(Phys.org)—Magnonics is an exciting extension of spintronics, promising new ways to compute and store magnetic data. What determines the magnetic state of a material is how the electron spins are arranged (not the daily spin, but the quantized angular momentum). If most of the spins point in the same direction, the material is ferromagnetic, like a fridge magnet. If half of the spins go in one direction and the other half in the opposite direction, the material is antiferromagnetic, with no daily magnetism.
There are other types of magnetism. In materials where the electrons are “roaming” – moving rapidly through the crystal lattice like a gas, so that their spins become strongly coupled to their motions – certain crystal structures can cause the spins to precess collectively to the right or to the left in a helix, producing a state called helimagnetism.
Helimagnetism occurs most often at low temperatures; the increase in heat collectively excites the spin structure and eventually destroys the order, releasing the magnetism. In quantum calculations, such collective excitations are treated as particles (“quasiparticles”); excitations that disturb magnetism are called magnons or spin waves. There is a well-developed theory of helimagnons, but little is known experimentally about how helimagnetism forms or relaxes on time scales less than a trillionth of a second, the scale at which magnetic interactions occur Actually.
A team of scientists from the Materials Science Division of the Berkeley Lab, the Physics Department of UC Berkeley, and the Technical University of Munich, led by Jake Koralek and Dennis Meier, studied magnons in a material that becomes helimagnetic below about 30 kelvin: iron silicide doped with cobalt. They studied how helimagnons evolve with increasing temperature, destroying the magnetic order, as well as how magnetic phases are affected by an external magnetic field.
Working in Joseph Orenstein’s lab, the team used an ultrashort laser pulse to excite the cobalt-doped iron silicide crystal, then followed with another laser pulse in quadrillionths of a second. This allowed them to measure how much the helical oscillations had relaxed and how the spin states evolved. The pump-probe experiments were performed over a range of temperatures at various external magnetic field strengths.
The pump pulses created spin waves, or helimagnons, which weakened the magnetic order. Because they were able to resolve helimagnons with ultrashort-time resolution, the researchers discovered an astonishing versatility in spin relaxation depending on the collective organization of electrons. They were able to reveal the underlying spin dynamics of a model traveling magnet system, paving the way for fruitful research programs in the burgeoning field of magnenics.
Go to the heart of frustrated magnetism
For a related study of electron spin transport and spin helices, visit prl.aps.org/abstract/PRL/v109/i24/e246603
Provided by Lawrence Berkeley National Laboratory
Quote: New insight into an intriguing state of magnetism (2012, December 18) retrieved January 15, 2022 from https://phys.org/news/2012-12-insight-intriguing-state-magnetism.html
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