Magnetostructural Transition Research Articles

Low hysteretic magnetostructural transformation in Cr-doped Ni-Mn-Ga Heusler alloy

Ni-Mn-Ga based alloys are widely studied due to their potential for practical applications, making use of their martensitic transformations. However, hysteresis is a long-standing drawback that reduces the chance of transferring these alloys from the laboratory to industry. In this work, we studied a Cr-doped Ni2.15Mn0.70Cr0.15Ga alloy. We arrived at this composition by integrating data obtained from the previous phase and hysteresis diagrams taken from the literature. The compound presents a magnetostructural transition at room temperature, with a ferromagnetic martensite phase, and moderate thermal hysteresis of approximately 4 K. The magnetocaloric and ferromagnetic shape memory effects were explored, showing a reversible entropy change of approximately 9 Jkg-1K-1 under 0–5 T field change, and a cyclical magnetic-field-induced deformation close to 0.81% under 0–9 T, an advance towards high reversibility for this family alloys.

Estimation of barocaloric effect across the magnetostructural transition in Mn–Co–Ge alloy from magnetization measurements under pressure

We report a novel yet simple method for estimating the barocaloric effect across the magnetostructural transition in Mn34.5Co33.1Ge32.4 alloy by relating the results of X-ray diffraction and magnetization measurements under pressure. The isothermal entropy change in the alloy is estimated to be about 56 Jkg−1K−1 for a moderate hydrostatic pressure change of 297 MPa. This entropy change is much higher than that achieved with a very large magnetic field of 7 T at ambient pressure. These results highlight the potential of MnCoGe based alloys for multicaloric applications where the second external stimulus which drives the phase transition enhances the caloric effects produced by magnetic field. Our proposed method of estimating the barocaloric effect across magnetostructural transitions utilizes some generally available commercial instruments and partly replaces the need to construct specialized apparatus for pressure dependent dilatometric and calorimetric measurements in the presence of magnetic field.

Spin pumping at interfaces with ferro- and paramagnetic Fe60Al40 films acting as spin source and spin sink

We present a study of spin pumping efficiency and determine the spin mixing conductance and spin diffusion length in thin bilayer films based on 3d transition metal alloy Fe60Al40. Due to its magnetostructural phase transition, Fe60Al40 can be utilized as a ferromagnetic (FM) or paramagnetic (PM) material at the same temperature depending on its structural order; thus a thin Fe60Al40 film can act as a spin source or a spin sink when interfaced with a paramagnet or a ferromagnet, respectively. Ferromagnetic resonance measurements were performed in a frequency range of 5–35 GHz on bilayer films composed of FM–Fe60Al40/Pd and PM–Fe60Al40/Ni80Fe20 (permalloy). The increase in damping with the thickness of the paramagnetic layer was interpreted as a result of spin pumping into the paramagnet. We determine the spin mixing conductance gPd↑↓=(3.8±0.5)×1018m−2 at the FM–Fe60Al40/Pd interface and the spin diffusion length λPd=9.1±2.0nm in Pd. For the PM–Fe60Al40/permalloy interface, we find a spin mixing conductance gFeAl↑↓=(2.1±0.2)×1018m−2 and a spin diffusion length λFeAl=11.9±0.2nm for PM–Fe60Al40. The demonstrated bi-functionality of the Fe60Al40 alloy in spin pumping structures may be promising for spintronic applications.

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.

Magnetocaloric performance optimized by simple compression in directionally solidified Ni50Mn18Cu7Ga25 alloy

The Magnetocaloric Effect (MCE) of directionally solidified Ni50Mn18Cu7Ga25 alloy was improved based on texturation and introduction of extra phase transition in this paper. Magneto-structural transition is realized in directionally solidified Ni50Mn18Cu7Ga25 alloy, with a value of Adiabatic Temperature Variation (ΔTad) of − 1.35 K under magnetic field of 1.5 T. Through simple unidirectional compression, preferred orientation is formed and intermartensitic transformation is introduced in the present alloy. Preferred orientation strengthens the coupling of magnetic and structural transition, intermartensitic transformation makes transformation path more diverse, which both enhance ΔTad of the directionally solidified alloy. A value of ΔTad of − 2.34 K is obtained in the deformed alloy under magnetic field of 1.5 T, with a 73.3 % increase compared with the initial state. Moreover, the two incompletely overlapping structural transitions broadens the temperature range of MCE from 4.3 K to 7 K. The present work provides new insight on the MCE optimization of Ni-Mn-Ga alloy by simple and short-term unidirectional compression in view of merging different strengthening mechanisms.

Magneto-Structural Transition and Refrigeration Property in All-D-Metal Heusler Alloys: A Critical Review

Abstract: All-d-metal Heusler alloys has attracted much attention due to its unique magnetic properties, martensite transformation behavior and related solid-state refrigeration performance. These unique type alloys are recently discovered in 2015 and have been widely studied; however, systematic reviews on their magneto-structural transition and refrigeration property are rare. In this review, we first summarize the preparation techniques and microstructure of the bulk alloys and ribbons. Then the magnetic transition and martensite transformation behavior are reviewed, focusing on the correlation between magneto-structural transition and refrigeration properties. The effects of element doping, external magnetic and mechanical fields on the martensite transformation and corresponding magnetic entropy change are summarized. We end this review by proposing the further development prospective in the field of all-d-metal Heusler alloys.

Magnetostructural phase transitions and magnetocaloric effect in Mn-Fe-Ni-Ge-B alloys

The search for room-temperature high-performance magnetocaloric materials is highly stimulated towards magnetic refrigeration techniques. Here we report the boron doping effect on the magnetostructural transition and magnetocaloric effect of the Mn 0.89 Fe 0.11 NiGe alloy. Our studies reveal that the addition of only 0.2 at% boron induces a large magnetic entropy change (∆ S m ) of − 69.4 J kg −1 K −1 at 298.5 K under μ 0 H up to 7 T, which is ~ 34.0% higher than that of − 51.8 J kg −1 K −1 in the host alloy Mn 0.89 Fe 0.11 NiGe obtained at a much lower temperature of 267.5 K. With the increase of boron content, the phase transition temperature M s showed a nonlinear change that first increased and then decreased. The investigation of the microstructure by transmission electron microscopy suggests that the minor B atoms will get into the interstitial site of Mn 0.89 Fe 0.11 NiGe alloy, increase the cell volume, and stabilize the orthorhombic structure of the alloy. This could be the main reason for the increase in magneto-structural transition temperatures. Otherwise, the excessive B atoms will introduce precipitates, and cause the reduction of the magnetostructural transition temperature. It suggests that proper doping point defects are effective to tailor magneto-structural transition toward achieving the magnetocaloric effect. • B causes a nonlinear change of the magneto-structural transition temperature of Mn 0.89 Fe 0.11 NiGe. • Adding 0.2 at% B enhances magnetic entropy change by~ 34.0%. • The minor boron atoms will increase the cell volume and stabilize the martensitic phase. • Nano-precipitates at high B contents hinder the phase transition and decrease the transition temperature.

Observation of a large magnetocaloric effect and suppressed transition in Ti doped Ni-Co-Mn-Sn ribbons upon annealing

We report the presence of austenite and its magnetostructural transition to martensite resulting in a large magnetocaloric effect in Ti doped Ni-Co-Mn-Sn textured ribbons. The evolution of the microstructure, micro-texture and the dynamics of the magnetostructural transition were studied for the as-spun and annealed Ni41.5Ti0.5Co9Mn39Sn10 ribbons. The as-spun ribbons revealed the evolution of a cubic superstructure of B2 ordering at room temperature, which is the characteristic of the austenite phase. The as-spun ribbons possess a strong preferred orientation at room temperature wherein, the< 100 > ║ND fiber texture is the dominant contribution at 90.2%. The austenite is ferromagnetic in nature and undergoes a magnetostructural transformation to weak magnetic martensite at 283.4 K. A large value of the isothermal entropy change of 6.62 J/kg/K, relative cooling power of 114.52 J/kg and an adiabatic temperature change of – 2.6 K have been calculated for a relatively low magnetic field change of 2 T. The annealing and quenching of the ribbons led to the grain growth as well as an overall suppression of the magnetostructural transformation. The austenite phase showed an overall enhancement in its magnetization when field cooled down to low temperatures of 4 K. The presence of strain glass clusters generated in the B2 lattice during the quenching process could be accounted for the observed behavior.

Magnetic glassy martensite induced reversible magnetocaloric effect in Heusler alloys

Heusler alloys hold great potential to act as cooling medium for next-generation solid state refrigeration due to their substantial entropy changes at field-driven magnetostructural transitions. One of the key impediments in the use of Heusler alloys for efficient cooling lies in the poor reversibility of magnetocaloric effect (MCE). In this work, a highly reversible MCE with large isothermal heat Q of ∼ 4.83–5.3 kJ/kg near room temperature, is achieved in Ni50Mn34In12Ga4 Heusler alloys at the transition between unfrozen canonical spin-glassy martensite and ferromagnetic austenite, crosschecked by indirect and direct methods. Phase field simulations reveal that the presence of spin glass in martensite state can result in reversible field-induced magnetostructural transitions in Heusler alloys, thus effectively circumventing the irreversibility of large MCE at strong first-order transitions without the need of any external stimuli such as mechanical load. The occurrence of such field-induced first-order transitions arose from the negative coupling between magnetic moment and the volume of the material. This work suggests the great power of ferroic glasses in improving the reversibility of promising MCE at first-order phase transitions and may push forward more Heusler alloys close to the practical refrigerant in highly efficient solid-state cooling protocols.

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 &amp;lt; x &amp;lt; 0.20. An additional antiferromagnetic–ferromagnetic-like transition was observed in the martensite phase for 0.05 &amp;lt; x &amp;lt; 0.10, which gradually vanished with increasing Co concentration (x &amp;gt; 0.10) or magnetic field (H &amp;gt; 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.

Effective Mass for Holes in Paramagnetic, Plasmonic Cu5FeS4 Semiconductor Nanocrystals.

The impact of a magneto-structural phase transition on the carrier effective mass in Cu5FeS4 plasmonic semiconductor nanocrystals was examined using Magnetic Circular Dichroism (MCD). Through MCD, the sample was confirmed as p-type from variable temperature studies from 1.8 - 75 K. Magnetic field dependent behavior is observed, showing an asymptotic behavior at high field with an value 5.98 at 10 T and 2.73 at 2 T. Experimentally obtained results are holistically compared to SQUID magnetization data and DFT results, highlighting a dependency on vacancy driven polaronic coupling, magnetocrystalline anisotropy, and plasmon coupling of the magnetic field all contributing to an overall decrease in the hole mean free path dependent on the magnetic field applied to Cu5FeS4.

Giant room temperature magnetocaloric response in a (MnNiSi)1−x(FeNiGa)x system

The coincidence of magnetic and structural transitions near room temperature is observed in (MnNiSi)1−x(FeNiGa)x (x = 0.16 and 0.17) systems, which leads to a coupled magnetostructural transition (MST) from a high-temperature paramagnetic Ni2In-type hexagonal phase to a low-temperature ferromagnetic TiNiSi-type orthorhombic phase associated with a substantial change in magnetization and a large change in structural unit cell volume, and thus, across MST, a giant magnetocaloric effect is obtained in these systems. The alloys with x = 0.16 and 0.17 are observed to show a giant isothermal magnetic entropy change (ΔSM) of about −26.2 and −63.2 J kg−1 K−1, accompanied with a large relative cooling power of about 220.1 and 264.5 J/kg, respectively, due to a magnetic field change (μ0ΔH) of 5 T only. Moreover, the material with x = 0.16 and 0.17 shows a large temperature average magnetic entropy change of about −21.64 and −34.4 J kg−1 K−1 over a temperature span of 10 K due to μ0ΔH ∼ 5 T. Thus, these low-cost materials with giant magnetocaloric responses are highly suitable to be used as magnetic refrigerants for room temperature solid-state-based cooling technology.

Magnetostructural Transition and Magnetocaloric Effect with Negligible Magnetic Hysteresis in MnCoGe1.02−xGax Alloys

The behavior of magnetostructural transition and the magnetocaloric effect in the MnCoGe1.02−xGax (x = 0, 0.02, 0.04, 0.06) alloys are investigated in this study. The addition of Ga changes the crystal structure of MnCoGe1.02−xGax alloys at room temperature and reduces the phase transition temperatures with increasing Ga content. The coupling of magnetostructural transition and negligible magnetic hysteresis is observed in the Mn-Co-Ge-Ga alloy. At 305 K, under the action of a 5 T magnetic field, the MnCoGeGa0.02 alloy exhibits 23.47 J/kg∙K magnetic entropy change, and its refrigeration capacity reaches 387 J/kg. The large magnetic entropy change near room temperature and the high refrigeration capacity in the Mn-Co-Ge-Ga alloy make it a promising new type of refrigeration material.

Investigation of the complex magnetic behavior of Ni46.86Co2.91Mn38.17Sn12.06 (at%) magnetic shape memory alloy at low temperatures

The magnetic properties, martensitic transformation characteristics, the magnetic field-induced transformation characteristics, and super spin-glass behaviour at low temperature of Ni46.86Co2.91Mn38.17Sn12.06 (at%) magnetic shape memory alloys (MSMAs) were investigated under various magnetic field levels over temperature intervals from 400 K to 10 K. We observe a small magnetization difference during the martensitic transition evidenced with a visible thermal hysteresis. To investigate the magnetic field induced phase fraction, the minimum magnetic field required to start and complete the magnetostructural phase transition is computed. Super-spin glass features in magnetic data are observed that interacting magnetic clusters are frozen below a critical temperature. Magnetization is computed as a function of temperature at various constant fields using molecular field theory. The critical exponent, β is deduced for the temperature-induced magnetization, which indicates that the MSMA exhibited ferromagnetic ordering during field-cooling and on heating an antiferromagnetic ordering at low temperatures and in low applied magnetic fields. These observations are consistent within the framework of an Ising or Heisenberg model.

Room temperature huge magnetocaloric properties in low hysteresis ordered Cu-doped Ni-Mn-In-Co alloys

The reduction of the thermal hysteresis in first order magnetostructural transition is a determining factor to decrease energy losses and to improve the efficiency of magnetocaloric cooling based systems. In this work, a Cu doped NiMnInCo metamagnetic shape memory alloy (MMSMA) exhibiting a narrow thermal hysteresis (around 5 K) at room temperature has been designed. In this alloy, the induced L21 ordering process affects the phase stability in an unusual way compared to that observed in NiMnInCo and other NiMn based alloys. This ordering produces an increase in the Curie temperature of the austenite but hardly affects the martensitic transformation temperatures. As a consequence, the ordering increases the magnetization of the austenite without changing the transformation temperatures, doubles the sensitivity of the transformation to magnetic fields (the Claussius-Clapeyron slope goes from 2.1 to 3.9 K/T), improves the magnetocaloric effect, the reversibility and finally, enhances the refrigeration capacity. In addition, the magnetic hysteresis losses are among the lowest reported in the literature and the effective cooling capacity coefficient RCeff reaches 86 J/Kg for 2 T (15 % higher than those found in Ni-Mn based alloys) and 314 J/Kg for 6 T fields. Therefore, the ordered alloy possesses an excellent combination of low thermal hysteresis and high RCeff, not achieved previously in metamagnetic shape memory alloys near room temperature.

Large enhancement of magnetocaloric effect induced by dual regulation effects of hydrostatic pressure in Mn0.94Fe0.06NiGe compound

• Pressure realizes dual effects of lowering t str and strengthening FM state. • The origin of regulation effect is studied by the first-principles calculations. • The magnetocaloric effect is enhanced by more than 200% by pressure. MM′X (M, M′ = transition metals, X = carbon or boron group elements) compounds could exhibit large magnetocaloric effect due to the magnetostructural transition, and the composition regulation has been widely studied to realize the magnetostructural transition. Moreover, the magnetostructural transition is also sensitive to the pressure. Herein, the effect of hydrostatic pressure on magnetostructural transformation and magnetocaloric effect has been investigated in Mn 0.94 Fe 0.06 NiGe compound. Dual regulation effect of lowering structural transition temperature and strengthening ferromagnetic (FM) state of martensite is realized by applying hydrostatic pressure, which would greatly improve the magnetocaloric effect of Mn 0.94 Fe 0.06 NiGe compound. Moreover, the first-principles calculations have also been performed to discuss the origin of the regulation effect under hydrostatic pressure, and it indicates that the hydrostatic pressure can stabilize the hexagonal structure and decrease the structural transition temperature. The maximum isothermal entropy change increases by 109% from 4.3 J/(kg K) under 0 GPa to 9.0 J/(kg K) under 0.402 GPa for a magnetic field change of 0–3 T. This work proves that the hydrostatic pressure is an effective method to regulate the magnetostructural transition and enhance magnetocaloric effect in MM′X compounds.

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.

Tuning magnetostructural phase transition in CoMn0.88Cu0.12Ge by application of hydrostatic pressure

Structural and magnetic properties of CoMn0.88Cu0.12Ge have been investigated using X-ray diffraction and differential scanning calorimetry (DSC) accompanied with investigation of magnetic properties under applied hydrostatic pressure up to 12 kbar. The orthorhombic crystal structure (TiNiSi-type), which is dominant at low temperatures, turns into the hexagonal one (Ni2In-type), slightly above 200 K. The structural transition is of the first-order type as confirmed by presence of distinct thermal hysteresis. The ac magnetic measurements indicate a ferromagnetic order below 238 K, followed by additional anomaly at lower temperatures – the latter one being related to the structural transition. Application of hydrostatic pressure leads to temperature separation of the purely magnetic transition, whose Curie temperature increases with applied pressure, and the magnetostructural transition characterized by decreasing critical temperature. Comparison of the DSC data for the investigated compound and the isostructural CoMn0.95Cu0.05Ge has made it possible to determine both the structural and magnetic components of entropy change.

Pressure-induced magnetic transformations in Cd3As2+MnAs hybrid composite

Considerable interest to magnetism of MnAs both in bulk or in the form of epitaxial films is stimulated by its applications as a magnetocaloric material and in spintronic devices. Since the MnAs films deposited on GaAs reproduce well a magnetic transformation related to α–β magnetostructural transition that occurs in bulk MnAs, this first-order phase transition occurs through a phase coexistence over a wide temperature range. Here, we considered the same magnetostructural transition in a bulk hybrid structure based on micrometer-scaled MnAs inclusions embedded into the Cd3As2 matrix. In particular, the effect of high pressure and magnetic fields on the ferromagnetic transition temperature, TC, in a composite Cd3As2 + 30 mol. % MnAs has been studied. We found that at ambient pressure, the transition from α-MnAs to β-MnAs is accompanied by the absence of thermal hysteresis of magnetization, implying a phase coexistence regime. The hysteresis width does not markedly increase even at pressures about P = 0.35 GPa, and displacement of TC occurs with a rate of dTC/dP ∼ −91.42 K/GPa. In the temperature region of the α–β phase coexistence, a local peak at T = 283 K and P = 1 GPa is observed, which is associated with an antiferromagnetic order of MnAs inclusions. Direct measurements of isothermal magnetization vs pressure indicate both the stabilization of the ferromagnetic hexagonal α phase at P &amp;lt; Pmax and the development of an orthorhombic antiferromagnetic long-range order, which propagate up to 5 GPa.

Martensitic transformation controlled by electromagnetic field: From experimental evidence to wireless actuator applications

Mechanical actuators based on shape memory alloys (SMA) are becoming a key component in the development of novel soft robotic applications and surgically implantable devices. Their working principle relies in the temperature induced martensitic transformation (MT), which is responsible of the actuation mechanism. In this work, we found experimental evidence to show that the martensitic transformation can be controlled by electromagnetic field (EF) by a wireless process in ferromagnetic shape memory alloys. It is shown that the martensitic transformation can be driven by an external EF (frequency 45 kHz) while the specific absorption rate (SAR), which was determined through real-time dynamic magnetization measurements, allows the instantaneous monitoring of the transformation evolution. On the basis of the obtained results, we propose a strategy to achieve a battery-free wireless SMA actuator that can be remotely controlled. This concept can be applicable to other SMA material that exhibit a similar magneto-structural phase transition.