SPIN TRANSITION POLYMER WITH A LARGE HYSTERESIS AROUND ROOM-TEMPERATURE - OPTICAL-RESPONSE AND ELECTRON-PARAMAGNETIC-RESONANCE

A polymer compound [Fe(NH(2)trZ)(3)](NO3)(2) has been studied by optic al response and electron spin resonance (EPR) using Cu2+ and Mn2+ as d opants and paramagnetic probes. The transition between low-spin (LS) a nd high-spin (HS) states of Fe2+ ions occurs with a broad hysteresis l oop around room temperature and is accompanied by a colour change from bright pink in the LS state to chalky white in the HS state. With inc reasing doping level the hysteresis loop narrows and shifts to lower t emperatures. In the HS state of Fe2+ the EPR spectra of Cu2+ and Mn2are severely broadened by spin-spin interactions with paramagnetic HS Fe2+ modulated by a rapid spin-lattice relaxation of the latter ions. The EPR data give evidence of the presence of domains of the LS and HS Fe2+ ions in the transition region.