The research team of Christian Binek focuses on interface induced phenomena in magnetic heterostructures grown by molecular beam epitaxy, a state of the art thermal evaporation technique. Ultra high vacuum is a key prerequisite enabling low material deposition rates while keeping rest gas contamination of the samples at a minimum. Deposition at low flux and thermal energies allows growing ultrathin crystalline layers of magnetic materials. Chemical and structural composition is controlled down to the atomic scale and high-purity multilayers with interfaces close to atomic sharpness become feasible. Interfaces of materials in atomic proximity deviate significantly from individual bulk properties.
Christian Binek

Heterostructures of ultra-thin films can be dominated by interface phenomena and provide artificial materials with potentially novel physical properties. Dr. Binek’s group focuses on those interface phenomena which are magnetic in origin. Controlling materials on the nanoscale or below enables the fabrication of new and potentially useful artificial structures. An important part of Binek’s work involves the investigation of multilayers combining magnetoelectric insulating antiferromagnets and metallic ferromagnetic thin films. Recently, a reversible electrically induced shift of the magnetic hysteresis loops along the magnetic field axis, known as electrically-controlled exchange bias, has been achieved by the team. Now they aim on realizing electrically controlled spin valves and tunneling magnetoresistance elements. This new family of spintronic devices uses thin films of magnetoelectric materials as key components. The electric field-induced magnetization of the latter allows switching magnetic states of exchange coupled layers by pure electrical means.

Research involving antiferromagnets as key components is in the tradition of Dr. Binek’s scientific background. He was born and raised in Duisburg, Germany in the heart of the largest economic area of Europe. He earned his PhD in 1995 and received 7 years later his Habilitation and status as Privatdozent at the University of Duisburg-Essen. Throughout this time his research interests involved antiferromagnets and their role as model systems in statistical physics and thermodynamics.

Dr. Binek’s team of graduate students Xi He, Tathagata Mukherjee, Srinivas Polisetty and Yi Wang works together with postdoctoral researcher Sarbeswar Sahoo supported by undergraduate Keith Jones. Together they aim on the realization of spintronic devices combining memory and simple logical functions which ultimately may exceed the functionality of today’s passive magnetoelectronics such as magnetic random access memories, magnetic field sensors and read heads.

Layered nanostructures which cannot be formed by chemical synthesis promise significant innovations in information technologies. At the same time this exciting field allows for fundamental studies in interface magnetism. Dr. Binek’s interests in fundamental aspects of thermodynamics leads to further investigations of dipolar interacting magnetic nanoparticles and magnetic multilayers using antiferromagnetically interacting entities to realize advanced magnetocaloric materials for magnetic refrigeration applications. The former transdisciplinary activity takes place in collaboration with chemist Dr. Redepenning. The latter collaboration obtains theoretical and experimental input from Dr. Skomski and Dr. Sellmyer.

Dr. Binek’s team uses magnetometry, magnetoresistance and magnetooptical methods to characterize nanoscaled magnetic systems. As a member of the Nebraska Center for Materials and Nanoscience (NCMN) and the Materials Research Science and Engineering Center (MRSEC) his group takes advantage of structural characterization techniques and opportunities for collaborations.

All aspects of Dr. Binek’s work are subject to significant funding. The research on nanoscale spintronic systems is funded by NSF through an early career award. Collaborative work on Designing Materials for Electrodes in Spintronic Devices is done together with Dr. Dowben and Dr. Belashchenko and funded by the Nebraska Research Initiative (NRI). Studies on magnetocaloric materials are supported by the Nebraska Center for Energy Sciences Research (NCESR) in addition to support from NCMN and MRSEC where collaboration takes place on a broader scale.

(Spring 2007)