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Articles 31 - 60 of 74
Full-Text Articles in Physics
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
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
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.
Magneto-Thermal Behavior Of A Granular Fecl2–Fe Heterostructure, Sarbeswar Sahoo, Christian Binek, Wolfgang Kleemann
Magneto-Thermal Behavior Of A Granular Fecl2–Fe Heterostructure, Sarbeswar Sahoo, Christian Binek, Wolfgang Kleemann
Christian Binek
A granular system consisting of ferromagnetic single-domain Fe particles in an antiferromagnetic FeCl2 matrix was prepared by coevaporation in an ultra-high vacuum environment. The structural and magnetic properties were investigated by X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. The heterostructure combines the properties of superparamagnetic Fe granules and the antiferromagnetism of the FeCl2 matrix. In addition, dipolar interaction-induced giant moments are observed below the Néel temperature of the FeCl2 matrix. The thermomagnetic properties of the giant moments are studied.
Interface Alloying And Magnetic Properties Of Fe/Rh Multilayers, K. Hanisch, W. Keune, R.A. Brand, Christian Binek, Wolfman Kleemann
Interface Alloying And Magnetic Properties Of Fe/Rh Multilayers, K. Hanisch, W. Keune, R.A. Brand, Christian Binek, Wolfman Kleemann
Christian Binek
Rh(20 Å)/57Fe(tFe) multilayers with Fe thicknesses tFe of 2, 5, 10, and 15 Å prepared by alternate evaporation in UHV have been investigated by x-ray diffraction (XRD), Mössbauer spectroscopy, and SQUID magnetometry. First- and second-order superstructure Bragg peaks (but no higher-order peaks) in small-angle XRD patterns suggest some compositional modulation. Mössbauer spectra taken at 4.2 K are characterized by a distribution P(Bhf) of hyperfine fields Bhf. Peaks observed in the P(Bhf) curves near 17 and 35 T are assigned to an fcc-RhFe interface alloy (~7–24 at. % Fe) with spin-glasslike properties and to a disordered ferromagnetic bcc-FeRh alloy (~96 at. …
Magnetic Relaxation Phenomena In The Superspin-Glass System [Co80Fe20/Al2O3]10, S. Sahoo, O. Petracic, Christian Binek, W. Kleemann, J. B. Sousa, S. Cardoso, P. P. Freitas
Magnetic Relaxation Phenomena In The Superspin-Glass System [Co80Fe20/Al2O3]10, S. Sahoo, O. Petracic, Christian Binek, W. Kleemann, J. B. Sousa, S. Cardoso, P. P. Freitas
Christian Binek
Relaxation and temperature cycles of thermoremanent magnetization, MTRM, in the superspin-glass phase of [Co80Fe20 (0.9 nm)/Al2O3 (3 nm)] 10 have been investigated. The relaxation of MTRM exhibits ageing phenomena. In negative temperature cycles for temperature steps larger than 1 K the magnetic state is retrieved (memory effect) on returning to the measurement temperature. This property is independent of the application of a field step during intermediate cooling. In positive temperature cycles the relaxation is suppressed after temporary heating. The observations are discussed in the light of both the droplet and the hierarchical picture.
Dynamic Enhancement Of The Exchange Bias Training Effect, Sarbeswar Sahoo, Srinivas Polisetty, Christian Binek, Andreas Berger
Dynamic Enhancement Of The Exchange Bias Training Effect, Sarbeswar Sahoo, Srinivas Polisetty, Christian Binek, Andreas Berger
Christian Binek
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 …
Kinetics Of Random-Field Induced Domains In The Two-Dimensional Ising Antiferromagnet Rb2co0.85mg0.15f4, Christian Binek
Kinetics Of Random-Field Induced Domains In The Two-Dimensional Ising Antiferromagnet Rb2co0.85mg0.15f4, Christian Binek
Christian Binek
The previous kinetics of the two-dimensional diluted Ising antiferromagnet Rb2Co0.85Mg0.15F4 is studied via the temporal relaxation of the field-induced magnetization after field cooling (FC) and zero-field cooling (ZFC), respectively, to T < TN = 75.2K. After FC different non-exponential decay laws indicate a crossover from domain reorientation to wall rearrangement at decreasing T. After ZFC rapidly saturating magnetization of naturally grown domain walls precedes the slow random-field-controlled disordering process.
Metamagnetic Domains And Dynamic Fluctuations In Febr2, O. Petracic, Christian Binek, W. Kleeman
Metamagnetic Domains And Dynamic Fluctuations In Febr2, O. Petracic, Christian Binek, W. Kleeman
Christian Binek
The mixed phase and the regime of non-critical fluctuations of the magnetic phase diagram of FeBr2 is investigated by SQUID susceptometry and light diffraction techniques. The experiments seem to evidence instability of the tricritical point as conjectured recently. The observation of stripe domains and light diffraction below and above Tm = 4.6 K and the virtual continuation of the phase transition line to above Tm are in agreement with the occurrence of a critical endpoint at Tm and of a bicritical endpoint at T > Tm. ©1997 American Institute of Physics.
Magnetoelectronics With Magnetoelectrics, Christian Binek, Bernard Doudin
Magnetoelectronics With Magnetoelectrics, Christian Binek, Bernard Doudin
Christian Binek
Magnetoelectric films are proposed as key components for spintronic applications. The net magnetic moment created by an electric field in a magnetoelectric thin film influences the magnetization state of a neighbouring ferromagnetic layer through exchange coupling. Pure electrical control of magnetic confi gurations of giant magnetoresistance spin valves and tunnelling magnetoresistance elements is therefore achievable. Estimates based on documented magnetoelectric tensor values show that exchange fields reaching 100 mT can be obtained. We propose a mechanism alternative to current-induced magnetization switching, providing access to a wide range of device impedance values and opening the possibility of simple logic functions.
Polydispersivity Of Non-Critical Field-Induced Fluctuations In Febr2, Christian Binek
Polydispersivity Of Non-Critical Field-Induced Fluctuations In Febr2, Christian Binek
Christian Binek
The field and temperature dependence of the complex low-frequency susceptibility of the metamagnet FeBr2 exhibits large anomalies in the vicinity of the second-order phase boundary Hc(T). The low-frequency losses reflect polydispersive dynamics with a broad distribution of relaxation times peaking at τ ≈ 0.2 s. The dispersion, χ versus ƒ, is well described within Chamberlin's model of dynamically coupled domains. The heterogeneous glass-like response gives rise to the intuitive picture of a magnetic fluid of high viscosity.
Temperature Dependence Of The Training Effect In A Co/Coo Exchange-Bias Layer, Christian Binek, Xi He, Srinivas Polisetty
Temperature Dependence Of The Training Effect In A Co/Coo Exchange-Bias Layer, Christian Binek, Xi He, Srinivas Polisetty
Christian Binek
The temperature dependence of the training effect is studied in a Co/CoO exchange-bias bilayer and a phenomenological theory is presented. After field cooling the sample to below its blocking temperature, the absolute value of the exchange-bias field decreases when cycling the heterostructure through consecutive hysteresis loops. This decrease is known as the training effect and is studied in the temperature range 5 < =T < =120 K. An implicit sequence, which has been recently derived using the Landau-Khalatnikov approach of relaxation, fits the respective data set for each individual temperature. The underlying discretized dynamic equation involves an expansion of the free energy …
Ac Susceptibility Studies Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek
Ac Susceptibility Studies Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek
Christian Binek
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.
Exchange Bias In A Generalized Meiklejohn-Bean Approach, Christian Binek
Exchange Bias In A Generalized Meiklejohn-Bean Approach, Christian Binek
Christian Binek
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.
Domain State Susceptibility In Fecl2/Copt-Heterostructures, Christian Binek
Domain State Susceptibility In Fecl2/Copt-Heterostructures, Christian Binek
Christian Binek
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 antiparallel …
Magnetic-Field-Induced Griffiths Phase Versus Random-Field Criticality And Domain Wall Susceptibility Of Fe0.47zn0.53f2, Christian Binek, S. Kuttler, Wolfgang Kleemann
Magnetic-Field-Induced Griffiths Phase Versus Random-Field Criticality And Domain Wall Susceptibility Of Fe0.47zn0.53f2, Christian Binek, S. Kuttler, Wolfgang Kleemann
Christian Binek
The well-known peak of the parallel ac susceptibility arising below TN in Fe0.47Zn0.53F2 splits into a narrow critical peak at Tc (H) and a broad field-induced Griffiths phase shoulder peaking at Tp>Tc(H) in magnetic fields H≳1.6 MA /m. Random-field (RF) criticality with α̃≈0 and subsequent rounding due to RF trapping of thermal fluctuations are observed upon zero-field cooling as T→Tc-(H). The frozen domain state obtained after rapid field cooling reveals excess susceptibility Δχw′∝H2.6, owing to rough walls with thermally activated stiffness.
Piezomagnetism In Epitaxial Cr2o3 Thin Films And Spintronic Applications, Sarbeswar Sahoo, Christian Binek
Piezomagnetism In Epitaxial Cr2o3 Thin Films And Spintronic Applications, Sarbeswar Sahoo, Christian Binek
Christian Binek
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 the sapphire …
Quenching Of The Exchange Bias Training In Fe/Cr2o3/Fe Trilayer, S. Sahoo, Christian Binek
Quenching Of The Exchange Bias Training In Fe/Cr2o3/Fe Trilayer, S. Sahoo, Christian Binek
Christian Binek
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 …
Light Diffraction By Field-Induced Non-Periodic Magnetic Domain Structures In Fecl2, Christian Binek
Light Diffraction By Field-Induced Non-Periodic Magnetic Domain Structures In Fecl2, Christian Binek
Christian Binek
The magnetic-field-induced mixed phase of the meta magnet FeCl2 gives rise to reduced transmittivity of circularly polarized light. Within the framework of the diffraction theory of thin random magnetic phase gratings and the assumption of field-dependent refractive indices of the antiferromagnetic domains the field dependence of the transmission is perfectly modeled.
Magnetic States Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek
Magnetic States Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek
Christian Binek
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.
Local Magnetic Properties Of Antiferromagnetic Febr2, J. Pelloth, R.A. Brand, S. Takele, M.M. Pereira De Azevedo, Wolfman Kleemann, Christian Binek, J. Kushauer, D. Bertrand
Local Magnetic Properties Of Antiferromagnetic Febr2, J. Pelloth, R.A. Brand, S. Takele, M.M. Pereira De Azevedo, Wolfman Kleemann, Christian Binek, J. Kushauer, D. Bertrand
Christian Binek
The antiferromagnet FeBr2 has been studied by Mössbauer spectroscopy in external fields both in the metamagnetic region below the multicritical temperature TMCP and in the second-order transition region above. The local magnetization shows that the metamagnetic transition occurs by spin flips, as in simple models. However, in the second-order transition region, the local magnetization of the sublattice oriented antiparallel to the external field varies continuously but remains parallel to the c axis. This can only be understood if the external magnetic field induces strong transversal spin precession of the moments on the antiparallel sublattice. This shows that the anomalous maxima …
Yang-Lee Edge Singularities From Experimental High Field Magnetization Data, Christian Binek
Yang-Lee Edge Singularities From Experimental High Field Magnetization Data, Christian Binek
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 theoretical prediction for the two-dimensional Ising …
Scaling Behavior Of The Exchange-Bias Training Effect, Christian Binek, Srinivas Polisetty, Sarbeswar Sahoo
Scaling Behavior Of The Exchange-Bias Training Effect, Christian Binek, Srinivas Polisetty, Sarbeswar Sahoo
Christian Binek
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. …
Magnetic Phase Diagram Of The Diluted Metamagnet Fe0.95Mg0.05Br2, H. Aruga Katori, K. Katsumata, O. Petracic, Wolfgang Kleemann, T. Kato, Christian Binek
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
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.
Training Of The Exchange-Bias Effect: A Simple Analytic Approach, Christian Binek
Training Of The Exchange-Bias Effect: A Simple Analytic Approach, Christian Binek
Christian Binek
raining of the exchange bias effect in antiferro-/ferromagnetic heterostructures is considered in the theoretical framework of spin configurational relaxation, which is activated through consecutively cycled hysteresis loops. The corresponding exchange bias fields, µ0 HEB(n), reveal relaxation from the initial state, n = 1, of high antiferromagnetic interface magnetization to the equilibrium state of reduced magnetization in the limit of large n. The evolution of µ0HEB vs n is calculated with the help of a discretized Landau-Khalatnikov equation, where the continuous time parameter is replaced by the loop index n. The result reveals the origin of the well established but hitherto …
Nonadiabatic Heat-Capacity Measurements Using A Superconducting Quantum Interference Device Magnetometer, A.I. Kharkovski, Christian Binek, W. Kleeman
Nonadiabatic Heat-Capacity Measurements Using A Superconducting Quantum Interference Device Magnetometer, A.I. Kharkovski, Christian Binek, W. Kleeman
Christian Binek
Nonadiabatic measurements of the heat capacity involving sample-inherent thermometry are proposed. The method is realized with superconducting quantum interference device magnetometry and applied to FeBr2 single crystals by using the magnetization for both thermometry and relaxation calorimetry. When heating with a step pulse of laser light, the magnetization relaxes on a characteristic time scale Ί = RC, where C is the heat capacity and R is the heat resistance between the sample and the bath. R is independently determined from the temperature dependence of the magnetic moment measured with and without stationary light irradiation. ©2000 American Institute of Physics.
Crossover From Pure Ising To Random-Exchange Dominated Behavior Of The Two-Dimensional Antiferromagnet Rb2Co1-XMgXF4, Christian Binek, Wolfgang Kleemann, David P. Belanger
Crossover From Pure Ising To Random-Exchange Dominated Behavior Of The Two-Dimensional Antiferromagnet Rb2Co1-XMgXF4, Christian Binek, Wolfgang Kleemann, David P. Belanger
Christian Binek
The temperature dependence of the uniform susceptibility χ of diluted two-dimensional Ising antiferromagnets Rb2Co1-xMgxF4, 0<~xN(x), but also in relation to the “local” phase transition temperatures TN′ throughout the Griffiths regime, TN(x)<~TN′<~TN(0), a satisfactory quantitative description of χ vs T is deduced for any x above the percolation threshold. ©1998 The American Physical Society
Evidence Of Dilution-Induced Griffiths Instabilities In K2Cu1-XZnXF4 And Fe1-XZnXF2, Christian Binek, Wolfgang Kleeman
Evidence Of Dilution-Induced Griffiths Instabilities In K2Cu1-XZnXF4 And Fe1-XZnXF2, Christian Binek, Wolfgang Kleeman
Christian Binek
Weak quasistatic singularities are evidenced within the Griffiths regime of temperatures Tc(x)≤T≤Tc(x=0) in the diluted antiferromagnet Fe1-xZnxF2, x=0.53, and in the diluted ferromagnet K2Cu1-xZnxF4, x=0.2, by measurements of the magnetic susceptibility, χ’ vs T, in zero external field. Significant deviations from classical (γ=1, for Fe0.47Zn0.53F2) and nonclassical (γ≳1, for K2Cu0.8Zn0.2F4) Curie-Weiss-type behavior, χ’∝[T-Tc(x)] -Y, are found just below Tc(x=0) by using linear-regression data analysis.
Exchange Bias In Fe0.6zn0.4f2 Heterostructures, Christian Binek
Exchange Bias In Fe0.6zn0.4f2 Heterostructures, Christian Binek
Christian Binek
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.
Domainlike Antiferromagnetic Correlations Of Paramagnetic Fecl2: A Field-Induced Griffiths Phase?, Christian Binek, Wolfgang Kleemann
Domainlike Antiferromagnetic Correlations Of Paramagnetic Fecl2: A Field-Induced Griffiths Phase?, Christian Binek, Wolfgang Kleemann
Christian Binek
Domainlike antiferromagnetic correlations are detected by SQUID measurements of the low-frequency susceptibility in the metamagnet FeCl2 when exposed to an axial magnetic field H at temperatures Tc (H)≤T≤TN. A distinct change of curvature of χ’’ vs T appearing at TN is explained in terms of fluctuating distributions of demagnetizing fields and, hence, transition temperatures. The field-induced dynamic domain phase—an analog of the Griffiths phase predicted for a ferromagnet with dilution x within Tc(x)≤T≤Tc(0)—is confirmed by elastic light scattering experiments.
Robust Isothermal Electric Control Of Exchange Bias At Room Temperature, Xi He, Yi Wang, Christian Binek, Peter Dowben
Robust Isothermal Electric Control Of Exchange Bias At Room Temperature, Xi He, Yi Wang, Christian Binek, Peter Dowben
Christian Binek
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 positive …
Giant Metamagnetic Moments In A Granular Fecl2-Fe Heterostructure, Sarbeswar Sahoo, Christian Binek, Wolfgang Kleemann
Giant Metamagnetic Moments In A Granular Fecl2-Fe Heterostructure, Sarbeswar Sahoo, Christian Binek, Wolfgang Kleemann
Christian Binek
Giant moments are observed at low temperatures in a granular FeCl2-Fe heterostructure owing to a local metamagnetic transformation of the antiferromagnetic (AF) FeCl2 matrix due to dipolar interactions. A model of metamagnetically (MM) "dressed" single-domain Fe particles is suggested to explain the observations. These include polydispersive ac susceptibility induced by AF-MM domain configurations and weak exchange bias due to non-spin-flipped AF crystallites.