Low and high frequency magnetic relaxations as markers of critical phenomena in chiral 2D metal–organic ferrimagnet

•Zero field ESR line corresponds to spin transitions in singlet states of Mn3+ ions.•Power saturation of zero field ESR line is sensitive to crystal chirality.•Low frequency magnetic relaxation corresponds to magnetic solitons.•ESR line centered at zero field corresponds to intermediate phase.•Chirality affects magnetic relaxation in X-band and low frequency regions. Chiral molecular magnets are important platforms for investigation of non-linear spin phenomena. Mapping of imaginary and real parts of magnetic susceptibility in coordinates field-temperature revealed two spin transitions at 15 K and 21 K in chiral 2D metal–organic ferrimagnet [MnII(HL-pn)(H2O)][MnIII(CN)6]•2H2O titled Brown Needle crystals. Curie temperature corresponds to 21 K, while the transition between ferrimagnetic and spin canting incommensurate phase happens at 15 K. We found that the second and third harmonics of non-linear magnetic susceptibility correspond to time irreversible domain walls displacement. High frequency spin relaxation was monitored by electron spin resonance (ESR) technique. Resonant line at zero field was analyzed in the frame of formalism developed for non-Kramers ions coupled by dipole–dipole interaction. The zero field ESR spectra originates from theS = 2 ground state of the Mn3+ions.This line appears in a narrow temperature range 18–22 K indicating the intermediate magnetic phase arising in the vicinity of the Curie point. Microwave power saturation of the ESR line corresponds to a fast relaxation ∼10 ns. We found the significant difference in this relaxation time in racemic and chiral crystals. Resonant response of the Mn3+ions controlled by dipole–dipole magnetic interaction provides very sensitive indication of crystal fields their modification and it allows one to judge on origin critical phenomena at magnetic phase transition.