A. V. Mashirov

Submicron-sized actuators based on enhanced shape memory composite material fabricated by FIB-CVD

An enhanced scheme for a functional bilayered composite material with shape memory effect has been successfully applied on the microscale to fabricate a thermally controlled microactuator. Fabrication of cantilever-type microactuators from melt spun ribbon of TiNiCu shape memory alloy included electro-chemical polishing followed by focused ion beam milling and ion-assisted chemical vapor deposition of Pt elastic layer. The smallest working microactuator had a volume of 0:9 m 3 . The structure and thermal stability of the Pt layer have been investigated. The fabricated actuator has been proposed for use as micromechanical nanotweezers for manipulation of submicron- and nano-sized objects. Manipulation of a carbon nanotube bunch has been demonstrated. (Some figures may appear in colour only in the online journal)

Direct Measurement of Magnetocaloric Effect in Metamagnetic Ni 43 Mn 37.9 In 12.1 Co 7 Heusler Alloy

The magnetocaloric effect in the metamagnetic Ni43Mn37.9In12.1Co7 Heusler alloy is directly studied experimentally under the adiabatic and quasi-isothermal conditions in a magnetic field with induction of up to 14 T.

Magnetocaloric and thermomagnetic properties of Ni2.18Mn0.82Ga Heusler alloy in high magnetic fields up to 140 kOe

Measurements of the adiabatic temperature change (ΔT) and the specific heat transfer (ΔQ) of Ni2.18Mn0.82Ga Heusler alloy were taken in order to quantify the direct giant magnetocaloric effect of the alloy when it is in the vicinity of magneto-structural phase transition (PT) from paramagnetic austenite to ferromagnetic martensite, and their results are presented. A new vacuum calorimeter was used to simultaneously measure ΔT and ΔQ of magnetocaloric materials with a Bitter coil magnet in fields of up to Hu2009=u2009140 kOe. Other thermomagnetic properties of this alloy were investigated using standard differential scanning calorimetry and PPMS equipment. The maximal values of magnetocaloric effect in Hu2009=u2009140 kOe were found to be ΔTu2009=u20098.4u2009K at initial temperature 340u2009K and ΔQu2009=u20094900u2009J/kg at 343u2009K. Using this direct method, we show that the alloy indeed demonstrates the largest value of ΔQ as compared with previously published results for direct measurements of magnetocaloric materials, even though at 140 kOe the ...

Magnetocaloric Effect of Gadolinium at Adiabatic and Quasi-Isothermal Conditions in High Magnetic Fields

High cooling power of magnetocaloric refrigeration can be achieved only at large amounts of heat, which can be transferred in one cycle from cold end to hot end at quasi-isothermal conditions. The simple experimental method for direct measurement of the transferred heat from material with magnetocaloric effect (MCE) to massive nonmagnetic block at quasi-isothermal conditions was proposed. The vacuum calorimeter was designed for the simultaneous measurements of MCE both at adiabatic conditions (∆T) and quasi-isothermal conditions (∆Q) in the magnetic fields of Bitter coil magnet. This calorimeter was tested on samples of pure polycrystalline Gd with direct MCE. The maximal obtained values were ∆T = 17.7 K and ∆Q = 5900 J/kg at initial temperature 20 °C in magnetic field 140 kOe.

Fine-grained structure and properties of a Ni2MnIn alloy after a settling plastic deformation

The structure and properties of a polycrystalline Ni–Mn–In Heusler alloy have been studied after a plastic deformation by upsetting. An analysis of points of a martensitic and magnetic phase transformations shows that the martensite transformation takes place at temperatures lower than the Curie point. At high temperatures in the range 930–1110 K the alloy undergoes the phase transformation of ordered phase L21 to disordered phase B2, and the melting temperature of the alloy is 1245 K. The flow curves of the alloy cylindrical samples at temperatures 773, 873, and 973 K have been built. An analysis of the alloy microstructure after upsetting at a temperature of 773 K leads to the conclusion that many macrocracks are initiated in the sample. The treatment at 873 and 973 K causes a fragmentation of the grains with grain sizes from several to several dozen micrometers. However, the upsetting at 873 K leads to insignificant scatter in the grain sizes, and the microstructure is more homogeneous and worked out.

Properties of metamagnetic alloy Fe48Rh52 in high magnetic fields

A technique for differential scanning calorimetry (DSC) of materials in high magnetic fields is developed. Based on Peltier elements, a differential calorimeter is designed to work in Bitter coil magnet fields (up to 140 kOe). Calorimetric studies are conducted for Fe48Rh52 alloy with the reverse magnetocaloric effect (MCE) in the vicinity of the metamagnetic structural phase transformation (PT). It is shown that the transition latent heat falls during both forward and reverse transformation as the magnetic field grows.

Experimental simulation of a magnetic refrigeration cycle in high magnetic fields

The complete magnetic refrigeration cycle has been simulated on a sample of gadolinium in magnetic fields of a Bitter coil magnet up to 12 T. The total change of temperature of the sample during the cycle is a consequence of magnetic refrigeration, and the dependence of the magnetization of the sample on the magnetic field exhibits a hysteretic behavior. This makes it possible to determine the work done by the magnetic field on the sample during the magnetic refrigeration cycle and to calculate the coefficient of performance of the process. In a magnetic field of 2 T near the Curie temperature of gadolinium, the coefficient of performance of the magnetic refrigeration is found to be 92. With an increase in the magnetic field, the coefficient of performance of the process decreases sharply down to 15 in a magnetic field of 12 T. The reasons, for which the coefficient of performance of the magnetic refrigeration is significantly below the fundamental limitations imposed by the reversed Carnot theorem, have been discussed.

Direct and Inverse Magnetocaloric Effect in Ni1.81Mn1.64In0.55 Multifunctional Heusler Alloy

The magnetocaloric effect (MCE) in Ni1.81Mn1.64In0.55 Heusler alloy has been measured by the direct method. The field dependences of the magnetization were obtained. The phase transition temperatures were determined. The maximal adiabatic temperature change ΔTad near the Curie temperature is 1.8 K under the magnetic field change ∆H = 18 kOe. The inverse MCE (∆Tad = -3.72 K) in the same field change takes place near the temperature of martensitic transformation.

Crystalline structure and magnetic behavior of the Ni41Mn39In12Co8 alloy demonstrating giant magnetocaloric effect

Magnetic cooling is a green cooling technology, which is more energy efficient than existing fluid-compression cooling machines. Ni41Mn39In12Co8 alloy, which demonstrates promising magnetocaloric performances, was investigated using neutron diffraction and thermomagnetic measurements. The austenite structure is cubic L-21 (Fm (3) over barm), while that of the martensite is a mix of 8 and 6 M modulated monoclinic structures (P 12/m 1). The austenitic site occupancy refinements reveal that all substituting Co atoms occupy Ni-sites. Most Mn atoms (65%) are in the Mn-sites and the rest go to In-sites (about 35%) and Ni-sites (less than 5%). This disorder of the magnetic atoms (Mn, Ni and Co) in the austenitic phase remains unchanged during the martensitic transition. The distortions of the interatomic distances due to the modulation of the martensitic structures further enhance the disorder in the magnetic interactions. Thermomagnetic measurements indicate that the austenitic phase is ferromagnetic. Cooling to below 250 K, where the alloy loses its ferromagnetic nature, and down to 50 K, the lack of any antiferromagnetic Bragg peaks suggests no antiferromagnetic ordering in the martensitic phase. At very low temperatures in the martensitic phase, spin glass magnetic nature is identified by magnetic measurements, and the spin-glass transition temperature is similar to 19 K.

Device for nanoobject manipulation based on two-layer composite with shape memory

A device for gripping of microand nanoobjects (nanotweezers) with a working body made of bimetal composite (fast-quenched Ti2NiCu alloy with shape memory and platinum layer) is developed and studied. A method for manufacturing of the composite material using local ion etching and ion-stimulated deposition from gas phase is proposed. A structure of nanotweezers based on such a composite and experiments on gripping and displacement of submicron objects are presented.