It is shown that a scanning probe microscope allows precise manipulation of an ensemble of upconversion nanoparticles deposited uncontrollably on the surface of a glass substrate. The possibility of controlled movement of such particles over distances of several tens of micrometers is demonstrated, leaving several upconversion nanoparticles separated from others (or small conglomerates of them) on a surface with an area of ∼104 μm2. The system of marks on the substrate makes it easy to find such particles and perform a series of manipulations, including movements over submicrometer distances and rotation at a given angle of a single upconversion nanoparticle. The force of an individual upconversion nanoparticle’s adhesion to the surface of a substrate is estimated.

In this study, the conditions for maintaining quasiuniform magnetization in planar square Ni particles with configurational anisotropy are investigated. Using computer modeling, a magnetic state diagram is constructed in the coordinates of “particle size – degree of configurational anisotropy,” and the conditions under which the quasiuniform state is energetically favorable are identified. Arrays of particles with two different shapes and varying sizes are fabricated experimentally. It is found that the quasiuniform magnetization structure can be preserved in particles with lateral sizes of several micrometers.

The authors consider using upconversion fluoride nanoparticles of NaYF4 doped with Yb3+ and Er3+ ions as ordered non-invasive hidden labels. At the first stage the synthesized upconversion fluoride nanoparticles have been deposited from the suspension onto the substrate with mechanical scratches used as large-scale markers. The scanning probe microscope is then used to move individual upconversion nanoparticles macroscopically significant distances and deposit them in a controlled manner onto a clean surface, thereby imprinting nanoobjects. The displacement and deposition process has been monitored using a conventional optical microscope. Luminescent signals from regularly placed labels have been recorded in an optical confocal microscope.

Square planar nickel microparticles deposited on the surface of single crystals of lithium niobate in the hexagonal phase and potassium titanyl phosphate were studied. Because the thermal expansion coefficients of these single crystals strongly differ, the uniaxial anisotropy is induced in the microparticles by heating or cooling relative to the deposition temperature. The phenomenon of the induction of anisotropy was explored using magnetic force microscopy and ferromagnetic resonance spectroscopy. Data obtained from ferromagnetic resonance spectra show that, in the ensemble of microparticles, with increasing temperature of the samples from –10 to 60°C, the axis of anisotropy rotates by 90°. This agrees well with the data about the domain structure of an individual microparticle, obtained by magnetic force microscopy.

The possibility of precise movement of YVO4:Yb,Er nanoparticles was studied in this work. Such nanoparticles exhibit upconversion luminescent properties and can serve as an accurate low-invasive probe of changes in the local parameters of the medium (in particular, temperature). Using an atomic force microscope, the substrate region with upconversion nanoparticles deposited from the solution and accompanying residues of the synthesis products was cleaned. The use of mechanical marks on the substrate made it possible to compare the atomic force and optical confocal images of the surface and to register the luminescence from an individual nanoparticle. Elemental analysis and luminescence spectra unambiguously identify the nanoparticle as YVO4:Yb,Er.

Rare earth-doped micro/nano-crystals are promising as microscopic fluorescent probes for monitoring local environment parameters, particularly for orientation tracking.

We present the results of the luminescence response studies of a single YVO4:Yb, Er particle of 1-µm size. Yttrium vanadate nanoparticles are well-known for their low sensitivity to surface quenchers in water solutions which makes them of special interest for biological applications. First, YVO4:Yb, Er nanoparticles (in the size range from 0.05 µm up to 2 µm), using the hydrothermal method, were synthesized. Nanoparticles deposited and dried on a glass surface exhibited bright green upconversion luminescence. By means of an atomic-force microscope, a 60 × 60 µm2 square of a glass surface was cleaned from any noticeable contaminants (more than 10 nm in size) and a single particle of 1-µm size was selected and placed in the middle. Confocal microscopy revealed a significant difference between the collective luminescent response of an ensemble of synthesized nanoparticles (in the form of a dry powder) and that of a single particle. In particular, a pronounced polarization of the upconversion luminescence from a single particle was observed. Luminescence dependences on the laser power are quite different for the single particle and the large ensemble of nanoparticles as well. These facts attest to the notion that upconversion properties of single particles are highly individual. This implies that to use an upconversion particle as a single sensor of the local parameters of a medium, the additional studying and calibration of its individual photophysical properties are essential.

The experimental results of the formation of polymer masks for the creation of planar microparticles of a given shape by scanning probe lithography are presented. The problems associated with the nonlinearity of the probe movement during the mask formation are considered. The possibility of increasing the lifetime of the probe by changing the mask formation procedure and (or) changing the sample temperature has been demonstrated. Improving the quality of the resulting mask is achieved through the use of chemical etching.

The influence of the thermally induced magnetoelastic effect on the magnetization reversal field in 0.9 × 0.3 × 0.03-μm Ni particles formed on a single crystalline lithium triborate (LiB 3 O 5 ) substrate has been studied. It has been shown experimentally that this substrate can reduce the magnetization reversal field of particles by a factor of more than 1.5 as the temperature of the sample increases from 30 to 45°C. This reduction of the reversal field is due to magnetoelastic anisotropy induced in the particles by the difference between the thermal expansion coefficients of the substrate along different crystallographic axes.

There is presented results studying of changes of the domain structure of a planar square microparticle with dimensions 7.5 × 7.5 × 0.04 μm under uniaxial mechanical stress. Microparticles were made from following materials: permalloy (18% Fe, 82% Ni), permendur (50% Co, 50% Fe), halfenol (16% Ga, 84% Fe), Ni, terfenol (Tb0.3Dy0.7Fe1.92). It was concluded about promising of using these materials for creating microsensors of mechanical stress and for creating straintronic devices for processing and storing information.

The possibility of precise movement of YVO4:Yb,Er nanoparticles was studied in this work. Such nanoparticles exhibit upconversion luminescent properties and can serve as an accurate low-invasive probe of changes in the local parameters of the medium (in particular, temperature). Using an atomic force microscope, the substrate region with upconversion nanoparticles deposited from the solution and accompanying residues of the synthesis products was cleaned. The use of mechanical marks on the substrate made it possible to compare the atomic force and optical confocal images of the surface and to register the luminescence from an individual nanoparticle. Elemental analysis and luminescence spectra unambiguously identify the nanoparticle as YVO4:Yb,Er.

The results of studying the changes in the domain structure of a planar square microparticle with size 7.5 x 7.5 x 0.04 μm under uniaxial mechanical stress is presented. Microparticles were made from the following materials: permalloy (18% Fe, 82% Ni), permendur (50% Co, 50% Fe), halfenol (16% Ga, 84% Fe), Ni, terfenol (Tb 0.3 Dy 0.7 Fe 1.92 ). The conclusions about the promising of using these materials for fabrication microsensors for stress detection and for fabrication straintronic devices for processing and storing information were made. Keywords: magnetoelastic effect, magnetic force microscopy, planar ferromagnetic particles, domain structure.

Results of studying the domain structure of planar Ni microparticles formed on single-crystal substrates from the lithium niobate and from the potassium titanyl phosphate at different temperatures are presented. The dependence of domain sizes on the sample temperature was studied. It is shown the observed change of the domain structure is caused by the magnetoelastic effect, which arises due to the difference in the thermal expansion coefficients of the substrate and microparticles as the sample temperature changes. It is shown, the sizes of magnetic domains, up to the creation of a state with a quasi-homogeneous magnetization may be set by the substrate temperature during the microparticles formation. Keywords: magnetoelastic effect, magnetic force microscopy, remagnetization, lithium niobate, potassium titanyl phosphate, temperature.

Results of studying the domain structure of planar Ni microparticles formed on single-crystal substrates from the lithium niobate and from the potassium titanyl phosphate at different temperatures are presented. The dependence of domain sizes on the sample temperature was studied. It is shown the observed change of the domain structure is caused by the magnetoelastic effect, which arises due to the difference in the thermal expansion coefficients of the substrate and microparticles as the sample temperature changes. It is shown, the sizes of magnetic domains, up to the creation of a state with a quasi-homogeneous magnetization may be set by the substrate temperature during the microparticles formation.

Solvothermal technology is used to synthesize YNaF4:Yb,Tm nanoparticles. Under the impact of laser radiation at a wavelength of 980 nm, the nanoparticles exhibit strong upconversion luminescence that corresponds to the emission of Tm3+ ions as a consequence of energy being transferred from Yb3+ ions. Recordings of the emission of single nanoparticles show the spectral lines at wavelengths of 480 and 495 nm are characterized by different polarizations.

Методами магнитно-силовой микроскопии были исследованы магнитные свойства (поле переключения) и переходы из многодоменного в однодоменное состояние планарных микрочастиц Co18Ni82 размером 7.5x7.5x0.03 μm3 при различных температурах. Использование в качестве подложки гексагонального монокристалла ниобата лития, обладающего отличающимися температурными коэффициентами линейного расширения вдоль разных кристаллографических осей, позволило индуцировать одноосные механические напряжения в микрочастицах путем относительно небольшого нагрева или охлаждения образца по сравнению с его температурой напыления. Показано, что за счет термоиндуцированного магнитоупругого эффекта увеличение температуры всего на 50 K может привести к семикратному уменьшению величины поля переключения. Ключевые слова: магнитоупругий эффект, магнитная силовая микроскопия, перемагничивание, ниобат лития, температура.

The magnetic-force microscopy has been used to study the magnetic properties (switching field) and the transitions from a multidomain state to a single-domain state of planar Co18Ni82 microparticles with sizes 7.5 × 7.5 × 0.03 μm3 at various temperatures. The use of a hexagonal single-crystal lithium niobate, which has different temperature linear expansion coefficients along different crystallographic axes as a substrate makes it possible to induce uniaxial mechanical stresses in microparticles by relatively insignificant heating or cooling a sample as compared to its deposition temperature. It is shown that the increase in temperature only by 50 K due to the thermostimulated magnetoelastic effect can lead to the seven-fold decrease in the switching field.

The influence of temperature on the magnetization distribution of planar Co18Ni82 microparticles deposited on a lithium niobate single crystal was studied using the magnetic force microscopy and computer simulation. The possibility to change the magnetization distribution of CoNi microparticles by changing only the temperature of the substrate (without applying an external magnetic field) was demonstrated. It was shown that the observed effect was due to a noticeable difference in the coefficients of linear thermal expansion of lithium niobate along different crystallographic axes. The quantitative parameter for characterization of the domain structure transformation as a result of temperature change was proposed.

The paper presents theoretical model of a straintronics magnetoelectric random-access memory (MeRAM) storage cell with configurational anisotropy. The MeRAM cell consists of ferromagnetic layers with different orientations of the quasi-uniform magnetization, which is divided into identical magnetic tunnel junction’s ferromagnet|insulator|ferromagnet, in the form of a sandwich of planar layers. The modified theory for magnetic tunnel junction is used to calculate the spin-dependent current and tunnel magnetoresistance like functions of orientations magnetizations of layers.