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Joel S. Helton, Assistant Professor
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Frustrated Magnetism

Frustration

In many crystalline solid materials, transition metal or rare earth ions have unpaired electrons in their outer orbitals, giving a net localized magnetic moment to these ions.  Exchange interactions between these magnetic spins will favor arrangements where neighboring moments are either parallel (ferromagnetic) or antiparallel (antiferromagnetic).  In geometrically frustrated magnets, the magnetic spins are arranged on a crystal lattice where no ordered state can simultaneously satisfy all nearest-neighbor interactions.  In materials featuring some combination of geometric frustration, low-dimensionality, strong quantum fluctuations, competing interactions, and disorder the static antiferromagnetic order can be destroyed in favor of novel quantum ground states.  Among these unique ground states are quantum spin liquids, spin glasses, and spin ice.  

Midshipmen interested in frustrated magnetism can become involved in this research in a variety of ways.  Students can work in lab to synthesize powder samples of new compounds that display low-spin magnetic moments on geometrically frustrated lattices.  Students can characterize and measure these samples at USNA through techniques such a x-ray diffraction and magnetometry.  And finally, interested physics majors can participate in collecting and analyzing data from neutron scattering experiments that directly probe the magnetic order and fluctuations in these samples.

Kagome Spectrum

Measured neutron scattering intensity of the spin-1/2 kagome lattice antiferromagnet ZnCu3(OH)6Cl2.  This data was measured using the MACS spectrometer at the NIST Center for Neutron Research.

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