513 research outputs found
Missense Mutation in the LDLR Gene: A Wide Spectrum in the Severity of Familial Hypercholesterolemia
Spin canting and ferromagnetism in a AuFe alloy: Mössbauer and magnetic measurements
We have made Mössbauer polarization and susceptibility measurements above technical saturation on Au-19 at.% Fe. Just below the magnetic ordering temperature the system behaves as a ferromagnet, but random local canting sets in at lower temperatures. A well-defined canting transition temperature cannot be established from the data, but canting begins above the temperature at which the low-field susceptibility shows a sharp falloff
Structure of Metastable States in Phase Transitions with High-Spin Low-Spin Degree of Freedom
Difference of degeneracy of the low-spin (LS) and high-spin (HS) states
causes interesting entropy effects on spin-crossover phase transitions and
charge transfer phase transitions in materials composed of the spin-crossover
atoms. Mechanisms of the spin-crossover (SC) phase transitions have been
studied by using Wajnflasz model, where the degeneracy of the spin states (HS
or LS) is taken into account and cooperative natures of the spin-crossover
phase transitions have been well described. Recently, a charge transfer (CT)
phase transition due to electron hopping between LS and HS sites has been
studied by using a generalized Wajnflasz model. In the both systems of SC and
CT, the systems have a high temperature structure (HT) and a low temperature
structure (LT), and the change between them can be a smooth crossover or a
discontinuous first order phase transition depending on the parameters of the
systems. Although apparently the standard SC system and the CT system are very
different, it is shown that both models are equivalent under a certain
transformation of variables. In both systems, the structure of metastable state
at low temperatures is a matter of interest. We study temperature dependence of
fraction of HT systematically in a unified model, and find several structures
of equilibrium and metastable states of the model as functions of system
parameters. In particular, we find a reentrant type metastable branch of HT in
a low temperature region, which would play an important role to study the
photo-irradiated processes of related materials.Comment: 19 pages, 11 figure
A Unified Theoretical Description of the Thermodynamical Properties of Spin Crossover with Magnetic Interactions
After the discovery of the phenomena of light-induced excited spin state
trapping (LIESST), the functional properties of metal complexes have been
studied intensively. Among them, cooperative phenomena involving low spin-high
spin (spin-crossover) transition and magnetic ordering have attracted
interests, and it has become necessary to formulate a unified description of
both phenomena. In this work, we propose a model in which they can be treated
simultaneously by extending the Wajnflasz-Pick model including a magnetic
interaction. We found that this new model is equivalent to
Blume-Emery-Griffiths (BEG) Hamiltonian with degenerate levels. This model
provides a unified description of the thermodynamic properties associated with
various types of systems, such as spin-crossover (SC) solids and Prussian blue
analogues (PBA). Here, the high spin fraction and the magnetization are the
order parameters describing the cooperative phenomena of the model. We present
several typical temperature dependences of the order parameters and we
determine the phase diagram of the system using the mean-field theory and Monte
Carlo simulations. We found that the magnetic interaction drives the SC
transition leading to re-entrant magnetic and first-order SC transitions.Comment: 30pages, 11figure
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