Predicting the structural, electronic and magnetic properties of few atomic-layer polar perovskite.

Density functional theory (DFT) calculations are performed to predict the structural, electronic and magnetic properties of electrically neutral or charged few-atomic-layer (AL) oxides based on polar perovskite KTaO3. Their properties vary greatly with the number of ALs (nAL) and the stoichiometric ratio. In the few-AL limit (nAL ≤ 14), the even AL (EL) systems with the chemical formula (KTaO3)n are semiconductors, while the odd AL (OL) systems with the formula Kn+1TanO3n+1 or KnTan+1O3n+2 are half-metal except for the unique KTa2O5 case which is a semiconductor due to the large Peierls distortions. After reaching a certain critical thickness (nAL > 14), the EL systems show ferromagnetic surface states, while ferromagnetism disappears in the OL systems. These predictions from fundamental complexity of polar perovskite when approaching the two-dimensional (2D) limit may be helpful for interpreting experimental observations later.

Magnetoelectric Coupling in Multiferroic Bilayer VS_{2}.

Based on the first-principles prediction, we report the magnetoelectric coupling effect in two-dimensional multiferroic bilayer VS_{2}. The ground-state 3R-type stacking breaks space inversion symmetry, therefore introducing a spontaneous polarization perpendicular to the layer plane. We further reveal that the out-of-plane ferroelectric polarization of bilayer VS_{2} can be reversed upon interlayer sliding of an in-plane translation. Each VS_{2} layer has a ferromagnetic state with an opposite magnetic moment between two antiferromagnetically ordered layers. We found that ferroelectricity and antiferromagnetism can be coupled together by a ferrovalley in bilayer VS_{2} to realize electronic control of magnetism. Remarkably, a net magnetic moment is generated by reducing the interlayer distance, and an electric field is able to achieve linear and second-order nonlinear magnetoelectric coupling in bilayer VS_{2}.

Size-Dependent Structural, Magnetic and Magnetothermal Properties of Y3Fe5O12 Fine Particles Obtained by SCS.

Iron-containing oxides are the most important functional substance class and find a tremendous variety of applications. An attractive modern application is their use in biomedical technologies as components in systems for imaging, drug delivery, magnetically mediated hyperthermia, etc. In this paper, we report the results of the experimental investigation of submicron Y3Fe5O12 garnet particles obtained in different sizes by solution combustion synthesis (SCS) using glycine organic fuel to discuss the interdependence of peculiarities of the crystal and magnetic structure and size's influence on its functional magnetothermal performance. A complex study including Mössbauer and Raman spectroscopy accompanied by X-ray diffractometry, SEM, and measurements of field and temperature magnetic properties were performed. The influence of the size effects and perfectness of structure on the particle set magnetization was revealed. The ranges of different mechanisms of magnetothermal effect in the AC magnetic field were determined.

Understanding the Dependence of Nanoparticles Magnetothermal Properties on Their Size for Hyperthermia Applications: A Case Study for La-Sr Manganites.

Magnetic oxides are promising materials for alternative health diagnoses and treatments. The aim of this work is to understand the dependence of the heating power with the nanoparticle (NP) mean size, for the manganite composition La0.75Sr0.25MnO3 (LSMO)-the one with maximum critical temperature for the whole La/Sr ratio of the series. We have prepared four different samples, each one annealed at different temperatures, in order to produce different mean NP sizes, ranging from 26 nm up to 106 nm. Magnetization measurements revealed a FC-ZFC irreversibility and from the coercive field as function of temperature we determined the blocking temperature. A phase diagram was delivered as a function of the NP mean size and, based on this, the heating mechanism understood. Small NPs (26 nm) is heated up within the paramagnetic range of temperature (T>Tc), and therefore provide low heating efficiency; while bigger NPs are heated up, from room temperature, within the magnetically blocked range of temperature (TT>TB), for intermediate mean diameter size of 37 nm, with maximum efficiency of heat transfer.

Enhanced cytotoxicity caused by AC magnetic field for polymer microcapsules containing packed magnetic nanoparticles.

Magnetic hyperthermia (MH) is a perspective tool to treat the tumor while the magnetic material is delivered. The key problems in MH development is to ensure an effective local heating within cancer cell without overheating other cells. In order to do that one has to reach substantial local accumulation of magnetic nanoparticles (MNPs) and/or magnetically sensitive objects with advanced heat properties. Absorbing heat energy for destroying tumor cells can be generated only if there is sufficient amount of locally placed MNPs. In this work, we propose polyelectrolyte microcapsules modified with iron oxide nanoparticles as an approach to tie magnetic materials in high concentration locally. These microcapsules (about 3 microns in diameter) can be readily internalized by various cells. The human fibroblasts uptake of the microcapsules and cytotoxic effect upon the influence of alternating magnetic field (AMF) while magnetic capsules are inside the cells is under study in this work. The cytotoxicity of the magnetic microcapsules was compared with the cytotoxicity of the MNPs while free in the solution to evaluate the effect of bounding MNPs. A cytotoxic effect on cells was found in the case of preliminary incubation of fibroblasts with capsules while the AMF is applied. In the case of MNPs in an equivalent dose per mass of magnetic material, there was no cytotoxic effect noticed after the treatment with the field. It is noteworthy that during the treatment of cells with the AMF, the increase in temperature of the incubation medium was not registered. The morphological changes on fibroblasts were consistent with the data of the viability assessment. Thus, the synthesized capsules are shown as a means for local enhancement of magnetic hyperthermia in the treatment of tumor diseases.

Electric-field-driven magnetic domain wall as a microscale magneto-optical shutter.

Nowadays, spintronics considers magnetic domain walls as a kind of nanodeviсe that demands for switching much less energy in comparison to homogeneous process. We propose and demonstrate a new concept for the light control via electric field applied locally to a magnetic domain wall playing the role of nanodevice. In detail, we charged a 15-µm-thick metallic tip to generate strong non-uniform electric field in the vicinity of the domain wall in the iron garnet film. The electric field influences the domain wall due to flexomagnetoelectric effect and causes the domain wall shift. The resulting displacement of the domain wall is up to 1/3 of domain width and allows to demonstrate a novel type of the electrically controlled magneto-optical shutter. Polarized laser beam focused on the electric-field-driven domain wall was used to demonstrate the concept of a microscale Faraday modulator. We obtained different regimes of the light modulation - linear, nonlinear and tri-stable - for the same domain wall with corresponding controllable displacement features. Such variability to control of domain wall's displacement with spatial scale of about 10 µm makes the proposed concept very promising for nanophotonics and spintronics.

Developing Antitumor Magnetic Hyperthermia: Principles, Materials and Devices.

BACKGROUND AND OBJECTIVE: Methods of local or loco-regional anticancer treatment are of the utmost importance because the therapeutic 'power' is applied directly to the disease site. Consequently, general toxicity is minimized. Hyperthermia, that is, a sustained increase of intratumoral temperature up to 45oC, has been investigated as a perspective treatment modality alone and/or in combination with ionizing radiation or chemotherapy. Still, the surrounding tissues can be damaged by the external heat. METHOD: Development of new materials and devices gave rise to methods of inducing hyperthermia by a high frequency magnetic or electromagnetic field applied to the tumor with exogenous nanosized particles captured within it. The idea of this approach is the release of local heat in the vicinity of the magnetic nanoparticle in a time-varying magnetic field due to transfer of external magnetic field energy into the heat. Therefore, tumor cells are heated whereas the peritumoral non-malignant tissues are spared. RESULTS: This review analyzes recent advances in understanding physical principles that underlie magnetic hyperthermia as well as novel approaches to obtain nanoparticles with optimized physico-chemical, toxicological and tumoricidal properties. Special focus is made on the construction of devices for therapeutic purposes. CONCLUSION: The review covers recent patents and general literature sources regarding magnetic hyperthermia, the developing approach to treat otherwise intractable malignancies. </p><p>.