Scientists solve riddle of strangely behaving magnetic material

Jun 21, 2013
Ames Laboratory scientists Bruce Harmon and Yongbin Lee show a model of the rhombohedral distortion in the structure of LaCoO3 which affects the total electronic energy of the material. Credit: Ames Laboratory

(Phys.org) —Materials scientists at the U.S. Department of Energy's Ames Laboratory have found an accurate way to explain the magnetic properties of a compound that has mystified the scientific community for decades.

The compound of , cobalt and oxygen (LaCoO3) has been a puzzle for over 50 years, due to its strange behavior. While most materials tend to lose magnetism at higher temperatures, pure LaCoO3 is a non-magnetic semiconductor at low temperatures, but as the temperature is raised, it becomes magnetic. With the addition of strontium on the La sites the become even more prominent until, at 18 percent strontium, the compound becomes metallic and ferromagnetic, like iron.

"It's just strange stuff. The material has attracted a lot of attention since about 1957, when people started picking it up and really studying it," said Bruce Harmon, senior scientist at Ames Laboratory. "Since then, there have been over 2000 pertinent papers published."

Traditional theories to describe the compound's behavior originated with physicist John B. Goodenough, who postulated that as temperature rises, the of the d-electrons of cobalt changes, yielding a net .

"Back then it was more of a chemist's of electron orbits that suggested what might be going on," explained Harmon. "It's a very local orbital picture and that theory has persisted to this day. It's become more sophisticated, but almost all the theoretical descriptions are based on that model."

But when Ames Laboratory research partners at the Argonne National Laboratory and the University of California, Santa Cruz performed X-ray measurements of the material, the theory didn't fit what they were observing.

"They knew that we could calculate x-ray absorption and magnetic dichroism, so we started doing that. It is a case where we fell into doing what we thought was a routine calculation, and it turned out we discovered a totally different explanation," said Harmon. "We found we could explain pretty much everything in really nice detail, but without explicitly invoking that local model," said Harmon.

The scientists found that a small rhombohedral distortion of the LaCoO3 lattice structure, which had largely been ignored, was key.

"We found that the total electronic energy of the lattice depends sensitively on that distortion," explained Harmon. "If the distortion becomes smaller (the crystal moves closer to becoming cubic), the magnetic state of the crystal switches from non-magnetic to a state with 1.3 Bohr magnetons per Co atom."

Ames Laboratory scientists Bruce Harmon and Yongbin Lee partnered with the researchers at the Argonne National Laboratory and the University of California, Santa Cruz to publish a paper in Physical Review Letters, "Evolution of Magnetic Oxygen States in Sr-Doped LaCO3."

This new understanding may help the further development of these materials, which are easily reduced to nanoparticles; these are finding use in catalytic oxidation and reduction reactions associated with regulation of noxious emissions from motor vehicles.

Explore further: Scientists discover new family of quasicrystals

More information: prl.aps.org/abstract/PRL/v109/i15/e157204

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User comments : 6

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Macksb
1 / 5 (2) Jun 21, 2013
Perhaps related to the structural phase transition in the superconductor fe/se, which is tetragonal to orthorhombic. Displacements of the fe atoms are involved. Magnetism is apparently not the driving force.
vacuum-mechanics
1 / 5 (6) Jun 21, 2013
The compound of lanthanum, cobalt and oxygen (LaCoO3) has been a puzzle for over 50 years, due to its strange behavior. While most materials tend to lose magnetism at higher temperatures, pure LaCoO3 is a non-magnetic semiconductor at low temperatures, but as the temperature is raised, it becomes magnetic. With the addition of strontium on the La sites the magnetic properties become even more prominent until, at 18 percent strontium, the compound becomes metallic and ferromagnetic, like iron.

Fundamentally we know that magnetic property in material was due to the spin of electrons inside, anyway we do not know why and how electrons' spin create magnetic field! Understand the working mechanism could help the research involve…
http://www.vacuum...21〈=en
ValeriaT
1 / 5 (3) Jun 21, 2013
The material becomes ferromagnetic, if it contains the asymmetric d- and/or f-orbitals, where the unpaired electrons rotate bellow or above the mirror symmetry plane. This axial unbalance induces the precession and vorticity of vacuum, which is known like the magnetic field. This unbalance can be induced with thermal stress of the lattice, which results into asymmetry of atom position withing atom lattice and hybridization of its electrons into axially unsymmetrical orbitals.
alfie_null
4.2 / 5 (5) Jun 22, 2013
Cheers for new discoveries from real scientists. Phooey on cranks who, undaunted, doggedly proselytize their gobbledy-gook pseudo-science (i.e. vacuum mechanics, aether universe).
Code_Warrior
not rated yet Jun 23, 2013
Traditional theories to describe the compound's behavior originated with physicist John B. Goodenough, who postulated that as temperature rises, the spin state of the d-electrons of cobalt changes, yielding a net magnetic moment.

The lab management knew that John B Goodenough to do the work when they hired him, but I wonder if they just settled for Goodenough because they couldn't afford these guys? I guess they thought that John B Goodenough to postulate. Maybe now, John B Goodenough to credit these guys with finding the answer. Sometimes Goodenough gets the job done, other times a higher standard is necessary. If I were Goodenough, I might have been able to come up with the correct answer, but I'm not, so I just poke fun at him in the comment section of a physics website.
TheGhostofOtto1923
3 / 5 (2) Jun 23, 2013
Strangely behaving? No this is strangely behaving
http://www.youtub...CYWlALEs

-Maybe aether is especially infinitely dense inside copper pipes. I dont know.

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