Magnetocaloric effect of (Gd_(1-x)Nd_x)Co_2 alloys in low magnetic field

The phases and magnetocaloric effect in the alloys （Gd1-xNdx）Co2 with x = 0, 0.1, 0.2, 0.3, and 0.4 were investigated by X-ray diffraction analysis and magnetization measurement. The samples are single phase with a cubic MgCu2-type structure. The To decreases obviously with increasing Nd content from 404 K of the alloy with x = 0 to 272 K of the alloy with x = 0.4; forx = 0.3, the To is 296 K, which is near room temperature. In the samples （Gd1-xNdx）Co2 with x = 0.0, 0.1, 0.2, 0.3, and 0.4, the maximum magnetic entropy change is 1.471, 1.228, 1.280, 1.381 and 1.610 J·kg^-1·K^-1, respectively, in the applied field range of 0-2.0 T. The results of Arrott plots confirmed that the transition type were second order magnetic transition forx = 0, 0.3, and 0.4.

Large Magnetic Entropy Effect in La_(2/3)Ca_(1/3)MnO_3

The magnetocaloric effect in the colossal magnetoresistance material La_(2/3)Ca_(1/3)MnO_3 was studied. From the measurements of temperature dependence of magnetization in various magnetic fields, the large magnetic entropy change associated with the ferromagnetic-paramagnetic transition was discovered. This result suggests that perovskite manganites are suitable candidates as working substance in magnetic refrigeration technology.

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.

Magnetocaloric effect of (Gd_(1-x)Ce_x)Co_2 compounds in low magnetic fields

The phases in the compounds （Gd1-xCex）Co2 with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 were investigated by X-ray diffraction, and the magnetocaloric effect for x = 0-0.4 was studied by magnetization measurements. The samples are almost single phase with a cubic MgCu2-type structure for x = 0-0.5. The magnetization decreases with an increase in Ce content. There is almost no magnetic transition for x = 0.5 at 100-350 K. The Curie temperature （To） of the （Gd1-xCex）Co2compounds with x from 0.1 to 0.4 are 350, 344, 340, and 338 K respectively. The maximum magnetic entropy change is 2.34 J·kg^-1·K^-1 when x = 0.3. The results of Arrott plots show that the magnetic phase transition is second-order magnetic phase transition in these compounds.

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.

Magnetocaloric effects in RT X intermetallic compounds(R = Gd–Tm, T = Fe–Cu and Pd, X = Al and Si)

The magnetocaloric effect（MCE） of RT Si and RT Al systems with R = Gd–Tm, T = Fe–Cu and Pd, which have been widely investigated in recent years, is reviewed. It is found that these RT X compounds exhibit various crystal structures and magnetic properties, which then result in different MCE. Large MCE has been observed not only in the typical ferromagnetic materials but also in the antiferromagnetic materials. The magnetic properties have been studied in detail to discuss the physical mechanism of large MCE in RT X compounds. Particularly, some RT X compounds such as Er Fe Si,Ho Cu Si, Ho Cu Al exhibit large reversible MCE under low magnetic field change, which suggests that these compounds could be promising materials for magnetic refrigeration in a low temperature range.

Magnetocaloric Effect in Colossal Magnetoresistance Material (La_(0.6)Dy_(0.1))Sr_(0.3)MnO_3

The magnetocaloric effect in the A-site doping colossal magnetoresistance material (La_(0.6)Dy_(0.1))Sr_(0.3)MnO_3 was studied. From the measurement and calculation of isothermal magnetization (M-H) curves under various temperatures, a large magnetocaloric effect with ferromagnetic-paramagnetic transition, additional magnetism exchange action introduces additional magnetic entropy change was discovered. This result suggests that (La_(0.6)Dy_(0.1))Sr_(0.3)MnO_3 is a suitable candidate as working substance at room temperature in magnetic refrigeration technology.

Influence of Sn substitution for Co in RCo_2 (R= Gd,Tb,Dy) alloys on the structure and magnetocaloric effect

The phases and the magnetocaloric effect in the alloys R（Co1-xSnx）2 with X = 0, 0.025, 0.050, 0.075, and 0.100 were investigated by X-ray diffraction analysis and magnetization measurement. The substitution of Sn in RCo2 is limited. The cubic MgCu2-type structure for the alloys of RCo2 was confirmed by X-ray powder diffraction and the remaining alloys mainly consisted of the RCo2 phase, along with some RCo3 and R5Sn3 impurity phases. The impurity phases increase with the increase of Sn content. The Tc of the alloys is not very sensitive to the Sn substitution for Dy（Co1-xSnx）2 and Tb（Co1-xSnx）2, whereas in Gd（Co1-xSnx）2, the Curie temperatures significantly increase. The maximum magnetic entropy changes in the alloys Dy（Co1-xSnx）2 （x = 0, 0.025, 0.050, 0.075） are 5.78, 5.43, 3.88, and 2.98 J·kg^-1·K^-1, respectively, and those in the Tb（Co1-xSnx）2 （x = 0, 0.025） are 3.44, and 2.29 J·kg^-1·K^-1 respectively in the applied field change of 0-2.0 T.

Research Advance on Magnetocaloric Effect of La-Fe-M(Al, Si) Compounds

Recent research progress on magnetocaloric effect of La-Fe-M (M = Al, Si) compounds was presented. La-Fe-M (M = Al, Si) compounds of high Fe content are excellent soft magnetic materials with NaZn13 structure. The Curie temperature of the compounds can be increased by substituting small amount of Co for Si, Al. The La(Fe1-xCoy)(x)Si13-x compounds with an appropriate ratio of Co and Si can produce giant magnetocaloric effect comparable to that for Gd5Si2Ge2 at room temperature. The La (FexSi1-x)(13) doped with H can also produce giant magnetocaloric effect at room temperature, which is much greater than that for Gd. For La (FexSi1-x)(13) compounds with low Si or high Si contents. The nature of phase transition near Curie temperature induced by temperature and magnetic field was described in detail.

Phase transition and magnetocaloric effect of Ni_(55.2)Mn_(18.6)Ga_(26.2-x)Gd_x (x=0,0.05,0.15) alloys

Phase transition process and magnetic entropy change -Delta S of Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys were studied. Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys still underwent simultaneous structural and magnetic transitions and transform from ferro-magnetic martensitic phase to paramagnetic austenitic phase during heating. Under a field of 2 T, the maximum magnetic entropy change -Delta S-M of Ni55.2Mn18.6Ga26.15Gd0.05 alloy was 7.7 J/kg.K at 317 K during heating and 8.6 J/kg.K at 314 K during cooling while it was 11.8 J/kg.K at 317 K in Ni55.2Mn18.6Ga26.05Gd0.15 alloy during heating.

Phase structure and magnetocaloric effect of (Tb_(1–x)Dy_x)Co_2 alloys

Phase structure and magnetocaloric effect of （Tb1-xDyx）Co2 alloys with x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 were investigated using X-ray diffraction analysis, differential thermal analysis, and magnetization measurement. The samples were single phase with cubic MgCu2- type structure; with the increase of Dy content, Tc decreased from 240 K （TbCo2） to 130 K （DyCo2）, and the maximum magnetic entropy change ｜ △SM,max｜ increased from 3.133 to 8.176 J/kg-K under low magnetic field of 0-2 T. The Arrott plot and the change of ｜△SM,max｜ showed that magnetic phase transition from second order to first order occured with the increase of Dy content between x=-0.6 and 0.8.

Influence of the Erbium Substitution for Gd in Gd_5Si_(1.8)Ge_(2.2) Alloys on the Magnetocaloric Effect in Low-Field

The phases and magnetocaloric effect in the alloys (Gd1-xErx)5Si1.8Ge2.2 with x=0, 0.1, 0.2 and 0.3 were investigated by X-ray diffraction analysis and magnetization measurement. The samples were single phase with the monoclinic Gd5Si2Ge2-type structure. With the increase of Er content, the Curie temperature (Tc) decreased obviously from 253 K of the alloy with x=0 to 114 K with x=0.3. The maximum magnetic entropy changed in the samples of (Gd1-xErx)5Si1.8Ge2.2 with x=0.0, 0.1, 0.2 and 0.3 were 6.88, 8.32, 9.59 and 10.24 J·kg-1·K-1 respectively in the applied field change of 0～2.0 T.

Influence of Tb substitution on low-field magnetocaloric effect in Gd_5Si_(1.72)Ge_(2.28) alloy

The lattice parameters, magnetic phase transition, Curie temperature and magnetocaloric properties for (Gd1-xTbx)5Si1.72- Ge2.28 alloys with x = 0, 0.15, 0.20 and 0.25 were investigated by X-ray powder diffractometry and magnetization measurements. The results show that suitable partial substitution of Tb in Gd5Si1.72Ge2.28 compound remains the first-order magnetic-crystallographic transition and enhances the magnetic entropy change, although Tb substitution decreases the Curie temperature (TC) of the compounds. The magnetic entropy change of (Gd1-xTbx)5Si1.72Ge2.28 alloys retains a large value in the low magnetic field of 1.0 T. The maximum magnetic entropy change for (Gd0.80Tb0.20)5Si1.72Ge2.28 alloy in the magnetic field from 0 to 1.0 T reaches 8.7 J/(kg·K), which is nearly 4 times as large as that of (Gd0.3Dy0.7)5Si4 compound (|-Smax| = 2.24 J/(kg·K), T_C = 198 K).

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 low-field reversible magnetocaloric effect in K_(3)Gd(PO_(4))_(2) at sub-Kelvin temperature

We synthesized a potassium gadolinium phosphate K3Gd(PO_(4))_(2)with monoclinic structure(P2_(1/m))by the high-temperature solid-state reaction method.Its lattice constants obtained by Rietveld refinements of XRD curve are a=0.7411 nm,b=0.5624 nm,and c=0.9433 nm.Magnetic and magnetocaloric properties of K_(3)Gd(PO_(4))_(2)were investigated in detail.The magnetic phase transition temperature of K3Gd(PO_(4))2 was determined by ultra-low temperature testing to be 0.58 K.K_(3)Gd(PO_(4))2 exhibits large magnetic entropy changes(-ΔSM).The maximum-ΔSM are 20.2 and 29.4 J/(kg·K)in the magnetic field variation(ΔH)of 1 and 2 T,respectively,which are larger than that of the commercial Gd_(3)Ga_(5)O_(12)(GGG).The maximum adiabatic temperature change(ΔT_(ad))reaches 5.91 K under a magnetic field change(ΔH)of 1 T.K_(3)Gd(PO_(4))_(2)is a potential magnetic refrigeration material for obtaining sub-Kelvin temperatures.

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.

Magnetocaloric Properties of (Gd_(1-x)Tb_x)_3Al_2 Compounds Near Room Temperature

Magnetic and thermal properties of the (Gd 1- x Tb x ) 3Al 2 compounds were studied as potential magnetic refrigerant materials which are used in magnetic refrigeration near room temperature at low magnetic field. The compounds (Gd 1- x Tb x ) 3Al 2 with x =0, 0.1, 0.2 and 0 3 exhibit a second order magnetic transition. Curie temperature varies from 255 K for x =0.3 to 280 K for x =0. The maximum of the isothermal magnetic entropy change Δ S increases by substituting Tb element for Gd element. Δ S max =18.9 kJ·m -3 ·K -1 for x =0.1 by changing the magnetic field from 0 to 1 T.

Estimation on Magnetic Refrigeration Material (Gd_(1-x)RE_x)_5Si_4 (RE=Dy,Ho)

A systematic （Gd1-xREx）sSi4 （RE=Dy, Ho） alloys are investigated to estimate their magnetocaloric effect. The Curie points of （Gd1-xREx）Si4 alloys can tunable from 266 K to 336 K when RE=Dy, Ho; z=0N0.35 and 0-0.15, respectively, and decrease nearly linearly with increasing x. These alloys keep orthorhombic structures GesSm4 and exhibit second order transition when they experience in a change magnetic field at about Curie points. The weight and voluminal magnetic entropy changes are about 3.5 J/（kg.K） and 23-29 mJ/（cm^3.K） when magnetic field changes 0-2 T. The adiabatic temperatures changes （△Tad） of these alloys at Curie points are larger than 1 K in a field change 0-1.4 T, the curve of ATad is wide as that of Gd. The relative cooling power is about 0.8-0.9 J/cm^3 when field changes 0-2 T, 55% of that of Gd. Comparing with Gds（Si1-xGex）4, these alloys do not contain expensive element Ge, so that their cost are lower than the former. Because they could work at temperature region 260-340 K due to their Curie points can be tuned, which is an advantage comparing with Gd, these alloys are potential magnetic refrigerants working in a magnetic refrigerator with a low magnetic field at room temperatures.

Preparation and magnetic properties of nanosized (La_(0.47)Gd_(0.2))Sr_(0.33)MnO_3

Nanosized (La0.47 Gd0.2)Sr0.33MnO3 perovskite oxides were prepared at relatively low calcinating temperature of 600℃ and 800℃ for 10h using amorphous complex precursor. Curie temperatureTc and magnetocaloric effects（MCE） were investigated. X-ray diffraction（XRD） and electron diffraction（ED） reveal that the resulting products are of pure single-phase rhombohedral perovskite structure. Transmission electron microscopy（TEM） observation finds that the particle sizes are about 40-50nm and 80-100nm, and the Tc are 285.1K and 285.9K, MCE are about 2.02J/（kg·K-1 ） and 3.90J/（kg·K-1 ） at 5T magnetic field. A relatively large MCE with a broad peak around Curie temperature is observed in sample sintered at 800℃ for 10h. This suggests that nanosized (La0.47 Gd0.2)Sr0.33MnO3 is a suitable material as working substance in magnetic refrigeration in room temperature.

Enhanced low-field magnetocaloric effect in Dy-doped hexagonal GdBO_(3) compounds

Borates have attained increasing attention attributed to their excellent thermal stability,distinctive thermodynamic property,and high mechanical strength in recent years.A series of polycrystalline Dydoped GdBO_(3) compounds was prepared,their crystal structures,magnetic properties,and cryogenic magnetocaloric effects were comprehensively investigated.The compounds crystallize in hexagonal structure(space group P6_(3)/mmc),the lattice constant decreases with the increase of Dy content.Dydoping in GdBO_(3) significantly reduces critical magnetic field and enhances low-field magnetocaloric effect.The maximum magnetic entropy changes for the Gd_(1-x)Dy_(x)BO_(3)(x=0.6,0.8,and 1)compounds in a field change of 2 T surpass 17.3 J/(kg·K)at 2.5 K,enhanced by nearly 120%compared to GdBO_(3)(8.0 J/(kg·K)).Besides,the corresponding refrigeration capacity increases from 33.9 to 62.2,57.2,and 72.5 J/kg,respectively,with an enhancement of 70%-110%.The considerable maximum magnetic entropy change,refrigerating capacity,and temperature averaged entropy change make them competitive candidates for cryogenic magnetic refrigeration.