Colloquium on April 28th, 2008

Novel routes to Multiferroics

As this new century unfolds the study of materials possessing coupled magnetic and ferroelectric order –multiferroics– is revitalized, after pioneering work in the 1950s-1960s [1,2]. New classes of materials were found to be ferroelectric and exhibiting an exceptionally strong sensitivity to applied magnetic fields. These multiferroics show many dramatic effects, such as a giant magneto-capacitance, magnetically induced electric polarization flops and a rotation of electric polarization in a periodically varying magnetic field [3-5]. These effects are not only interesting from a fundamental point of view but can also be directly relevant for sensor, transducer and memory device applications [2]. This motivated Science Magazine a few months ago to identify the field of multiferroics as an Area to Watch [6]. In the colloquium I will discuss new theoretical possibilities to obtain multiferroic couplings in systems that exhibit combinations of charge and spin order [6-10].

[1] N. Spaldin and M. Fiebig, Science 309, 391 (2005).
[2] W. Eerenstein, N. Mathur and J. F. Scott, Nature 442, 759 (2006).
[3] T. Kimura, et al., Nature 426, 55 (2003).
[4] T. Goto, et al., Phys. Rev. Lett. 92, 257201 (2004).
[5] N. Hur, et al., Nature 429, 392 (2004).
[6] Science, 318, 21 (2007).
[7] D. Efremov, J. van den Brink and D. Khomskii, Nature Materials 3, 853 (2004).
[8] J. Betouras G. Giovannetti and J. van den Brink, Phys. Rev. Lett. 98, 257601 (2007).
[9] G. Giovannetti and J. van den Brink, preprint cond-mat/0802.0653 (2008).
[10] J. van den Brink and D. Khomskii, preprint cond-mat/0803.2964 (2008).