius), the archer, and the various planets.

All seems in order, there are a few constellations I wasn’t familiar with – the hare (turns out to be lepus), the air pump (that’s Antlia) and “poop”. Poop? Nice! I did a quick search on some French astronomy websites and came up with the answer, Poop is what the French call Puppis. This one was originally part of the larger constellation Argo Navis. Indeed, it was the stern, or poop deck of the mythological ship, the Argo.

So, not only am I ignorant of the constellations, I don’t know my classics well enough either. But, thankfully the poop isn’t the last turd in constellations.