Frequency Pulling Effects In The Quasi-Two-Dimensional Ferromagnet Mn-54-Mn(Cooch3)(2)Center Dot 4h(2)O Studied By Nuclear Orientation Techniques

Continuous wave NMR thermally detected by nuclear orientation has been used to investigate the magnetic properties and spin dynamics of the quasi-two-dimensional ferromagnet Mn-54-Mn(COOCH3)(2). 4H(2)O. The system exhibits a frequency pulling effect due to the indirect Suhl-Nakamura interaction between nuclear spins and the electronic spin excitation spectrum is related to the coupling strength of the nuclear spins. The temperature dependence of the frequency pulling effect was measured for the two crystalline sublattices MnI and Mn2 in low magnetic field. The spectra show a structure not predicted theoretically. The current theory is valid only for I = 1/2 with uniaxial crystalline anisotropy fields. The theory of frequency pulling has been extended here to the case of I greater than or equal to 1/2 and nonuniaxial crystalline anisotropy fields and the resonant frequencies and linewidths have been calculated as a function of temperature. The new theory and data agree well in terms of the magnitude and temperature dependence of the frequency pulling. Discrepancies are likely due to simplifying assumptions when calculating the electronic magnon spectrum. Classical and quantum numerical simulations confirm qualitatively the predictions of the model.