Curie Temperature Of Austenite Research Articles

Relative cooling power enhancement by tuning magneto-structural stability in Ni-Mn-In Heusler alloys

Off-stoichiometric Ni2MnIn Heusler alloys have drawn recent attention due to their large magnetocaloric entropy change associated with the first-order magneto-structural transition. Here we present crystal structural, calorimetric and magnetic studies of three compositions. Temperature-dependent X-ray diffraction shows clear structural transition from a 6M modulated monoclinic to a L21 cubic. A significant enhancement of relative cooling power (RCP) was achieved by tuning the magnetic and structural stability through minor compositional changes, with the measured results quantitatively close to the prediction as a function of the ratio between the martensitic transition (Tm) temperature and austenite Curie temperature (TC) although the maximal magnetic induced entropy change (ΔSmax) reduction is observed in the same time. The results provided an evaluation guideline of RCPs as well as magnetic-induced entropy change in designing practical active materials.

Double magnetocaloric peak feature observed in quaternary Ni-Mn-In based Heusler alloys

We present the results of the studies of magnetic and magnetocaloric (MCE) properties of quaternary Heusler alloys Ni48.5Mn35In15Co1.5 and Ni50Mn35In13.5Al1.5 in temperature range between 80 K and 400 K. While doping initial ternary Ni-Mn-In alloy with 1.5 at.% Al does not change TCA as well as MS, doping with 1.5 at.% Co significantly increases both TCA and MS. The direct magnetocaloric measurements around martensitic transition and austenite Curie temperature reveal the competition between the contributions of different signs. The latter is related to the vicinity of transition temperatures of austenite and martensite, resulting in mixed state, where both phases undergo magnetic order-disorder transformation in the same temperature region. Additionally temperature dependencies of adiabatic temperature change ΔTad and magnetic entropy ΔSM of the system exhibit additional peak feature which we attribute to intermartensitic transition occurring in these alloys.

Effect of cobalt doping on martensitic transformations and the magnetic properties of Ni50−xCoxMn37Sn13 (x = 1, 2, 3) Heusler ribbons

The effect of cobalt doping on martensitic transformations and the magnetic properties of Ni50−xCox Mn37Sn13 (x = 1, 2, 3) magnetic shape memory alloys obtained by melt spinning in the form of ribbons is studied. The crystallographic structure of all of the ribbons at room temperature is austenite cubic L21. SEM micrographs indicate the formation of textured ribbons with columnar grains growing up perpendicular to the ribbon plane. For all of the ribbons, DSC cyclic scans reveal the martensitic transformation on cooling and the reverse austenitic transformation upon heating below room temperature. In addition, they indicate that the martensitic transformation temperatures decrease with an increasing cobalt content.Thermomagnetic curves reveal the coexistence of AFM and FM exchange interactions at low temperatures. Likewise, the magnetization change (ΔM) between the martensite and austenite phase, as well as the austenite Curie temperature (TCA), increase with increasing cobalt content in the ribbons. Structural transformations are also sensitive to the external applied magnetic field. This fact suggests that the structural transformation temperatures of the ribbons could be tuned to the desired functional temperature by controlling the cobalt amount through the replacement of Ni as well as by changing the applied magnetic field, which could lead to an enhancement of the magnetic properties.

Influence of Ni/Mn ratio on magnetostructural transformation and magnetocaloric effect in Ni48−xCo2Mn38+xSn12 (x = 0, 1.0, 1.5, 2.0, and 2.5) ferromagnetic shape memory alloys**Project supported by the National Natural Science Foundation of China (Grant Nos. 51601092, 51571121, and 11604148), the Fundamental Research Funds for the Central Universities, China (Grant Nos. 30916011344 and 30916011345), Jiangsu Natural Science Foundation for Distinguished Young

An investigation on the magnetostructural transformation and magnetocaloric properties of Ni48–xCo2Mn38+xSn12 (x = 0, 1.0, 1.5, 2.0, and 2.5) ferromagnetic shape memory alloys is carried out. With the partial replacement of Ni by Mn in the Ni48Co2Mn38Sn12 alloy, the electron concentration decreases. As a result, the martensitic transformation temperature is decreased into the temperature window between the Curie-temperatures of austenite and martensite. Thus, the samples with x = 1.5 and 2.0 exhibit the magnetostructural transformation between the weak-magnetization martensite and ferromagnetic austenite at room temperature. The structural transformation can be induced not only by the temperature, but also by the magnetic field. Accompanied by the magnetic-field-induced magnetostructural transformation, a considerable magnetocaloric effect is observed. With the increase of x, the maximum entropy change decreases, but the effective magnetic cooling capacity increases.

Martensitic transition, inverse magnetocaloric effect and shape memory characteristics in Mn48−xCuxNi42Sn10 Heusler alloys

In this paper, we have systematically prepared a serials of polycrystalline Mn48−xCuxNi42Sn10 alloys (x=0, 1, 3, 5, 6, 8, 10 and 12) and investigated the influence of the Cu doping on martensitic transition (MT) as well as magnetic properties. Experimental results indicate that the MT temperature and the martensite Curie temperature (TcM) shift to high temperature with increasing the substitution of Cu (from Mn rich alloy to Ni rich alloy), while the austenite Curie temperature (TcA) is almost unchanged. It was found that the structures undergo L21 and 4O with the increasing of Cu concentration near room temperature. Therefore, the magnetostructural transition can be tuned by appropriate Cu doping in these alloys. Moreover, we mainly studied the multiple functional properties for inverse magnetocaloric effect and shape memory characteristics associated with the martensitic transition. A large positive isothermal entropy change of Mn48Ni42Sn10 was obtained, and the maximum transition entropy change achieves about 48J/kgK as x=8. In addition, a considerable temperature-induced spontaneous strain with the value of 0.16% was obtained for Mn48Ni42Sn10 alloys.

Martensitic transformation and magnetocaloric properties in Ni40.4Mn46.5Sn10.9Sb2.2 ribbons

The Ni40.4Mn46.5Sn10.9Sb2.2 ribbons were prepared by melt-spun method. The martensitic transformation (MT) and magnetocaloric effect in melt-spun and annealed Ni40.4Mn46.5Sn10.9Sb2.2 ribbons were investigated. After the heat treatment, the MT temperature increases obviously in the annealed ribbons. The large values of magnetic entropy changes and the effective refrigerant capacity around the MT and Curie temperature of the austenite are found to be 30.9 and −2.2 J/kg K, 70.6 and 132.6 J/kg, respectively, under the field change of 30 kOe for the annealed ribbons. The annealing effect on the MT and magnetocaloric effect, together with the origin of the large magnetic entropy changes, has been discussed in this paper.

Effects of Sn vacancy and excess Sn doping on structural, magnetic and electrical properties of Ni47Mn40Sn13 ferromagnetic shape memory alloy

In this work, the effects of Sn vacancy and excess Sn doping on the structural, magnetic and electrical properties of Ni47Mn40Sn13±x (x = 0, 0.5, 1) ferromagnetic shape memory alloys were investigated. X-ray diffraction pattern of the Ni47Mn40Sn13±x alloys indicated austenitic phase with L21 structure for x = 0. However, with increasing Sn vacancy, the coexistence of austenitic and martensitic phases was obtained, while all the compounds of the Ni47Mn40Sn13+x were in the austenitic phase at room temperature. By creating Sn vacancy and excess Sn doping, the martensitic transformation (MT) temperature decreased and Curie temperature of austenite (TcA) did not show a significant change. In addition, the electrical resistivity behaviors of all the samples revealed a good agreement with AC susceptibility measurements. The decrease of the MT temperature with the increase of Sn vacancy and excess Sn doping was also discussed on the basis of the valence electron concentration and cell volume variation.

Martensite transformation and magnetic properties of Fe-doped Ni-Mn-Sn alloys with dual phases

Ni-Mn-Sn alloys exhibit high magnetocaloric effect (MCE) during the magnetic-field-induced martensite to austenite phase transformation. However, the low magnetization of the austenite, narrow working temperature interval and high magnetic hysteresis reduced their magnetic refrigeration capacity. Here, the effects of Fe doping on the structural and magnetic transitions of Ni50-xFexMn38Sn12 alloys were investigated. The doping of Fe higher than 2.9% induced the occurrence of a secondary γ phase, creating a dual phase alloy. The martensite transformation temperature significantly decreased with the occurrence of the secondary phase. However, the Curie temperatures of both austenite and martensite changed slightly with the formation of the secondary phase. As a result, the magnetostructural coupling, i.e. overlap of the structural and magnetic transitions between the ferromagnetic austenite and the paramagnetic martensite, occurred in the alloys with x = 0.5 - ∼4.2. Furthermore, the magnetization of the austenite and martensite both increased with increasing Fe content from x = 0 to x = 5.5, with the magnetization difference between the austenite and martensite saturating at x = 4.2. The dual phase Ni45.8Fe4.2Mn38Sn12 alloy, exhibiting a magnetic field dependence of martensite transformation temperature ΔTM/μΔH - 0.28 K/kOe, showed a wider working temperature interval than that of the un-doped Ni50Mn38Sn12 alloy. This demonstrated that the Ni45.8Fe4.2Mn38Sn12 alloy might exhibit a high magnetic entropy change, wide working temperature interval and low magnetic hysteresis, and thus may be a promising magnetic refrigeration material.

Magneto-structural transformations in Ni50Mn37.5Sn12.5−xInx Heusler powders

The effect of ball milling and subsequently annealing of melt spun ribbons on magneto-structural transformations in Ni50Mn37.5Sn12.5−xInx (x=0, 2, 4, 6) ribbons is presented. Short time vibration milling allows to obtain chemically homogenous powders of angular particle shapes and size within 10–50μm. Milling does not change the characteristic temperatures of martensitic transformation in comparison to the melt spun ribbons. The effect of In substitution for Sn on martensitic transformation has a complex mechanism, associated with electron density change. Substitution of Sn by In in both milled and annealed powders leads to decrease of Curie temperature of austenite and increase of martensitic transformation temperature, stabilizing martensitic phase. The coexistence of magnetic transformation of austenite and martensitic transformation at low magnetic field was observed. The intermartensitic transformation of 4O martensite to L10 martensite was observed during cooling at low magnetic field and this was confirmed by TEM microstructure observations. The annealing process of as-milled powders leads to the change of their martensitic structure due to relaxation of internal stresses associated with anisotropic columnar grain microstructure formed during melt spinning process. The level of stresses introduced during milling of ribbons has no significant influence on martensitic transformation. The annealing process of as milled powders leads to enhancement of their magnetic properties, decrease of Curie temperature of austenite, and marginal change of temperature of martenisitic transformation.

STUDY OF MARTENSITIC TRANSFORMATION AND STRAIN BEHAVIOR IN Ni50-xCoxMn39Sn11 (x=0, 2, 4, 6) HEUSLER ALLOYS

The crystal structure, phase transformations and magnetic properties for Ni50xCoxMn39Sn11 (x=0, 2, 4, 6) Heusler alloys have been systematically studied by means of structure and magnetism measurements. The results show that with increase of Co concentration, the martensitic transformation temperatures are obviously decreased, while the Curie temperatures of austenite are gradually increased, and they present different structures at room temperature. At the same time, with increasing Co content, the austenitic magnetism rapidly enhances, while the martensitic magnetism almost keeps unchanged. This leads to a significant improvement of difference magneti*国家自然科学基金项目11364035, 11404186和51371111,云南省科技厅应用基础研究项目2013FZ110和2012FD051,以及曲靖师范 学院创新团队研究计划项目TD201301资助 收到初稿日期: 2015-01-26,收到修改稿日期: 2015-04-28 作者简介:李 哲,男, 1981年生,副教授 DOI: 10.11900/0412.1961.2015.00071 第1010-1016页 pp.1010-1016

Enhancement of the martensitic transformation and magnetocaloric effect of Ni-Mn-V-Sn ribbons by annealing treatment

The rapidly solidified Ni41.98Mn42.97V2.08Sn12.97 ribbons are prepared by the melt-spinning technique. The microstructure, martensitic transformation (MT), and magnetocaloric effect of the ribbons are greatly affected by annealing treatment. The equiaxed crystallized grains with the relatively homogeneous size distribution are observed for these ribbons. After annealing, the grain size becomes obviously large, the lattice constants decreases, and the exchange bias effect gets improved. The MT temperatures increase obviously for the annealed ribbons. Large magnetic entropy change (ΔS) is obtained in the annealed Ni–Mn–V–Sn ribbons. The peak values of ΔS in the annealed ribbons are 41.6 and −2.3 J kg−1 K−1 in the vicinity of MT temperature and Curie temperature of austenite, respectively, for the field change of 30 kOe.

Giant magnetocaloric effect in MnCoGe with minimal Ga substitution

The effects of Ga-doping on the phase transition behaviors and magnetocaloric properties of MnCoGe alloys are systematically investigated through calorimetry and magnetic measurements. The magneto-structural coupling between the structural and magnetic transitions is achieved in the MnCoGe1–xGax alloys by decreasing the structural transition temperature via Ga substitution. An 80K Curie-temperature window is established between Curie temperatures of austenite and martensite phases. Within the window, a magnetic entropy change of 34Jkg−1K−1 can be obtained near room temperature under the application of a 5T magnetic field.

ChemInform Abstract: Interacting Magnetic Cluster‐Spin Glasses and Strain Glasses in Ni—Mn Based Heusler Structured Intermetallics

AbstractReview: 78 refs.

Effect of Ni/Sn ratio on martensitic transformation and magnetic properties in high-Mn content Mn2Ni1.64−xSn0.36+xferromagnetic shape memory alloys

The effect of variation in Ni/Sn ratio on martensitic transformation (MT) and magnetic properties was investigated in high-Mn content Mn2Ni1.64−xSn0.36+x alloys. With the increase of Sn content, the MT temperature shifts substantially towards lower temperature, while the Curie temperature of austenite remains almost unchanged. The reverse MT temperature decreases from 268 to around 80 K for Mn2Ni1.64−xSn0.36+x alloys as x increases from 0.02 to 0.08. Under the low field of 1.2 T, the peak values of magnetic entropy changes are 9.8 J/kg K, 10.1 J/kg K, 10.3 J/kg K, and 6.1 J/kg K for x = 0.02, 0.04, 0.06, and 0.08, respectively. The abrupt changes in magnetization around MT temperatures and the field-induced metamagnetism should account for the large magnetic entropy changes. Incorporating the advantages of inexpensive and non-toxic raw materials, these high-Mn content alloys exhibit very promising prospects for the applications in magnetic refrigeration.

First-principles and Monte Carlo studies of C-doped Ni45Co5Mn37In13Heusler alloys

In this work, we report the study of the effect of carbon on electronic and magnetic properties of the Ni 45 Co 5 Mn 37 In 13 alloy. Two compounds with addition of 5 at.% C for Mn and In with ferro- and ferrimagnetic spin configurations have been discussed in the framework of first-principles and Monte Carlo calculations. In order to calculate the magnetic exchange parameters, magnetic moments, and electronic density of states curves we have used the SPR-KKR package. We have shown that the addition of carbon leads to enhancement of antiferromagnetic exchange interactions between Mn atoms in martensite of both compounds. The temperature dependences of magnetizations as well as Curie temperatures of austenite and martensite have been obtained.

Effect of niobium addition on the martensitic transformation and magnetocaloric effect in low hysteresis NiCoMnSn magnetic shape memory alloys

The effect of Nb substitution for Ni in Ni45Co5Mn40Sn10 magnetic shape memory alloys on their magnetic properties, martensitic transformation characteristics, transformation hysteresis, and magnetocaloric properties was studied using wavelength-dispersive X-ray spectroscopy, differential scanning calorimetry, and the temperature and field dependence of the magnetization. Ni45Co5Mn40Sn10 alloy has a very low transformation hysteresis; however, the martensitic transformation temperatures are notably above room temperature, which is not desirable for magnetic refrigeration applications. In this study, small quantities of Nb substitution were shown to drastically shift the transformation temperatures to lower temperatures, at a rate of 68 K/at. % Nb, which is needed for household refrigeration. The austenite Curie temperature also decreased with increasing Nb content. However, a decrease in the latent heat of the martensitic transition was observed, which negatively affects the magnetic field-induced adiabatic temperature change capability. Still, the relatively large transformation entropy and the low transformation hysteresis make the Nb-doped Ni45Co5Mn40Sn10 alloys potential candidates for solid state refrigeration near room temperature.

Critical behavior and magnetic entropy change at magnetic phase transitions in Ni50Mn35In14Si1 ferromagnetic shape memory alloy

We have investigated critical behaviour and magnetocaloric effect in polycrystalline Ni50Mn35In14Si1 alloy near the second-order ferromagnetic phase transitions (SOPT) at austenite Curie temperature and at martensite Curie temperature by determining the critical exponents, β, γ and δ corresponding to the temperature dependence of spontaneous magnetization, initial susceptibility and isothermal magnetization, respectively. The field dependence of the maximum value of the magnetic entropy change at the two TC's was estimated using the Maxwell relation as well as from the values of the critical exponents. Values of obtained by these two methods at both the SOPT are in remarkable agreement with each other. The critical exponents have been determined by analysing isothermal magnetization data using two different methods, viz., the modified Arrott plot method and the Widom scaling relation. The scaling plots depicted on linear as well as logarithmic scales confirm the reliability of the values of critical exponents obtained. The values of the critical exponents of polycrystalline Ni50Mn35In14Si1 alloy at both the TC's are close to those predicted by mean-field theory confirming the presence of long-range magnetic ordering in the investigated alloy.

Ab Initio and Monte Carlo Approaches For the Magnetocaloric Effect in Co- and In-Doped Ni-Mn-Ga Heusler Alloys

The complex magnetic and structural properties of Co-doped Ni-Mn-Ga Heusler alloys have been investigated by using a combination of first-principles calculations and classical Monte Carlo simulations. We have restricted the investigations to systems with 0, 5 and 9 at% Co. Ab initio calculations show the presence of the ferrimagnetic order of austenite and martensite depending on the composition, where the excess Mn atoms on Ga sites show reversed spin configurations. Stable ferrimagnetic martensite is found for systems with 0 (5) at% Co and a c=a ratio of 1.31 (1.28), respectively, leading to a strong competition of ferro- and antiferro-magnetic exchange interactions between nearest neighbor Mn atoms. The Monte Carlo simulations with ab initio exchange coupling constants as input parameters allow one to discuss the behavior at finite temperatures and to determine magnetic transition temperatures. The Curie temperature of austenite is found to increase with Co, while the Curie temperature of martensite decreases with increasing Co content. This behavior can be attributed to the stronger Co-Mn, Mn-Mn and Mn-Ni exchange coupling constants in austenite compared to the corresponding ones in martensite. The crossover from a direct to inverse magnetocaloric effect in Ni-Mn-Ga due to the substitution of Ni by Co leads to the appearance of a “paramagnetic gap” in the martensitic phase. Doping with In increases the magnetic jump at the martensitic transition temperature. The simulated magnetic and magnetocaloric properties of Co- and In-doped Ni-Mn-Ga alloys are in good qualitative agreement with the available experimental data.

Effects of the substitution of gallium with boron on the physical and mechanical properties of Ni–Mn–Ga shape memory alloys

The effects of the substitution of gallium with boron on the physical, mechanical and magnetic shape memory properties of Ni51Mn28.5Ga20.5−x B x (at.%) (x = 0, 1, 2, 3) polycrystalline alloys are investigated. It has been found that transformation temperatures are decreasing while hardness is increasing with boron addition. B-doping of NiMnGa alloys results in the formation of a second phase that increases its ductility and strength in compression. Moreover, saturation magnetization of austenite is decreasing, while Curie temperature of austenite is increasing with B-doping.

Magnetic and magnetocaloric properties in Cu-doped high Mn content Mn50Ni40−xCuxSn10 Heusler alloys

The effects of Cu substitution on the phase transitions and magnetocaloric effect of Mn50Ni40−xCuxSn10 Heusler alloys were investigated. With the increase of Cu content, the martensitic transformation (MT) temperature shifts substantially towards lower temperature, while the Curie temperature of austenite remains almost unchanged. The reverse MT temperature decreases from 180 to 171 K for Mn50Ni39Cu1Sn10 alloy as the magnetic field increases from 1 to 30 kOe. Under an applied magnetic field of 30 kOe, the maximum values of magnetic field induced entropy changes are 19.6, 28.9, and 14.2 J/kg K for x = 0, 1, and 2, respectively. The effective refrigerant capacities and hysteresis losses for these alloys were discussed in this paper.