Exchange bias in magnetic metal/insulator heterosystems: exchange bias (EB) denotes a magnetic coupling phenomenon at ferromagnetic (FM)/antiferromagnetic (AF) interfaces with strong implications in modern spintronics. It manifests most strikingly in a shift of the FM hysteresis along the magnetic field axis. Although the theoretical details of this unidirectional anisotropy are still unclear, it turns out, that a net AF interface magnetization is essential for the EB and allows for extrinsic control of the effect. Dr. Binek realizes this control in a fully electric manner with the help of novel artificial heterostructures. They combine thin films of magnetoelectric insulators with metallic FM layers grown by MBE and sputtering methods. The magnetoelectric material gives rise to electric induced interface magnetization which couples to the adjacent FM film. Hence, electric tuning of the EB and a new family of spintronic devices become feasible. Their electric transport properties will be explored in collaboration with Dr. Doudin.
Matrix insulated magnetic nanoparticles: When scaling down the FM representation of a bit, thermally activated magnetization reversal of single domain particles has to be considered. The dynamic behavior of such superparamagnetic states and interaction induced collective magnetism in superspin systems are of fundamental interest. Examples for interaction-dominated systems are discontinuous multilayers of CoFe nanoparticles embedded in an Al2O3-matrix. SQUID-magnetometry and low frequency susceptibility are powerful tools in order to probe collective phenomena akin to spinglass-like dynamics. Dr. Binek is interested in mechanisms, which assist the dipolar interaction stabilizing long-range order and domain states. Moreover, an AF matrix gives rise to EB effects and retroactivity of the particles onto the matrix which provides new magnetic properties.
Experimental approach to fundamental aspects of statistical physics: Predicting universal properties of complex systems requires information about the spatial dimensionality and symmetry of the interaction. Magnetic model systems provide access to these parameters. Dr. Binek uses an experimental approach in order to study fundamental aspects of statistical physics with the help of magnetic model systems. Examples are the verification of Griffiths-anomalies and the determination of Lee-Yang zeros by SQUID-susceptometry and magnetometry. Magnetization data of prototypical Ising ferromagnets for instance provide access to the distribution of the LY-zeros. In addition, aspects of non-equilibrium thermodynamics are studied, e.g., from the training effect in EB heterostructures, where relaxation of the AF spin configuration is triggered by consecutively cycled hysteresis loops.
- Ch. Binek, Physics 6, 13 (2013). Controlling Magnetism with a Flip of a Switch
- Ch. Binek and V. Burobina, Appl. Phys. Lett., 102, 031915 (2013). Near-room-temperature refrigeration through voltage-controlled entropy change in multiferroics
- Ch. Binek, Ferroelectrics 426, 2 (2012). Tribute to Professor W. Kleemann
- H. Lu, T. A. George, Y. Wang, I. Ketsman, J. D. Burton, C.-W. Bark, D. J. Kim, J. Wang, C. M. Folkman, Ch. Binek, P. A. Dowben, A. Sokolov, C.-B. Eom, E. Y. Tsymbal, and A. Gruverman, Appl. Phys. Lett. 100, 232904 (2012). Electric modulation of magnetization at the BaTiO3/La0.6Sr0.3MnO3 interfaces
- S. Sahoo, S. Polisetty, Yi Wang, T. Mukherjee, Xi He, S. S. Jaswal, and Ch. Binek, J. Phys.: Condens. Matter 24, 096002 (2012). Asymmetric magnetoresistance in an exchange bias Co/CoO bilaye
- X. He, W. Echtenkamp, and Ch. Binek, Ferroelectrics 426, 81 (2012). Scaling of the Magnetoelectric Effect in Chromia Thin Films
- T. Mukherjee, R. Skomski, S. Michalski, D. J. Sellmyer, and Ch. Binek, J. Appl. Phys. 111, 07A931 (2012). Spin and elastic contributions to isothermal entropy change
- S. Michalski, R. Skomski, X.-Zh. Li, D. Le Roy, T. Mukherjee, Ch. Binek, and D. J. Sellmyer, J. Appl. Phys. 111, 07A931 (2012). Isothermal entropy changes in nanocomposite Co:Ni67Cu33
- Yi Wang, Xi He, T. Mukherjee, M. R. Fitzsimmons, S. Sahoo, and Ch. Binek, J. Appl. Phys. 110, 103914 (2011). Magnetometry and transport data complement polarized neutron reflectometry in magnetic depth profiling
- S. Singamaneni Srikanth, V. N. Bliznyuk, Ch. Binek E. Y. Tsymbal, J. Mater. Chem. 21, 16819 (2011). Magnetic nanoparticles: recent advances in synthesis, self-assembly and applications
- P.A. Dowben, Ning Wu, and Christian Binek, Journal of Physics: Condensed Matter as a viewpoint, J. Phys.: Condens. Matter 23, 171001 (2011). When measured spin polarization is not spin polarization
- T. Mukherjee, S. Michalski, R. Skomski, D.J. Sellmyer, and Ch. Binek, Phys. Rev. B, 83, 214413 (2011). Overcoming the spin-multiplicity limit of entropy by means of lattice degrees of freedom: a minimalist model
- Ning Wu, Xi He, Aleksander Wysocki, Uday Lanke, Takashi Komesu, Kirill D., Belashchenko, Christian Binek and Peter A. Dowben, Phys. Rev. Lett. 106, 087202 (2011). Imaging and control of surface magnetization domains in a magnetoelectric antiferromagnet
- S. Michalski, R. Skomski, T. Mukherjee, X.-Zh. Li, Ch. Binek, and D. J. Sellmyer, J. Appl. Phys. 109, 07A936 (2011). Magnetic entropy changes in nanogranular Fe:Ni61Cu39