5 research outputs found
Manifestation of finite temperature size effects in nanogranular magnetic graphite
In addition to the double phase transition (with the Curie temperatures
T_C=300K and T_{Ct}=144K), a low-temperature anomaly in the dependence of the
magnetization is observed in the bulk magnetic graphite (with an average
granular size of L=10nm), which is attributed to manifestation of the size
effects below the quantum temperature. The best fits of the high-temperature
data (using the mean-field Curie-Weiss and Bloch expressions) produced
reasonable estimates for the model parameters, such as defects mediated
effective spin exchange energy J=12meV (which defines the intragranular Curie
temperature T_C) and proximity mediated interactions between neighboring grains
(through potential barriers created by thin layers of non-magnetic graphite)
with energy J_t=exp(-d/s)J=5.8meV (which defines the intergranular Curie
temperature T_{Ct}) with d=1.5nm and s=2nm being the intergranular distance and
characteristic length, respectively
Hyperfine magnetic field in ferromagnetic graphite
Information on atomic-scale features is required for a better understanding
of the mechanisms leading to magnetism in non-metallic, carbon-based materials.
This work reports a direct evaluation of the hyperfine magnetic field produced
at 13C nuclei in ferromagnetic graphite by nuclear magnetic resonance (NMR).
The experimental investigation was made possible by the results of
first-principles calculations carried out in model systems, including graphene
sheets with atomic vacancies and graphite nanoribbons with edge sites partially
passivated by oxygen. A similar range of maximum hyperfine magnetic field
values (18-21T) was found for all systems, setting the frequency span to be
investigated in the NMR experiments; accordingly, a significant 13C NMR signal
was detected close to this range without any external applied magnetic field in
ferromagnetic graphite
Temperature oscillations of magnetization observed in nanofluid ferromagnetic graphite
We report on unusual magnetic properties observed in the nanofluid
room-temperature ferromagnetic graphite (with an average particle size of
l=10nm). More precisely, the measured magnetization exhibits a low-temperature
anomaly (attributed to manifestation of finite size effects below the quantum
temperature) as well as pronounced temperature oscillations above T=50K
(attributed to manifestation of the hard-sphere type pair correlations between
ferromagnetic particles in the nanofluid)
devitocodes/devito: v4.2.3
Synopsis
Performance optimizations in the symbolic layer and generated code for x86, GPU and MPI.
Various minor correctness and performance bug fixes.
Improvements to application developer API.
Added new tutorial notebooks.
Increased test coverage - particularly for MPI and GPU's.Synopsis Performance optimizations in the symbolic layer and generated code for x86, GPU and MPI. Various minor correctness and performance bug fixes. Improvements to application developer API. Added new tutorial notebooks. Increased test coverage - particularly for MPI and GPU's.4.2.