106 research outputs found
Memory in nanomagnetic systems: Superparamagnetism versus Spinglass behavior
The slow dynamics and concomitant memory (aging) effects seen in nanomagnetic
systems are analyzed on the basis of two separate paradigms : superparamagnets
and spinglasses. It is argued that in a large class of aging phenomena it
suffices to invoke superparamagnetic relaxation of individual single domain
particles but with a distribution of their sizes. Cases in which interactions
and randomness are important in view of distinctive experimental signatures,
are also discussed.Comment: 11 pages and 19 figure
Ferromagnetic feature from Mn near room temperature in the fine particles of GdMn2Ge2 and TbMn2Ge2
The magnetization behaviors of GdMn2Ge2 and TbMn2Ge2 in the bulk and in the
fine particles obtained by high-energy ball-milling are compared. Pronounced
modificayions in the spontaneous, remnent and high-field magnetization in the
fine particle form, attributable to Mn are observed. The results indicate that
the antiferromagnetism of Mn sub-lattice known for the bulk form in the range
100-300 K gets weakened in favor of ferromagnetism in the fine particles. On
the basis of this observation, we infer that there are other factors like size
(and possibly defects) also play a role to decide the exact nature of magnetic
ordering of Mn in this ternary family of compounds, contrasting the
traditionally held view that the basal plane Mn-Mn distance is the crucial
controlling parameter.Comment: Communicated for publication on 2nd January 201
Suicide by unusual methods: a rare case of complex suicide
Genital Self-Mutilation (GSM) is usually associated with mental illness. It is considered as the most brutal form of self-harm. Many cases of such self-harm have been described by various authors in different times. However, its existence in absence of any mental illness and using it as a method of suicide is a matter of question. Although, some cases are reported; its incidence is very low. Its association with complex suicide is even much lower. Usually, in complex suicide, the victim chooses some methods which are less painful. Such a complicated case of complex suicide was brought to the tertiary care center of Dibrugarh, Assam for post mortem examination. The deceased, a 36 years old male was brought with history of cutting his external genitalia followed by hanging. The case has been described in this paper with relevant review literature.
Melting artificial spin ice
Artificial spin ice arrays of micromagnetic islands are a means of
engineering additional energy scales and frustration into magnetic materials.
Despite much progress in elucidating the properties of such arrays, the `spins'
in the systems studied so far have no thermal dynamics as the kinetic
constraints are too high. Here we address this problem by using a material with
an ordering temperature near room temperature. By measuring the temperature
dependent magnetization in different principal directions, and comparing with
simulations of idealized statistical mechanical models, we confirm a dynamical
`pre-melting' of the artificial spin ice structure at a temperature well below
the intrinsic ordering temperature of the island material. We thus create a
spin ice array that has real thermal dynamics of the artificial spins over an
extended temperature range
Spin canting across core/shell Fe3O4/MnxFe3−xO4 nanoparticles
Magnetic nanoparticles (MNPs) have become increasingly important in biomedical applications like magnetic imaging and hyperthermia based cancer treatment. Understanding their magnetic spin configurations is important for optimizing these applications. The measured magnetization of MNPs can be significantly lower than bulk counterparts, often due to canted spins. This has previously been presumed to be a surface effect, where reduced exchange allows spins closest to the nanoparticle surface to deviate locally from collinear structures. We demonstrate that intraparticle effects can induce spin canting throughout a MNP via the Dzyaloshinskii-Moriya interaction (DMI). We study ~7.4 nm diameter, core/shell Fe3O4/MnxFe3−xO4 MNPs with a 0.5 nm Mn-ferrite shell. Mössbauer spectroscopy, x-ray absorption spectroscopy and x-ray magnetic circular dichroism are used to determine chemical structure of core and shell. Polarized small angle neutron scattering shows parallel and perpendicular magnetic correlations, suggesting multiparticle coherent spin canting in an applied field. Atomistic simulations reveal the underlying mechanism of the observed spin canting. These show that strong DMI can lead to magnetic frustration within the shell and cause canting of the net particle moment. These results illuminate how core/shell nanoparticle systems can be engineered for spin canting across the whole of the particle, rather than solely at the surface
Enforcing Multifunctionality: A Pressure-Induced Spin-Crossover Photomagnet
Photomagnetic compounds are usually
achieved by assembling preorganized
individual molecules into rationally designed molecular architectures
via the bottom-up approach. Here we show that a magnetic response
to light can also be enforced in a nonphotomagnetic compound by applying
mechanical stress. The nonphotomagnetic cyano-bridged Fe<sup>II</sup>–Nb<sup>IV</sup> coordination polymer {[Fe<sup>II</sup>(pyrazole)<sub>4</sub>]<sub>2</sub>[Nb<sup>IV</sup>(CN)<sub>8</sub>]·4H<sub>2</sub>O}<sub><i>n</i></sub> (<b>FeNb</b>) has been
subjected to high-pressure structural, magnetic and photomagnetic
studies at low temperature, which revealed a wide spectrum of pressure-related
functionalities including the light-induced magnetization. The multifunctionality
of <b>FeNb</b> is compared with a simple structural and magnetic
pressure response of its analog {[Mn<sup>II</sup>(pyrazole)<sub>4</sub>]<sub>2</sub>[Nb<sup>IV</sup>(CN)<sub>8</sub>]·4H<sub>2</sub>O}<sub><i>n</i></sub> (<b>MnNb</b>). The <b>FeNb</b> coordination polymer is the first pressure-induced spin-crossover
photomagnet
Overexpression of CD44 accompanies acquired tamoxifen resistance in MCF7 cells and augments their sensitivity to the stromal factors, heregulin and hyaluronan
Background: Acquired resistance to endocrine therapy in breast cancer is a significant problem with relapse being associated with local and/or regional recurrence and frequent distant metastases. Breast cancer cell models reveal that endocrine resistance is accompanied by a gain in aggressive behaviour driven in part through altered growth factor receptor signalling, particularly involving erbB family receptors. Recently we identified that CD44, a transmembrane cell adhesion receptor known to interact with growth factor receptors, is upregulated in tamoxifen-resistant (TamR) MCF7 breast cancer cells. The purpose of this study was to explore the consequences of CD44 upregulation in an MCF7 cell model of acquired tamoxifen resistance, specifically with respect to the hypothesis that CD44 may influence erbB activity to promote an adverse phenotype. Methods: CD44 expression in MCF7 and TamR cells was assessed by RT-PCR, Western blotting and immunocytochemistry. Immunofluorescence and immunoprecipitation studies revealed CD44-erbB associations. TamR cells (± siRNA-mediated CD44 suppression) or MCF7 cells (± transfection with the CD44 gene) were treated with the CD44 ligand, hyaluronon (HA), or heregulin and their in vitro growth (MTT), migration (Boyden chamber and wound healing) and invasion (Matrigel transwell migration) determined. erbB signalling was assessed using Western blotting. The effect of HA on erbB family dimerisation in TamR cells was determined by immunoprecipitation in the presence or absence of CD44 siRNA. Results: TamR cells overexpressed CD44 where it was seen to associate with erbB2 at the cell surface. siRNA-mediated suppression of CD44 in TamR cells significantly attenuated their response to heregulin, inhibiting heregulin-induced cell migration and invasion. Furthermore, TamR cells exhibited enhanced sensitivity to HA, with HA treatment resulting in modulation of erbB dimerisation, ligand-independent activation of erbB2 and EGFR and induction of cell migration. Overexpression of CD44 in MCF7 cells, which lack endogenous CD44, generated an HA-sensitive phenotype, with HA-stimulation promoting erbB/EGFR activation and migration. Conclusions: These data suggest an important role for CD44 in the context of tamoxifen-resistance where it may augment cellular response to erbB ligands and HA, factors that are reported to be present within the tumour microenvironment in vivo. Thus CD44 may present an important determinant of breast cancer progression in the setting of endocrine resistance
- …