Dr. Christian Binek, Associate Professor
Physics & Astronomy
University of Nebraska - Lincoln
310G T. Jorgensen Hall
Lincoln, NE 68588-0299
office: 402 472-5231
fax:
cbinek2@unl.edu
website: http://physics.unl.edu/~cbinek/index.htm
Current Research
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.
Recent Publications
T.. Mukherjee, S. Sahoo, R. Skomski, D. J. Sellmyer, and Ch. Binek, Magnetocaloric properties of Co/Cr superlattices, Phys. Rev. B. 79, 144406 (2009)
V. Bliznyuk, S Singamaneni, S. Polisetty, S.Sahoo, Xi He, and Ch. Binek, Self-assembly of magnetic Ni nanoparticles into 1D arrays with antiferromagnetic order, Nanotechnology 20, 105606 (2009).
Ch. Binek, “Ising-Type Antiferromagnets: Model Systems iT.. Mukherjee, S. Sahoo, R. Skomski, D. J. Sellmyer, and Ch. Binek, Magnetocaloric properties of Co/Cr superlattices, Phys. Rev. B. 79, 144406 (2009)
S. Polisetty, S. Sahoo, and Ch. Binek, "Scaling Behavior of the Exchange-Bias Training Effect", Phys. Rev. B. 76, 184423 (2007).
S. Sahoo, S. Polisetty, C.-G. Duan, Sitaram S. Jaswal, E. Y. Tsymbal, and Ch. Binek, "Ferroelectric control of magnetism in BaTiO3 /Fe heterostructures via interface strain coupling," Phys. Rev. B 76, 092108 (2007).
S. Sahoo, T. Mukherjee, K. D. Belashchenko, and Ch. Binek, "Isothermal low-field tuning of exchange bias in epitaxial Fe/Cr2O3/Fe," Appl. Phys. Lett. 91, 172506 (2007).
Ch. Binek, S. Polisetty, Xi He, and A. Berger, "Exchange bias training effect in coupled all ferromagnetic bilayer structures," Phys. Rev. Lett. 96, 067201(2006).
Ch. Binek, Xi He, and S. Polisetty, "Temperature dependence of the training effect in a Co/CoO exchange-bias layer," Phys. Rev. B. 72, 054408 (2005).
P. Borisov, A. Hochstrat, X. Chen, W. Kleemann, and Ch. Binek, "Magnetoelectric switching of exchange bias", Phys. Rev. Lett. 94, 117203 (2005).
Ch. Binek and B. Doudin, "Magnetoelectronics with magnetoelectrics," J. Phys. Condens. Matter 17, L39 (2005).
P. Borisov, A. Hochstrat, X. Chen, W. Kleemann, and Ch. Binek, Magnetoelectric switching of exchange bias, Phys. Rev. Lett. 94, 117203 (2005).
Ch. Binek, B.Doudin, Magnetoelectronics with magnetoelectrics, J. Phys. Condens. Matter 17, L39 (2005).
Ch. Binek, Training of the exchange- bias effect: A simple analytic approach, Phys. Rev. B. 70, 014421 (2004).
Ch. Binek, Ising-type antiferromagnets: Model Systems in Statistical Physics and in the Magnetism of Exchange Bias, STMP Vol. 196, Springer-Verlag Berlin Heidelberg (2003). n Statistical Physics and in the Magnetism of Exchange Bias”, in: Springer tracts in modern physics 196, Springer, Berlin, 2003.