SPring-8, the large synchrotron radiation facility

Scientists at Japanese Synchrotron Radiation Research Institute (JASRI; President, Tetsuhisa Shirakawa) have clarified, for the first time in the world, the magnetic ordering formed by only two atomic layers of Ti ions at the interface of an artificial superlattice thin film despite the ferromagnetism of the entire thin film, in collaboration with scientists of Complutense University of Madrid and other institutions.  They also demonstrated the possibility of controlling the magnetic ordering of Ti ions.  In the above-mentioned artificial superlattice thin film, several atomic layers of manganite LaMnO₃ (LMO) and titanite SrTiO₃ (STO), both of which have a perovskite structure^*1, were alternately laminated.

Heterostructure artificial superlattice thin films have different lattice spacings between different ions, thus allowing the ions to distort each other.  This distortion affects electrons and spins, and new electric and magnetic properties that had not been observed have been discovered one after another.  The use of these properties is expected to markedly increase the amount of recordable information in new devices compared with conventional devices; hence, competitive research is ongoing worldwide.  Although Ti exhibits hardly any magnetism under general conditions, it has been theoretically predicted that Ti ions in a perovskite structure may exhibit magnetism and contribute to the increase in the amount of recordable information.  However, it has not been possible to clarify the state of Ti ions in artificial superlattice thin films using conventional experimental techniques because they contain ferromagnetic Mn ions that obscure the magnetism of Ti ions.

The scientists in this research group attempted to individually examine the magnetism of Ti and Mn using the soft X-ray magnetic circular dichroism (XMCD) measurement technique available at SPring-8, which enables high-sensitivity measurement of the magnetism of specific elements.  They succeeded in observing the ferromagnetism of Ti ions that had been theoretically predicted.  The achievements of this research were not only the discovery of the magnetism of Ti ions but also the demonstration that the orientation of the magnetic coupling between Ti and Mn ions can be reversed, i.e., the magnetism of Ti ions can be selectively controlled simply by changing the number of LMO layers.

This discovery indicates that the microscopic magnetism of artificial perovskite-oxide superlattices can be controlled, enabling the use of two different magnetic states as new signals.  These research findings are expected to accelerate the development of next-generation devices, such as high-sensitivity tunnel magnetoresistive (TMR) devices and devices based on electric-field spin control.

This research was jointly carried out by J. Garcia-Barriocanal, F. Y. Bruno, A. Rivera-Calzada, C. Leon, and J. Santamaria of Complutense University of Madrid; J. C. Cezar, P. Thakur, and N. B. Brookes of the European Synchrotron Radiation Facility (ESRF); C. Utfeld and S. B. Dugdale of the University of Bristol; S. R. Giblin and J. W. Taylor at the Rutherford Appleton Laboratory; J. A. Duffy of the University of Warwick; T. Nakamura (senior scientist) and K. Kodama (cooperative scientist; currently assistant professor of Nara National College of Technology) of JASRI; and S. Okamoto of the Oak Ridge National Laboratory.  The achievements of this research were published online in the British scientific journal Nature Communications on 21 September 2010.

(Publication)
"Spin and orbital Ti magnetism at LaMnO₃ / SrTiO₃ interfaces"
J. Garcia-Barriocanal, J.C. Cezar, F.Y. Bruno, P. Thakur, N.B. Brookes, C. Utfeld, A. Rivera-Calzada, S.R. Giblin, J.W. Taylor, J.A. Duffy, S.B. Dugdale, T. Nakamura, K. Kodama, C. Leon, S. Okamoto & J. Santamaria
Nature Communications 1, Article number:82 (2010), published online 21 September 2010