Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 14 of 14

Full-Text Articles in Physics

Dilution-Induced Enhancement Of The Blocking Temperature In Exchange-Bias Heterosystems, Xi Chen, Christian Binek, A. Hochstrat, Wolfgang Kleemann Dec 2001

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

Christian Binek Publications

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.


Exchange Bias In Fef20-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek Nov 2001

Exchange Bias In Fef20-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek

Christian Binek Publications

The previous exchange bias effect is measured in heterosystems with perpendicular anisotropy consisting of Co/Pt multilayers on top of the (0 0 1) face of a previous FeF2 single crystal. The resulting previous exchange field HE exhibits a strong dependence on temperature and the axial freezing field, HF. Within the framework of an Ising-type model, the HE vs. T as well as the HE vs. HF data are explained in terms of the microscopic spin structure at the interface.


Ac Susceptibility Studies Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek Nov 2001

Ac Susceptibility Studies Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek

Christian Binek Publications

Discontinuous metal–insulator multilayers [Co80Fe20(t)/Al2O3(3 nm)]10 are prepared by ion-beam sputtering and investigated by SQUID magnetometry and previous AC susceptometry. For 1.0less-than-or-equals, slanttless-than-or-equals, slant1.6 nm, two coexisting subsystems of dipolar coupled nanoparticles are encountered. While a spin-glass-like freezing particulate fraction dominates at t=1.0 nm, a percolating dipolar ferromagnetic fraction becomes increasingly important at higher nominal thickness of t.


Transverse Magnetism Of The Diluted Antiferromagnet Fe1-Xmgxbr2 (X=0.15), Christian Binek Nov 2001

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

Christian Binek Publications

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.


Magnetic States Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek Oct 2001

Magnetic States Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek

Christian Binek Publications

Discontinuous metal–insulator multilayers [Co80Fe20(t)/Al2O3(3 nm)]n were studied by SQUID magnetometry and AC susceptometry. CoFe forms ferromagnetic particles in the Al2O3 matrix. In this paper, we focus on the field dependence of the AC susceptibility of samples with t=1.3 nm. We find strong evidence for transitions from a superpara- to a superferromagnetic and, finally, to a reentrant superspin glass previous state.


Exchange Bias In Fe0.6zn0.4f2 Heterostructures, Christian Binek Oct 2001

Exchange Bias In Fe0.6zn0.4f2 Heterostructures, Christian Binek

Christian Binek Publications

The previous exchange bias field, He, is measured in Fe0.6Zn0.4F2/Fe heterosystems prepared from Fe layers of 14 and 5 nm thickness which are deposited on top of the compensated (1 1 0) surface of the antiferromagnet. Deviations from a linear dependence of He on the magnetization of the Fe layer are attributed to ferromagnetic domains. Moreover, piezomagnetism and its influence on He are evidenced.


Domain State Susceptibility In Fecl2/Copt-Heterostructures, Christian Binek Sep 2001

Domain State Susceptibility In Fecl2/Copt-Heterostructures, Christian Binek

Christian Binek Publications

Magnetic heterostructures with perpendicular anisotropy consisting of antiferromagnetic (111)-oriented FeCl2 single crystals and thin ferromagnetic CoPt-multilayers are investigated by ac-susceptometry after cooling in various axial magnetic fields to below the Néel temperature. The freezing process drives the system into a metastable antiferromagnetic domain state which gives rise to a huge excess contribution to the complex parallel susceptibility on heating in zero magnetic field. Its glow curve-like temperature dependence is modeled within the framework of a simple analytical approach. It involves the susceptibility of thermally activated clusters originating from antiferromagnetic stacking faults as well as the contribution of pairs of ...


Off-Diagonal Exchange-Induced Transverse And Field-Induced Spin-Flop Order In The Diluted Metamagnet Fe0.85Mg0.15Br2, Wolfgang Kleeman, H. Aruga Katori, T. Kato, Christian Binek, K. Katsumata Sep 2001

Off-Diagonal Exchange-Induced Transverse And Field-Induced Spin-Flop Order In The Diluted Metamagnet Fe0.85Mg0.15Br2, Wolfgang Kleeman, H. Aruga Katori, T. Kato, Christian Binek, K. Katsumata

Christian Binek Publications

Specific heat and Faraday rotation magnetometry were used to determine the axial magnetic phase diagram of the dilute hexagonal antiferromagnet Fe0.85Mg0.15Br2. In contrast to metamagnetic pure FeBr2, the first-order line of transverse phase transitions, H1(T), is disconnected with the antiferro-to-paramagnetic phase line Hc(T) and extends down to Ht=0 at Tt≈8.7 . This is attributed to symmetric off-diagonal exchange in the presence of structural disorder. Moreover, a spin-flop phase emerges beyond Hc(T) up to a bicritical point (Tb≈9.3 , μoH ...


Exchange Bias In A Generalized Meiklejohn-Bean Approach, Christian Binek Aug 2001

Exchange Bias In A Generalized Meiklejohn-Bean Approach, Christian Binek

Christian Binek Publications

A generalized Meiklejohn–Bean model is considered in order to derive an analytic expression for the dependence of the previous exchange bias term field on the layer thickness involved in ferromagnetic/antiferromagnetic heterosystems, on the orientation of the applied magnetic field with respect to the magnetic easy axes and on the quenched magnetization MAF of the antiferromagnetic pinning layer. While MAF is a well-known feature of field-cooled dilute antiferromagnets, it seems to occur quite generally also in pure AF pinning substrates. The new analytic expressions are successfully compared with recent experimental results and Monte Carlo investigations.


Yang-Lee Edge Singularities From Experimental High Field Magnetization Data, Christian Binek Aug 2001

Yang-Lee Edge Singularities From Experimental High Field Magnetization Data, Christian Binek

Christian Binek Publications

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 ...


Yang-Lee Edge Singularities Determined From Experimental High-Field Magnetization Data, Christian Binek, Wolfgang Kleemann, H. Aruga Katori Aug 2001

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

Christian Binek Publications

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 ...


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 Jul 2001

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 Publications

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


Magnetic Phase Diagram Of The Diluted Metamagnet Fe0.95Mg0.05Br2, H. Aruga Katori, K. Katsumata, O. Petracic, Wolfgang Kleemann, T. Kato, Christian Binek Mar 2001

Magnetic Phase Diagram Of The Diluted Metamagnet Fe0.95Mg0.05Br2, H. Aruga Katori, K. Katsumata, O. Petracic, Wolfgang Kleemann, T. Kato, Christian Binek

Christian Binek Publications

The axial magnetic phase diagram of the antiferromagnet Fe0.95Mg0.05Br2 is studied by specific heat, superconducting quantum interference device, and Faraday rotation techniques. The diamagnetic impurities give rise to random-field criticality along the second-order phase line Hc(T) between TN=13.1 K and a multicritical point at Tm≈5 K, and to a spin-flop line between Tm and the critical end-point temperature Te≈3.5 K. The phase line H1(T)c(T) ending at Tm is probably due to symmetric nondiagonal exchange.


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 2001

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 Publications

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.