Coexistence of glassiness and canted antiferromagnetism in triangular quantum Heisenberg antiferromagnets with weak Dzyaloshinskii-Moriya interaction

We present magnetic studies of three triangular quantum Heisenberg antiferromagnets (TQHAF's) with weak additional Dzyaloshinskii-Moriya interaction, Cu-2(OH)(3)(CmH2m+1COO), m=7, 9, and 11. Fits of the de susceptibility data to high-temperature series expansions agree with high-temperature TQHAF behavior. At low temperatures the deviations from the TQHAF predictions suggest a canted antiferromagnetic type of ordering, while the strong peak in the second harmonic of the nonlinear ac susceptibility indicates the development of a spontaneous moment. The frequency dependence of the linear ac susceptibility and the irreversibility in the field-cooled/zero-field-cooled magnetization show that frustration is strong enough to cause glassiness. We propose that the interplay of Heisenberg and Dzyaloshinskii-Moriya exchanges leads to the unusual coexistence of glassiness and canted antiferromagnetism in these geometrically frustrated systems.