B5: Spin-dependent transport and exchange-biasing in multiferroic heterostructures
Multiferroic materials open up perspectives for new potential applications such as memory elements with electric writing and magnetic reading capability or four-state logic elements fabricated from tunneling junctions with multiferroic or ferroelectric tunneling barriers. In this project new functionalities arising from magnetoelectric effects in multiferroic heterostructures are studied. The project focuses on spin-dependent tunneling as well as exchange biasing in heterostructures based on manganites (La0.7Sr0.3MnO3, YMnO3, TbMnO3, HoMnO3) and titanates (Eu1-xYxTiO3, BaTiO3, PZT).
In the first stage of the project multiferroic single layers are grown by pulsed laser deposition. The electric and magnetic properties of these layers are characterized by a variety of techniques such as SQUID magnetometry, impedance spectroscopy and magnetotransport measurements. The thermodynamically stable bulk phase of HoMnO3 or YMnO3 is of hexagonal symmetry, but films grown on SrTiO3 (001) substrates are orthorhombic. These films show a strong coupling between the complex magnetic order and electric properties. Aim of these studies is a characterization of the magnetic phase transitions as well as a determination of the critical thickness for the ferroelectric order.
In further stages the electric control of exchange-biasing between a multiferroic manganite layer and the archetypical oxide ferromagnet La0.7Sr0.3MnO3 will be studied. This is done by SQUID and ac susceptibility measurements on trilayer samples in which the multiferroic is sandwiched between the ferromagnetic layer and a nonmagnetic electric gate. Moreover, tunneling junctions with multiferroic barriers will be investigated. The idea is not only to use the electric polarization of the multiferroic to influence the tunneling characteristics, but also to seek for signatures of magnetic transitions of the multiferroic barrier in the tunneling conductance. In order to determine the influence of inhomogeneities, defect structures and finite size effects measurements will be made on samples that are patterned on a lateral length scale from 1 mm down to 100 nm.
Principal Investigators
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PD Dr. Michael Ziese ⇒
phone: +49 (0) 341/97 32752 fax: +49 (0) 341/97 32668 |
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Prof. Dr. Pablo D. Esquinazi ⇒
phone: +49 (0) 341/97 32751 fax: +49 (0) 341/97 32668 |
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