“Magnets are all around us – holding postcards on the refrigerator, pointing to magnetic north on a compass, and in speakers and headphones – yet some mysteries remain,” says Joseph H. Thywissen, a professor of physics at the University of Toronto and a visiting member of the Massachusetts Institute of Technology-based team leading the research. “We have perhaps found the simplest situation in which permanent magnetism can exist."
The scientists observed the behaviour in a gas of lithium atoms trapped in the focus of an infrared laser beam. The gas was cooled to 150 nK, less than a millionth of a degree above absolute zero, which is at -273 C. When repulsive forces between the atoms were gradually increased, several features indicated that the gas had become ferromagnetic. The cloud first became bigger and then suddenly shrunk, and when the atoms were released from the trap, they suddenly expanded faster. These observations were reported in the 18 Sept 2009 issue of Science, in a paper titled “Itinerant Ferromagnetism in a Fermi Gas of Ultracold Atoms”.
This and other observations agreed with theoretical predictions for a transition to a ferromagnetic state. Ferromagnetic materials are those that, below a specific temperature, become magnetized even in the absence of a strong magnetic field. In common magnets, such as iron and nickel that consist of a repeating crystal structure, ferromagnetism occurs when unpaired electrons within the material spontaneously align in the same direction.
“Magnetism only occurs in a strongly interacting regime, where calculations – even using today’s fastest computers – are difficult,” says Thywissen. “Since naturally occurring gases do not have strong enough interactions to address the question, we turned to ultra-cold gases for answers.”
If confirmed, these results may enter textbooks on magnetism, showing that a gas of fermions does not need a crystalline structure to exhibit magnetic properties. “The evidence is pretty strong, but it is not yet a slam dunk,” says MIT physics professor and co-principal investigator David E. Pritchard. “We were not able to observe regions where the atoms all point in the same direction. They started to form molecules and may not have had enough time to align themselves.”
Thywissen's interest in the topic of ultra-cold ferromagnetism originated in theoretical work at Toronto led by Professor Arun Paramekanti in the physics department, along with graduate student Lindsay LeBlanc. "We assumed that ferromagnetism did exist for a gas, and then asked what its properties would be," explains LeBlanc. "Surprisingly, we found there were simple energetic signatures of ferromagnetism – that were eventually observed at MIT."
At MIT, the team was led by principal investigator Wolfgang Ketterle, and included graduate students Gyu-Boong Jo, Ye-Ryoung Lee and Caleb A. Christensen, post-doctoral associate Jae-Hoon Choi, and undergraduate student Tony H. Kim. Thywissen is affiliated with the University of Toronto’s Centre of Quantum Information and Quantum Control, and is a Senior Fellow at Massey College.
Canadian funding agencies include the National Science and Engineering Research Council (NSERC) and the Canadian Institute for Advanced Research (CIfAR). US funding included the National Science Foundation, the Office of Naval Research, through a Multidisciplinary University Research Initiative (MURI) program, and by the Army Research Office with funds from the Defense Advanced Research Projects Agency (DARPA) Optical Lattice Emulator (OLE) program.
MEDIA CONTACTS:Sean Bettam
Sean Bettam | EurekAlert!
First Juno science results supported by University of Leicester's Jupiter 'forecast'
26.05.2017 | University of Leicester
Measured for the first time: Direction of light waves changed by quantum effect
24.05.2017 | Vienna University of Technology
Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.
Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....
Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.
The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....
An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.
We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
24.05.2017 | Event News
23.05.2017 | Event News
22.05.2017 | Event News
26.05.2017 | Life Sciences
26.05.2017 | Life Sciences
26.05.2017 | Physics and Astronomy