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Direct studies of the adiabatic temperature change (ΔTad) in the Ni47Mn40Sn12.5Cu0.5 Heusler alloy in steady magnetic fields up to 8 T by the extraction method and in pulsed magnetic fields up to 50 T were carried out in this paper. The alloy Ni47Mn40Sn12.5Cu0.5 demonstrates a magnetostructural phase transition (MSPT) of the first order in the 254–283 K temperature range as well as a second order phase transition near the Curie temperature TC = 313 K. An inverse magnetocaloric effect (MCE) was found in the region of the MSPT, and it reaches the maximum value ΔTad = −12 K in 20 T at the initial temperature T0 = 275 K. The irreversible part of the MCE reached ΔTir = −10 K when the field is completely removed. We consider the dynamics of the MCE in the vicinity of the MSPT and discuss the mechanisms that cause the giant irreversibility of the MCE as well as the possibilities of its application in hybrid cooling systems. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect (MCE) in samples of the Gd2In compound has been studied by the direct method in temperature range of 4–240 K in magnetic fields of Bitter coil up to 14 T. The maximum detected value of the inverse MCE at cryogenic temperatures in the 1st-order metamagnetic phase transition (PT) is ∆Tad = − 0.5 K at T0 = 45 K in the field of 1.8 T. The MCE in this temperature range changes sign with increasing of the magnetic field up to 5 T, and the direct MCE is observed with further increasing of the field. The kinetic arrest of the 1st-order metamagnetic PT is observed on the temperature dependence of magnetization in the steady magnetic field of 5 T. The direct MCE in the Curie temperature Tc = 200 K increases with increasing of the magnetic field, and the effect maximum shifts to higher temperatures. The maximum detected value of the direct MCE is ∆Tad = 7.8 K at T0 = 215 K in the field of 14 T. [ABSTRACT FROM AUTHOR]

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=8.4K at initial temperature 340K 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 magnetic field-induced magnetostructural PT is still not complete. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present a new technique for experimental study of kinetics of phase transitions (PTs) and direct measurement of the magnetocaloric effect (MCE) in pulsed magnetic fields by using the fast response temperature probe with infrared fiber optical (IRFO) sensor. As demonstration of the new technique, the results are presented of MCE measurements for Gd near Curie point: ΔT ad = 21.3 K under pulsed magnetic field µ 0 H = 12.7 T; and inverse MCE for Fe 48 Rh 52 sample at initial temperature 305.1 K: ΔT ad = −4.5 K under pulsed magnetic field µ 0 H = 8.5 T. Also, the energy losses on magnetization near the 1st order PT were calculated from the results of direct measurements of magnetization versus time for Fe 48 Rh 52 sample: W = 45 J/kg. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect in the Fe49Rh51 alloy was systematically studied using three different approaches: in-field differential scanning calorimetry, standard direct measurement of the adiabatic temperature change, and a non-contact method based on a thermo-optical phenomenon, the mirage effect, which was able to directly test the magnetocaloric response induced by a fast magnetic field variation. The metamagnetic phase transition of Fe49Rh51 was studied in the temperature range of 290–330 K at magnetic fields up to 1.8 T through magnetic and calorimetric measurements. The estimated parameters of phase transition were comparable with the literature data. The values of adiabatic temperature change obtained with the three methods (calorimetry, standard direct measurement, and mirage-based technique), which explore three different time scales of the field variation (static field, 1 T s−1, 770 T s−1), were consistent, proving the absence of dynamic constraints in the first-order magnetostructural transition at the maximum field sweep rate. [ABSTRACT FROM AUTHOR]

Here, we present the results of an experimental and numerical study of controllable spin-wave propagation in the yttrium iron garnet stripe with an Fe-Rh slab. The transformation of spin-wave dispersion and transmission are observed by the focusing laser light on top of the Fe-Rh slab. It was shown that the geometry variation and design of the Fe-Rh slab significantly affect spin-wave propagation. The static internal magnetic field profile in the yttrium iron garnet is subject to position and the geometric parameters of the Fe-Rh slab. Additionally, the possibility of width mode filtering was shown for a surface magnetostatic spin wave by the means of micromagnetic simulation. The qualitative correspondence between the behavior of spin waves in the numerical simulation and microwave spectroscopy data was observed. The proposed structure can be used as a functional unit with the simultaneous frequency selective and spin-wave mode filtration regime in planar magnonic networks. [ABSTRACT FROM AUTHOR]

The magnetic and magnetocaloric measurements are reported for Ni49.9Mn37.03Sb12.3Fe0.77. The application of magnetic field was found to result in a shift of characteristic temperatures of the martensitic transformation (MT) by 0.7 K/T. Direct measurements of magnetocaloric effect (MCE) were employed to evaluate potential of this alloy for magnetic refrigeration. Peak values of MCE in magnetic field of 5 T were determined to be ~ −0.6 K in the interval of MT, and ~1 K in the vicinity of Curie temperature. [ABSTRACT FROM PUBLISHER]

In this paper, we focus on understanding the magnetic field and temperature dependences of the heat capacity CP, electrical resistivity ρ, and magnetocaloric effect ΔTad in Fe48Rh52 alloy near room temperatures. The phase diagram is constructed according to the CP(H, T) and ρ(H, T) data, and the field shift of the critical temperature is found to be 9.6 K/T. The experimental results on the heat capacity do not confirm the existing assumption about the electronic nature of the antiferromagnet–ferromagnet phase transition in the FeRh alloy. An increase in resistance through the ferromagnetic–antiferromagnetic phase transition is explained by a sharp decrease of the carrier density and simultaneously the appearance of an additional conducting channel. The adiabatic temperature change ΔTad at a field change of 1.8 T equals −9.8 K, and the maximum value of the entropy change ΔS estimated from CP(H, T) and ΔTad(H, T) data is equal to 12.8 J/kg K. The differences in the magnetocaloric effect values in the heating and cooling run in weak magnetic fields are explained based on the thermal expansion data. An almost reversible degradation of the magnetocaloric effect was discovered upon the continuous application of a cyclic magnetic field at temperatures near the magnetostructural transition. [ABSTRACT FROM AUTHOR]

This paper is devoted to the study of magnetocaloric effect (MCE) in Ni-Mn-In-Co Heusler alloys by direct methods in high magnetic fields. Ni-Mn-In-Co Heusler alloys demonstrate the inverse MCE in the magnetostructural transition area. The adiabatic temperature change value ( \Delta T\mathrm {ad} ) is determined by direct extraction method in magnetic fields up to 10 T. It is shown that the value of \Delta T\mathrm {ad} increases with decrease in the difference between the temperature of magnetostructural transition and the Curie point temperatures of the compounds. The amount of isothermal heat emission (sorption) for Ni43Mn37.8In12.2Co7 alloy is determined as a result of magnetization in magnetic field up to 10 T in the magnetostructural transition area. The obtained results are discussed from the viewpoint of magnetic and lattice subsystems influences on the total entropy change ( \Delta St ). [ABSTRACT FROM AUTHOR]

In present work we have investigated magnetostrictive ultrasound generation by spiral magnets in the vicinity of magnetic field induced phase transition from spiral to collinear state. We found that such magnets may generate transverse sound waves with the wavelength equal to the spiral period. We have examined two types of spiral magnetic structures: with inhomogeneous exchange and Dzyaloshinskii–Moriya interactions. Frequency of the waves from exchange-caused spiral magnetic structure may reach some THz, while in case of Dzyaloshinskii–Moriya interaction-caused spiral it may reach some GHz. These waves will be emitted like a sound pulses. Amplitude of the waves is strictly depends on the phase transition speed. Some aspects of microwaves to hypersound transformation by spiral magnets in the vicinity of phase transition have been investigated as well. Results of the work may be interesting for investigation of phase transition kinetics as well, as for various hypersound applications. [ABSTRACT FROM AUTHOR]

The dynamics of the magnetocaloric effect (MCE) in a ribbon sample Ni50Mn35Al2Sn13 in a cyclic magnetic field of 1.8 T was studied by a direct method. It was shown that near magnetostructural phase transition (MSPT), due to the irreversibility of the MSPT in a magnetic field of 1.8 T, the value of the inverse effect depends on the rate of temperature change. The higher the scanning rate, the greater the value of the MCE, which is associated with the phase transition kinetics and with relaxation processes that manifest themselves in the first-order MSPT region. At scanning rates below 1 K/min, a direct MCE appears with ΔT = 0.21 K, at a maximum rate of 10 K/min, an inverse MCE appears with a value of ΔT = − 0.12 K. [ABSTRACT FROM AUTHOR]

The bi- and tri- layered magnetoelectric composites were fabricated from magnetic Fe49Rh51 and piezoelectric PbZr0.53Ti0.47O3 materials. It was shown the electric field-induced stresses reduce the magnetization around magnetic phase transition temperature of Fe49Rh51: by 5.4% for tri-layer PZT/FeRh/PZT composite and by 3.6% for bi-layer FeRh/PZT composite. The magnetoelectric properties were studied at 320 K, the magnetization rate was estimated for the magnetic field of 0.5 T. The heterogeneous distributions of stresses and magnetization in volume of magnetic layer under applied magnetic and electric fields were demonstrated using COMSOL Multiphysics software. The obtained results demonstrate the tri-layered composite is more effective for tuning the magnetization [ABSTRACT FROM AUTHOR]

• Demonstration of the new method of studding shape memory alloys in magnetic field. • Stress-temperature-magnetic field dependence for Ni 54 Mn 21 Ga 25 , Ni 50 Mn 41.2 In 8.8 alloys. • Ability of full recoverable deformation of ferromagnetic alloy in magnetic field. • Influence of magnetic field on the martensite transition temperature. • Bilayered functional composite of new type with enhanced properties. Recently the new scheme of layered composite with shape memory effect (SME) for thermal and magnetic actuation was suggested and proved to demonstrate the reversible actuation on micro- and nanoscale. The principles of magnetic field induced martensitic transition (MFIMT) and magnetic field controlled shape memory effect (MFCSME) have the advantages of magnetic-field-controlled actuation at constant temperature, extremely small size of an actuator and compatibility with modern nanotechnologies. The present paper is devoted to experimental study of MFCSME in two ferromagnetic Heusler alloys Ni 54 Mn 21 Ga 25 and Ni 50 Mn 41.2 In 8.8 with positive and negative shift of the martensitic transition temperature in a magnetic field. The three points bending device for dilatometric tests of plate-like samples of the alloys was designed and placed in the field of Bitter coil magnet. The bending deformations versus temperature were measured at various magnetic fields up to 10 T and at mechanical stresses up to 45 MPa. The temperature shifts of thermoelastic martensitic phase transition were found to be 0.55 K/T and −0.95 K/T for Ni 54 Mn 21 Ga 25 and Ni 50 Mn 41.2 In 8.8 respectively. For direct MFCSME study the dependences of the bending deformation on magnetic fields up to 14 T were also obtained at constant temperatures for these alloys. Practically complete recoverable deformation of 0.2% due to MFIMT was obtained at 14 T in Ni 54 Mn 21 Ga 25 alloy in temperature range 316–318 K and stress 8.6 MPa. The new variant of the layered functional composite actuator scheme based on the alloys with MFCSME is suggested. The proposed functional composite combines the layers of the alloys with positive and negative temperature shifts of martensitic transition temperature in magnetic field. It is argued that this combination of the alloys can improve the performance of the composite actuators driven by MFCSME, particularly, it can provide higher generated force, actuation stroke, sensitivity to magnetic field and frequency of actuation. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect (MCE) in an Fe48Rh52 alloy and Sm0.6Sr0.4MnO3 manganite was studied in cyclic magnetic fields. The adiabatic temperature change in the Fe48Rh52 alloy for a magnetic field change (ΔB) of 8 T and a frequency (f) of 0.13Hz reaches the highest value of (ΔTad) of -20.2K at 298 K. The magnitude of the MCE in Sm0.6Sr0.4MnO3 reaches DTad=6.1K at the same magnetic field change at 143K. The temperature regions, where a strong MCE is exhibited in an alternating magnetic field, are bounded in both compounds. In the case of the Fe48Rh52 alloy, the temperature range for this phenomenon is bounded above by the ferromagnetic to antiferromagnetic transition temperature in the zero field condition during cooling. In the case of the Sm0.6Sr0.4MnO3 manganite, the temperature range for the MCE is bounded below by the ferromagnetic-paramagnetic transition temperature in zero field during heating. The presence of these phase boundaries is a consequence of the existence of areas of irreversible magnetic-field-induced phase transitions. It is found that the effect of long-term action of thousands of cycles of magnetization/demagnetization degrades the magnetocaloric properties of the Fe48Rh52 alloy. This can be explained by the gradual decrease in the size of the ferromagnetic domains and increasing role of the domain walls due to giant magnetostriction at the ferromagnetic to antiferromagnetic transition temperature. The initial magnetocaloric properties can be restored by heating of the material above their Curie temperature. [ABSTRACT FROM AUTHOR]

We present our recent results on temperature behaviour of magnetization observed inHeusler alloys. Three regions can be distinguished in theM–Tdiagram: (I) low temperature martensitic phase (with the Curie temperature K), (II) intermediate mixed phase (with the critical temperature K) exhibiting a reentrant like behavior (betweenand) and (III) high temperature austenitic phase (with the Curie temperature K) exhibiting a rather wide plateau region (betweenand). By arguing that powerful structural transformations, causing drastic modifications of the domain structure in alloys, would also trigger strong fluctuations of the order parameters throughout the entireM–Tdiagram, we were able to successfully fit all the data by incorporating Gaussian fluctuations (both above and below the above three critical temperatures) into the Ginzburg–Landau scenario. [ABSTRACT FROM PUBLISHER]