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Full-Text Articles in Physics

Voltage Controlled Magnetism In Cr2o3 Based All-Thin-Film Systems, Junlei Wang, Will Echtenkamp, Ather Mahmood, Christian Binek May 2019

Voltage Controlled Magnetism In Cr2o3 Based All-Thin-Film Systems, Junlei Wang, Will Echtenkamp, Ather Mahmood, Christian Binek

Christian Binek Publications

Voltage-control of exchange biases through active selection of distinct domain states of the magnetoelectric and antiferromagnetic pinning layer is demonstrated for Cr2O3/CoPd heterostructures. Progress and obstacles towards an isothermal switching of exchange bias are discussed. An alternative approach avoiding exchange bias for voltage-controlled memory exploits boundary magnetization at the surface of Cr2O3 as voltage-controlled state variable. We demonstrate readout and switching of boundary magnetization in ultra-thin Cr2O3/Pt Hall bar devices where reversal of boundary magnetization is achieved via magnetoelectric annealing with simultaneously applied ±0.5 V and 400 mT electric and magnetic fields.


Space-Charge Limited Conduction In Epitaxial Chromia Films Grown On Elemental And Oxide-Based Metallic Substrates, C.-P. Kwan, Mike Street, Ather Mahmood, Will Echtenkamp, M. Randle, K. He, J. Nathawat, N. Arabchigavkani, B. Barut, S. Yin, R. Dixit, Uttam Singisetti, Christian Binek, J. P. Bird May 2019

Space-Charge Limited Conduction In Epitaxial Chromia Films Grown On Elemental And Oxide-Based Metallic Substrates, C.-P. Kwan, Mike Street, Ather Mahmood, Will Echtenkamp, M. Randle, K. He, J. Nathawat, N. Arabchigavkani, B. Barut, S. Yin, R. Dixit, Uttam Singisetti, Christian Binek, J. P. Bird

Christian Binek Publications

We study temperature dependent (200 – 400 K) dielectric current leakage in high-quality, epitaxial chromia films, synthesized on various conductive substrates (Pd, Pt and V2O3). We find that trap-assisted space-charge limited conduction is the dominant source of electrical leakage in the films, and that the density and distribution of charge traps within them is strongly dependent upon the choice of the underlying substrate. Pd-based chromia is found to exhibit leakage consistent with the presence of deep, discrete traps, a characteristic that is related to the known properties of twinning defects in the material. The Pt- and V2O3-based films, in contrast, show ...


Electromagnon Excitation In Cupric Oxide Measured By Fabry-Pérot Enhanced Terahertz Mueller Matrix Ellipsometry, Sean Knight, Dharmalingam Prabhakaran, Christian Binek, Mathias Schubert Feb 2019

Electromagnon Excitation In Cupric Oxide Measured By Fabry-Pérot Enhanced Terahertz Mueller Matrix Ellipsometry, Sean Knight, Dharmalingam Prabhakaran, Christian Binek, Mathias Schubert

Christian Binek Publications

Here we present the use of Fabry-Pérot enhanced terahertz (THz) Mueller matrix ellipsometry to measure an electromagnon excitation in monoclinic cupric oxide (CuO). As a magnetically induced ferroelectric multiferroic, CuO exhibits coupling between electric and magnetic order. This gives rise to special quasiparticle excitations at THz frequencies called electromagnons. In order to measure the electromagnons in CuO, we exploit single-crystal CuO as a THz Fabry-Pérot cavity to resonantly enhance the excitation’s signature. This enhancement technique enables the complex index of refraction to be extracted. We observe a peak in the absorption coefficient near 0.705 THz and 215 K ...


Dielectric Properties Of Thin Cr2o3 Films Grown On Elemental And Oxide Metallic Substrates, Ather Mahmood, Mike Street, Will Echtenkamp, Chun Pui Kwan, Jonathan P. Bird, Christian Binek Apr 2018

Dielectric Properties Of Thin Cr2o3 Films Grown On Elemental And Oxide Metallic Substrates, Ather Mahmood, Mike Street, Will Echtenkamp, Chun Pui Kwan, Jonathan P. Bird, Christian Binek

Christian Binek Publications

In an attempt to optimize leakage characteristics of α-Cr2O3 thin films, its dielectric properties were investigated at local and macroscopic scale. The films were grown on Pd(111), Pt(111), and V2O3 (0001), supported on Al2O3 substrate. The local conductivity was measured by conductive atomic force microscopy mapping of Cr2O3 surfaces, which revealed the nature of defects that formed conducting paths with the bottom Pd or Pt layer. A strong correlation was found between these electrical defects and the grain boundaries revealed in the corresponding topographic scans ...


Elastic Properties Of Superconductors And Materials With Weakly Correlated Spins, Christian Binek Jul 2017

Elastic Properties Of Superconductors And Materials With Weakly Correlated Spins, Christian Binek

Christian Binek Publications

It is shown that in the ergodic regime, the temperature dependence of Young’s modulus is solely determined by the magnetic properties of a material. For the large class of materials with paramagnetic or diamagnetic response, simple functional forms of the temperature derivative of Young’s modulus are derived and compared with experimental data and empirical results. Superconducting materials in the Meissner phase are ideal diamagnets. As such, they display remarkable elastic properties. Constant diamagnetic susceptibility gives rise to a temperature independent elastic modulus for ceramic and single crystalline superconductors alike. The thermodynamic approach established in this report, paves the ...


Tuning The Effective Anisotropy In A Voltage-Susceptible Exchange-Bias Heterosystem, Will Echtenkamp, Mike Street, Ather Mahmood, Christian Binek Mar 2017

Tuning The Effective Anisotropy In A Voltage-Susceptible Exchange-Bias Heterosystem, Will Echtenkamp, Mike Street, Ather Mahmood, Christian Binek

Christian Binek Publications

Voltage- and temperature-tuned ferromagnetic hysteresis is investigated by a superconducting quantum-interference device and Kerr magnetometry in a thin-film heterostructure of a perpendicular anisotropic Co/Pd ferromagnet exchange coupled to the magnetoelectric antiferromagnet Cr2O3. An abrupt disappearance of exchange bias with a simultaneous more than twofold increase in coercivity is observed and interpreted as a competition between the effective anisotropy of Cr2O3 and the exchange-coupling energy between boundary magnetization and the adjacent ferromagnet. The effective anisotropy energy is given by the intrinsic anisotropy energy density multiplied by the effective volume separated from the bulk through ...


Dispersion Of Electric-Field-Induced Faraday Effect In Magnetoelectric Cr2o3, J. Wang, Christian Binek Mar 2016

Dispersion Of Electric-Field-Induced Faraday Effect In Magnetoelectric Cr2o3, J. Wang, Christian Binek

Christian Binek Publications

The frequency dependence of the electric-field-induced magneto-optical Faraday effect is investigated in the magnetoelectric antiferromagnet chromia. Two electrically induced Faraday signals superimpose in proportion to the linear magnetoelectric susceptibility α and the antiferromagnetic order parameter η. The relative strength of these contributions is determined by the frequency of the probing light and can be tuned between extreme characteristics following the temperature dependence of α or η. The frequency dependence is analyzed in terms of electric dipole transitions of perturbed Cr3+ crystal-field states. The results allow us to measure voltage-controlled selection, isothermal switching, and temperature dependence of η in a ...


Magnetic Entropy Changes In Nanogranular Fe:Ni61Cu39, Steven A. Michalski, Ralph A. Skomski, Tathagata Mukherjee, Xingzhong Li, Christian Binek, David J. Sellmyer Apr 2011

Magnetic Entropy Changes In Nanogranular Fe:Ni61Cu39, Steven A. Michalski, Ralph A. Skomski, Tathagata Mukherjee, Xingzhong Li, Christian Binek, David J. Sellmyer

Christian Binek Publications

Artificial environment-friendly Gd-free magnetic nanostructures for magnetic cooling are investigated by temperature-dependent magnetic measurements. We consider two-phase nanocomposites where nanoclusters (Fe) are embedded in a Ni61Cu39 matrix. Several composite films are produced by cluster deposition. The average Fe cluster size depends on the deposition conditions and can be tuned by varying the deposition conditions. The quasiequilibrium Curie temperature of the Fe particles is high, but slightly lower than that of bulk Fe due to finite-size effects. Our experiments have focused on ensembles of 7.7 nm Fe clusters in a matrix with a composition close to Ni ...


When Measured Spin Polarization Is Not Spin Polarization, Peter A. Dowben, Ning Wu, Christian Binek Apr 2011

When Measured Spin Polarization Is Not Spin Polarization, Peter A. Dowben, Ning Wu, Christian Binek

Christian Binek Publications

Spin polarization is an unusually ambiguous scientific idiom and, as such, is rarely well defined. A given experimental methodology may allow one to quantify a spin polarization but only in its particular context. As one might expect, these ambiguities sometimes give rise to inappropriate interpretations when comparing the spin polarizations determined through different methods. The spin polarization of CrO2 and Cr2O3 illustrate some of the complications which hinders comparisons of spin polarization values.


Imaging And Control Of Surface Magnetization Domains In A Magnetoelectric Antiferromagnet, Ning Wu, Xi He, Aleksander L. Wysocki, Uday Lanke, Takashi Komesu, Kirill D. Belashchenko, Christian Binek, Peter A. Dowben Feb 2011

Imaging And Control Of Surface Magnetization Domains In A Magnetoelectric Antiferromagnet, Ning Wu, Xi He, Aleksander L. Wysocki, Uday Lanke, Takashi Komesu, Kirill D. Belashchenko, Christian Binek, Peter A. Dowben

Christian Binek Publications

We report the direct observation of surface magnetization domains of the magnetoelectric Cr2O3 using photoemission electron microscopy with magnetic circular dichroism contrast and magnetic force microscopy. The domain pattern is strongly affected by the applied electric field conditions. Zero-field cooling results in an equal representation of the two domain types, while electric-field cooling selects one dominant domain type. These observations confirm the existence of surface magnetization, required by symmetry in magnetoelectric antiferromagnets.


Magnetometry And Transport Data Complement Polarized Neutron Reflectometry In Magnetic Depth Profiling, Yi Wang, Xi He, Tathagata Mukherjee, Mary Lee Fitzsimmons, Sarbeswar Sahoo, Christian Binek Jan 2011

Magnetometry And Transport Data Complement Polarized Neutron Reflectometry In Magnetic Depth Profiling, Yi Wang, Xi He, Tathagata Mukherjee, Mary Lee Fitzsimmons, Sarbeswar Sahoo, Christian Binek

Christian Binek Publications

Exchange coupled magnetic hard layer/soft layer thin films show a variety of complex magnetization reversal mechanisms depending on the hierarchy of interaction strengths within and between the films. Magnetization reversal can include uniform rotation, soft layer biasing, as well as exchange spring behavior. We investigate the magnetization reversal of a CoPt/Permalloy/Ta/Permalloy heterostructure. Here, Stoner-Wohlfarth-type uniform magnetization rotation of the virtually free Permalloy layer and exchange spring behavior of the strongly pinned Permalloy layer are found in the same sample. We investigate the complex magnetization reversal by polarized neutron reflectometry, magnetometry, and magneto-transport. The synergy of combining ...


Robust Isothermal Electric Control Of Exchange Bias At Room Temperature, Xi He, Yi Wang, Christian Binek, Peter A. Dowben Jun 2010

Robust Isothermal Electric Control Of Exchange Bias At Room Temperature, Xi He, Yi Wang, Christian Binek, Peter A. Dowben

Christian Binek Publications

Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with highspeed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr2O3 has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr2O3 single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between ...


Probing Equilibrium By Nonequilibrium Dynamics: Aging In Co/Cr Superlattices, Tathagata Mukherjee, M. Pleimling, Christian Binek Jan 2010

Probing Equilibrium By Nonequilibrium Dynamics: Aging In Co/Cr Superlattices, Tathagata Mukherjee, M. Pleimling, Christian Binek

Christian Binek Publications

Magnetization relaxation is investigated in a structurally ordered magnetic Co/Cr superlattice. Tailored nanoscale periodicity creates mesoscopic spatial magnetic correlations with slow relaxation dynamics when quenching the system into a nonequilibrium state. Magnetization transients are measured after exposing the heterostructure to a magnetic set field for various waiting times. Scaling analysis reveals an asymptotic powerlaw behavior in accordance with a full aging scenario. The temperature dependence of the relaxation exponent shows pronounced anomalies at the equilibrium phase transitions of the antiferromagnetic superstructure and the ferromagnetic to paramagnetic transition of the Co layers. The latter leaves only weak fingerprints in the ...


Piezoelectric Tuning Of Exchange Bias In A Batio3/Co/Coo Heterostructure, Srinivas Polisetty, W. Echtenkamp, Keith Jones, X. He, Sarbeswar Sahoo, Christian Binek Jan 2010

Piezoelectric Tuning Of Exchange Bias In A Batio3/Co/Coo Heterostructure, Srinivas Polisetty, W. Echtenkamp, Keith Jones, X. He, Sarbeswar Sahoo, Christian Binek

Christian Binek Publications

Piezoelectrically controlled strain is used for electric tuning of exchange-bias fields. A generic exchange-bias Co/CoO bilayer is deposited on the surface of a ferroelectric and thus piezoelectric BaTiO3 substrate which allows to apply electrically and thermally tunable stress in the adjacent ferromagnetic Co thin film. The stress-induced strain alters foremost the magnetic anisotropy of the Co film and by that the magnetization orientation at the Co/CoO interface modifying the exchange-bias field. This results in a pronounced electrically induced weakening of the exchange bias but also includes the possibility of tuning the exchange-bias field through a subtle sign ...


Magnetocaloric Properties Of Co/Cr Superlattices, Tathagata Mukherjee, Sarbeswar Sahoo, David J. Sellmyer, Christian Binek Apr 2009

Magnetocaloric Properties Of Co/Cr Superlattices, Tathagata Mukherjee, Sarbeswar Sahoo, David J. Sellmyer, Christian Binek

Christian Binek Publications

Nanostructured materials for refrigeration applications are experimentally realized by molecular beam epitaxial growth of Co/Cr superlattices using mean-field theoretical concepts as guiding principles. Magnetocaloric properties are deduced from measurements of the temperature and field dependence of the magnetization of our samples. More generally, the potential of artificial antiferromagnets for near room-temperature refrigeration is explored. The effects of intraplane and interplane exchange interactions on the magnetic phase diagram in Ising-type model systems are revisited in mean-field considerations with special emphasis on tailoring magnetocaloric properties. The experimental results are discussed in light of our theoretical findings, and extrapolations for future improved ...


Self-Assembly Of Magnetic Ni Nanoparticles Into 1d Arrays With Antiferromagnetic Order, Valery Bliznyuk, Srikanth Singamaneni, Sarbeswar Sahoo, Srinivas Polisetty, Xi He, Christian Binek Jan 2009

Self-Assembly Of Magnetic Ni Nanoparticles Into 1d Arrays With Antiferromagnetic Order, Valery Bliznyuk, Srikanth Singamaneni, Sarbeswar Sahoo, Srinivas Polisetty, Xi He, Christian Binek

Christian Binek Publications

In this paper, we report on the magnetic properties of isolated nanoparticles and interacting nanochains formed by the self-assembly of Ni nanoparticles. The magnetic properties were studied using superconducting quantum interference device (SQUID) magnetometry and magnetic force microscopy (MFM). We demonstrate that single-domain Ni nanoparticles spontaneously form one-dimensional (1D) chains under the influence of an external magnetic field. Furthermore, such magnetic field-driven self-assembly in conjunction with surface templating produces regular arrays of 1D nanochains with antiferromagnetic intra-chain order. The antiferromagnetic order, which is in striking contrast to what is found for non-interacting nanoparticle assemblies within the chains, can be evidenced ...


Temperature Dependence Of The Training Effect In Exchange Coupled Ferromagnetic Bilayers, Christian Binek, Srinivas Polisetty, Sarbeswar Sahoo Nov 2008

Temperature Dependence Of The Training Effect In Exchange Coupled Ferromagnetic Bilayers, Christian Binek, Srinivas Polisetty, Sarbeswar Sahoo

Christian Binek Publications

The temperature dependence of the training effect is studied in an exchange coupled thin-film bilayer composed of a hard ferromagnetic pinning (CoPtCrB) layer in proximity of a soft ferromagnetic pinned (CoCr) layer. Interlayer exchange shifts the hysteresis loops of the soft layer along the magnetic-field axis. This shift is quantified by the bias field in far reaching analogy to the exchange bias field of conventional antiferromagnetic/ferromagnetic heterostructures. A ferromagnetic domain state induced in the hard layer experiences aging very similar to the training behavior of the antiferromagnetic domain state in conventional exchange bias systems. Training originates from changes in ...


Quenching Of The Exchange Bias Training In Fe/Cr2o3/Fe Trilayer, Sarbeswar Sahoo, Christian Binek Oct 2008

Quenching Of The Exchange Bias Training In Fe/Cr2o3/Fe Trilayer, Sarbeswar Sahoo, Christian Binek

Christian Binek Publications

Exchange bias (EB) and its associated training effects are studied in an epitaxial Fe(10 nm)/Cr2O3(2.7 nm)/Fe(10 nm) trilayer heterostructure grown by molecular beam epitaxy. The EB decreases linearly with increasing temperature from T = 5 K to T = 50 K. It changes sign and becomes positive within 50 K < T < 200 K, finally changing back to regular EB for T<200K up to the highest measured temperature of T = 395 K. Remarkably, the latter is far above the bulk Néel temperature TN = 307 K. EB training effects occur only at 5 K < T < 50 K. We show that this training can be quenched by subjecting the system to DC magnetic field, µ0HDC <= 7 T. The applied field most likely induces a temperature dependent spin-flop transition. Upon its removal the antiferromagnetic Cr2O3 pinning layer evolves uniformly into its quasi-equilibrium spin configuration thus leading to quasi-equilibrium EB.


Electrically Controlled Magnetism, Christian Binek, Xi He, Yi Wang, Sarbeswar Sahoo Sep 2008

Electrically Controlled Magnetism, Christian Binek, Xi He, Yi Wang, Sarbeswar Sahoo

Christian Binek Publications

Manipulation of magnetically ordered states by electrical means is a promising approach towards novel spintronics devices. We report on the electric control of surface magnetism in Cr2O3 thin films and uniaxial anisotropy in ferroelectric/ferromagnetic heterostructures, respectively. Artificial magnetoelectricity is realized in a BaTiO3/Fe heterostructure. Here, thermally induced coercivity changes of the Fe hysteresis loop are used to derive the stress imposed by the ferroelectric BaTiO3 substrate on the adjacent Fe film. Electrically induced coercivity changes give rise to a giant magnetoelectric susceptibility in the vicinity of the magnetic coercive field.


Christian Binek: List Of Publications Jul 2008

Christian Binek: List Of Publications

Christian Binek Publications

Lists citations for 60 published articles and one monograph by Christian Binek of the Department of Physics and Astronomy at the University of Nebraska-Lincoln. Includes some links. Current as of July 2008.


Optimization Of Magneto-Optical Kerr Setup: Analyzing Experimental Assemblies Using Jones Matrix Formalism, Christian Binek May 2008

Optimization Of Magneto-Optical Kerr Setup: Analyzing Experimental Assemblies Using Jones Matrix Formalism, Christian Binek

Christian Binek Publications

We present a comparative study on an experimental and theoretical optimization of magneto-optical Kerr setups based on photoelastic modulation and phase sensitive detector methodology. The first and second harmonics, Iomega,2omega, of the reflected light intensity are measured for a CoO/Co magnetic reference film. The magnetic field dependence of the optical off-diagonal Fresnel reflection coefficients rps and rsp follows the sample magnetization. Different Kerr setups provide various dependencies of Iomega,2omega on the reflection coefficients and, hence, on the Kerr ellipticity epsilonK and rotation thetaK. Jones matrix formalism has been used to analyze the impact of a systematic variation ...


Temperature Dependence Of The Training Effect In Exchange Coupled Ferromagnetic Bilayers, Srinivas Polisetty, Sarbeswar Sahoo, Andreas Berger, Christian Binek Jan 2008

Temperature Dependence Of The Training Effect In Exchange Coupled Ferromagnetic Bilayers, Srinivas Polisetty, Sarbeswar Sahoo, Andreas Berger, Christian Binek

Christian Binek Publications

The temperature dependence of the training effect is studied in an exchange coupled thin-film bilayer composed of a hard ferromagnetic pinning (CoPtCrB) layer in proximity of a soft ferromagnetic pinned (CoCr) layer. Interlayer exchange shifts the hysteresis loops of the soft layer along the magnetic-field axis. This shift is quantified by the bias field in far reaching analogy to the exchange bias field of conventional antiferromagnetic/ferromagnetic heterostructures. A ferromagnetic domain state induced in the hard layer experiences aging very similar to the training behavior of the antiferromagnetic domain state in conventional exchange bias systems. Training originates from changes in ...


Isothermal Low-Field Tuning Of Exchange Bias In Epitaxial Fe/Cr2o3/Fe, Sarbeswar Sahoo, Tathagata Mukherjee, Kirill D. Belashchenko, Christian Binek Oct 2007

Isothermal Low-Field Tuning Of Exchange Bias In Epitaxial Fe/Cr2o3/Fe, Sarbeswar Sahoo, Tathagata Mukherjee, Kirill D. Belashchenko, Christian Binek

Christian Binek Publications

Moderate dc magnetic fields of less than 1 T allow tuning the exchange bias in an epitaxially grown Fe 10 nm/Cr2O3 2.7 nm/Fe 10 nm trilayer between negative and positive bias fields. Remarkably, this tunable exchange bias is observed at least up to 395 K which exceeds the Néel temperature of bulk Cr2O3 (307 K). The presence of spontaneous exchange bias and the absence of training effects at room temperature suggest the existence of stable interface moments independent of antiferromagnetic long range order in Cr2O3. Furthermore, the coercivity ...


Ferroelectric Control Of Magnetism In Batio3 /Fe Heterostructures Via Interface Strain Coupling, Sarbeswar Sahoo, Srinivas Polisetty, Chun-Gang Duan, Sitaram S. Jaswal, Evgeny Y. Tsymbal, Christian Binek Oct 2007

Ferroelectric Control Of Magnetism In Batio3 /Fe Heterostructures Via Interface Strain Coupling, Sarbeswar Sahoo, Srinivas Polisetty, Chun-Gang Duan, Sitaram S. Jaswal, Evgeny Y. Tsymbal, Christian Binek

Christian Binek Publications

Reversible control of magnetism is reported for a Fe thin film in proximity of a BaTiO3 single crystal. Large magnetization changes emerge in response to ferroelectric switching and structural transitions of BaTiO3 controlled by applied electric fields and temperature, respectively. Interface strain coupling is the primary mechanism altering the induced magnetic anisotropy. As a result, coercivity changes up to 120% occur between the various structural states of BaTiO3. Up to 20% coercivity change is achieved via electrical control at room temperature. Our all solid state ferroelectric-ferromagnetic heterostructures open viable possibilities for technological applications.


Scaling Behavior Of The Exchange-Bias Training Effect, Christian Binek, Srinivas Polisetty, Sarbeswar Sahoo Aug 2007

Scaling Behavior Of The Exchange-Bias Training Effect, Christian Binek, Srinivas Polisetty, Sarbeswar Sahoo

Christian Binek Publications

The dependence of the exchange-bias training effect on temperature and ferromagnetic film thickness is studied in detail and scaling behavior of the data is presented. Thickness-dependent exchange bias and its training are measured using the magneto-optical Kerr effect. A focused laser beam is scanned across a Co wedge probing local hysteresis loops of the Co film which is pinned by an antiferromagnetic CoO layer of uniform thickness. A phenomenological theory is best fitted to the exchange-bias training data resembling the evolution of the exchange-bias field on subsequently cycled hysteresis loops. Best fits are done for various temperatures and Co thicknesses ...


Piezomagnetism In Epitaxial Cr2o3 Thin Films And Spintronic Applications, Sarbeswar Sahoo, Christian Binek Mar 2007

Piezomagnetism In Epitaxial Cr2o3 Thin Films And Spintronic Applications, Sarbeswar Sahoo, Christian Binek

Christian Binek Publications

Stress-induced perturbation of the antiferromagnetic long-range order in epitaxially grown Cr2O3 thin films gives rise to pronounced piezomagnetism and a significant reduction of the antiferromagnetic ordering temperature. The temperature dependence of the piezomagnetic moment measured by superconducting quantum interference device magnetometry reveals a power law behaviour with a critical exponent 2B=0.66 in accordance with the Ising anisotropy of a three-dimensional system. The observed shift of the Neel temperature allows estimating the internal lateral stress which is in excellent agreement with an independent estimate based on the elastic properties of Cr2O3 and the lattice mismatch at the interface between ...


Dynamic Enhancement Of The Exchange Bias Training Effect, Sarbeswar Sahoo, Srinivas Polisetty, Christian Binek, Andreas Berger Mar 2007

Dynamic Enhancement Of The Exchange Bias Training Effect, Sarbeswar Sahoo, Srinivas Polisetty, Christian Binek, Andreas Berger

Christian Binek Publications

Exchange bias in coupled magnetic thin films and its accompanying training effect are fundamental interface phenomena with significant impact in spintronic applications. Both effects are well known in heterosystems of ferro- and antiferromagnetic thin films. Here, we report on the dynamic enhancement of the training effect in an exchange coupled bilayer of soft and hard ferromagnetic materials. Training is referred to as a gradual change of the bias field, which evolves upon cycling the soft layer through consecutive hysteresis loops. Its dynamic enhancement is observed with increasing sweep rate of the applied magnetic field from quasistatic to the fully dynamic ...


Reversible Hysteresis Loop Tuning, Andreas Berger, Christian Binek, D. T. Margulies, A. Moser, E. E. Fullerton Nov 2005

Reversible Hysteresis Loop Tuning, Andreas Berger, Christian Binek, D. T. Margulies, A. Moser, E. E. Fullerton

Christian Binek Publications

We utilize antiferromagnetically coupled bilayer structures to magnetically tune hysteresis loop properties. Key element of this approach is the non-overlapping switching fi eld distribution of the two magnetic layers that make up the system: a hard magnetic CoPtCrB layer (HL) and a soft magnetic CoCr layer (SL). Both layers are coupled antiferromagnetically through an only 0.6-nm-thick Ru interlayer. The nonoverlapping switching fi eld distribution allows the measurement of magnetization reversal in the SL at low fi elds while keeping the magnetization state of the HL unperturbed. Applying an appropriate high fi eld or high fi eld sequence changes the ...


Electrically Controlled Exchange Bias For Spintronic Applications, Christian Binek, A. Hochstrat, X. Chen, Pavel Borisov, Wolfman Kleemann, Bernard Doudin May 2005

Electrically Controlled Exchange Bias For Spintronic Applications, Christian Binek, A. Hochstrat, X. Chen, Pavel Borisov, Wolfman Kleemann, Bernard Doudin

Christian Binek Publications

Exchange coupling between a magnetoelectric (111)-oriented Cr2O3 single crystal and a CoPt multilayer with perpendicular anisotropy exhibits an exchange bias field proportional to the applied axial electric field. Extrapolation from bulk to thin film magnetoelectric pinning system suggests promising spintronic applications due to coupling between the electric field-controlled magnetization and the magnetization of a neighbor ferromagnetic layer. Pure voltage control of magnetic configurations of tunneling magnetoresistance spin valves is an attractive alternative to current-induced magnetization switching. ©2005 American Institute of Physics


Perpendicular Exchange Bias And Its Control By Magnetic, Stress And Electric Fields, Christian Binek, Pavel Borisov, Xi Chen, S. Sahoo, Wolfman Kleemann Mar 2005

Perpendicular Exchange Bias And Its Control By Magnetic, Stress And Electric Fields, Christian Binek, Pavel Borisov, Xi Chen, S. Sahoo, Wolfman Kleemann

Christian Binek Publications

erpendicular exchange bias (PEB) involving perpendicular magnetic anisotropy (PMA) in both the antiferromagnetic (AF) pinning and the ferromagnetic (FM) sensor layer is expected to become important in future perpendicular recording and sensing devices. Further, because of the reduced spin dimensionality, PEB promises to be easier understandable than the conventional planar exchange bias (EB). In addition to its first realization using the Ising-type AF compounds FeF2 and FeCl2 we have tested control strategies of EB being alternative to the conventional magnetic and thermal ones. Indeed, specific symmetry properties of the pinning layer have been shown to enable mechanical (viz ...