Origin of Multiferroicity in the Hexagonal Manganite and Ferrite Systems

<strong>Seminar of the School of Physical Sciences</strong> <strong>Origin of Multiferroicity in the Hexagonal Manganite and Ferrite Systems</strong> <strong>Hena Das</strong> (University of California, Berkeley) Date:&nbsp;<strong>November 22, 2016</strong> <strong>Abstract:</strong>&nbsp;In recent years Transitional Metal Oxides (TMOs) have captivated the imagination of the researchers in the field of Material Science because of their tremendous utilitarian worth for the next generation energy and information technologies. This class of materials displays a fascinating range of phenomenon which includes ferromagnetism, ferroelectricity, colossal magneto-resistivity, high temperature superconductivity, magneto optics etc. The key to the discovery of what other interesting properties these materials exhibit and in how many more ways their potential can be harnessed in device applications lies in the development of microscopic understanding of structural, magnetic and electronic properties of known materials. Here I will discuss the origin of room temperature multiferroicity in hexagonal manganite and ferrite systems, as revealed in course of my research through first-principles approach. We explained the non-trivial origin of magneto electric (ME) coupling in hexagonal manganite and ferrite systems using a combination of theoretical tools like Density Functional Theory (DFT) based first-principles electronic structure methods, group theoretic techniques and microscopic models [1,2]. Our researches showed how a non-polar trimer lattice distortion not only induced a polarization but also a net magnetization and bulk ME coupling. We were led to propose that this induced polarization, net magnetization and bulk ME coupling, in turn led to the existence of a bulk linear ME vortex domain structure or a bulk ME coupling such that if the direction of the polarization was reversed so did the direction of magnetization. Our recent findings showed that how these improper ferroelectrics could be used to construct room temperature multiferroic superlattices with strong magnetization and ME coupling [3]. It was revealed to us that the same trimer lattice distortion enhanced magnetic transition temperature by reducing the geometric frustration at the triangular ferrite layer, which directed a wide compositional space to find new room temperature magnetoelectric multiferroic hexagonal TMOs. [1] Hena Das, Aleksander L. Wysocki, Yanan Geng, Weida Wu and Craig J Fennie, Nature Communications 5, 2998 (2014). [2] Yanan Geng, Hena Das, Aleksander L. Wysocki, N. Lee, Y.J. Choi, S-W. Cheong, M. Mostovoy, Craig J. Fennie, and Weida Wu, Nature Materials 13, 163-167 (2014). [3] Julia A. Mundy, Charles M. Brooks, Megan E. Holtz, Jarrett A. Moyer, Hena Das, Alejandro F. Rebola, James D. Clarkson, John T. Heron, Steven M. Disseler, Rainer Held, Robert Hovden, Elliot Padgett, Qingyun Mao, Hanjong Paik, Rajiv Misra, Lena F. Kourkoutis, Julie A. Borchers, William D. Ratcliff, Ramamoorthy Ramesh, Craig J. Fennie, Peter Schiffer, David A. Muller and Darrell G. Schlom, Accepted in Nature (2016). &nbsp;