© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 724 www.advmat.de www.MaterialsViews.com COMMUNICATION wileyonlinelibrary.com Adv. Mater. 2012, 24, 724–727 DOI: 10.1002/adma.201104250 The renaissance of the field of magnetoelectrics, see Figure 1, [1] which started around the beginning of the last decade, has to date yielded a much deeper understanding of the subject of single phase [2,3] and composite [4,5] magnetoelectrics. The effort on composites yielded first applications, e.g. electric field assisted memory operations [6] and magnetic field sensors. [7,8] Similarly, much progress has been made in magnetic shape memory alloys. [9,10] So far, most attention was devoted to inorganic crystalline magnetoelectrics. There, one can distinguish a variety of mech- anism giving rise to the coupling of the electric and magnetic order parameters. For instance, asymmetric charge ordering in transition metal compounds gives rise to Type-I magnetoelec- tricity [11] in LuFe 2 O 4 [12] and crystalline (TMTTF) 2 X. [13] Type-II magnetoelectrics can be formed by the charges created by non- centrosymmetric spin density waves. [14] In general, magneto- electric order occurs in systems where the kinetic energy of the interacting electrons is smaller than the magnetoelectric poten- tial. Since this potential is usually small, the Curie temperatures of all known magnetoelectrics fall below room temperature. A similar restriction does not apply for excitonic ferromagnets. [15] It is thus in principle possible to find room temperature exci- tonic ferromagnets and even excitonic magnetoelectrics. Here, we present and describe such an excitonic room temperature magnetoelectric, organic semiconducting single crystal poly- 3(hexylthiophene) nanowires (nw-P3HT) doped with buckmin- sterfullerene (C 60 ). Excitonic magnetoelectrics has great potential in spintronics using the effect to control magnetization with an electric field. As present classical spintronic components are based on crystalline materials for which interaction with photons is very limited and controversial. [16] P3HT is a widely exploited material in organic photovoltaic and transistor research. [17] The functionality of photovoltaic materials depends critically on the charges created by light. Singlet (S) excitation generation and subsequent dissociation/ recombination reactions leading to free charge generation are then of primary interest. [18] By contrast, the triplet (T) excitation is only of secondary importance. However, the generation of tri- plets could give rise to excitonic ferromagnetism. [16] We there- fore investigated the potential ferromagnetism of a number of doped n-P3HT polymers concentrating on (nw-P3HT) x (C 60 ) 1-x compositions. In an effort to efficiently create excitons by charge transfer, 10-nm-diameter and approximately 1-μm-long single crystal P3HT nanowires doped with C 60 were prepared (see methods) for this investigation. The charge-transfer exci- tons could lead to anharmonic interaction [19] with the single crystal P3HT lattice which shows an orthorhombic crystal unit cell with lattice constants a ∼ 16.60 Å, b ∼ 7.80 Å, and c ∼ 8.36 Å. [20] We found that the room temperature magnetic moment is large for the composition x = 0.75. Magnetization curves for this composite are shown in Figure 2. There, it can be seen that the thermalized moment determined in a darkened room reaches 10 emu/cm 3 and that saturation is achieved in a field Shenqiang Ren * and Manfred Wuttig* Organic Exciton Multiferroics Prof. S. Ren Department of Chemistry University of Kansas Lawrence, Kansas 66045, USA E-mail: shenqiang@ku.edu Prof. M. Wuttig Department of Materials Science and Engineering University of Maryland College Park, Maryland 20742, USA E-mail: wuttig@umd.edu Figure 1. Traditional triangle indicating the principal interactions between the three extensive parameters, strain, polarization and magnetic moment but now augmented by photonic interactions. Figure 2. Dark, , and illuminated with with a 20 mW 615 nm laser, , room temperature magnetization of nw-P3HT doped with C 60 .