Magnetocaloric Response Research Articles

Magnetic Properties of Melt-Spun CoMnSi(B) Alloys

MnCoSi and MnCoSiB0.5 alloys were obtained by melt-spinning technique in order to attain polycrystalline microstructures with average grain sizes well below 10 microns. Phase distribution studied by X-ray analysis indicated single-phase materials with orthorhombic structure and TiNiSi-type crystal symmetry. Chemical homogeneity was verified by means of scanning electron microscopy, whereas magnetic behavior corresponded to soft magnetic materials with coercivity values lower than 20 Oe and saturation magnetization of 80 emu/g. Magnetocaloric response of these MnCoSiB alloys was characterized by a maximum magnetic entropy change of 1.0 J/kg K (for a magnetic field variation of 2.0 Tesla) and attractive refrigerant capacity over 100 J/kg, which represents a significant enhancement respect to equivalent MnCoGe alloys.

Evidence of a moderate refrigerant capacity in cation disordered Ruddlesden-Popper compounds A1.4Sr1.6Mn2O7 (A = La, Pr, Nd) probed with various figures of merit

We investigated the influence of structural disorders on the magnetic and magnetocaloric (MC) properties upon A-site rare-earth substitution in A1.4Sr1.6Mn2O7 (A = La, Pr, Nd) Ruddlesden-Popper (R–P) compounds. The samples were produced through the solid-state method, and the structural analysis indicated formation of R–P phase with the Jahn-Teller distortion parameter varying from highest in La1.4Sr1.6Mn2O7 (LSMO) to Nd1.4Sr1.6Mn2O7 (NSMO) and followed by Pr1.4Sr1.6Mn2O7 (PSMO). Hence, the magnetization value was increased in LSMO sample implying an enhanced interbilayer and interlayer spin correlations. It resulted in a high value of MC parameters like temperature average entropy change (TEC) and relative cooling power (RCP) of 4.21 J/kgK and 87 J/kg for LSMO, while lowest value of 0.53 J/kgK and 27 J/kg for PSMO respectively, at 2.5 T field. The room temperature MC response in PSMO, whereas a large TEC in LSMO and NSMO compounds advocate their candidacy in broad range of refrigeration applications.

Analysis of magnetocaloric effect in parallel Ni-Mn-Ga Heusler alloy nanowires

In this article, a magnetocaloric effect of electrodeposited Ni-Mn-Ga - based Heusler nanowires is presented using the indirect approach. The structural characterization revealed that the prepared nanowires exhibit a martensitic transformation capability above room temperature (at 350 K). The martensitic transformation results in a relatively high magnetic entropy change of> 2.5 J.kg−1. K−1. Moreover, the magnetocaloric effect analysis reveals a maximum magnetic entropy change at a moderate magnetic field of only 2 T. The presented cheap fabrication method, together with the strong magnetocaloric response of the nanowires at moderate magnetic fields, opens up new possibilities in the field of nanosized Heusler alloys operating as refrigerants, actuators, or sensors

Magnetocaloric effect in (Tm67Cu33)80Al20 amorphous alloy

The new amorphous alloy with the composition of (Tm67Cu33)80Al20 is designed with the deep binary eutectic composition of Tm67Cu33. The (Tm67Cu33)80Al20 alloy exhibits a fully amorphous structure. As the Cu and Al elements have no magnetic moment, there is only Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetic interaction existing in (Tm67Cu33)80Al20 amorphous alloy, leading to its low Curie temperature (TC) (4.4 ± 0.3 K). The peak value of the magnetic entropy change and refrigeration capacity of the (Tm67Cu33)80Al20 amorphous alloy under a magnetic field change of 5 T are 13.4 ± 0.7 J kg−1K − 1 and 174.2 ± 10.5 J kg−1, respectively. The (Tm67Cu33)80Al20 amorphous alloy possesses a relatively high magnetocaloric response compared with that of the reported RE-based alloys with the similar TC. These results indicate that the (Tm67Cu33)80Al20 amorphous alloy could be a promising candidate material for magnetic refrigeration applications in the liquid helium temperature range.

Manipulation of thermal hysteresis and magnetocaloric effect in the Ni-Co-Mn-In alloys through lattice contraction: Effect of Ge substitution for In

First-order magnetostructural transformation can be utilized to generate giant magnetocaloric effect for the magnetic refrigeration applications, but the intrinsic hysteresis always cripples the refrigeration efficiency. In this work, the strategy of lattice contraction was exploited to manipulate the thermal hysteresis and magnetocaloric response in the Ni-Co-Mn-In magnetocaloric alloys. Such strategy was effectuated by using Ge to replace In on account of the relatively smaller atomic radius of Ge, yielding a significant reduction in the thermal hysteresis. In a Ni46Co3Mn37In10Ge4 alloy with the combination of low thermal hysteresis of ∼4 K and large magnetization difference of 83.1 Am2kg−1 associated with the magnetostructural transformation, giant effective refrigeration capacity RCeff of 311 Jkg−1 and reversible entropy change ΔSM up to 22.8 Jkg−1K−1 were demonstrated by varying the field of 5 T. Besides, a large reversible adiabatic temperature change ΔTad of –3.0 K was also obtained by using a low field change of 1.5 T. Based on the displacement gradient tensor determined by the orientation relationship governing the martensitic transformation, it was presented that Ge substation for In effectively decreased the lattice misfit, thus lowering the elastic energy accompanying the structural transformation and the related transformation hysteresis.

Ionic radius effect on the evolution of the griffiths phase and the magnetocaloric response at low temperature of A2Mn2O7 (A: Fe, Al and La)

In the present paper a comparative research study has been conducted on the magnetic and magnetocaloric response of the materials of A2Mn207 (A: Fe, Al and La) oxides. . The XRD refinement analysis suggests that the A2Mn207 oxides are crystallized in monoclinic structure with space group P2/m. The thermal evolution of the magnetization reveals a ferromagnetic transition and a presence of a Griffith's phase at low temperature. A2Mn207 oxides exhibit a clear correlation between the ionic radius rA3+, in the A-site, and the magnetic transition temperature and that of Griffiths. However, this correlation is not obvious for the value of the universal exponent λ. In addition, the current study reveals an increase in the Relative Cooling Power (RCP) value with a decrease in ionic radius. Furthermore, the magnetocaloric effect (MCE) value, has been found to be exploited over a wide temperature range by increasing the cationic radius rA3+.

Prediction of Magnetocaloric Effect Induced by Continuous Modulation of Exchange Interaction: A Monte Carlo Study.

A magnetic-to-thermal energy conversion, derived from the continuous modulation of intrinsic exchange energy, is conceived and studied by performing Monte Carlo simulations. On the basis of thermodynamics and Weiss's molecular field theories, we modified the Maxwell formula, where the magnetic entropy change (∆SM) is calculated by integrating the temperature derivative of magnetization under a continuously increasing exchange interaction, rather than an external magnetic field, from zero to a given value. For the conventional ∆SM induced through increasing magnetic field, the ∆SM maximum value is enhanced with increasing magnetic field, while the ∆SM peak temperature is weakly influenced by the magnetic field. On the contrary, the ∆SM induced by changing the exchange interaction is proportional to the exchange interaction while suppressed by a magnetic field. Another feature is that the relative cooling power calculated from the ∆SM induced by changing the exchange interaction is fully independent of the magnetic field perspective for obtaining the magnetically stabilized self-converted refrigerants. The controlled variation of exchange interaction could be realized by partial substitution or the application of hydrostatic pressure to lower the cost of magnetic energy at no expense of magnetocaloric response, which opens an avenue to develop the practical and energy-saving devices of conversion from magnetic energy to thermal energy, highly extending the material species of the magnetocaloric effect.

Contrasting response on magnetocaloric effect and refrigeration capacity due to Ni or Mn substitution by Fe in Ni-Mn-In-Co-Fe alloys

We set the composition of two Ni-Mn-In-Co-Fe alloys as (Ni46.8Fe1.2)Co2Mn36.5In13.5 and Ni48Co2(Mn34.5Fe2)In13.5 in order to display the martensitic transformation near to room temperature. Under a magnetic field change of 5 T the polycrystalline low Co content alloys displayed a large magnetocaloric effect ΔSMag of 15.5 and 20.0 Jkg-1K-1; and giant refrigeration capacity RCFWHM up to 422 and 292 Jkg-1 for (Ni46.8Fe1.2)Co2Mn36.5In13.5 and Ni48Co2(Mn34.5Fe2)In13.5, respectively. The XRD patterns showed cubic L21 structure with space group 225 in both alloys and via Rietveld refinement negligible differences were found in lattice parameter of 0.598(7) and 0.598(9) nm for (Ni46.8Fe1.2)Co2Mn36.5In13.5 and Ni48Co2(Mn34.5Fe2)In13.5, respectively. Nevertheless, the magnetocaloric response in the alloys exhibited remarkable dissimilarities. Whilst the applied magnetic field shifted the martensitic transformation − 3.4 KT-1 in the Ni48Co2(Mn34.5Fe2)In13.5 alloy this sensibility increased up to − 6.8 KT-1 in the (Ni46.8Fe1.2)Co2Mn36.5In13.5 alloy; consequently the span in the Full Width Half Maximum of the ΔSMag(T) curve was 17 and 32 K, respectively.

Room-temperature polymer-assisted additive manufacturing of microchanneled magnetocaloric structures

Magnetic refrigeration is an energy-efficient, sustainable, environmentally-friendly alternative to the conventional vapor-compression cooling technology. There are several magnetic refrigerator device designs in existence today that are predicted to be highly energy-efficient, on condition that suitable working materials can be developed. This challenge in manufacturing magnetocaloric devices is unresolved, mainly due to issues related to shaping the mostly brittle magnetocaloric alloys into thin-walled channeled regenerator structures to facilitate efficient heat transfer between the solid refrigerant and the heat exchange fluid in an active magnetic regenerator (AMR) cooling device. To address this challenge, a novel extrusion-based additive manufacturing (AM) method has been developed to 3D print microchanneled magnetocaloric structures. The printing ink consists of magnetocaloric powders, a polymer binder, and multiple solvents to achieve desirable shear-thinning property, which is critical for a robust printing process. Acting as a sacrificial binding agent for the magnetic powders, the polymer binder holds the 3D printed structures in place and is removed subsequently using a two-step heat-treatment process. To demonstrate the effectiveness of the fabrication process, spatially designed microchannels with minimum dimensions of 150 µm were achieved using nanoscaled La 0.6 Ca 0.4 MnO 3 powders (diameter~10 nm). Results indicate that the crystallographic properties and magnetofunctional response of the sintered 3D printed samples are comparable to that of the precursor powders. Overall, this study provides a promising route for realizing low-cost magnetic regenerators, thus potentially eliminating one of the main barriers to the commercialization of magnetic cooling technology. • Room temperature extrusion-based method for 3D printing magnetocaloric structures. • Significant magnetocaloric response in 3D printed LCMO scaffolds (ΔS=4.9 J/kg-K at 5 T). • Microchanneled magnetocaloric structures with record spatial resolution (dia∼150 µm). • Overcoming a crucial barrier to the commercialization of magnetic cooling technology.

Magnetic and magnetocaloric properties of the double perovskite Sm-doped Ho2CoMnO6

The polycrystalline compounds Ho2-xSmxCoMnO6 (0 ≤ x ≤ 1) was synthesized by the conventional solid-state process. The structural study has been solved by X-ray powder diffraction (XRD) indicating that all studied samples adopt a monoclinic structure with the space group P21/n. The magnetic properties of the Ho2-xSmxCoMnO6 (0 ≤ x ≤ 1) compounds, show a ferromagnetic transition at the Curie temperature (TC), thus the latter increases with Sm doping. Finally, the magnetocaloric effect (MCE) study revealed that the maximum magnetic entropy change (-ΔSM)max, at TC under a magnetic-field-change (h = μ0ΔH) of 5 T, decreases with Sm doping from 4.97 to 1.86 J kg−1 K−1 for x = 0 to x = 1, respectively. The results show that Sm doping increases TC but lowers the magnetocaloric response, but obtained values of Relative Cooling Power (RCP) and adiabatic temperature (ΔTad) remain reasonably high. Hence, the investigated compounds, given their high stability and eco-friendly, could be promising materials for magnetic refrigeration technology.

All-d-metal Ni(Co)-Mn(X)-Ti (X = Fe or Cr) Heusler alloys: Enhanced magnetocaloric effect for moderate magnetic fields

All-d-metal Ni(Co)-Mn-Ti Heusler alloys show high magnetocaloric/barocaloric effects ascribed to the occurrence of a martensitic transformation together with excellent mechanical properties. However, high magnetic fields are needed to fully drive the transformation and to obtain their maximum responses. To further tune the martensitic transition and the associated magnetocaloric response, we systematically investigate the role of partial Mn substitution by Fe or Cr on the parent composition Ni36Co14Mn35Ti15. On the one hand, Cr doping increases the entropy change of the transformation but causes a tighter overlap of both martensitic and Curie transitions. This significantly reduces the magnetization difference between austenite and martensite and, consequently, strongly decreases the magnetocaloric response. On the other hand, Fe doping reduces the entropy change of the transformation and separates both martensitic and Curie transitions while keeping the magnetization difference among both phases. These two combined features reduce the magnetic field needed to completely drive the martensitic transformation and leads to higher and broader isothermal entropy change peaks for moderate magnetic field changes, reaching up to 25% enhancement for 2 T when compared to the undoped alloy.

Microstructure, magnetism and critical behavior of hot pressed Ni-Mn-Ga/Al magnetocaloric composites with enhanced thermal conductivity and mechanical properties

In the application of magnetic refrigeration technology, magnetocaloric materials are required to possess large magnetocaloric effect and broad working temperature range with good thermal conductivity and mechanical properties. To address this elusive combination of properties, we prepared Ni-Mn-Ga/Al magnetocaloric composites via hot pressing method. Phase composition and element distribution revealed the influence of sintering temperature on composites' microstructure. The magnetic properties and magnetocaloric effect of hot pressed Ni-Mn-Ga alloy and Ni-Mn-Ga/Al composites were studied, indicating their largely broadened working temperature range of 71 K and maximum magnetic entropy change of 2.2–3.0 J/(kg K). Based on thermomagnetic measurements, critical behavior was investigated via modified Arrott plots and Kouvel-Fisher method, and mean-field theory model could best explain the samples' critical behavior. The Ni-Mn-Ga/Al composite also possessed enhanced fracture stress of 306 MPa, much higher than that of bulk Ni-Mn-Ga alloy by arc melting. The good magnetocaloric response of the composites, which is comparable or even better than that of many other Ni-Mn-Ga particle and microwire counterparts, is accompanied by improved thermal conductivity and mechanical properties, extending the applicability of magnetocaloric materials with large specific surface area. The novel findings of this systematic study offer new insights into magnetocaloric composites and provide an approach to reach a significant balance when fulfilling multiple requirements of magnetic refrigeration technology. • Hot pressed Ni-Mn-Ga/Al was thoroughly studied in view of refrigeration application. • HP samples had good MCE comparable to their counterparts with reduced length scale. • MAP and KF method were used to compute critical exponents and study critical behavior. • Order of phase transition was ascertained by both Banerjee criterion and exponent n. • Thermal conductivity and mechanical properties were improved after making composites.

Magnetocaloric response with significant mechanical efficiency in frustrated intermetallic compound Pr2Co0.86Si2.88

Magnetically frustrated materials are considered as a promising unconventional members of caloric materials. Here, the magnetocaloric properties of the frustrated Pr2Co0.86Si2.88 have been investigated and discussed with the aid of density functional theory (DFT) calculations. The material exhibits a magnetic entropy change (−ΔSM) of 13.1 J/kg-K for ΔH = 70 kOe around low-temperature transition TL ∼ 4 K associated with the antiferromagnetic coupling between localized Pr-4f and itinerant Co-3d moments. Despite the absence of any long-range magnetic order, the obtained − ΔSM is one of the highest among the known Pr-based good magnetocaloric materials at cryogenic temperature range. It also exhibits a relative cooling power (RCP) of ∼ 201 J/kg and an adiabatic temperature change of 6.3 K around TL at 70 kOe. Moreover, the compound also exhibits a high mechanical efficiency and moderate electrical efficiency, being beneficial for possible technological applications.

The Magnetocaloric Behaviors of Gd-based Microwire Arrays with Different Curie Temperatures

The desirable table-like magnetocaloric effect (MCE) was obtained by designing a new magnetic bed, which comprises three kinds of Gd-based microwire arrays with different Curie temperatures (TC). The TC interval among these wires is ~10 K. This new magnetic bed shows a smooth ferromagnetic to paramagnetic transition at ~100 K. In addition, a table-like magnetic entropy change (ΔSM) was obtained, ranging from ~92 K to ~107 K, with a maximum entropy change (−ΔSMmax) of 9.42 J/kgK for a field change (μ0ΔH) of 5 T. Notably, the calculated results of −ΔSM(T) corresponded to the experimental data for μ0ΔH = 5 T, suggesting that a microwire array-based magnetic bed with desirable magnetocaloric response can be designed. In addition, it was shown that a larger table-like temperature range and cooling efficiency can be achieved by increasing the interval of TC among microwire arrays. These important findings indicate that the newly designed magnetic bed is very promising for active magnetic cooling technology.

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.

Tunable magnetic properties and magnetocaloric response of Mn0.5Fe0.5NiGe alloys by heat treatments

The hexagonal MM’X alloys with magnetocaloric effect have been considered as potential solid-state magnetic refrigeration materials. In this work, the Mn0.5Fe0.5NiGe alloys with different heat treatments were fabricated and investigated the structural, magnetic and magnetocaloric properties. The results show all alloys crystalize the TiNiSi-type orthorhombic phase. The Curie temperature of martensite (TCM) can be tailored from 168 K to higher temperature of 240 K with the increase of annealing-quenching temperature. The maximum values of magnetic entropy change (ΔSm), refrigerant capacity (RC) and relative cooling power (RCP) reach −1.3 J/kgK, 67.1 J/kg, 80.1 J/kg with the magnetic field change of 5 T (ΔH = 5 T), respectively. The results indicate that the method of heat treatments is an efficient way to enhance the magnetic response properties in MnNiGe-based alloys.

Magnetic performance of amorphous manganese nanoparticles doped with rare earth elements

We studied magnetic and magnetocaloric response in nanoparticle manganite oxides (ABO3-type manganese oxides), which were chemically prepared by sol–gel method with different composition RMnO3 (R = Gd, Tb, Ce) (GMO, TMO, CMO). The structural characterization was performed by EDX (Energy-dispersive X-ray spectroscopy) technique, using TEM (Transmission electron microscopy) methods and XRD and confirmed the nanosized character and morphology of studied manganites. Despite the amorphous character of the samples RMnO3 (R = Gd, Tb), the relatively large magnetic entropy change − ΔSM(7 K) ∼15 J/kgK and − ΔSM (13 K) ∼8 J/kgK has been observed in the case of GMO and TMO, respectively. Sample CMO, despite of its crystalline character, exhibits the lowest magnetic entropy change and the magnetic properties are affected by Jahn-Teller distortion in Mn3O4 nanoparticles (NPs). All systems GMO, TMO, CMO exhibit the Arrott plots with linear behavior and positive slopes that is according to the Banerjee criterion a signature of the second order phase transition. This is in line with our conclusions on the presence of AFM-PM phase transitions in the systems that we drew from ZFC-FC data. Our results confirm that also amorphous manganites especially with Gd show feasible properties for potential magnetic refrigeration applications.

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.

Formation and magnetocaloric properties of the amorphous Fe88La7-xCexB5 (x = 0, 1, 3, 5, 7) ribbons

The formability and magnetocaloric response of the amorphous Fe88La7-xCexB5 (x = 0, 1, 3, 5, 7) alloys were studied in this work. When the alloys were prepared into ribbons with a thickness of ∼40 μm, only the Fe88La7-xCexB5 (x = 3, 5, 7) ribbons are fully amorphous and the best glass former is Fe88La2Ce5B5. The amorphous ribbons show rather high magnetic entropy change (−ΔSm) peak, while the Curie temperature of these ribbons decreases with the Ce addition. Based on these results, several amorphous hybrids with flattened −ΔSm profiles were designed. Among these, the hybrid composed of 45% (wt.%) Fe88Ce7B5, 3% (wt.%) Fe88La2Ce5B5 and 52% (wt.%) Fe86Ce7B5Co2 amorphous ribbons is considered to be a better candidate for the working materials of a domestic magnetic air conditioner.

Competing ferromagnetic and antiferromagnetic interactions drive the magnetocaloric tunability in Gd55Co30NixAl15−x microwires

We have employed Gd55Co30NixAl15−x (x = 10, 5 and 0) amorphous microwires as a model system to unravel the impact of multiple magnetic interactions on the magnetism and the magnetocaloric behavior in Gd-alloy microwire systems. Our study shows that in addition to the RKKY ferromagnetic (FM) interaction (Gd-Gd), antiferromagnetic (AFM) interactions (Gd-Co, Gd-Ni) coexist and contribute to the magnetic and magnetocaloric response of the system. The dilution effect of Al element on the FM Gd-Gd interaction is responsible for the decrease of the Curie temperature (TC), whereas the increase of the saturation magnetization (MS) is originated from the reduced AFM Gd-Ni interaction. A thorough analysis of critical exponents suggests that the presence of the AFM interactions hinders the system to exhibit a long-range FM order below the TC. Adjusting these interactions is shown to preserve the large refrigerant capacity (RC) while tuning the TC over a wide temperature range, which is desirable for active magnetic refrigeration.