Solution-processed multiferroic thin-films with large magnetoelectric coupling at room-temperature

Experimental realization of thin films with a significant room-temperature magnetoelectric coupling coefficient, α_ME, in the absence of an external DC magnetic field, has been thus far elusive. Here, a large coupling coefficient of 750 ± 30 mV Oe^-1 cm^-1 is reported for multiferroic polymer nanocomposites (MPCs) thin-films in the absence of an external DC magnetic field. The MPCs are based on PMMA-grafted cobalt-ferrite nanoparticles uniformly dispersed in the piezoelectric polymer poly(vinylidene fluoride-co-trifluoroethylene, P(VDF-TrFE). It is shown that nanoparticle agglomeration plays a detrimental role and significantly reduces α_ME. Surface functionalization of the nanoparticles by grafting a layer of poly(methyl methacrylate) (PMMA) via atom transfer radical polymerization (ATRP) renders the nanoparticle miscible with P(VDF-TRFE) matrix, thus enabling their uniform dispersion in the matrix even in submicrometer thin films. Uniform dispersion yields maximized interfacial interactions between the ferromagnetic nanoparticles and the piezoelectric polymer matrix leading to the experimental demonstration of large α_ME values in solution-processed thin films, which can be exploited in flexible and printable multiferroic electronic devices for sensing and memory applications.