Curie Temperature Of Austenite Research Articles

Magnetocaloric effect and phase transformation of Zn-doped Ni–Mn–Ti all-d metal Heusler alloys

Ni–Mn–Ti Heusler alloys have gained a great consideration recently due to their important magnetoresistance and magnetocaloric properties. Herein, the structure, martensitic transition (MT), and magnetocaloric effect (MCE) of Ni50-xZnxMn35Ti15 (x = 0, 2, 4, and 6) Heusler alloys have been studied. XRD results show that the studied alloy with x = 0 display a monoclinic (5 M) martensite phase. Besides, the examined alloy with x = 2 presents a combination of monoclinic (5 M) martensite and cubic (B2) austenite phases, whereas the alloys with x = 4 and x = 6 exhibit only a cubic (B2) austenite phase. By increasing Zn content x up to 6, the Curie temperature of austenite decreases from 283 K to 132 K, and the MT temperatures decrease from ferromagnetic austenite to weak-magnetic martensite, which is apparently due to the exchange interaction of Mn–Mn and the low power of d-d hybridization between the A/C and B(D) sites. The best maximum magnetic entropy change (ΔSM, max) and refrigeration capacity (RC) are for the studied alloy with x = 4 (5.22 J kg−1K−1 and 217 J kg−1 at 120 kOe, respectively). The Zn addition not only facilitates the formation of B2-type Heusler phases but also offer the possibility to tune the MT and establish strong ferromagnetic coupling.

Inverse Magnetocaloric Effect in Heusler Ni44.4Mn36.2Sn14.9Cu4.5 Alloy at Low Temperatures

Direct measurements of the magnetocaloric effect were performed in a Heusler Ni44.4Mn36.2Sn14.9Cu4.5 alloy at cryogenic temperatures in magnetic fields up to 10 T. The maximum value of the inverse magnetocaloric effect in a 10 T field was ∆Tad = –2.7 K in the vicinity of the first-order magnetostructural phase transition at T0 = 117 K. Ab initio and Monte Carlo calculations were performed to discuss the effect of Cu doping into a Ni-Mn-Sn compound on the ground-state structural and magnetic properties. It is shown that with increasing Cu content the martensitic transition temperature decreases and the Curie temperature of austenite slightly increases. In general, the calculated transition temperatures and magnetization values correlated well with the experimental ones.

Magneto-structural transformations and magnetocaloric effect in the Heusler type Ni48Cu2Mn36Sn14-xTix melt-spun ribbons

The Heusler type Ni–Mn-Z (Z = Ga, ln, Sn, or Sb) alloys with magneto-structural transformations (MSTs) have received widespread research interests due to the exhibition of multifunctional characters. To further understand MSTs and improve the magnetocaloric performance of these alloys, in this work, the Ti doped Ni48Cu2Mn36Sn14-xTix (x = 0, 1, 2, 3) ribbons have been fabricated and systematically determined with regard to the structural, magnetic, and magnetocaloric properties by means of X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC), and magnetization measurements. All the ribbons are found to crystallize in the ordered cubic L21 austenite phases at room temperature and with the equiaxed austenite morphology. With the increasing Ti content, the average grain size and the MST temperature increase but the austenite Curie temperature (TAC) decrease gradually. Moreover, the thermal hysteresis and magnetic hysteresis loss are greatly reduced with the Ti doping. The value of average hysteresis loss (AHL) is reduced from 86 Jkg−1 for Ti0 to 25.5 Jkg−1 for Ti3 ribbon under 7 T. Additionally, enhanced magnetocaloric effect has been observed by Ti-doping. With the magnetic field change (ΔH) of 0–7 T, the largest value of magnetic entropy change reaches 15.4 Jkg−1K−1 (Ti2) among the Ni48Cu2Mn36Sn14-xTix ribbons. The present work indicates that reasonable Ti doping could be a useful way to regulation the MSTs and improve the magnetocaloric performance of the Heusler type Ni–Mn–Sn-based alloys.

Structure stability driven large magnetocaloric response in Ni–Co–Mn–In–Si Heusler alloy

Ni–Mn–In Heusler alloys have received considerable attention in the field of magnetic refrigeration owing to their eco-friendliness and large magnetocaloric (MC) response. In this paper, samples of Ni45Co5Mn37In12Si1 thus heat-treated for 0 h and 15 h have prepared by means of arc-melting followed by quenching. X-ray diffraction analysis confirms L21-type crystal structure and stabilization of austenite phase at room temperature. FE-SEM equipped with EDS reveals the surface morphology and elemental composition of 15 h heat-treated Ni45Co5Mn37In12Si1 alloy with well-distinguished larger grains and a dendritic structure. Thermomagnetic measurements of 15 h heat-treated Ni45Co5Mn37In12Si1 shows the magnetostructural transition TCM at the temperature of ∼262 K and Curie temperature of austenite, TCA was found to be above ∼396 K with increase in the annealing time. Metamagnetic behavior and magnetic hysteresis are seen in isothermal magnetization curves. Interestingly, a large change in magnetic entropy ΔSM ∼9.3 J kg−1 K−1 was obtained with refrigeration capacity (RC) of ∼416.6 J kg−1 under an applied field change of 5T with a broad temperature window of ∼86 K for Ni45Co5Mn37In12Si1 alloy thus annealed for 15 h which makes it to be suitable for magnetic refrigeration applications.

Magnetocaloric properties of a ribbon sample of Heusler alloy Ni-=SUB=-45-=/SUB=-Co-=SUB=-5-=/SUB=-Mn-=SUB=-31-=/SUB=-Al-=SUB=-19-=/SUB=-: experimental and theoretical studies

The results of experimental and theoretical studies of magnetocaloric properties of a ribbon sample of alloy Ni45Co5Mn31Al19 in the range of T=80-350 K in magnetic fields of up to 8 T are given. This alloy demonstrates a first-order magnetostructural phase transition (MSPT) in the temperature range of 270 K, as well as a second-order transition --- at the Curie temperature of 294 K. The magnetocaloric effect (MCE) was studied both by the direct method of magnetic field modulation in cyclic fields up to 8 T and by the classical extractive method. Field dependence of MCE have a different nature for first- and second-order phase transitions. A reverse MCE near MSPT is irreversible, i.e. the final sample temperature is 0.75 K below the initial one. Theoretical studies of magnetic properties and MCE of the studied sample were performed by ab initio calculations and Monte Carlo modeling. Theoretical temperature dependences of MCE are characterized by a similar interval of effect manifestation in the region of martensitic transformation and a narrower interval in the region of austenite Curie temperature as compared to the experiments, which is conditioned by the presence of a heterogeneous mixed state of austenite in the experimental sample. On the whole, theoretical data qualitatively and quantitatively reproduce the experimental dependences. Keywords: magnetocaloric effect, cyclic fields, Heusler alloy, Monte Carlo method.

Martensitic transformation, magnetic entropy, and adiabatic temperature changes in bulk and ribbon Ni48Mn39.5Sn12.5\u2212xInx (x\u2009=\u20092, 4, 6) metamagnetic shape memory alloys

Martensitic transformation, magnetic entropy, and direct adiabatic temperature changes in Ni48Mn39.5Sn12.5−xInx (x = 2, 4, 6) metamagnetic Heusler bulk and grain-constrained ribbon alloys were studied. All alloys showed a typical L21 structure in austenite and the 4O structure in martensite. Their relative volume contributions changed depending on In content. With increasing In concentration, the martensitic transformation temperature increased, whereas the Curie temperature of austenite decreased. The magnetic entropy change under magnetic field of 5 T attained maximum of 20 J/kgK in the bulk and 14.4 J/kgK in the ribbon alloys with the Ni48Mn39.5Sn8.5In4 nominal composition. The corresponding adiabatic temperature change under 1.7 T yielded 1.3 K for the Ni48Mn39.5Sn8.5In4 bulk alloy. Despite grain confinement, melt spinning was found to stabilize martensite phase. Changes observed were discussed with relation to strengthened covalency imposed by In substitution.Graphic abstract

Magnetic properties, martensitic transformations and magnetocaloric performances in Ni44Mn45-xFexSn11 (x = 0–3) Heusler alloys

The structural, magnetic, and magnetocaloric properties of Ni44Mn45-xSn11Fex (x = 0, 1, 2 and 3) Heusler alloys have been studied detailly by means of X-ray diffraction, differential scanning calorimetry, and magnetization measurements. The martensitic transition temperature (TM) and austenite Curie temperature (TAC) increase gradually with increasing Fe content. Large differences in magnetization between the ferromagnetic austenite and weakly magnetic martensite phases and obvious thermal hysteresis have also been observed during the martensite transformation. With the magnetic field change up to 0–7 T, the maximum value of magnetic entropy changes reaches 26.7 and 23 J kg−1K−1 for x = 1 and 2, respectively, which are much larger than the undoped sample (9.8 J kg−1K−1). Whereas, the effective refrigerant capacity RCeff reduced due to Fe doping increased the hysteresis loss. The alloy for x = 1 has highest RC value of 172 (255) J kg−1 for a magnetic field change of 0–5 T (0–7 T), furthermore, a large magnetic entropy change and moderate RCeff has been obtained around room temperature.

On the synthesis, structural transformation and magnetocaloric behavior of Ni37.5Co12.5Mn35Ti15 melt-spun ribbons

We fabricated Ni37.5Co12.5Mn35Ti15 melt-spun ribbons at linear wheel speeds (WS) of 20 and 8 ms-1 (series A and B, respectively). The effect of a short time thermal annealing (30 min.) between 1023 K and 1173 K on the martensitic-like structural transition and the crystal structure, microstructure and magnetic entropy change ΔSM(T) curves and related parameters for as-solidified (AS) samples of series A were studied. Whereas the Curie temperature of austenite (AST) TCA keeps nearly constant, both the reduction of the solidification rate and the increase on the thermal annealing temperature increase the temperature of the structural transformation reducing the magnetization change across the AST to martensite (MST) transition. The martensitic transformation (MT) in AS samples undergoes from a B2-type ferromagnetic (FM) AST with TCA = 328 K to a monoclinic martensite (MST); SEM images evidenced a partially grain-oriented microstructure formed by columnar in shape-elongated grains with their major axis oriented along the thermal gradient during solidification. Magneto-structural transition for AS ribbons of series A occurs in the vicinity of room temperature and is accompanied by a magnetization change of around 63 Am2kg-1. For a magnetic field change of 2 T these samples showed a maximum magnetic entropy change |ΔSM|max of 13.8 (9.5) J kg-1 K-1 for the MST→AST (AST→MST) transformation. This is below the previously reported for this alloy composition (27.2 J kg-1 K-1), and is related to the broader magneto-structural transition.

Effect of Co substitution on the magnetic properties and magnetocaloric effects of Ni–Co–Mn–Sn alloys

AbstractNi–Mn–Sn-based magnetic refrigeration materials have a coupling ability of structure transformation and magnetic transition to improve their magnetocaloric effects. In this work, the influence of the Co doping on Curie temperature, structure and magnetocaloric properties of Ni43-xCoxMn46Sn11 (x = 0, 1, 2, 3) alloys prepared by melt-spinning were investigated by means of X-ray diffraction, Differential Scanning Calorimetry and Vibrating Sample Magnetometry. It was found that the crystal structure of samples changes from 4O modulated martensite to L21 cubic austenite with increasing temperature. The magnetic phase diagram of Ni43-xCoxMn46Sn11 system was constructed from thermomagnetic curves. Increasing Co content enhanced the Curie temperature of L21 cubic austenite from 279 K to 354 K, however, shifted the transition temperature of martensitic down to lower temperature, 170 K. As for the sample with x = 3, it only has ferromagnetic–paramagnetic second order magnetic transition, and no structural transformation was observed. The sensitivity of martensitic transformation induced by magnetic field can be improved up to − 3.52 K · T−1. Under 0–5 T, the maximum values of magnetic entropy change, refrigerant capacity and the adiabatic temperature change are improved by 60.5%, 59.0% and 17.5%, respectively. The results indicate that the relatively large martensitic transformation sensitivity and magnetocaloric effects make these alloys good candidates in the range of 150–300 K.

Ferromagnetic martensitic transformation and large magnetocaloric effect in Ni35Co15−xFexMn35Ti15 (x = 2, 4, 6, 8) alloys

The crystal structure, ferromagnetic martensitic transformation, and magnetocaloric effect of Ni35Co15−xFexMn35Ti15 (x = 2, 4, 6, 8) alloys have been investigated. All the alloys crystallize in a B2-type cubic structure at room temperature. The Curie temperature of austenite between paramagnetic and ferromagnetic states decreases from 349.0(7) K to 287.2(8) K with increasing Fe content x up to 8, whereas the corresponding martensitic transformation temperature from ferromagnetic austenite to weak-magnetic martensite increases continuously from 182 K to 230 K, and the accompanied thermal hysteresis decreases gradually. The maximum values of magnetic entropy change (ΔSM)/refrigeration capacity reach 9.5(8) J kg−1 K−1/79.4(5) J kg−1 (0–20 kOe) and 24.0(4) J kg−1 K−1/206.8(4) J kg−1 (0–50 kOe), respectively. The present results indicate that the Ni35Co15−xFexMn35Ti15 alloys are considerable for magnetic refrigeration.

Magnetic-field-driven reverse martensitic transformation with multiple magneto-responsive effects by manipulating magnetic ordering in Fe-doped Co-V-Ga Heusler alloys

Nowadays, searching for the materials with multiple magneto-functional properties and good mechanical properties is vital in various fields, such as solid-state refrigeration, magnetic actuators, magnetic sensors and intelligent/smart devices. In this work, the magnetic-field-induced metamagnetic reverse martensitic transformation (MFIRMT) from paramagnetic martensite to ferromagnetic austenite with multiple magneto-responsive effects is realized in Fe-doped Co-V-Ga Heusler alloys by manipulating the magnetic ordering. The martensitic transformation temperature Tm reduces quasi-linearly with increasing Fe-content. In strikingly contrast with the Fe-free alloys, the magnetization difference (ΔM') across martensitic transformation increases by three orders of magnitude for Fe-doped alloys. The increased ΔM' should be ascribed to the reduction of Tm, almost unchanged Curie temperature of austenite and the increased magnetic moment in the samples with higher Fe-content. The large ΔM' provides strong driving force to realize the MFIRMT and accordingly multiple magneto-responsive effects, such as magnetocaloric, magnetoresistance and magnetostriction effects. Meanwhile, giant Vickers hardness of 518 HV and compressive strength of 1423 MPa are achieved. Multiple magneto-responsive effects with exceptional mechanical properties make these alloys great potential candidates for applications in many fields.

Effect of Cr and Ni on Phase Formation in a Mechanically Synthesized Nanocomposite Based on Fe75C25

The formation and doping of phases during mechanical synthesis followed by annealing in the (Fe0.80Cr0.05Ni0.15)75C25 alloy are studied by the method of X-ray diffraction, Mossbauer spectroscopy, and magnetic measurements. It is shown that after mechanical synthesis, the nanocomposite contains mainly two phases (amorphous phase and cementite A). During annealing, as a result of crystallization of the amorphous phase, cementite B is formed, in which the nickel concentration is higher than in mechanically synthesized cementite A. Upon an increase in the annealing temperature, austenite with a nonuniform nickel concentration is formed. The Curie temperature of such austenite reaches 500°C. It is established that cementite in mechanically synthesized nanocomposite (Fe,Cr,Ni)75C25 has a higher stability to temperature variations than mechanically synthesized composite (Fe,Ni)75C25.

Combined effect of magnetic field and hydrostatic pressure on the phase transitions exhibited by Ni-Mn-In metamagnetic shape memory alloy

We present a systematic study of the magnetostructural and magnetic transitions in the prototype metamagnetic shape memory alloy Ni50Mn34.5In15.5 under hydrostatic pressure and combined pressure and magnetic field. Pressure extends the area of stability of the antiferromagnetic martensitic phase. At low magnetic field the pressure derivatives of the Curie temperatures of austenite, TCA, and martensite, TCM, show opposite signs. This fact is described in the framework of the Landau thermodynamic model as arising from a weak long-range antiferromagnetic state of martensite. Two volume magnetoelastic constants were estimated using the experimental values of the pressure derivatives of TCA and TCM. A correlation between the signs of the pressure shifts of TCA, and TCM and the distance between Mn-Mn nearest neighbours is established, which matches the empirical Castelliz-Kanomata diagram. The entropy change at martensitic transformation (MT), ΔSMT, grows up when the MT temperature, TM, is approaching TCA under the influence of pressure, but under constant non-zero pressure this dependence is inverse.

Martensitic transformation and magnetotransport properties of Ni47Mn42In11 alloy

The structure, electrical and magnetic properties of the Ni47Mn42In11 alloy, in which the temperature of the martensitic transformation is close to room temperature and practically coincides with the Curie temperature of austenite, have been investigated. The martensitic transformation in the Ni47Mn42In11 alloy proceeds with the formation of modulated martensite type 14M. It has been established that the spontaneous transformation from martensite to austenite is accompanied by a decrease in the specific resistance of 45%. In the martensitic transformation induced by a magnetic field of 18 kOe, a negative magnetoresistance is observed, reaching ~ 15%.

Investigation of Ti substituting for Ni on magnetic, magnetocaloric and phase transition characteristics of Ni50Mn36In14

We have investigated the magnetic and magnetocaloric properties together with transition hysteresis of Ni48.5Ti1.5Mn36In14 magnetic shape memory alloy under several magnetic field levels at a temperature interval from 400 K down to 10 K. We observe a small magnetization difference between austenite and martensite phase with a thermal hysteresis around the martensitic transition. We have investigated the minimum magnetic field required to start and to complete the magnetostructural phase transition. We observed small values of inverse and conventional magnetocaloric effect around the martensitic transition and around Curie temperature of austenite, respectively. This is attributed to the hysteresis loss during the martensitic transformation.

Martensite Transformation, Magnetotransport Properties, and Magnetocaloric Effect in Ni47Mn42In11 Alloy

The structure, electric properties, and magnetocaloric effect in Ni47Mn42In11 ferromagnetic alloy in which the martensite transformation temperature is close to room temperature and nearly coincides with the austenite Curie temperature are studied. It is revealed that the spontaneous transformation of martensite to austenite is accompanied with the decrease by 45% in its resistivity. In the martensite transformation induced by a magnetic field, a negative magnetoresistance is observed; it reaches ≈15% in the magnetic field with a strength of 18 kOe. The temperature dependence of the maximum change in the entropy in the martensite transformation induced by the magnetic field was calculated by using the Clausius–Clapeyron equation. It is shown that the maximum values of the magnetoresistance and magnetocaloric effect are observed near the temperature of the spontaneous martensite transformation.

Magnetic phase diagram, magnetocaloric effect, and exchange bias in Ni43Mn46Sn11−xGax Heusler alloys

Abstract In this work, the effect of Ga substitution on the crystal structure, phase transitions, magnetocaloric effect, and exchange bias properties, was systematically investigated in Ni43Mn46Sn11−xGax alloys. With increasing Ga content, the Curie temperature of austenite slightly decreases, while the martensitic transformation temperature shifts to a higher temperature and finally disappears, due to the emergence of γ phase. Large low-field magnetic entropy changes around the martensitic transformation were observed as the transition from a paramagnetic martensitic phase to a ferromagnetic austenitic phase took place. Ni43Mn46Sn11 has a reentrant-spin-glass ground state, and Ga doping can enhance the antiferromagnetic interaction arising from lattice contraction, leading to close of intermediate ferromagnetic windows and establishment of canonical spin-glass for x > 2. Prominently, the zero-field-cooled exchange was achieved in the spin-glass region with 5 ⩽ x ⩽ 10 .

Мартенситное превращение, магнитотранспортные свойства и магнитокалорический эффект в сплаве Ni-=SUB=-47-=/SUB=-Mn-=SUB=-42-=/SUB=-In-=SUB=-11-=/SUB=-

AbstractThe structure, electric properties, and magnetocaloric effect in Ni_47Mn_42In_11 ferromagnetic alloy in which the martensite transformation temperature is close to room temperature and nearly coincides with the austenite Curie temperature are studied. It is revealed that the spontaneous transformation of martensite to austenite is accompanied with the decrease by 45% in its resistivity. In the martensite transformation induced by a magnetic field, a negative magnetoresistance is observed; it reaches ≈15% in the magnetic field with a strength of 18 kOe. The temperature dependence of the maximum change in the entropy in the martensite transformation induced by the magnetic field was calculated by using the Clausius–Clapeyron equation. It is shown that the maximum values of the magnetoresistance and magnetocaloric effect are observed near the temperature of the spontaneous martensite transformation.

Structural, magnetic and magnetocaloric effect studies of Ni42.5(Fe, Co, Ni, Cu)0.5Mn46Sn11 Heusler alloys

We investigated the structural and magnetic properties of Ni42.5(Fe, Co, Ni, Cu)0.5Mn46Sn11 alloys fabricated by arc melting. Substitution of Ni by Fe, Co and Cu causes lattice expansions consistent with increasing atomic sizes. The zero-field cooled and field cooled results show second-order magnetic transition at the high-temperature austenite phase to a first-order magnetic transition in the low-temperature martensite phase. The substitution of Ni by Fe and Co increases the austenite Curie temperature TCA from 282 K to 289 K and 294 K respectively while Cu reduces it to 278 K. The martensitic transition temperature TM increased from 221 K to 241 K for Fe substitution and decreased to 210 K and 209 K for Co and Cu respectively. The coercive field HC increased significantly from 457 Oe for Ni at 100 K to 729 Oe for Co at 80 K. The increase to 763 Oe for Fe and 769 Oe for Cu occurred at the same temperature of 40 K. We attribute such increases to domain wall pinning effects due to the inclusions of Fe, Co and Cu. The HC exhibited an anomalous temperature dependence in all the samples. The exchange bias field HEX also showed a significant enhancement below 40 K from 196 Oe for Ni to 476 Oe, 430 Oe and 434 Oe for Fe, Co, and Cu substitutions respectively. The fits to the temperature dependence of the HC reveal significant changes in the competition between ferromagnetic and antiferromagnetic interactions. The peak magnetic entropy change ΔSMpk has a linear dependence on the magnetic field H2/3. The highest value of 28.8 J kg-1 K−1 for ΔSM is obtained in the first order magnetic transition compared to 3.0 J kg-1 K−1 in the second order transition. We report an effective cooling power of 155 J kg-1 in the second order magnetic transition.

Realization of Magnetostructural Transition and Magnetocaloric Properties of Ni–Mn–Mo–Sn Heusler Alloys

As magnetic cooling refrigerant, Ni–Mn–Sn Heusler alloys have gained significant potentials for a wide range of practical applications as compared with other expensive Ga-doped Ni–Mn based Heusler alloys, toxic As and P doped Mn-based alloys and rare-earth elements like Gd-based alloys. Consequently, an inclusive investigation on magnetostructural transition and magnetocaloric features of Ni43Mn47−xMoxSn10 alloys is carried out. The alloys are assembled through arc-melting technique and their X-ray diffraction analysis confirms their B2-type crystal structure at room temperature. As the Mo contents are increased, the magnetostructural transition temperature increases for a temperature range between Curie temperature of austenite and martensite phases. Obvious metamagnetic behavior and magnetic hysteresis are observed in isothermal magnetization curves, suggesting that the temperature and magnetic field can be used as robust tools for tuning the structural transformation in Heusler alloys. The noticeable magnetocaloric effect suggests that the prepared alloys can be an attractive choice for magnetic refrigeration applications.