  In this letter we investigated the temperature-dependent Raman spectra of
CaMn7O12 helimagnet from room temperature down to 10 K. The temperature
dependence of the Raman mode parameters show remarkable anomalies for both
antiferromagnetic and incommensurate transitions that this compound undergoes
at low temperatures. The anomalies observed at the magnetic ordering transition
indicate a spin-phonon coupling at higher-temperature magnetic transition in
this material, while a magnetostrinction effect at the lower-temperature
magnetic transition.
