Magnetic properties and magnetic entropy changes of La1-xPrxFe11.5Si1.5 compounds with 0 ≤ x ≤ 0.5

Magnetic properties and magnetic entropy changes in LaFe11.5Si1.5 have been investigated by partially substituting Pr by La. It is found that La1-xPrxFe11.5Si1.5 compounds remain cubic NaZn13-type structures even when the Pr content is increased to 0.5, i.e. x = 0.5. Substitution of Pr for La leads to a reduction in both the crystal constant and the Curie temperature. A stepwise magnetic behaviour in the isothermal magnetization curves is observed, indicating that the characteristic of the itinerant electron metamagnetic （IEM） transition above Tc becomes more prominent with the Pr content increasing. As a result, the magnetic entropy change is remarkably enhanced from 23.0 to 29.4 J/kg·K as the field changes from 0 to 5T, with the value of x increasing from 0 to 0.5. It is more attractive that the magnetic entropy changes for all samples are shaped into high plateaus in a wide range of temperature, which is highly favourable for Ericsson-type magnetic refrigeration.

Magnetic entropy change and magnetic phase transition of LaFe11.4Al1.6Cx （x=0-0.8） compounds

The unit cell volume and phase transition temperature of LaFe11.4Al1.6Cx compounds have been studied. The magnetic entropy change, refrigerant capacity and the type of magnetic phase transition are investigated in detail for LaFe11.4Al1.6Cx with x=0.1, All the LaFe11.4Al1.6Cx （x=0-0.8） compounds have the cubic NaZn13-type structure. The addition of carbon atoms brings about a considerable increase in the lattice parameter. The bulk expansion results in the change of phase transition temperature （Tc）, Tc increases from 187K to 269 K with x varying from 0.1 to 0.8, Meanwhile an increase in the lattice parameter can also cause a change of the magnetic ground state from antiferromagnetic to ferromagnetic. Large magnetic entropy change IASI is found over a large temperature range around Tc and the refrigerant capacity is about 322J/kg for LaFe11.4Al1.6C0.1. The magnetic phase transition belongs in weakly first-order one for x=0.1.

Magnetic entropy change involving martensitic transition in NiMn-based Heusler alloys

Our recent progress on magnetic entropy change（S） involving martensitic transition in both conventional and metamagnetic NiMn-based Heusler alloys is reviewed.For the conventional alloys,where both martensite and austenite exhibit ferromagnetic（FM） behavior but show different magnetic anisotropies,a positive S as large as 4.1 J·kg^-1·K^-1 under a field change of 0-0.9 T was first observed at martensitic transition temperature T M～197 K.Through adjusting the Ni：Mn：Ga ratio to affect valence electron concentration e/a,T M was successfully tuned to room temperature,and a large negative S was observed in a single crystal.The △S attained 18.0 J·kg^-1·K^-1 under a field change of 0-5 T.We also focused on the metamagnetic alloys that show mechanisms different from the conventional ones.It was found that post-annealing in suitable conditions or introducing interstitial H atoms can shift the T M across a wide temperature range while retaining the strong metamagnetic behavior,and hence,retaining large magnetocaloric effect（MCE） and magnetoresistance（MR）.The melt-spun technique can disorder atoms and make the ribbons display a B2 structure,but the metamagnetic behavior,as well as the MCE,becomes weak due to the enhanced saturated magnetization of martensites.We also studied the effect of Fe/Co co-doping in Ni 45（Co1-xFex）5 Mn36.6In13.4 metamagnetic alloys.Introduction of Fe atoms can assist the conversion of the Mn-Mn coupling from antiferromagnetic to ferromagnetic,thus maintaining the strong metamagnetic behavior and large MCE and MR.Furthermore,a small thermal hysteresis but significant magnetic hysteresis was observed around TM in Ni51Mn49-xInx metamagnetic systems,which must be related to different nucleation mechanisms of structural transition under different external perturbations.

Magnetoresistances and magnetic entropy changes associated with negative lattice expansions in NaZn13-type compounds LaFeCoSi

Magnetoresistances and magnetic entropy changes in NaZn13-type compounds La（Fel-xCox）11.9Si1.1 （x=0.04, 0.06, and 0.08） with Curie temperatures of 243 K, 274 K, and 301 K, respectively, are studied. The ferromagnetic ordering is accompanied by a negative lattice expansion. Large magnetic entropy changes in a wide temperature range from ～230 K to ～320 K are achieved. Raising Co content increases the Curie temperature but weakens the magnetovolume effect, thereby causing a decrease in magnetic entropy change. These materials exhibit a metallic character below Tc, whereas the electrical resistance decreases abruptly and then recovers the metal-like behaviour above Tc. Application of a magnetic field retains the transitions via increasing the ferromagnetic ordering temperature. An isothermal increase in magnetic field leads to an increase in electrical resistance at temperatures near but above Tc, which is a consequence of the field-induced metamagnetic transition from a paramagnetic state to a ferromagnetic state.

Martensitic transformation and giant magnetic entropy change in Ni_(42.8)Mn_(40.3)Co_(5.7)Sn_(11.2) alloy

The crystal structure, phase transition, and magnetocaloric effect in Ni42.8Mn40.3Co5.7Sn11.2 alloy are investigated by structure analysis and magnetic measurements. A large magnetic entropy change of 45.6 J/kg.K is obtained at 215 K under a magnetic field of 30 kOe （1 Oe = 79.5775 A.m-1）. The effective refrigerant capacity of Ni42.8Mn40.3Co5.7Sn11.2 alloy reaches 72.1 J/kg under an applied field changing from 0 to 30 kOe. The external magnetic field shifts the martensitic transition temperature about 3-4 K/10 kOe towards low temperature, indicating that magnetic field can retard the phase transition to a certain extent. The origin of large magnetic entropy change is discussed in the paper.

Relationship Between Magnetic Field-Induced Entropy Change and Magnetic Field

The ingots with the composition oi LaFe13-x Six （ 1.2 〈 x 〈 2.2） were prepared by arc-melting, and subsequently homogenized by annealing for a long time. The sample was mainly composed of a single NaZn13-type phase. The dependence of magnetization on the magnetic field was measured at different temperatures for LaFe13- xSix （ 1.2 ≤ x ≤ 2.2） compound, and the entropy change （△S） was calculated using Maxwell relation. The variation of AS with H was discussed according to both the Landau second-order phase transition theory and the scaling law under mean-field approximation. The results show that the relation of △S ∝ H^2/3 is satisfied for the LaFe13-x Six compounds. The parameters obtained by the simulation of peak value of entropy change can be used to determine the degree of first-order magnetic phase transition. The present work may be useful for the research of the magnetic refrigeration.

Magnetic Transition and Magnetic Entropy Change of Gd_5Si_(1.75)Ge_(1.75)Sn_(0.5)

Gd5Si1.75 Ge1.75 Sn0.5 was prepared by arc melting method. The crystal structure and magnetic properties were investigated by XRD and VSM, respectively. The magnetization of the Gd5Si1.75 Ge1.75 Sn0.5 alloy changes abruptly near its corresponding Curie temperature 269 K, possesses a typical first which means that the alloy order phase transition. The Gd5Si1.75Ge1.75 Sn0.5 adopts in Gd5Si2Ge2-type monoclinic structure at room temperature, the maximal magnetic entropy change at a magnetic field change of 1.8 T is as large as 16.7 J·kg^-1·K^-1, exceeding that of Gd about two times and is a little larger than that of Gd5Si2Ge2.

Magnetic Entropy Change of (Gd_(1-x)RE_x)_5Si_4(RE=Dy, Ho) Alloys

The magnetic properties, including Curie points, magnetic phases transition and magnetic entropy changes, of （Gd1-xREx）5Sin（RE = Dy, Ho） alloys were systematically studied. The results show that the alloys keep the Sm5Ge4 orthorhombic structures as Gd5Si4, and the Curie points of the alloys almost linearly decrease with increasing content of x, so that the Curie points can be adjusted by adding different concentrations of Dv or Ho in the alloys. The magnetic properties of these alloys obey second order transition. The costs of these alloys are cheaper than that of Gd- Si-Ge alloys because there is not expensive element such as Ge. The large magnetic entropy change at low fields （ 〈 2 T） and wide temperature ranges of these alloys suggest that they are suitable to be the gradient function materials and candidates of magnetic refrigerants at room temperature with low fields.

Magnetic Field Induced Entropy Change for La-Fe Based NaZn_(13)-Typed Compounds

Magnetic field induced entropy change was investigated for La-Fe based NaZn13-type compounds with magnetic first-order phase transition. In view of magnetic refrigeration at room temperature, the developing of the materials and the understanding of the entropy change were., reviewed. For La-Fe-Si compounds, the entropy change about 29 J·kg^- 1·K^-1 was obtained at 190 K under the magnetic field of 5 T.While a large entropy change of about 15 J·kg^-1·K^-1 near room temperature under 5 T can be obtained by the substitution of Co for Fe in the compounds. It is found that the entropy change is mainly composed of that contributed from magnetic ordering and crystal lattice. The large entropy change consumed by lattice contribution is mainly due to the magnetic ordering one.

Coexistence of positive and negative magnetic entropy changes in CeMn_2(Si_(1-x)Ge_x)_2 compounds

A series of CeMn2（Si1-xGex）2（x = 0.2, 0.4, 0.6, 0.8） compounds are prepared by the arc-melting method. All the samples primarily crystallize in the Th Cr2Si2-type structure. The temperature dependences of zero-field-cooled（ZFC） and FC magnetization measurements show a transition from antiferromagnetic（AFM） state to ferromagnetic（FM） state at room temperature with the increase of the Ge concentration. For x = 0.4, the sample exhibits two kinds of phase transitions with increasing temperature： from AFM to FM and from FM to paramagnetic（PM） at around TN-197 K and T C-300 K,respectively. The corresponding Arrott curves indicate that the AFM–FM transition is of first-order character and the FM–PM transition is of second-order character. Meanwhile, the coexistence of positive and negative magnetic entropy changes can be observed, which are corresponding to the AFM–FM and FM–PM transitions, respectively.

Study on structure and magnetic entropy changes of Ce_(2-x)Pr_xFe_(16.5)Co_(0.5) alloys

A series of Ce2-xPrxFe16.5Co0.5 alloys were prepared by arc melting under purified argon atmosphere. The structure and magnetic entropy changes in Ce2-xPrxFe16.5Co0.5 alloys were investigated by means of X-ray diffraction pattern and MPMS XL-7 magnetometer. The experimental results show that the crystal structure of Ce2-xPrxFe16.5Co0.5 alloys keeps in Th2Zn17-type rhombohedral, and the Curie temperature of Ce2-xPrxFe16.5Co0.5 alloys can be shifted to room temperature around by a composition adjustment. The magnetic entropy changes (-ΔSM) in Ce2-xPrxFe16.5Co0.5 alloys are relatively large, and a platform of magnetic entropy changes appears near the temperature TC. Ce2-xPrxFe16.5Co0.5 alloys are the potential working media for magnetic refrigeration with their stable chemical properties and especially low price.

Magnetic Phase Transition and Magnetic Entropy Change in La_(0.8)Pr_(0.2)Fe_(11.4)Si_(1.6) Compound

The magnetic properties and the phase transformation of the partial substitution of Pr for La in LaFe11.4Si1.6 have been investigated by the means of X-ray diffraction (XRD) and vibrating sample magnetic (VSM). The results indicated that the single phase NaZn13-type cubic structure is stabilized for the compound La0.8Pr0.2Fe11.4Si1.6 and large values of the isothermal magnetic entropy change SM around the curie temperature TC～194 K in relative low magnetic fields. The maximum value︱SM︱max～37.07 J/kg·K-1 under a field of 1.5 T. Such large MCEs are attributed to the sharp change of the magnetization at the Curie temperature, the field-induced IEM transition and a strong temperature dependence of the critical field BC.

Study of Magnetic Entropy Changes in Gd1-x Tx ( T = Ti, Cr, Fe and Cu) Alloys

Magnetic refrigeration techniques based on the magnetocaloric effect (MCE) were demonstrated as a promising alternative to conventional vapour-cycle refrigeration.Recently, scientists focused their research on room temperature magnetic refrigeration.The rare earth Gd metal is regarded as a prototype for room temperature magnetic refrigerant.Considering the various requirements in application, it is necessary to search for the magnetic refrigerant possessing qualities as good as Gd but having different Tc above or below room temperature.In this article, we report the magnetic entropy changes in Gd1 -xTx(T = Ti, Cr, Fe and Cu) alloys.With a small quantity of T atoms introduced in Gd, the Curie temperature increases.The values of magnetic entropy change in these alloys are almost the same as or a little less than that of Gd.But the refrigerant capacities of these alloys are obviously larger than that of Gd.All these facts suggest that Gd1-xTx(T = Ti, Cr, Fe and Cu) alloys may be good refrigerants for room temperature magnetic refrigeration.

Entropy change-induced elastic softening of lithiated materials

To understand the ＂elastic softening＂ of Li-Si alloys for the development of Li-ion batteries, the effect of stress-induced change of entropy on the mechanical properties of lithiated materials is examined within the theories of thermodynamics and linear elasticity, An approach is presented whereby the change of Gibbs free energy is governed by the change of the mixture entropy due to stress-induced migration of mobile atoms, from which the contribution of the change of the mixture entropy to the apparent elastic modulus of lithiated materials is determined. The reciprocal of the apparent elastic modulus of a lithiated material is a linear function of the concentration of mobile Li-atoms at a stress-free state and the square of the mismatch strain per unit mole fraction of mobile Li-atoms.

Simultaneously realizing good volumetric entropy change and mechanical strength of La_(0.8)Ce_(0.2)Fe_(11.51)Mn_(0.19)Si_(1.3)H_(y) plates

It is hard to get a high-strength La(Fe,Si)_(13)-based hydrides owing to the brittle feature of hydrides.In this work,we fabricated the La_(0.8)Ce_(0.2)Fe_(11.51)Mn_(0.19)Si_(1.3)plates through hot pressing at 1323 K for various time.Subsequently,the saturated hydrogenization is achieved at 593 K in H_2 atmosphere of 0.13 MPa for 210 min.The microstructure and magnetocaloric properties were investigated by an X-ray diffractometer,a scanning electron microscope and the Versa-Lab.Under magnetic fields of 0-2 T,the maximal volumetric entropy change is 91.4 mJ/(cm^(3)·K)at 297 K for the hydride plates.The hydride plate simultaneously has excellent mechanical properties with the maximum bending strength of 213 MPa,which suggest that the hot pressing followed by hydrogenation could be an effective route of fabricating La(Fe,Si)_(13)-based hydrides for the potential application in the magnetic refrigerator.

Thermodynamic theory of flotation for a complex multiphase solid -liquid system and high-entropy flotation

The flotation of complex solid–liquid multiphase systems involve interactions among multiple components,the core problem facing flotation theory.Meanwhile,the combined use of multicomponent flotation reagents to improve mineral flotation has become an important issue in studies on the efficient use of refractory mineral resources.However,studying the flotation of complex solid–liquid systems is extremely difficult,and no systematic theory has been developed to date.In addition,the physical mechanism associated with combining reagents to improve the flotation effect has not been unified,which limits the development of flotation theory and the progress of flotation technology.In this study,we applied theoretical thermodynamics to a solid–liquid flotation system and used changes in the entropy and Gibbs free energy of the reagents adsorbed on the mineral surface to establish thermodynamic equilibrium equations that de-scribe interactions among various material components while also introducing adsorption equilibrium constants for the flotation reagents adsorbed on the mineral surface.The homogenization effect on the mineral surface in pulp solution was determined using the chemical potentials of the material components of the various mineral surfaces required to maintain balance.The flotation effect can be improved through synergy among multicomponent flotation reagents;its physical essence is the thermodynamic law that as the number of compon-ents of flotation reagents on the mineral surface increases,the surface adsorption entropy change increases,and the Gibbs free energy change of adsorption decreases.According to the results obtained using flotation thermodynamics theory,we established high-entropy flotation theory and a technical method in which increasing the types of flotation reagents adsorbed on the mineral surface,increasing the adsorption entropy change of the flotation reagents,decreasing the Gibbs free energy change,and improving the adsorption efficiency and stability of the flotation reagents improves refractory mineral flotation.

Effect of impurity phase on corrosion resistance and magnetic entropy change for LaFe_(11.3)Co_(0.4)Si_(1.3)C_(0.15) magnetocaloric compound

Effect of impurity phase（α-Fe phase and La-rich phase） on corrosion resistance and magnetic entropy change of LaFe_（11.3）Co_（0.4）Si_（1.3）C_（0.15） compound was studied using scanning electron microscopy, potentiodynamic polarization, electrochemical impedance spectroscopy techniques and magnetism testing. With the decrease of impurity phase, the corrosion resistance of LaFe_（11.3）Co_（0.4）Si_（1.3）C_（0.15） compound was first enhanced and then slightly impaired. Corrosion resistance could be significantly improved by the decrease of α-Fe phase. However, the matrix phase was corroded if the La-rich phase as anode was too few. This caused the corrosion resistance to decrease slightly. After immersing the sample in distilled water for 15 d, -？S_（max） of the samples annealed for 3, 12 h, 3 and 7 d decreased about 50%, 41%, 16% and 17%, respectively.

Large magnetic entropy change and adiabatic temperature rise of a ternary Gd_(34)Ni_(33)Al_(33) metallic glass

A low cost Gd_(34)Ni_(33)Al_(33) metallic glass with excellent magnetocaloric properties was successfully prepared in the present work.The magnetic properties of the ribbons were measured by constructing the relationship of magnetic entropy change(-ΔS_(m)) on temperature as well as magnetic field.The amorphous alloy shows typical magnetocaloric behaviors,large maximum-ΔS_(m)(11.06 J/(kg·K) under 5 T)and adiabatic temperature rise(4.3 K under 5 T) near 40 K,indicating that the low cost Gd_(34)Ni_(33)Al_(33) metallic glass is a good candidate material for low temperature magnetic refrigeration.

Effect of proportion change of aluminum and silicon on magnetic entropy change and magnetic properties in La0.8Ce0.2Fe11.5Al1.5-xSix compounds

The microstructure, magnetic entropy changes, hysteresis and magnetic properties of La_（0.8）Ce_（0.2）Fe_（11.5）Al_（1.5–x）Si_x（x=0.4, 0.5, 0.6, 0.7） compounds were studied by X-ray diffraction（XRD） and a superconducting quantum interference device magnetometer（SQUID）. The results showed that all the compounds presented cubic Na Zn13-type structure. Their Curie temperatures changed complicatedly with decreasing Al content due to changes of antiferromagnetic and ferromagnetic interaction. Under a field change from 0 to 2 T, the maximum magnetic entropy change for La_（0.8）Ce_（0.2）Fe_（11.5）Al_（1.1）Si_（0.4）, La_（0.8）Ce_（0.2）Fe_（11.5）Al_（1.0）Si_（0.5）, La_（0.8）Ce_（0.2）Fe_（11.5）Al_（0.9）Si_（0.6） and La_（0.8）Ce_（0.2）Fe_（11.5）Al_（0.8）Si_（0.7） were found to be –9.6, –4.8, –5.8 and –11.7 J/（kg·K）, respectively. Moreover, their hysteresis losses were 1.13 J/（kg·K） or less. The large magnetic entropy changed and small hysteresis losses made them potential candidates for practical magnetic refrigeration application.

Giant isothermal entropy change In(111)-oriented PMN-PT thin film

An isothermal entropy change of 240 nm(111)-oriented PMN–PT 65/35 film near the ferroelectric Curie temperature,relative cooling power(RCP)and change of heat capacity have been investigated.The extracted data characterized giant isothermal entropy change of more than 16 J/kgK in electric field shift△E of 455 kV cm^(-1),which is nearly twice than that found for PbZr_(0.9)5Ti_(0.05)O_(3)thin film at 492 kV cm^(-1)near the Curie point.Furthermore,the RCP≈700 J/kg and change of heat capacity≈233 J/kgK in electric field shift△E of 747 kV cm^(-1).