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Articles 61 - 74 of 74
Full-Text Articles in Physics
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
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
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 , μoHb≈1.3 ).
Cole-Cole Analysis Of The Superspin Glass System Co80Fe20/Al2O3, O. Petracic, Sarbeswar Sahoo, Christian Binek, Wolfgang Kleemann, J.B. Sousa, Susana Cardoso De Freitas, P.P. Freitas
Cole-Cole Analysis Of The Superspin Glass System Co80Fe20/Al2O3, O. Petracic, Sarbeswar Sahoo, Christian Binek, Wolfgang Kleemann, J.B. Sousa, Susana Cardoso De Freitas, P.P. Freitas
Christian Binek
Ac susceptibility measurements were performed on discontinuous magnetic multi-layers [Co80Fe20 (t)/Al2O3 (3 nm)] 10, t = 0.9 and 1.0 nm, by Superconducting Quantum Interference Device (SQUID) magnetometry. The CoFe forms nearly spherical ferromagnetic single-domain nanoparticles in the diamagnetic Al2O3 matrix. Due to dipolar interactions and random distribution of anisotropy axes the system exhibits a spin-glass phase. We measured the ac susceptibility as a function of temperature 20 ≤ T ≤ 100 K at different dc fi elds and as a function of frequency 0.01 ≤ f ≤ 1000 Hz. The spectral data were successfully analyzed by use of the phenomenological …
Probing Equilibrium By Nonequilibrium Dynamics: Aging In Co/Cr Superlattices, Tathagata Mukherjee, M. Pleimling, Christian Binek
Probing Equilibrium By Nonequilibrium Dynamics: Aging In Co/Cr Superlattices, Tathagata Mukherjee, M. Pleimling, Christian Binek
Christian Binek
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 equilibrium …
Nonextensivity In Magnetic Nanoparticle Ensembles, Christian Binek, Srinivas Polisetty, Xi He, Tathagata Mukherjee, Rajasekaran Rajesh, Jody G. Redepenning
Nonextensivity In Magnetic Nanoparticle Ensembles, Christian Binek, Srinivas Polisetty, Xi He, Tathagata Mukherjee, Rajasekaran Rajesh, Jody G. Redepenning
Christian Binek
A superconducting quantum interference device and Faraday rotation technique are used to study dipolar interacting nanoparticles embedded in a polystyrene matrix. Magnetization isotherms are measured for three cylindrically shaped samples of constant diameter but various heights. Detailed analysis of the isotherms supports Tsallis' conjecture of a magnetic equation of state that involves temperature and magnetic field variables scaled by the logarithm of the number of magnetic nanoparticles. This unusual scaling of thermodynamic variables, which are conventionally considered to be intensive, originates from the nonextensivity of the Gibbs free energy in three-dimensional dipolar interacting particle ensembles. Our experimental evidence for nonextensivity …
Temperature- And Field-Induced Entropy Changes In Nanomagnets, Ralph Skomski, Christian Binek, Tathagata Mukherjee, Sarbeswar Sahoo, David J. Sellmyer
Temperature- And Field-Induced Entropy Changes In Nanomagnets, Ralph Skomski, Christian Binek, Tathagata Mukherjee, Sarbeswar Sahoo, David J. Sellmyer
Christian Binek
Room-temperature magnetic-entropy changes in nanostructures for magnetic refrigeration are investigated by model calculations. Using a mean-field approach, the magnetic entropy is calculated as a function of temperature, magnetic field, particle size, anisotropy, and interaction strength. Both isotropic (Heisenberg) and uniaxial (Ising and XY) anisotropies are considered. The nanoparticle entropy strongly depends on the character of the anisotropy, in contrast to atomic ferromagnetism, where the anisotropy energy is much smaller than the interaction energy. Most promising are isotropic particles and particles with weak easy axis anisotropy, as well as easy-plane particle with the field in the plane. The optimum nanoparticle size …
Blocking Of Logarithmic Temporal Relaxation Of Magnetic Remanence By Piezomagnetically Induced Domains In Fe1-XZnXF2, J. Kushauer, Christian Binek, Wolfgang Kleemann
Blocking Of Logarithmic Temporal Relaxation Of Magnetic Remanence By Piezomagnetically Induced Domains In Fe1-XZnXF2, J. Kushauer, Christian Binek, Wolfgang Kleemann
Christian Binek
Faraday rotation and superconducting quantum interference device magnetometry were used to investigate the relaxation of the weak-field induced remanence, µ, of the random-field Ising model system Fe1-xZnxF2. The stretched logarithmic decay law, as predicted by Nattermann and Vilfan for the case of compact domains with fractal surfaces, was confirmed for freezing fields of 3≤B≤5 T. Virtually constant remanence, µ, was found at low fields, 0.0002≤B≤1.5 T. This ferrimagnetic moment is due to the piezomagnetic effect acting on random-stress induced immobile domains. Chemical etching, which removes surface stress originating from the sample preparation, proves to decrease the remanence by about 50%, …
Magnetic Neutron-Scattering Investigation Of The Field-Induced Griffiths Phase In Fecl2, Christian Binek, D. Bertrand, L.P. Regnault, Wolfgang Kleemann
Magnetic Neutron-Scattering Investigation Of The Field-Induced Griffiths Phase In Fecl2, Christian Binek, D. Bertrand, L.P. Regnault, Wolfgang Kleemann
Christian Binek
Quasielastic neutron scattering has been utilized to investigate the Griffiths phase induced by an axial magnetic field in FeCl2 at temperatures Tc(H)⩽T⩽TN, where Tc(H) is the transition temperature in an external magnetic field H. We present the temperature dependence of the integrated neutron-scattering intensity at fixed scattering vectors for various magnetic fields. On cooling below TN the antiferromagnetic short-range fluctuations decrease due to an increase of the volume fraction which is already antiferromagnetically ordered. A weighted average of the local contributions to the antiferromagnetic susceptibility quantitatively describes the scattering cross section.
Random-Field Critical And Spin-Flop Behavior Of The Anisotropic Heisenberg Antiferromagnet Fe0.9mg0.1br2 In Axial Magnetic Fields, Christian Binek
Random-Field Critical And Spin-Flop Behavior Of The Anisotropic Heisenberg Antiferromagnet Fe0.9mg0.1br2 In Axial Magnetic Fields, Christian Binek
Christian Binek
Faraday optical measurements on the dilute hexagonal antiferromagnet Fe0.85Mg0.15Br2 in an external axial field reveal a spin-flop phase line ending at a multicritical point (Tm=8.1 K, Hm=1050 kA m-1) and crossover from random-exchange to random-field Ising criticality with an exponent Phi =1.40+or-0.04 in the vicinity of TN=11.1 K. Cusp-like behaviour of the specific heat at TN is discussed in view of recent Monte Carlo results.
Domain Wall Relaxation, Creep, Sliding, And Switching In Superferromagnetic Discontinuous Co80Fe20/Al2O3 Multilayers, X. Chen, O. Sichelschmidt, W. Kleeman, Christian Binek, J.B. Sousa, S. Cardoso, P.P. Freitas
Domain Wall Relaxation, Creep, Sliding, And Switching In Superferromagnetic Discontinuous Co80Fe20/Al2O3 Multilayers, X. Chen, O. Sichelschmidt, W. Kleeman, Christian Binek, J.B. Sousa, S. Cardoso, P.P. Freitas
Christian Binek
The ac susceptibility of a superferromagnetic discontinuous multilayer [Co80Fe20(1.4 nm)/ Al2O3(3 nm)]10 is measured as a function of temperature, frequency, and field amplitude and compared to static and dynamic hysteresis loops. Its properties are successfully mapped onto the predicted [T. Nattermann, V. Pokrovsky, and V. M. Vinokur, Phys. Rev. Lett. 87, 197005 (2001).] dynamical phase transitions, which link the relaxation, creep, sliding, and switching regimes of pinned domain walls.
Exchange Bias In Fef20-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek
Exchange Bias In Fef20-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek
Christian Binek
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.
Electrically Controlled Magnetism, Christian Binek, Xi He, Yi Wang, S. Sahoo
Electrically Controlled Magnetism, Christian Binek, Xi He, Yi Wang, S. Sahoo
Christian Binek
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.
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
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
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.
Training Of The Exchange-Bias Effect In Nio-Fe Heterostructures, A. Hochstrat, Christian Binek, Wolfgang Kleemann
Training Of The Exchange-Bias Effect In Nio-Fe Heterostructures, A. Hochstrat, Christian Binek, Wolfgang Kleemann
Christian Binek
The training effect of a NiO(001)/Fe(110) heterostructure is studied from magnetic hysteresis loops measured by superconducting quantum interference device magnetometry. Consecutive hysteresis loops exhibit a decreasing exchange bias effect. This behavior is known as the training effect, which reflects the dependence of the exchange bias field on the antiferromagnetic interface magnetization. In order to evidence this dependence, we study the decrease of the total saturation magnetization of the heterostructure for an increasing number of hysteresis cycles. Assuming proportionality between the interface magnetization and the total saturation magnetization, the description of the data is consistent within the phenomenological Meiklejohn Bean approach.
Crossover From Transient Spin Structures Ot The Field-Induced Griffiths Phase Of Febr2, Christian Binek
Crossover From Transient Spin Structures Ot The Field-Induced Griffiths Phase Of Febr2, Christian Binek
Christian Binek
In the presence of an applied axial magnetic field Ha the uniaxial antiferromagnets FeCl2 and FeBr2 show fluctuating domain-like antiferromagnetic correlations above the phase boundary Tc(Ha). They are detected by SQUID measurements of the low frequency out-of-phase susceptibility gc″ and indicate a field-induced Griffiths phase at temperatures Tc(Ha) < T < TN. In contrast to FeCl2, important additional frustration-induced intraplanar non-critical contributions to χ″ vs. T are found in FeBr2. For external fields above the Tc(Ha) line, Ha > 2.6 MA/m, they are shown to superimpose linearly on the Griffiths contributions. These dominate at Ha = 2.67 MA/m and are unequivocally modeled within the Landau theory of fluctuations near phase transitions by introducing a Lorentzian Tc distribution.