Magnetostructural Phase Transition Research Articles

Study of the magnetoelastic phase transition in near equiatomic FeRh alloys through T-FORC analysis and neutron diffraction

Fe100-xRhx alloys with x ∼ 50 undergo a first-order magnetoelastic phase transition close to room temperature from the low-temperature antiferromagnetic (AFM) to the high-temperature ferromagnetic (FM) state. For Fe50Rh50, the AFM-FM-AFM transitions may occur involving various coexistent mechanisms. Although the Fe49Rh51 composition closely resembles the equiatomic counterpart, its first-order phase transition exhibits notable disparities, whose underlying process remains unexplained. We combined neutron thermo-diffraction and magnetization measurements to study the phase transformation in the two alloys. The Kolmogorov-Johnson-Mehl-Avrami (KJMA) model and temperature first-order reversal curve (T-FORC) analysis are applied to explore this matter. The techniques were applied to both alloys, Fe50Rh50 and Fe49Rh51, to use the former as reference to emphasize the distinct characteristics of the latter. The study highlights the defect-based growth hindering in Fe50Rh50 and the almost complete absence of it in Fe49Rh51, accompanied by a significant effect of the FM phase magnetostatic field. This work presents a new way to obtain detailed information from the T-FORCs by analyzing their T-derivative curves. This method indicates that the superposition of applied and magnetostatic fields causes the notable differences observed in alloys with such close atomic composition. It reveals and explains peculiar features of the Fe49Rh51 temperature-driven transition, such as the anomalous cross-over of the first-order reversal magnetization curves at low temperatures, that could pave the way to a deeper understanding of the mechanisms driving the magnetostructural phase transition in these alloys.

Stability of the first-order character of phase transition in HoCo2

HoCo2 exhibits a giant magnetocaloric (MC) effect at its first-order magnetostructural phase transition around 77 K, and understanding the thermodynamic nature of this transition in response to external magnetic fields is crucial for its MC applications. In this study, we present a comprehensive investigation of specific heat and magnetization measurements of HoCo2 under varying magnetic fields. The specific heat measurements qualitatively indicate a transformation from first- to second-order behavior of this phase transition at higher magnetic fields. However, analysis of the power-law dependence of the magnetic entropy change (ΔSM∝Hn) and the breakdown of universal behavior in the temperature dependence of ΔSM suggest that the first-order nature remains intact, even up to 7 T. This stability of the first-order nature is further manifested through the distinctive non-linear behavior of modified Arrott plots, with a negative slope in the 6–7 T range.

Enhanced Magnetocaloric Properties of the (MnNi)0.6Si0.62(FeCo)0.4Ge0.38 High-Entropy Alloy Obtained by Co Substitution.

In order to improve the magnetocaloric properties of MnNiSi-based alloys, a new type of high-entropy magnetocaloric alloy was constructed. In this work, Mn0.6Ni1-xSi0.62Fe0.4CoxGe0.38 (x = 0.4, 0.45, and 0.5) are found to exhibit magnetostructural first-order phase transitions from high-temperature Ni2In-type phases to low-temperature TiNiSi-type phases so that the alloys can achieve giant magnetocaloric effects. We investigate why chexagonal/ahexagonal (chexa/ahexa) gradually increases upon Co substitution, while phase transition temperature (Ttr) and isothermal magnetic entropy change (ΔSM) tend to gradually decrease. In particular, the x = 0.4 alloy with remarkable magnetocaloric properties is obtained by tuning Co/Ni, which shows a giant entropy change of 48.5 J∙kg-1K-1 at 309 K for 5 T and an adiabatic temperature change (ΔTad) of 8.6 K at 306.5 K. Moreover, the x = 0.55 HEA shows great hardness and compressive strength with values of 552 HV2 and 267 MPa, respectively, indicating that the mechanical properties undergo an effective enhancement. The large ΔSM and ΔTad may enable the MnNiSi-based HEAs to become a potential commercialized magnetocaloric material.

Multicaloric response tuned by electric field in cylindrical MnAs/PZT magnetoelectric composite

The possibility observation of the electric field controlled multicaloric response through quasi-isostatic compression as a result of the converse piezoelectric effect was demonstrated on the cylindrical type magnetoelectric composite MnAs/PZT. It was shown that an electric voltage of 100 V corresponding to an electric field of E ∼0.3 kV/mm applied to the walls of the piezoelectric component PZT of the MnAs/PZT composite contributes to an increase in the maximum adiabatic temperature change by 0.2 K in the temperature range of the magnetostructural phase transition of MnAs ∼317 K at a magnetic field change of 1.8 T. Numerical analysis using the finite element method has shown that an electric field voltage of 100 V is capable of creating a quasi-isostatic mechanical stress in the region inside a cylindrical PZT tube of ∼3 MPa. Moreover, in the region of weak pressures up to 10 MPa, the contribution to the total adiabatic temperature change from piezo-mechanical compression linearly depends on the electrical voltage that can be used for control by magnetic and caloric properties of multicaloric materials.

Investigation of the effect of martensitic phase transition temperature and Curie temperature difference on magnetic and magnetocaloric properties under low magnetic field on Si-doped Ni-Mn-In Heusler alloys

This study examines the impact of substituting Si for Mn on the structural, magnetic, and magnetocaloric properties of Ni43Mn46−x Si x In11 (x = 0.3 and 0.6) alloys. To this end, a range of analytical techniques are employed, including scanning electron microscopy (SEM), room temperature x-ray powder diffraction (XRD), and magnetization measurements. Above the martensitic transition temperature, the Ni43Mn46−x Si x In11 alloys exhibit cubic L2 1 (space group FM-3M). Below this temperature they adopt a tetragonal L1 0 (space group I4/mmm). The martensitic transition temperature decreased when Si is substituted for Mn. The magnetic field-induced entropy change is calculated from magnetic field-dependent magnetization measurements using Maxwell’s equations. The maximum magnetic field-induced entropy changes for Ni43.16Mn45.56Si0.29In11 and Ni43.51Mn44.82Si0.59In11 alloys are calculated 8.20 J kg−1K−1 and 3.15 J kg−1 K−1, respectively, in the vicinity of the magnetostructural phase transition for a magnetic field change of 18 kOe. It is demonstrated that the temperature differential between the high-temperature austenite phase's Curie point (T C ) and the mean martensitic transformation temperature (T M ), namely (T M -T C ), influences the martensitic transition temperatures and, consequently, on the magnetic field-induced entropy change (ΔS M ).

Multicaloric Cryocooling Using Heavy Rare-Earth Free La(Fe,Si)13-Based Compounds.

The transition toward a carbon-neutral society based on renewable energies goes hand in hand with the availability of energy-efficient technologies. Magnetocaloric cooling is a very promising refrigeration technology to fulfill this role regarding cryogenic gas liquefaction. However, the current reliance on highly resource critical, heavy rare-earth-based compounds as magnetocaloric material makes global usage unsustainable. Here, we aim to mitigate this limitation through the utilization of a multicaloric cooling concept, which uses the external stimuli of isotropic pressure and magnetic field to tailor and induce magnetostructural phase transitions associated with large caloric effects. In this study, La0.7Ce0.3Fe11.6Si1.4 is used as a nontoxic, low-cost, low-criticality multiferroic material to explore the potential, challenges, and peculiarities of multicaloric cryocooling, achieving maximum isothermal entropy changes up to -28 J (kg K)-1 in the temperature range from 190 K down to 30 K. Thus, the multicaloric cooling approach offers an additional degree of freedom to tailor the phase transition properties and may lead to energy-efficient and environmentally friendly gas liquefaction based on designed-for-purpose, noncritical multiferroic materials.

Pressurized Phase Transitions Cascade in BaMn2P2 and BaMn2As2

The structural analogue of iron-based superconductors the BaMn2P2 and BaMn2As2 compounds under hydrostatic pressure upto 140 GPa were studied within the framework of DFT + U. The transition from an antiferromagnetic insulator to an antiferromagnetic metal is observed under pressure of 6.4 GPa for BaMn2P2 and 8.3 GPa for BaMn2As2. This second order phase transition to the AFM metallic state provides an appropriate normal state for possible superconductivity in these materials. Moreover, further increase in pressure leads to a series of first order magnetostructural phase transitions between different antiferromagnetic phases, then to a ferromagnetic metal and finally to a nonmagnetic metal. In case of doping, these compounds could potentially be superconductors under pressure (above 6–8 GPa) with critical temperature growing under pressure.

Accelerating the Laser‐Induced Phase Transition in Nanostructured FeRh via Plasmonic Absorption

AbstractBy ultrafast x‐ray diffraction (UXRD), it is shown that the laser‐induced magnetostructural phase transition in FeRh nanoislands proceeds faster and more complete than in continuous films. An intrinsic 8 ps timescale is observed for the nucleation of ferromagnetic (FM) domains in the optically excited fraction of both types of samples. For the continuous film, the substrate‐near regions are not directly exposed to light and are only slowly transformed to the FM state after heating above the transition temperature via near‐equilibrium heat transport. Numerical modeling of the absorption in the investigated nanoislands reveals a strong plasmonic contribution near the FeRh/MgO interface. The larger absorption and the optical excitation of the electrons in nearly the entire volume of the nanoislands enables a rapid phase transition throughout the entire volume at the intrinsic nucleation timescale.

Magneto-structural phase transitions and two-dimensional spin waves in graphite

We have previously found experimental evidence for several quantum phenomena in oxygen-ion implanted of hydrogenated graphite: ferromagnetism, antiferromagnetism, paramagentism, triplet superconductivity, Andreev states, Little-Parks oscillations, Lamb shift, Casimir effect, colossal magnetoresistance, and topologically-protected flat-energy bands [1-6]. Triplet superconductivity results in the formation of Josephson junctions, thus with potential of being used for spintronics applications in the critical area of quantum computing. In this paper, we are showing new experimental evidence for the formation of two-dimensional (2D) spin waves in oxygen-ion enriched and in hydrogenated highly oriented pyrolytic graphite. The temperature evolution of the remanent magnetization M rem(T) data confirms the formation of spin waves that follow the 2D Heisenberg model with a weak uniaxial anisotropy. In addition, the step-like features also found in the temperature dependence of the electrical resistivity between insulating and metallic states suggest several outstanding possibilities, such as a structural transition, triplet superconductivity, and chiral properties.

The varying nature of the martensitic phase transition and associated entropy changes in a Co and Cr doped pseudo-ternary Heusler alloy system

We have investigated the magnetostructural phase transitions and the associated entropy changes in a system of three Heusler alloys, namely: Ni2Mn0.55Cr0.45Ga, Ni2Mn0.55Co0.10Cr0.35Ga, and Ni2.15Mn0.75Cr0.1Ga. All three alloys exhibited first-order martensitic phase transition. An inter-martensitic phase transition raised the magnetic and structural phase transition temperatures, and partially decoupled the said transitions. Furthermore, field magnetization measurements demonstrated that a significant reduction in magnetic hysteresis is achieved in the Ni2Mn0.55Co0.10Cr0.35Ga compound, resulting in improved effective refrigerant capacity values. The largest magnetic entropy change of −23.5 J/kg K and refrigeration capacity of 97.7 J/kg were observed in Ni2.15Mn0.75Cr0.1Ga. This observation of mitigated deficiencies in materials experiencing a first-order phase transition is relevant towards their application in magnetic refrigeration.

Effect of temperature and magnetic field induced hysteresis on reversibility of magnetocaloric effect and its minimization by optimizing the geometrical compatibility condition in Mn–Ni–Fe–Si alloy

The advancement of magnetic materials with coupled magneto-structural phase transition (MST) to fulfill the ultimate objectives of practical solid-state cooling applications requires a better understanding of the hysteresis phenomenon linked across the phase transition region along with the large magnetocaloric parameters. For the present sample Mn0.65Ni0.65Fe0.70Si, the MST is associated with a sharp jump in magnetization along with a small thermal hysteresis of ∼13 K. A giant isothermal magnetic entropy change (|ΔSMmax|) of ∼37.6 J kg−1 K−1 at 299 K and effective refrigerant capacity (RCeffe) of ∼214.3 J kg−1 under ΔH = 30 kOe is obtained with excellent compatibility between the martensite and austenite phases. The geometrical compatibility condition, i.e., very small (∼0.55%) deviation of the middle eigenvalue (λ2) from unity justifies the observation of small hysteresis in the present material. The investigation of hysteresis behavior under different extents of the driving forces (temperature or magnetic field) reveals that both the driving forces trigger equally the phase transition and are responsible equivalently for the hysteresis phenomenon. The present study provides a pathway to understand the complexity of the hysteresis behavior, its impact on the reversibility of magnetocaloric effect, and its minimization by optimizing the geometrical compatibility condition between the austenite and martensite phases.

Effect of Ta buffer layer on the structural and magnetic properties of stoichiometric intermetallic FeAl alloy

The magnetostructural phase transition in Fe50Al50 alloy with chemically ordered paramagnetic B2 and disordered ferromagnetic (FM) A2 phase has applications in spintronics such as phase-change magnetic memory and magnonic devices. We first conducted a systematic first-principles density functional theory study of the A2 and B2 phases in the Fe50Al50 alloy. A theoretical understanding of this equiatomic alloy’s electronic and spin-dynamical properties leads us to the experimental exploration of the FM A2 phase. Therefore, we deposit the 50 nm Fe50Al50 alloy thin film using sputtering and investigate the influence of the Ta buffer layer on its structural and magnetic properties. Our results reveal that the film with a buffer layer exhibits the A2 phase with appreciably higher saturation magnetization (848 emu/cc) than the film without a buffer layer (576 emu/cc). However, the surface roughness and Gilbert damping (α) slightly increase with the presence of the buffer layer from 0.41 to 0.56 nm and 4.35 × 10−3–4.94 × 10−3, respectively. The enhancement in α is due to extrinsic contributions induced by surface inhomogeneities.

Multi-field synergistic regulation enhanced multicaloric effect in all-d-metal Ni37Co13Mn35Ti15 alloy

Solid-state cooling technology has attracted great attention to replace traditional vapor-compression cooling technology due to its advantages of environmentally friendly, energy conservation, and high efficiency. However, the cooling performance of a single field (magnetic, stress or electric field) induced caloric effect is still insufficient. Recently, a larger multicaloric effect is expected to be achieved by the synergistic regulation of multiple fields. In this study, we choose all-d-metal Ni37Co13Mn35Ti15 alloy with magnetostructural phase transition and systematically study the multicaloric effect through the synergistic regulation of external stress and magnetic fields based on our homemade multicaloric effect testing device. The magnetic field and stress field play opposite effects on the phase transition, thus contributing contradictory caloric effect to multicaloric effect. By loading stress without magnetic field while unloading stress under magnetic field of 1.1 T, the stress hysteresis and energy hysteresis loss can be reduced by up to 45.2% and 54.8% in comparison with those obtained from a non-ideal regulation protocol. Moreover, the maximum adiabatic temperature change |ΔTad| during unloading increases by 24% from 6.3 K to 7.8 K with the application of magnetic field (1.1 T), suggesting a larger multicaloric effect than that of a single elastocaloric effect. These results prove that multi-field synergistic regulation is an effective means to enhance the multicaloric effect and reduce the hysteresis and energy loss of materials with the magnetostructural transition.

Reconstruction of thermomagnetic and phase transformation loops in magnetostructural transitions using selective integration of temperature first-order reversal curves (TFORC) distributions

The temperature variant of the first-order reversal curves (TFORC) analysis technique is emerging as a useful tool for the study of the thermal hysteresis in magnetocaloric alloys undergoing first-order phase transitions. This work demonstrates the capabilities of the TFORC technique for reconstructing and deconvoluting the reversible and irreversible components of thermomagnetic transitions through the integration of the TFORC distributions. Through numerical simulations, the influence of applying smoothing protocols, the presence of noise in the magnetization curves or the distance between the hysteretic first-order phase transition and the Curie transitions of the phases have been tested. By employing the appropriate integration protocol of TFORC distributions, the transformed phase fraction can be separated from the total thermomagnetic behavior. The results obtained from the numeric simulations have been confirmed by applying the proposed analysis methods to the experimental TFORC results of a Ni-Mn-In Heusler alloy sample undergoing magnetic first-order phase transition. In this way, the TFORC technique can be stablished as a valuable characterization method for magnetostructural phase transition materials.

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.

Giant irreversibility of the inverse magnetocaloric effect in the Ni47Mn40Sn12.5Cu0.5 Heusler alloy

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

Magnetocaloric effect in large temperature window on off-stoichiometric Ni-Mn-Ga-based Heusler alloys

Nickel-Manganese-Gallium-based Heusler alloys have been extensively studied for magnetic cooling applications with different compositions. However, the large hysteresis and narrow range of working temperatures associated with the first-order phase transition make limit their practical application. In this direction, the magnetocaloric effect was analyzed for three different off-stoichiometric compositions of Ni50+y+zMn25+x-yGa25‐x‐z alloys, where x, y, and z vary once at a time. Ni50Mn27Ga23 (NMG 1) and Ni54Mn21Ga25 (NMG 2) samples show large magnetocaloric effects across the second-order ferromagnetic to paramagnetic phase transition. Another sample Ni54Mn25Ga21 (NMG 3) undergoes coupled magneto-structural transition near room temperature with very low hysteresis loss (⁓4 J/kg) and a very high sensitivity of the martensite transition temperature (⁓3.6 K/T) with the field. By cyclic cooling protocol reliable magnetic entropy changes are found to be maxima of − 1.98 ± 0.09, − 1.90 ± 0.11 and − 3.53 ± 0.14 J/kg-K for 3 T field change with large effective RCP values of 235.8 ± 0.1, 161.5 ± 0.1 and 144.7 ± 0.3 J/kg for NMG 1, NMG 2 and NMG 3, respectively. The presence of inter-martensite transition along with the magnetic transition or magneto-structural phase transition widens the range of working temperature which effectively enhances the magnetic cooling performance of these materials. The TC and TM are tuned in Ni-Ga-Mn-based alloys by changing the chemical composition with considering the electron concentrations.

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.

Additive manufacturing of Ni-Mn-Sn shape memory Heusler alloy – Microstructure and magnetic properties from powder to printed parts

Ni-Mn-based Heusler alloys such as Ni-Mn-Sn show both elastocaloric and magnetocaloric effects during the magneto-structural phase transition, making these materials interesting for solid-state cooling applications. Material processing by additive manufacturing can overcome difficulties related to the machinability of the alloys, caused by their intrinsic brittleness. Since the magnetic properties and transition temperature are highly sensitive to the chemical composition, it is essential to understand and monitor these properties over the entire processing chain. In the present work, the microstructural and magnetic properties from gas-atomized powder to post-processed Ni-Mn-Sn alloy are investigated. Directed energy deposition was used for processing, promoting the evolution of a polycrystalline microstructure being characterized by elongated grains along the building direction. A complete and sharp martensitic transformation can be achieved after applying a subsequent heat treatment at 1173 K for 24 h. The Mn-evaporation of 1.3 at.% and the formation of Mn-oxide during DED-processing lead to an increase of the transition temperature of 21 K and a decrease of magnetization, clearly pointing at the necessity of controlling the composition, oxygen partial pressure and magnetic properties over the entire processing chain.

STRUCTURAL AND MAGNETIC TRANSITION IN MULTICOMPONENT R5X4 COMPOUNDS

The structure, magnetic, magnetothermal, and magnetoelastic properties of Gd5Si2-xGe2-xIn2x (x = 0–0.1) intermetallic compounds have been studied in the region of magnetostructural phase transitions. It is shown that introduction of indium creates the effect of negative pressure, leading to a change in the critical temperature of the magnetic phase transition in the monoclinic phase of the compounds studied and to partial separation of the magnetic and structural phase transitions in them.