Magnetic dipolar effects in the spin-cluster resonance spectra of [(CH3)(3)NH]FeCl3 center dot 2H(2)O

Electron magnetic-resonance (EMR) spectra observed at liquid-helium tempera tures in the one-dimensional Ising ferromagnet [(CH3)(3)NH]FeCl3. 2H(2)O re sult from transitions within the first excited set of cluster states. Impro ved fits of the EMR data in the range 10-35 GHz are presented both with and without the inclusion of the magnetic dipolar interaction within a ferrous chain. In the absence of spin canting, an expression independent of the ch ain length is derived for the matrix elements of the dipolar interaction. J ustification for the omission of spin canting is obtained from the rotation al behavior of the 17-GHz spectrum, which supports a canting angle of less than 10 degrees.