Dissipative dynamics of an extended magnetic nanostructure: Spin necklace in a metallic environment

We study theoretically the dynamics of an ``xxz'' spin necklace coupled to a conduction electron sea, a model system for a nanostructure in a dissipative environment. We extract the long-time behavior via a mapping to a multichannel Coulomb gas problem followed by a scaling analysis. The strong quantum fluctuations of the necklace cause a nontrivial dependence of couplings on system size which we extract via an analysis involving the ``boundary condition changing operator'', and confirm via a detailed numerical evaluation of one case.Comment: 4 pages, 4 figure

Effects of infrared and ultraviolet radiation on the viability of cells immobilized in porous TiNi-based alloy scaffold

Сell responses to electromagnetic radiation are due to many factors including the cellular microenvironment. The aim of the present study was to explore the effects of ultraviolet (UV) and infrared (IR) irradiation of low intensity on cultured cells derived from different biological tissues (spleen, bone marrow, and Ehrlich's adenocarcinoma), which were immobilized in a porous TiNi-based alloy scaffold. Accordingly, the following objectives were set: i) to evaluate the impact of low-intensity radiation on cell suspensions, and ii) to carry out a comparative analysis of the viability of cells immobilized in porous TiNibased alloy and IR- and UV-irradiated. The data show that the extracellular environment of bone marrow, tumor and spleen cel

First- and second-order transitions of the escape rate in ferrimagnetic or antiferromagnetic particles

Quantum-classical escape-rate transition has been studied for two general forms of magnetic anisotropy in ferrimagnetic or antiferromagnetic particles. It is found that the range of the first-order transition is greatly reduced as the system becomes ferrimagnetic and there is no first-order transition in almost compensated antiferromagnetic particles. These features can be tested experimentally in nanomagnets like molecular magnets.Comment: 11 pages, 3 figures, to appear in Europhys. Let

The influence of the surface layer on the combination of properties of thin TiNi alloy wires

We have studied the influence of the surface layer on the parameters of the multiply repeated shape memory effect, developing stresses, characteristic temperatures, and intervals of martensitic transformations in thin (1 mm diameter) wires made of TiNi-based alloys. Examination of the surface layer structure showed that, in 1-mm-diameter TN-1V grade alloy wire, the oxide layer is about 15 μm thick and consists mostly of titanium, nickel, oxygen, and carbon. Removal of this surface layer leads to an increase in the maximum accumulated deformation, shift of the temperature interval of formation toward higher temperatures, and increase in the strength and plasticity characteristics

Reaction sintering of porous shape-memory titanium-nickelide-based alloys

The problems of reaction sintering of porous shape-memory Ti−Ni-based alloys are examined. An analysis of the structure and parameters of shape-memory materials produced with the use of different reaction sintering modes is performed. The temperature and time intervals are determined over which liquid-phase sintering points responsible for a qualitative change in the TiNi phase of the reaction-sintered Ti−Ni system are observed. The morphological structure and properties of the porous materials are investigated. Models for interactions between phases and phase transformations in the sintered alloys are built. It has been found that changes in the deformation parameters of the porous titanium nickelide-based alloys correlate with an increase in the volume fraction of the TiNi phase and with its wholeness as the sintering time is increased

The effect of cobalt additives on martensitic transformations and deformation in sintered porous nickel titanium alloys

Porous nickel titanium (TiNi) shape memory alloys with cobalt additives have been obtained by reaction and diffusion sintering. Analysis of the experimental temperature dependence of the electric resis tance and multiple shape memory effect leads to a conclusion that Co additives below 1 at % in reaction sin tered, and even more so in diffusionsintered, alloys lead to a reduction in intrinsic internal stresses in the TiNi phase. Additives above 1 at % induce dispersion hardening of the alloy. At all concentrations, cobalt additives lead to obstacles for the martensitic phase transformations

Influence of cobalt and molybdenum additives on the structure and shape memory parameters of reaction-sintered porous nickel titanium alloys

We have studied the structure and properties of porous nickel titanium (TiNi) alloys obtained upon reaction sintering of Ti and Ni powders with Co and Mo additives. It is established that Co and Mo doping additives retain the compaction of Ni powder achieved at the initial stage of sintering. The maximum deformation of porous samples loaded in the austenite state was observed upon adding Co, while the addition of Mo resulted in minimum deformation. The addition of Co leads to single-stage martensitic transformation in TiNi phase, while the addition of Mo leads to the two-stage transformation that is more homogeneous over the volume. Both Co and Mo additives lead to increase in the maximum accumulated strain due to the formation of favorably oriented stress-induced martensite and reoriented quench-induced martensite

Investigation of the effect of copper addition on physical and mechanical properties of TiNi-Cu porous alloy

This work is devoted to the physical and mechanical properties of porous alloys based on TiNi alloyed with different amounts of Cu additive. We show that by doping a porous TiNi alloy with copper instead of nickel, it is possible to obtain characteristics acceptable for use in implantology and superior to those of known porous TiNi alloys. Cu addition in the range from 1 to 10 at.% is shown to optimize the properties of tested alloys. There is a decrease in the minimal martensitic transformation stress τminMs from 37 to 17 MPa when compared to initial unalloyed TiNi. Alloys with 3 and 6 at.% of Cu are found to be optimal for use in medical practice. Along with a wide temperature range of reversible deformations that cover the range of operating temperatures (273–313 K), such alloys demonstrate their martensitic transformation stress values below 28 MPs. This permits to model implantable structures of complex configuration from such materials under a certain temperature regime

Study of structural features of porous TiNi-based materials produced by SHS and sintering

Structural properties of porous TiNi-based materials produced by SHS method and sintering have been investigated. The material having different pore wall surface topography, porosity and pore size distribution was shown to be produced depending on the powder metallurgy method for porous TiNi-based alloy. All the materials having porosity of 55-70%, mean pore size 90-150 μm, as well as normal pore size distribution are most preferable. Ultimate strength and breaking point were determined to depend on porosity, pore size distribution, pore intersections and phase chemical composition of the material. Strength properties of the sintered alloy are twice as much compared to the SHS-produced ones due to homogeneity of its macrostructure, low chemical heterogeneity and TiNi3 precipitations strengthening the TiNi matrix.</jats:p

Low-Temperature Quantum Relaxation in a System of Magnetic Nanomolecules

We argue that to explain recent resonant tunneling experiments on crystals of Mn$_{12}$ and Fe$_8$, particularly in the low-T limit, one must invoke dynamic nuclear spin and dipolar interactions. We show the low-$T$, short-time relaxation will then have a $\sqrt{t/\tau}$ form, where $\tau$ depends on the nuclear $T_2$, on the tunneling matrix element $\Delta_{10}$ between the two lowest levels, and on the initial distribution of internal fields in the sample, which depends very strongly on sample shape. The results are directly applicable to the $Fe_8$ system. We also give some results for the long-time relaxation.Comment: 4 pages, 3 PostScript figures, LaTe