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Full-Text Articles in Physics

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.


Light Diffraction By Field-Induced Non-Periodic Magnetic Domain Structures In Fecl2, Christian Binek Mar 2012

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.


Crossover From Transient Spin Structures Ot The Field-Induced Griffiths Phase Of Febr2, Christian Binek Mar 2012

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.


Transient Spin Structures At The Antifero-To-Paramagnetic Phase Boundary Of Febr2, Christian Binek Aug 2000

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

Christian Binek Publications

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.


Crossover From Transient Spin Structures Ot The Field-Induced Griffiths Phase Of Febr2, Christian Binek Aug 2000

Crossover From Transient Spin Structures Ot The Field-Induced Griffiths Phase Of Febr2, Christian Binek

Christian Binek Publications

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.


Light Diffraction By Field-Induced Non-Periodic Magnetic Domain Structures In Fecl2, Christian Binek May 1993

Light Diffraction By Field-Induced Non-Periodic Magnetic Domain Structures In Fecl2, Christian Binek

Christian Binek Publications

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.


Properties Of Rigid Foams For Application As Materials For Light Weight Structures In Space, Huichen Chi May 1993

Properties Of Rigid Foams For Application As Materials For Light Weight Structures In Space, Huichen Chi

All Graduate Theses and Dissertations

The mechanical and mesoscopic structural properties of rigid cellular foam made of polystyrene have been investigated. Basic properties (e.g., density, total and available porosity, permeability, surface area, isotropicity, and cell size and cell wall thickness distributions) were measured. In most cases, alternative methods were used to determine which methods were most appropriate for the type of samples we studied. Standard compression and deflection mechanical tests were performed. The stress-strain curves and related mechanical properties were found to agree with standard cellular structural models of open-cell foams.

We investigated the effects of small (~<5 >atm) hydrostatic stress applied to foam samples ...