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Full-Text Articles in Physics

Magnetoelectric Switching Of Exchange Bias, Pavel Borisov, Andreas Hochstrat, Xi Chen, Wolfgang Kleeman, Christian Binek Mar 2012

Magnetoelectric Switching Of Exchange Bias, Pavel Borisov, Andreas Hochstrat, Xi Chen, Wolfgang Kleeman, Christian Binek

Christian Binek

The perpendicular exchange bias field, HEB, of the magnetoelectric heterostructure Cr2O3(111)/(Co/Pt)3 changes sign after field cooling to below the Néel temperature of Cr2O3 in either parallel or antiparallel axial magnetic and electric freezing fields. The switching of HEB is explained by magnetoelectrically induced antiferromagnetic single domains which extend to the interface, where the direction of their end spins controls the sign of HEB. Novel applications in magnetoelectronic devices seem possible.


When Measured Spin Polarization Is Not Spin Polarization, Peter A. Dowben, Ning Wu, Christian Binek Mar 2012

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

Christian Binek

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.


Yang-Lee Edge Singularities Determined From Experimental High-Field Magnetization Data, Christian Binek, Wolfgang Kleemann, H. Aruga Katori Mar 2012

Yang-Lee Edge Singularities Determined From Experimental High-Field Magnetization Data, Christian Binek, Wolfgang Kleemann, H. Aruga Katori

Christian Binek

The isothermal magnetization m (H) of the metamagnet FeCl2 is measured in axial magnetic fields 0 ≤ μ0Ha ≤ 12 T at temperatures 34 ≤ T ≤ 53 K above the Néel temperature, where the system is essentially a two-dimensional Ising ferromagnet. The analysis of the data indicates experimental accessibility of the critical exponent μ of the Yang-Lee edge singularities. They manifest themselves in divergences of the density functions g(θ), which quantify the distribution of the zeros of the partition function on the Lee-Yang unit circle in the complex plane. In accordance with the hypothesis of universality, a critical exponent close to the ...


Electrically Controlled Exchange Bias For Spintronic Applications, Christian Binek, A. Hochstrat, X. Chen, P. Borisov, W. Kleeman, B. Doudin Mar 2012

Electrically Controlled Exchange Bias For Spintronic Applications, Christian Binek, A. Hochstrat, X. Chen, P. Borisov, W. Kleeman, B. Doudin

Christian Binek

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


Reversible Hysteresis Loop Tuning, Andreas Berger, Christian Binek, D. T. Margulies, A. Moser, E. E. Fullerton Mar 2012

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

Christian Binek

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 ...


Exchange Bias Training Effect In Coupled All Ferromagnetic Bilayer Structures, Christian Binek, Srinivas Polisetty, Xi He, A. Berger Mar 2012

Exchange Bias Training Effect In Coupled All Ferromagnetic Bilayer Structures, Christian Binek, Srinivas Polisetty, Xi He, A. Berger

Christian Binek

Exchange coupled bilayers of soft and hard ferromagnetic thin films show remarkable analogies to conventional antiferromagnetic/ferromagnetic exchange bias heterostructures. Not only do all these ferromagnetic bilayers exhibit a tunable exchange bias effect, they also show a distinct training behavior upon cycling the soft layer through consecutive hysteresis loops. In contrast with conventional exchange bias systems, such all ferromagnetic bilayer structures allow the observation of training induced changes in the bias-setting hardmagnetic layer by means of simple magnetometry. Our experiments show unambiguously that the exchange bias training effect is driven by deviations from equilibrium in the pinning layer. A comparison ...


Entropy Localization In Magnetic Compounds And Thin-Film Nanostructures, Ralph Skomski, Christian Binek, Steven A. Michalski, Tathagata Mukherjee, Axel Enders, David J. Sellmyer Mar 2012

Entropy Localization In Magnetic Compounds And Thin-Film Nanostructures, Ralph Skomski, Christian Binek, Steven A. Michalski, Tathagata Mukherjee, Axel Enders, David J. Sellmyer

Christian Binek

The effect of nanostructuring on the magnetic entropy of materials for room-temperature magnetic cooling is investigated by model calculations. The materials are structurally inhomogeneous with a large number of nonequivalent crystallographic sites. In the mean-field Heisenberg model, the entropy density is a unique function of the local magnetization so that the coupled set of nonlinear mean-field equations yields not only the magnetization but also the entropy density. Since most of the entropy is localized near grain boundaries, nanomagnetic cooling requires small feature sizes. Magnetic anisotropy is a substantial complication, even on a mean-field level, but the corresponding corrections are often ...


Magnetic States Of Granular Layered Cofe-Al2O3, J.B. Sousa, G.N. Kakazei, Y.G. Pogorelov, J.A.M. Santos, O. Petracic, Wolfgang Kleemann, Christian Binek, Susana Cardoso De Freitas, P.P. Freitas, M.M. Pereira De Azevedo, N.A. Lesnik, Stanislav Rokhlin, P.E. Wigen Mar 2012

Magnetic States Of Granular Layered Cofe-Al2O3, J.B. Sousa, G.N. Kakazei, Y.G. Pogorelov, J.A.M. Santos, O. Petracic, Wolfgang Kleemann, Christian Binek, Susana Cardoso De Freitas, P.P. Freitas, M.M. Pereira De Azevedo, N.A. Lesnik, Stanislav Rokhlin, P.E. Wigen

Christian Binek

The granular layered magnetic system Co80Fe20(t)/Al2 O3 (3 nm), where the Co80Fe20 layers of nominal thickness t form separate, almost spherical magnetic granules of typical diameter 2-3 nm between the Al2O3 spacers, was studied. We discuss measurements of the dc and ac magnetic susceptibility χ for 1 nm


Freezing Field Dependance Of The Exchange Bias In Uniaxial Fef2-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek Mar 2012

Freezing Field Dependance Of The Exchange Bias In Uniaxial Fef2-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek

Christian Binek

The exchange bias effect is measured for the first time in FeF2–CoPt heterosystems with perpendicular anisotropy. The exchange previous field exhibits a strong dependence on the axial previous freezing field. This behavior is explained in terms of the microscopic spin structure at the interface, which is established on cooling to below TN. We calculate the dependence of the spin structure on the previous freezing field within the framework of an Ising model. It takes into account the Zeeman energy as well as an antiferromagnetic exchange coupling between the adjacent layers at the interface.


Field-Induced Transverse Spin Ordering In Febr2, O. Petracie, Christian Binek, Wolfgang Kleemann, U. Neuhausen, H. Lueken Mar 2012

Field-Induced Transverse Spin Ordering In Febr2, O. Petracie, Christian Binek, Wolfgang Kleemann, U. Neuhausen, H. Lueken

Christian Binek

Weak first-order phase transitions from axial to oblique spin ordering in FeBr2 are evidenced by superconducting quantum interference device magnetometry in axial fields H1(T) above the multicritical point, Hm=2.4 MA/m, Tm=4.6 K, and below the antiferro-to-paramagnetic phase line, Hc (T), in agreement with recent specific-heat data [H. Aruga Katori, K. Katsumata, and M. Katori, Phys. Rev. B 54, R9620 (1996)]. The ordering of the in-plane moments is probably due to nondiagonal coupling to the longitudinal ones, both of which increase discontinuously at H1 (T) only under an additional symmetry-breaking transverse field.


Interacting Ferromagnetic Nanoparticles In Discontinuous Co80Fe20/Al2O3 Multilayers: From Superspin Glass To Reentrant Superferromagnetism, W. Kleeman, O. Petracic, Christian Binek, G.N. Kakazei, Yu. G. Pogorelov, J.B. Sousa, Susana Cardoso De Freitas, P.P. Freitas Mar 2012

Interacting Ferromagnetic Nanoparticles In Discontinuous Co80Fe20/Al2O3 Multilayers: From Superspin Glass To Reentrant Superferromagnetism, W. Kleeman, O. Petracic, Christian Binek, G.N. Kakazei, Yu. G. Pogorelov, J.B. Sousa, Susana Cardoso De Freitas, P.P. Freitas

Christian Binek

Dipolar superferromagnetism with reentrant low-temperature superspin glass behavior is observed on a randomly distributed ferromagnetic nanoparticle systems in discontinuous metal-insulator multilayers [Co80Fe20/Al2O3 (3 nm)] 10 with nominal thickness 1.1<~t<~1.3 nm by use of ac susceptometry and dc magnetometry. At t=1.0 nm, superspin glass-like freezing is evidenced by the criticality of dynamic and nonlinear susceptibilities.


Magnetic Entropy Changes In Nanogranular Fe:Ni61Cu39, Steven A. Michalski, Ralph A. Skomski, Tathagata Mukherjee, Xingzhong Li, Christian Binek, David J. Sellmyer Mar 2012

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

Christian Binek

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 Ni61Cu39, which has a ...


Superspin Glass Behaviour Of Interacting Ferromagnetic Nanoparticles In Discontinuous Magnetic Multilayers, Christian Binek Mar 2012

Superspin Glass Behaviour Of Interacting Ferromagnetic Nanoparticles In Discontinuous Magnetic Multilayers, Christian Binek

Christian Binek

Discontinuous magnetic multilayers [Co80Fe20(t)/Al2O3(3nm)]10 with t = 0.9 and 1.0nm are studied by SQUID magnetometry and ac susceptibility. Owing to dipolar interaction the superparamagnetic cluster systems undergo collective glass-like freezing upon cooling. While both samples exhibit very similar glass temperatures Tg » 45 K and critical exponents zn » 10 and g » 1.4 as obtained from the temperature dependencies of the relaxation time, t, and the nonlinear susceptibility, c3, dynamical scaling reveals different critical exponents, b(0.9nm) »1.0 and b(1.0nm) » 0.6, respectively.


Magnetocaloric Properties Of Co/Cr Superlattices, Tathagata Mukherjee, Sarbeswar Sahoo, David J. Sellmyer, Christian Binek Mar 2012

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

Christian Binek

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 ...


Optimization Of Magneto-Optical Kerr Setup: Analyzing Experimental Assemblies Using Jones Matrix Formalism, Christian Binek Mar 2012

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

Christian Binek

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 ...


Isothermal Low-Field Tuning Of Exchange Bias In Epitaxial Fe/Cr2o3/Fe, S. Sahoo, T. Mukherjee, K. Belashchenko, Christian Binek Mar 2012

Isothermal Low-Field Tuning Of Exchange Bias In Epitaxial Fe/Cr2o3/Fe, S. Sahoo, T. Mukherjee, K. Belashchenko, Christian Binek

Christian Binek

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 remains constant, independent of the exchange bias field. In ...


Density Of Zeros On The Lee-Yang Circle Obtained From Magnetization Data Of A Two-Dimensional Ising Ferromagnet, Christian Binek Mar 2012

Density Of Zeros On The Lee-Yang Circle Obtained From Magnetization Data Of A Two-Dimensional Ising Ferromagnet, Christian Binek

Christian Binek

In order to provide experimental access to the statistical theory of Lee and Yang [Phys. Rev. 87, 410 (1952)] the density function g(θ) of zeros on the Lee-Yang circle has been determined for the first time by analyzing isothermal magnetization data m(H) of the Ising ferromagnet FeCl2 in axial magnetic fields H at temperatures 34≤T≤99 K. The validity of our approach is demonstrated by the perfect agreement of magnetic specific heat data as calculated from g(θ) and m(H) via Maxwell's relation. Moreover, the correct in-plane exchange constant of FeCl2 emerges from the series ...


Temperature Dependence Of The Training Effect In Exchange Coupled Ferromagnetic Bilayers, S. Polisetty, Sarbeswar Sahoo, A. Berger, Christian Binek Mar 2012

Temperature Dependence Of The Training Effect In Exchange Coupled Ferromagnetic Bilayers, S. Polisetty, Sarbeswar Sahoo, A. Berger, Christian Binek

Christian Binek

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 ...


Self-Assembly Of Magnetic Ni Nanoparticles Into 1d Arrays With Antiferromagnetic Order, Valery Bliznyuk, Srikanth Singamaneni, Sarbeswar Sahoo, Srinivas Polisetty, Xi He, Christian Binek Mar 2012

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

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 ...


Neutron Scattering Study Of Transverse Magnetism, Christian Binek, T. Kato, Wolfgang Kleemann, O. Petracic, D. Bertrand, F. Bourdarot, P. Burlet, H. Aruga Katori, K. Katsumata, K. Prokes, S. Welzel Mar 2012

Neutron Scattering Study Of Transverse Magnetism, Christian Binek, T. Kato, Wolfgang Kleemann, O. Petracic, D. Bertrand, F. Bourdarot, P. Burlet, H. Aruga Katori, K. Katsumata, K. Prokes, S. Welzel

Christian Binek

In order to clarify the nature of the additional phase transition at H1 (T) < Hc (T) of the layered antiferromagnetic (AF) insulator FeBr2 as found by Aruga Katori et al. (1996) we measured the intensity of different Bragg-peaks in different scattering geometries. Transverse AF ordering is observed in both AF phases, AFI and AFII. Its order parameter exhibits a peak at T1 = T (H1) in temperature scans and does not vanish in zero field. Possible origins of the step-like increase of the transverse ferromagnetic ordering induced by a weak in-plane field component when entering AFI below T1 are discussed.


Dilution-Induced Enhancement Of The Blocking Temperature In Exchange-Bias Heterosystems, Xi Chen, Christian Binek, A. Hochstrat, W. Kleeman Mar 2012

Dilution-Induced Enhancement Of The Blocking Temperature In Exchange-Bias Heterosystems, Xi Chen, Christian Binek, A. Hochstrat, W. Kleeman

Christian Binek

The temperature dependence of the exchange bias field is investigated by superconducting quantum interference device magnetometry in Fe1-xZnxF2(110)/Fe14 nm/Ag35 nm, x=0.4. Its blocking temperature exhibits a significant enhancement with respect to the global ordering temperature TN=46.9 K, of the bulk antiferromagnet Fe0.6Zn0.4F2. The enhancement is attributed to fluctuations of the diamagnetic dilution which creates clusters on all length scales having a Zn dilution of 0<~x<~1. While the infinite clusters give rise to the well-known Griffiths phase, finite clusters also provoke a local enhancement of the exchange bias. The temperature dependence of the integral exchange bias effect is modeled by averaging all local contributions of the antiferromagnetic surface magnetization which exhibit a surface critical behavior.


Superspin-Glass Nature Of Discontinuous Co80Fe20/Al2O3 Multilayers, Sarbeswar Sahoo, O. Petracic, Christian Binek, Wolfgang Kleemann, J.B. Sousa, Susana Cardoso De Freitas, P.P. Freitas Mar 2012

Superspin-Glass Nature Of Discontinuous Co80Fe20/Al2O3 Multilayers, Sarbeswar Sahoo, O. Petracic, Christian Binek, Wolfgang Kleemann, J.B. Sousa, Susana Cardoso De Freitas, P.P. Freitas

Christian Binek

Ferromagnetic single domain particles of CoFe in discontinuous magnetic multilayers [Co80Fe20 (0.9 nm)/ Al2O3(3 nm)] 10 reveal spin-glass ordering below Tg=43.6 K as evidenced by the criticality of the nonlinear susceptibility. Dynamic critical scaling yields exponents zν=8.0 and β=1.0 in both zero and weak applied field, where an Almeida-Thouless line is encountered. In fields exceeding 2 mT a crossover into a chiral glass regime seems to occur.


Superferromagnetic Domain State Dynamics In Discontinuous Cofe/Al2o3, Christian Binek Mar 2012

Superferromagnetic Domain State Dynamics In Discontinuous Cofe/Al2o3, Christian Binek

Christian Binek

Magnetization hysteresis and AC susceptibility measurements were performed on the discontinuous metal–insulator multilayer [Co80Fe20(1.4 nm)/Al2O3(3 nm)]10. CoFe forms ferromagnetic single-previous domain term particles being embedded in the Al2O3 matrix. Due to strong dipolar inter-particle interactions a “previous superferromagnetic term” correlation of particle moments was previously stated. The dynamical magnetic properties of the superferromagnet can be understood in the framework of previous domain term wall motion in an impure ferromagnet. Kinetic simulations are employed, which are based on field and temperature-dependent previous domain term wall velocities. The magnetization hysteresis as well as the AC susceptibility ...


Piezoelectric Tuning Of Exchange Bias In A Batio3/Co/Coo Heterostructure, Srinivas Polisetty, W. Echtenkamp, Keith Jones, X. He, Sarbeswar Sahoo, Christian Binek Mar 2012

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

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 change ...


The Effect Of Diamagnetic Dilution On The Spin-Phonon Interaction And Scattering Cross Section In Fe1-Xznxf2, Christian Binek Mar 2012

The Effect Of Diamagnetic Dilution On The Spin-Phonon Interaction And Scattering Cross Section In Fe1-Xznxf2, Christian Binek

Christian Binek

The temperature dependences of the first moments of phonon Raman scattering lines are studied for Fe1-xZnxF2. The diamagnetic dilution diminishes the spin-phonon coupling strength of phonons with both A1g and Eg symmetry in proportion to the decrease in the ordering temperature TN. Moreover, the Eg mode shows an asymmetrical lineshape for Zn concentrations x>0.3. It is explained by an unresolved superposition of two modes, one of which is ascribed to perturbed ZnF2 with broken translational symmetry.


Temperature Dependence Of The Training Effect In Exchange Coupled Ferromagnetic Bilayers, Christian Binek, Srinivas Polisetty, Sarbeswar Sahoo Mar 2012

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

Christian Binek

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 ...


Transverse Magnetism Of The Diluted Antiferromagnet Fe1-Xmgxbr2 (X=0.15), Christian Binek Mar 2012

Transverse Magnetism Of The Diluted Antiferromagnet Fe1-Xmgxbr2 (X=0.15), Christian Binek

Christian Binek

Neutron diffraction and magnetization measurements of the diluted crystal Fe1−xMgxBr2 (xnot, vert, similar0.15) were performed. Successive phase transitions at zero applied field at TN1not, vert, similar12 K and TN2not, vert, similar10 K were found. A previous transverse term ferromagnetic moment was detected just below TN2.


Transient Spin Structures At The Antifero-To-Paramagnetic Phase Boundary Of Febr2, Christian Binek Mar 2012

Transient Spin Structures At The Antifero-To-Paramagnetic Phase Boundary Of Febr2, Christian Binek

Christian Binek

Excess magnetization and anomalous susceptibility loss is observed on antiferromagnetic FeBr2 in an axial field H below and above its H-T-phase boundary between the multicritical temperature (Tm = 4.6 K) and the Néel temperature (TN = 14.1 K). These and other unusual properties of FeBr2 are attributed to frustration-induced intraplanar non-critical spin fluctuations, which can be simulated within the framework of a triaxial version of the 2D-ANNNI model.


Perpendicular Exchange Bias And Its Control By Magnetic, Stress And Electric Fields, Christian Binek, Pavel Borisov, Xi Chen, S. Sahoo, Wolfman Kleemann Mar 2012

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

Christian Binek

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. piezomagnetic via ...


Extrinsic Control Of The Exchange Bias, Christian Binek Mar 2012

Extrinsic Control Of The Exchange Bias, Christian Binek

Christian Binek

A new control mechanism for the exchange bias effect in magnetic heterostructures is proposed. It takes advantage of the magnetoelectric effect which takes place in the antiferromagnetic pinning layer. In contrast with the pioneering AC measurements of the magnetoelectric effect, we investigate the magnetic response of the prototypical magnetoelectric compound Cr2O3 on static electric fields. The linear dependence of the magnetic moment on the applied axial electric field and the temperature dependence of the corresponding slopes αshort parallel are measured by DC SQUID magnetometry. The contribution of the field-induced surface magnetization and its impact on the exchange bias effect is ...