Response of magnetic nanoparticles to microwaves

Walton, Derek; Boehnel, Harald; Dunlop, David J.
November 2004
Applied Physics Letters;11/29/2004, Vol. 85 Issue 22, p5367
Academic Journal
Two important processes in ferromagnetic resonance are the first-order absorption of a photon and creation of a single magnon, and a second-order process in which the absorption of a photon results in the creation of two magnons of equal and opposite wave vector [M. Sparks, Ferromagnetic Relaxation (McGraw–Hill, New York, 1964)]. We have found that under resonance conditions for the second-order process, samples containing ∼0.1% magnetite absorb energy from the microwave field at the same rate as a solid magnetite sample. The resultant very high-energy density in the magnetic nanoparticles, coupled with a significant thermal energy barrier with the matrix, leads to a large temperature difference between the grains and their surroundings that makes it possible to magnetize and demagnetize the sample with a relatively small increase in sample temperature.


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