Elvina Dilmieva

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 H = 140 kOe. Other thermomagnetic properties of this alloy were investigated using standard differential scanning calorimetry and PPMS equipment. The maximal values of magnetocaloric effect in H = 140 kOe were found to be ΔT = 8.4 K at initial temperature 340 K and ΔQ = 4900 J/kg at 343 K. 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.

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.

Rapidly quenched ferromagnetic ribbons with shape memory for magnetically controlled micromechanic devices

One-way shape-memory effect (SME) controlled by temperature and magnetic field in rapidly melt-quenched (RMQ) Heusler-alloy (Ni53Mn24Ga23) ribbons is experimentally studied. Two-way SME that results from training is demonstrated for submicron Ni53Mn24Ga23 samples. Reversible thermally and magnetically controlled bending of no less than 1.5% and deflection of no less than 2 μm are reached for composite Ni53Mn24Ga23/Pt microactuators with sizes of 25 × 2.3 × 1.7 μm3 in the presence of magnetic field of μ0Н = 8 T at an initial temperature of 63°С.

Research of magnetocaloric effect of Ni-Mn-In-Co- based Heusler alloys by the direct method in magnetic fields up to 14 T

The magnetocaloric effect (MCE) is the adiabatic temperature change (dTad) or (and) the isothermal entropy change (dS) of magnet under the influence of a magnetic field.

General working characteristics of magnetocaloric materials in high magnetic fields

A big interest is attracted to the application of materials with a large magnetocaloric effect (MCE) at magnetic and magnetostructural phase transitions (PT) for creation of household refrigerators, operating near room temperature.

Revision of Clausius–Clapeyron Relation for the First-Order Phase Transition in Ni–Mn–In Heusler Alloys

The derivation is presented of the Clausius–Clapeyron relation (CCR) in the second order of expansion of free energy potential on the change of temperature and magnetic field on the example of Ni–Mn–In Heusler alloys with the first-order metamagnetostructural phase transition (FOMMSPT), which can be treated as thermoelastic structural transition: austenite—martensite merging with metamagnetic transition: ferromagnet–antiferromagnet. It is shown that the second-order CCR describes satisfactory the nonlinear shift in the characteristic temperatures of the FOMMSPT in magnetic fields up to 25 T. It qualitatively and quantitatively explains the observed nonlinear dependence of the characteristic temperatures and the hysteresis of FOMMSPT including its elimination in some compositions of the Ni–Mn–In Heusler alloys under sufficiently high magnetic field.

Formation of a martensitic twins structure in Ni 2.16 Mn 0.84 Ga heusler alloy by high magnetic fields under adiabatic and isothermal conditions

The results are presented from experimental studies of the formation of martensitic twin structures in Ni2.16Mn0.84Ga Heusler alloy under the effect of magnetic fields of up to 14 T using a specially developed optical microscope under isothermal and adiabatic conditions. A qualitative model is proposed that explains the differences between the progress magnetoinduced magnetostructural first-order phase transitions under different thermodynamic conditions.