First-order Magnetostructural Transition Research Articles

The effects of high-pressure annealing on magnetostructural transitions and magnetoresponsive properties in stoichiometric MnCoGe

In this study, phase transitions (structural and magnetic) and associated magnetocaloric properties of stoichiometric MnCoGe have been investigated as a function of annealing pressure. Metastable phases were generated by annealing at 800 °C followed by rapid cooling under pressures up to 6.0 GPa. The x-ray diffraction results reveal that the crystal cell volume of the metastable phases continuously decreases with increasing thermal processing pressure, leading to a decrease in the structural transition temperature. The magnetic and structural transitions merge and form a first-order magnetostructural transition between the ferromagnetic orthorhombic and paramagnetic hexagonal phases over a broad temperature range (>80 K) spanning room temperature, yielding considerable magnetic entropy changes. These findings demonstrate the utility of thermal processing under high pressure, i.e., high-pressure annealing, to control the magnetostructural transitions and associated magnetocaloric properties of MnCoGe without altering its chemical composition.

Microstructure, first-order magnetostructural transition, magnetocaloric properties and exchange bias effect in Ni45−xBixMn44Sn11 alloys

Microstructure, first-order magnetostructural transition, magnetocaloric properties and exchange bias effect in Ni45−xBixMn44Sn11 alloys

Tuning martensitic transformation and magnetocaloric effect with Bi substitution in MnCo1-xBixGe alloys

In this work, the substitution of Bi for Co atoms in MnCo1-xBixGe (x = 0.01, 0.02, 0.04, 0.06, 0.08, 0.1) alloys was prepared. The crystal structure, magnetic properties, and magnetocaloric effect have been analyzed. By tuning the Bi-content in MnCoGe alloys, the reduction of martensitic transformation (MT) temperature and the presence of a first-order magnetostructural transition (MST) were observed. Magnetic field-induced MT indicates that the magnetic field is much harder to drive MT compared to the temperature. With the Bi-content for 0.01 ≤ x ≤ 0.06, orthorhombic-type phase and hexagonal-type phase coexist. Furthermore, we observed an increase in the fraction of the hexagonal-type phase and a corresponding decrease in the fraction of the orthorhombic-type phase. It is beneficial to the refrigeration capacity for the isothermal magnetization curves M(H) on magnetization and demagnetization procedures with small magnetic hysteresis loss. With a magnetic field of 5 T, magnetocaloric effect (MCE) can be observed involving magnetic entropy change (-ΔSM) of 26.42 J kg−1 K−1 for x = 0.06 and refrigeration capacity (RC) of 259.78 J kg−1 for x = 0.01. Thus, this material is considered a fabulous candidate for magnetic refrigeration cooling applications at room temperature.

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.

Entropy change reversibility in MnNi1−x Co x Ge0.97Al0.03 near the triple point

The nature of the phase transition has been studied in MnNi1−x Co x Ge0.97Al0.03 (x= 0.20–0.50) through magnetization, differential scanning calorimetry and x-ray diffraction measurements; and the associated reversibility in the magnetocaloric effect has been examined. A small amount of Al substitution for Ge can lower the structural phase transition temperature, resulting in a coupled first-order magnetostructural transition (MST) from a ferromagnetic orthorhombic to a paramagnetic hexagonal phase in MnNi1−x Co x Ge0.97Al0.03. Interestingly, a composition-dependent triple point (TP) has been detected in the studied system, where the first-order MST is split into an additional phase boundary at higher temperature with a second-order transition character. The critical-field-value of the field-induced MST decreases with increasing Co concentration and disappears at the TP (x= 0.37) resembling most field-sensitive MST among the studied compositions. An increase of the hexagonal lattice parameter a hex near the TP indicates a lattice softening associated with an enhancement of the vibrational amplitude in the Ni/Co site. The lattice softening leads to a larger field-induced structural entropy change (structural entropy change≫ magnetic entropy change, for this class of materials) with the application of a lower field, which results in a larger reversibility of the low-field entropy change (|ΔS rev| = 6.9 J kg−1 K for Δμ 0 H = 2 T) at the TP.

The Effect of Substitution of Mn by Pd on the Structure and Thermomagnetic Properties of the Mn1-xPdxCoGe Alloys (Where x = 0.03, 0.05, 0.07 and 0.1).

In the present paper, the influence of partial substitution of Mn by Pd on structure, thermomagnetic properties, and phase transitions in the MnCoGe alloys was investigated. The studies of phase constitution revealed an occurrence of the orthorhombic TiNiSi-type and hexagonal Ni2Ti- type phases. Deep analysis of the XRD pattern supported by the Rietveld analysis allowed us to notice the changes in lattice parameters and quantity of recognized phases depending on the Pd content. An increase of palladium in alloy composition at the expense of manganese induced a rise in the Curie temperature. The values of ΔSM measured for the variation of external magnetic field ~5 T equaled 8.88, 23.99, 15.63, and 11.09 for Mn0.97Pd0.03CoGe, Mn0.95Pd0.05CoGe, Mn0.93Pd0.07CoGe, and Mn0.9Pd0.1CoGe alloy, respectively. The highest magnetic entropy change ΔSM was observed for samples with Pd content x = 0.05 induced by magnetostructural transformation. The analysis of the n vs. T curves allowed confirmation of the XRD and DSC results of an occurrence of the first-order magnetostructural transition in Mn0.95Pd0.05CoGe and Mn0.93Pd0.07CoGe alloys samples.

Anomalous magnetic entropy changes of bulk and powder Mn0.5Fe0.5-xNi1+xSi0.94Al0.06 intermetallic system

The multi-component MnTX (T = Ni, Co; X = p-block elements) intermetallic system have attracted intensive attention due to their tunable magneto-structural phase transition and associated giant magnetocaloric effect. Here, we report an experimental study on the magnetic, magnetocaloric, and electrical properties of alloys that belong to the MnTX family- Mn0.5Fe0.5-xNi1+xSi0.94Al0.06. For all values of x (0≤ x ≤0.10), the materials exhibited a first-order magneto-structural phase transition from a low-temperature ferromagnetic orthorhombic phase to a high-temperature paramagnetic hexagonal phase. The transition was accompanied by large magnetic entropy changes of up to –22 and −57 J kg−1K−1 at T = 322 K for field changes of 2 T and 5 T, respectively. Most noticeably, a sharp jump in electrical resistivity was observed at T = 320 K for x = 0.1, which confirmed that the first-order phase transition preserved the mechanical stability of the material. The alloy with x = 0.1 was further crushed into powder and the magnetic properties were compared to its bulk counterpart. The enhanced mechanical stability and nearly zero magnetic hysteresis loss along with the fact that the system is constituted of cheap, non-toxic elements make this system worthy of consideration for near-room temperature magnetic refrigeration applications.

Effect of heat treatment on coupled magnetostructural transition and magnetocaloric effect of MnNiGe system

Material with coupled magnetic and structural transition is of significant interest in the field of energy-efficient technology. In this work, a sharp first-order magneto-structural transition (MST) from a ferromagnetic orthorhombic TiNiSi-type martensite phase to a paramagnetic hexagonal Ni2In-type austenite phase is observed in hexagonal Mn0.85Fe0.15NiGe compound through the heat treatment technique. Through heat treatment, the first-order MST for Mn0.85Fe0.15NiGe sample is observed to decrease drastically from 279.1 K to 211.8 K for the elevated annealing temperatures from 873 K to 1173 K. Furthermore, total entropy change (ΔS) is synergistically associated with the magnetic and structural entropy change in this system. This synergic feature governs a large ΔS ∼ 62.7 Jkg-1K−1, while magnetic entropy change is about 31.3 Jkg-1K−1 (∼52.1%) and the lattice part contributes the remaining ∼48.7% for the sample annealed at 1073 K due to the field change of 5T. In addition, a large effective refrigerant capacity reaches 226.7 Jkg−1 at 226 K for the sample due to the field change of 5T. Henceforth, this work shows an effective and efficient scheme to control the MST temperature of hexagonal phase-transition families using heat treatment method without changing the chemical composition of the sample. Our results based on heat treatment methodology provide a feasible platform for tuning MST and the associated caloric properties.

Magnetocaloric and Magneto-transport Properties in Polycrystalline Ni<sub>56</sub>Mn<sub>20</sub>Ga<sub>24</sub> Heusler Alloy

Polycrystalline ingots of Ni-rich Ni56Mn20Ga24 alloy were prepared by conventional arc melting procedure. The magnetocaloric and magnetotransport properties of the alloy were investigated within a temperature range from 4.2-300 K and up to a magnetic field of 8 T. A large magnetocaloric effect (∆SM ~ 29 J/Kg K) was observed in the alloy in the vicinity of magneto-structural transition temperature at a change of 5 T magnetic field. From magnetic measurements, it was observed that the martensite to austenite transition was accompanied by higher to lower magnetization in higher magnetic fields. The large entropy change was explained by considering the first-order magneto-structural transition in this alloy. A high negative magnetoresistance (⁓7 %) associated with magnetic field induced first order magneto-structural transition was also observed near room temperature due to a change of 8 T magnetic field for this alloy.

Large reversible magnetocaloric effect across the first-order magneto-structural transition in (Mn0.45Fe0.55) (Ni0.6Co0.4) Si alloy

Magnetic materials with reversible magnetocaloric effect across their respective first-order magneto-structural transitions (MST) have vital significance for further advancement towards the ultimate goal of practical magnetic cooling applications. In this present study, the reversibility of the MST is investigated by analyzing the isofield curves under different minor and major thermal hysteresis loops and the isothermal curves under different magnetic field cycles. The reversibility of the magnetocaloric effect (MCE) depends upon the width of the nucleation energy barrier existing across the MST. Minor hysteresis loops are found to be minimizing the energy loss by preventing the nucleation of the martensite phase and can be easily returned to the austenite phase immediately while switching from cooling to heating. A large reversible isothermal magnetic entropy change ΔSM of −14.4 J kg−1 K−1 nearly at 322 K is observed for the (Mn0.45Fe0.55) (Ni0.6 Co0.4) Si alloy under a low magnetic field change of 3 T. The observed large reversible MCE, very low magnetic field-induced hysteresis loss, and large reversible RCeffe ∼ 155 J kg−1 will be beneficial for reducing the energy loss during several magnetic field cycles in practical cooling applications which makes this alloy promising for the development of efficient magnetic refrigerants.

Magnetostructural transition and magnetocaloric effect in Mn0.5Fe0.5NiSi1−xAlx melt-spun ribbons (x = 0.055 and 0.060)

Melt-spun ribbons samples of the multicomponent alloy Mn0.5Fe0.5NiSi0.940Al0.060 were prepared and the magnetostructural transition (MST) and related magnetocaloric properties studied for as-solidified ribbons and ribbon samples annealed between 800 and 950 °C for 4 h. The results are compared with those reported in the literature for melt-spun ribbons with an Al content x = 0.055 and bulk alloys. It is shown that all samples undergo a first-order MST from a paramagnetic Ni2In-type hexagonal structure to a ferromagnetic TiNiSi-type orthorhombic one. Ribbons show broader isothermal entropy change ΔST(T) curves with moderate maximum values of |ΔST|max at 2 T (7.2–7.3 J kg−1 K−1) in comparison with the reported for bulk alloys. However, the average value of the magnetic hysteresis loss linked to the hexagonal-to-orthorhombic transition is low in comparison with the one reported for most magnetocaloric materials with first-order magnetostructural transitions. This work underlines the effectiveness of this rapid solidification technique to produce highly homogeneous ribbon samples of multicomponent alloys.

Температурно-барические особенности магнитных характеристик в системах со структурными переходами типа смещения

Using pnictides MnAs and germaindes Mn0.89Cr0.11NiGe as an example, the transformation of thermobaric features of their magnetic characteristics at high pressures is considered. A unified approach is used to describe paramagnetic (PM) structural transitions of the displacement type with a change in the symmetry PM(P63/mmc)-PM(Pnma) from hexagonal to orthorhombic. It is shown that the competition between the parameters of the structural and magnetic orders in both systems manifests itself differently in the stabilization and alternation of the so-called high-spin and low-spin magnetically ordered states initiated by pressure. As a consequence, the structural contribution in these systems weakens (MnAs) or enhances (Mn0.89Cr0.11NiGe ) the giant magnetocaloric effect in the temperature-baric region of the first-order magnetostructural phase transitions.

Temperature-baric features of magnetic characteristics in systems with structural transitions of the displacement type

Using pnictides MnAs and germaindes Mn0.89Cr0.11NiGe as an example, the transformation of thermobaric features of their magnetic characteristics at high pressures is considered. A unified approach is used to describe paramagnetic (PM) structural transitions of the displacement type with a change in the symmetry PM(P6_3/mmc)-PM(Pnma) from hexagonal to orthorhombic. It is shown that the competition between the parameters of the structural and magnetic orders in both systems manifests itself differently in the stabilization and alternation of the so-called high-spin and low-spin magnetically ordered states initiated by pressure. As a consequence, the structural contribution in these systems weakens (MnAs) or enhances Mn0.89Cr0.11NiGe the giant magnetocaloric effect in the temperature-baric region of the first-order magnetostructural phase transitions. Keywords: structural phase transitions of the displacement type, magnetostructural phase transitions, helimagnetism, ferromagnetism, high spin-low spin states, direct magnetocaloric effect.

Влияние долговременного воздействия циклических полей на магнитокалорические свойства сплава Гейслера Ni-=SUB=-43.18-=/SUB=-Mn-=SUB=-45.15-=/SUB=-In-=SUB=-11.67-=/SUB=-

The thermal expansion (Delta l/l0), magnetocaloric effect (Delta Tad) and the magnetostriction (λ) of a polycrystalline sample of the Ni43.18Mn45.15In11.67 Heusler alloy were studied. A correlation has been established between the magnetocaloric effect and magnetostriction. The smaller value of the MCE in the cooling run can be explained by the smaller contribution of the lattice subsystem to the total measured MCE. It is found that the long-term action of the cyclic magnetic field results in a decrease in the value of Delta Tad in the region of the first-order magnetostructural phase transition. The virgin properties of the alloy can be restored by transformation the sample to the austenite phase. The Heusler alloy Ni43.18Mn45.15In11.67 can be used as a working body in magnetic cooling technology, provided that the alloy periodically transforms to the austenite phase.

Simulation of a Hybrid Thermoelectric-Magnetocaloric Refrigerator with a Magnetocaloric Material Having a First-Order Transition

A simple hybrid thermoelectric-magnetocaloric (TE-MC) system is analytically and numerically simulated using the working parameters of commercial Peltier cells and the properties of a material with a first-order and low-hysteresis magneto-structural phase transition as La(Fe,Mn,Si)13H1.65. The need for a new master equation of the heat diffusion is introduced to deal with these materials. The equation is solved by the Crank–Nicolson finite difference method. The results are compared with those corresponding to a pure TE system and a pure MC system with ideal thermal diodes. The MC material acts as a heat “elevator” to adapt its temperature to the cold or hot source making the TE system very efficient. The efficiency of the realistic hybrid system is improved by at least 30% over the pure Peltier system for the same current supply and is similar to the pure MC with ideal diodes for the same cooling power.

Complete and reversible magnetostructural transition driven by low magnetic field in multiferroic NiCoMnIn alloys

Magnetic-field-induced first-order magnetostructural transition (MFI-FOMST) brings about an ample variety of intriguing magnetoresponsive effects including magnetocaloric effect, magnetoresistance and magnetostrain. Metamagnetic shape memory alloys (MSMAs) exhibit MFI-FOMST and thus giant magnetoresponsive effects, but the critical field for complete and reversible MFI-FOMST, (μ0∆H)min, is too high (usually >5 T), which has been a longstanding bottleneck for practical applications. Here, we successfully achieved complete and reversible MFI-FOMST under a low field of 1.5 T, which can be generated by permanent magnets, in a prototype MSMA. The significant reduction of (μ0∆H)min is realized by simultaneously enlarging the distance between Curie transition and magnetostructural transition and manipulating the geometric compatibility between the transforming phases. The low (μ0∆H)min provides a great opportunity for attaining low-field-induced large reversible magnetoresponsive effects. For instance, a large reversible magnetocaloric effect is achieved under 1.5 T. Our realization of low-field-induced complete and reversible first-order magnetostructural transition may push a significant step forward towards the practical use of MSMAs. This work is instructive for developing novel magnetic materials with low-field-actuated first-order phase transition for applications as magnetic actuators, magnetoresistors and solid-state refrigerants.

Effects of doping, hydrostatic pressure, and thermal quenching on the phase transitions and magnetocaloric properties in Mn1−xCoxNiGe

The effects of doping, hydrostatic pressure, and thermal quenching on the phase transitions and magnetocaloric properties of the Mn1−xCoxNiGe system have been investigated. Cobalt doping on the Mn site shifted the martensitic structural transition toward lower temperature until it was ultimately absent, leaving only a magnetic transition from a ferromagnetic (FM) to a paramagnetic (PM) state in the high-temperature hexagonal phase. Co-occurrence of the magnetic and structural transitions to form a first-order magnetostructural transition (MST) from the FM orthorhombic to the PM hexagonal phase was observed in samples with 0.05 < x < 0.20. An additional antiferromagnetic–ferromagnetic-like transition was observed in the martensite phase for 0.05 < x < 0.10, which gradually vanished with increasing Co concentration (x > 0.10) or magnetic field (H > 0.5 T). The application of external hydrostatic pressure shifted the structural transition to lower temperature until an MST was formed in samples with x = 0.03 and 0.05, inducing large magnetic entropy changes up to −80.3 J kg−1 K−1 (x = 0.03) for a 7-T field change under 10.6-kbar pressure. Similar to the effects of the application of hydrostatic pressure, an MST was formed near room temperature in the sample with x = 0.03 by annealing at high temperature (1200 °C) followed by quenching, resulting in a large magnetic entropy change of −56.2 J kg−1 K−1. These experimental results show that the application of pressure and thermal quenching, in addition to compositional variations, are effective methods to create magnetostructural transitions in the MnNiGe system, resulting in large magnetocaloric effects.

Large magnetocaloric effect and magnetoresistance in Fe-Co doped Ni50-(FeCo) Mn37Ti13 all-d-metal Heusler alloys

The effect of substituting FeCo in Ni site maintaining their same ratio on structural, magnetocaloric, and magneto-transport properties of all- d -metal Ni 50- x (FeCo) x Mn 37 Ti 13 ( x = 16, 18, and 20) Heusler alloys are investigated. These alloys undergo a first-order magnetostructural transition (MST) between low temperature weak magnetic martensite (monoclinic or orthorhombic structure) to a high temperature ferromagnetic (FM) austenite (cubic structure) phase around room temperature. The MST temperature is observed to shift towards the lower temperature with increasing (FeCo) x content. These alloys with x = 16, 18, and 20 exhibit isothermal magnetic entropy change (∆S M ) as large as about ~ 13.8 , ~ 12.7 and ~ 11.8 JkgK −1 across their MST associated with an effective refrigerant capacity (RC eff ) of about 119.9 , ~ 126.2 and ~ 194.4 J/kg respectively due to an application of 5 T magnetic field. It is interesting to note that ∆S M remains almost identical over a large temperature region with (FeCo) x content from 16 to 20 at%. In addition, the maximum values of large magnetoresistance (MR)~ − 26.1 % for x = 16, − 25.4 % for x = 18, and − 24.3 % for x = 20 are achieved at the field of 5 T. These materials with large magnetocaloric response in an extended temperature window around room temperature as well as large negative MR can be considered as potential candidates for multifunctional application. • We report the co-doping effect on magnetocaloric effect and magnetoresistance in all- d -metal Heusler alloys. • The magnetostructural transition (MST) shifts towards lower temperature with doping contents. • We observe large isothermal entropy change ( ∆ S M ) , and large magnetoresistance near room temperature.

Low-melting metal bonded MM′X/In composite with largely enhanced mechanical property and anisotropic negative thermal expansion

MM′X (M, M′ = transition metals, X = carbon or boron group elements) compounds experiencing magnetostructural transition have great potential in multifunctional applications due to the various magnetoresponsive effects. However, the poor mechanical properties hinder their practical applications. In the present work, the low-melting metal bonded MM′X/In composites are fabricated. The dense structure with low porosity, formed due to the high ductility of In, greatly improves the machinability and thermal conductivity. The thermal cycling tests prove the excellent integrality and stability of MM′X/In composites. The introduction of ductile In reduces the constraints of structural transition so that weakens the first-order magnetostructural transition of MM′X compounds, thus lowering the hysteresis loss. Besides, the MM′X/In composite with 30 wt.% In (In30) exhibits a larger magnetocaloric effect than that of the benchmark magnetocaloric material Gd. In addition, zero thermal expansion (ZTE) property is achieved in In30 composite over a wide temperature range. Moreover, magnetic oriented In30 composite displays a strongly anisotropic thermal expansion performance. An obvious positive thermal expansion (PTE) with linear PTE coefficient of 5.2 × 10−6 K−1 is observed along the direction parallel to pressure, while large negative thermal expansion (NTE) can be obtained along the directions perpendicular and parallel to field. The NTE in the direction parallel to field is as high as −40.6 × 10−6 K−1, which is comparable to those of some typical NTE materials. Consequently, the present result highlights the potential multifunctional applications of low-melting metal bonded MM′X/In composites, especially as magnetic refrigerants and NTE materials around room temperature.

Simultaneous Multi-Property Probing During Magneto-Structural Phase Transitions: An Element-Specific and Macroscopic Hysteresis Characterization at ID12 of the ESRF

We present a new instrument for advanced magnetic studies based on the high field X-ray magnetic circular dichroism (XMCD) end-station developed at the beamline ID12 of the European Synchrotron Radiation Facility (ESRF, Grenoble, France). It offers a unique possibility to measure simultaneously element-specific and macroscopic properties related to magnetic, electronic, and structural degrees of freedom of magnetic materials. Under strictly the same experimental conditions, one can measure the XMCD response, macroscopic magnetization, volume changes, and caloric properties of a magnetic material as a function of magnetic field (up to 17 T) and temperature (5–325 K). To illustrate the performance of this new instrument, we present a case study of an equiatomic FeRh alloy across the first-order magneto-structural transition. This development is the first step toward a new fully dedicated end-station based on a 7 T split-coil superconducting magnet with an additional capability to perform X-ray diffraction experiments.