SPIN-CLUSTER RESONANCE AT 9 GHZ IN THE ONE-DIMENSIONAL ISING FERROMAGNET [(CH3)3NH]FECL3.2H2O

Low-temperature magnetic-resonance spectra at 9.2-9.3 GHz in single cr ystals of the one-dimensional Ising ferromagnet FeTAC, [(CH3)3NH] FeCl 3.2H2O, were strongly anisotropic with minima in the field occurring f or H parallel to the easy axis. A ''strong'' signal in this orientatio n with a g value of 8.8 at 5.5 K (after correction for internal demagn etization and exchange fields) is identified with transitions between neighboring spin-cluster resonances. Possible origins of broad and wea k lines, with maximum corrected g values of 13 and 3.7 are discussed. Spectra from samples of different shape are consistent with sample-dep endent demagnetization fields.