63,65Cu NMR study of the magnetically ordered state of the multiferroic CuFeO2

Ogloblichev, Vasily
Sadykov, Almaz
Furukawa, Yuji
Ding, Qing-Ping
Smolnikov, Alexey
Piskunov, Yuri
Mikhalev, Konstantin
Gerashenko, Alexander
Wu, Anhua
Barilo, Sergei
Shiryaev, Sergei
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Ames Laboratory
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Physics and Astronomy
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Field-swept 63,65Cu NMR spectra under magnetic fields up to 8.3 T at a constant NMR frequency and temperatures T < 12 K on a single crystalline sample of multiferroic CuFeO2 were measured and analyzed. When the magnetic field is applied along the c axis, a nearly zero internal magnetic field at the Cu site in magnetic ordered state was observed. This is explained by the perfect cancellation of the internal fields produced by the 6 nearest neighbor Fe3+ (S = 5/2) ions, revealing the magnetic structure to be a collinear four-sublattice structure. On the other hand, when the magnetic field is applied along the ab plane, we observed a finite internal field at the Cu sites, which is due to the canting of the Fe moments. Strong change in the NMR signal intensity is observed around 7–8 T, corresponding to the magnetic phase transition from the collinear magnetic to ferroelectric incommensurate states. The ratio of the two magnetic phases significantly depends on the history of the change in the external magnetic field and the temperature of the sample. The details of history dependence of the ratio were discussed.

63, 65Cu NMR, Frustrated systems, Collinear magnetic structure, Delafossite structure