Bi Mn过共晶合金分别从3个不同状态凝固,合金中MnBi析出相均在磁场作用下以晶体的c轴平行磁场取向,形成规则排列组织,并且所得材料的剩磁都具有明显的各向异性。合金从低于355℃的固液两相区凝固时,铁磁性MnBi析出相在1.0T磁场中迅速... Bi Mn过共晶合金分别从3个不同状态凝固,合金中MnBi析出相均在磁场作用下以晶体的c轴平行磁场取向,形成规则排列组织,并且所得材料的剩磁都具有明显的各向异性。合金从低于355℃的固液两相区凝固时,铁磁性MnBi析出相在1.0T磁场中迅速形成均布的织构组织,并能在无磁场条件下保持稳定,材料无需热处理就有很好的剩磁性能。因此,磁场凝固技术能够高效率地、直接制备出性能优良的MnBi/Bi磁性功能复合材料。展开更多
The reactions of 6-phosphononicotinic acid (pnaH3) and metal salts result in three new compounds, namely, M(pnaH)-(H2O)3·H2O [M = Co(Ⅱ) (1), Ni(Ⅱ) (2), Zn(Ⅱ) (3)]. These compounds are isostructural and contain...The reactions of 6-phosphononicotinic acid (pnaH3) and metal salts result in three new compounds, namely, M(pnaH)-(H2O)3·H2O [M = Co(Ⅱ) (1), Ni(Ⅱ) (2), Zn(Ⅱ) (3)]. These compounds are isostructural and contain 21 helical chains made up of corner-sharing {MO5N} octahedra and {PO3C} tetrahedra. The chains are further connected by extensive hydrogen bonds to form a three-dimensional supramolecular structure. Magnetic studies reveal that dominant antiferromagnetic interactions are mediated in both 1 and 2. Interestingly the dehydrated compound 1 shows metamagnetic behavior at low temperature.展开更多
The dynamic magnetic behavior of the kinetic metamagnetic spin-5/2 Blume-Capel model is examined, within a mean-field approach, under a time-dependent oscillating magnetic field. To describe the kinetics of the system...The dynamic magnetic behavior of the kinetic metamagnetic spin-5/2 Blume-Capel model is examined, within a mean-field approach, under a time-dependent oscillating magnetic field. To describe the kinetics of the system, Glauber- type stochastic dynamics has been utilized. The mean-field dynamic equations of the model are obtained from the Master equation. Firstly, these dynamic equations are solved to find the phases in the system. Then, the dynamic phase transition temperatures are obtained by investigating the thermal behavior of dynamic sublattice magnetizations. Moreover, from this investigation, the nature of the phase transitions （first- or second-order） is characterized. Finally, the dynamic phase diagrams are plotted in five different planes. It is found that the dynamic phase diagrams contain the paramagnetic （P）, antiferromagnetic （AF5/2, AF3/2, AF1/2） phases and five different mixed phases. The phase diagrams also display many dynamic critical points, such as tricritical point, triple point, quadruple point, double critical end point and separating point.展开更多
Two manganese phosphonates Mn3（4-piH）2（H2O）3·H2O （1） and Mns（4-piH）2（4-piH2）2（phen）2（H2O）4 （2） （4-pill4 = 4-phosphonoisophthalic acid, phen = 1,10-phenanthroline） have been synthesized under hyd...Two manganese phosphonates Mn3（4-piH）2（H2O）3·H2O （1） and Mns（4-piH）2（4-piH2）2（phen）2（H2O）4 （2） （4-pill4 = 4-phosphonoisophthalic acid, phen = 1,10-phenanthroline） have been synthesized under hydrothermal conditions in the pres- ence of organic co-ligand. Both compounds exhibit layer structures but with different topologies. In compound 1, a complicated ＂ladder-like＂ chain of {Mn3O3}O2 which contains three- and six-member rings made up of triangular shaped {Mn3O3} tri- mers is found. The chains are linked by the PO3C groups to form an inorganic layer. The phenyl and protonated carboxylate groups are pendent between the layers with extensive hydrogen bonds. In compound 2, tetramers of {MnnO6 } are connected by the { MnO6 } octahedra through corner-sharing to form an infinite chain, which is further bridged by 4-pill3- ligands into a thick hybrid layer. Magnetic measurements reveal that antiferromagnetic interactions are dominant in both compounds. Metamag- netism is observed in compound 1 at low temperature, while no long range ordering is found in compound 2 down to 1.8 K.展开更多
A cyanide-bridged Fei^III2Coll double zigzag chain, { [Fen1（bipy）（CN）4]2Con（btab）2}n [bipy=2,2＇-bipyridine, btab=4,4＇-（1,3-phen- ylene）-bis-4H-1,2,4-triazole] （1）, was obtained with tetracyanometalate prec...A cyanide-bridged Fei^III2Coll double zigzag chain, { [Fen1（bipy）（CN）4]2Con（btab）2}n [bipy=2,2＇-bipyridine, btab=4,4＇-（1,3-phen- ylene）-bis-4H-1,2,4-triazole] （1）, was obtained with tetracyanometalate precursors and Con ions. The chains were further linked by the ditopic btab ligands to a layer. Magnetic property studies demonstrate that 1 shows both metamagnetism with a critical field He=400 Oe and single-chain magnet behavior.展开更多
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...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.展开更多
The magnetic properties,magnetic phase transition and magnetocaloric effects(MCE) of Er_(3)Si_(2)C_(2) compound were investigated based on theoretical calculations and experimental analysis.Based on the first principl...The magnetic properties,magnetic phase transition and magnetocaloric effects(MCE) of Er_(3)Si_(2)C_(2) compound were investigated based on theoretical calculations and experimental analysis.Based on the first principles calculations,the antiferromagnetic(AFM) ground state type in Er_(3)Si_(2)C_(2) compound was predicted and its electronic structure was investigated.The experimental results show that Ei_(3)Si_(2)C_(2) compound is an AFM compound with the Neel temperature(T_(N) of 7 K and undergoes a field-induced firstorder magnetic phase transition from AFM to ferromagnetic(FM) under magnetic fields exceeding 0.6 T at 2 K.The magnetic transition process of Er_(3)Si_(2)C_(2) compound was investigated and discussed.The values of the maximum magnetic entropy change(-ΔS_(M)^(max)) and the refrigeration capacity(RC) are 17 J/(kg·K)and 193 J/kg under changing magnetic fields of 0-5 T,respectively.As a potential cryogenic magnetic refrigerant,the Er_(3)Si_(2)C_(2) compound also provides an interesting research medium to study the magnetic phase transition process.展开更多
The FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were prepared by hot pressing(HP). The microstructure,corrosion behavior and magnetocaloric effect(MCE) of FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were investiga...The FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were prepared by hot pressing(HP). The microstructure,corrosion behavior and magnetocaloric effect(MCE) of FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were investigated systematically. The results show that the corrosion resistance of FeNi coated LaFe_(11.6)Si_(1.4)Sn composites is better than that of LaFe_(11.6)Si_(1.4)/Sn composites in deionized water. The maximum magnetic entropy change((-△S_M)^(max)) and relative cooling power(RCP) of FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites are 13.30 J/(kg-K) and 146.25 J/kg, respectively, which are larger than that((-△S_M)^(max), 10.65 J/(kg·K) and RCP, 106.53 J/kg) of LaFe_(11.6)Si_(1.4)/Sn composites in a low magnetic field change of 2 T. FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites possess a more negative slope. The improvement of magnetic properties is due to high permeability FeNi permalloy(1 J85) which improves the itinerant-electron metamagnetic(IEM) transition. So, the method of coating FeNi can provide a new idea for enhancing the corrosion resistance and magnetocaloric effect of La(Fe_xSi_(1-x))_(13)-based materials.展开更多
The magnetic properties of cobalt-based oxypnictides SmCoAsO are investigated by measuring magnetization,magnetoresistance and specific heat.The compound undergoes a ferromagnetic(FM) transition around Tc of 80 K,and ...The magnetic properties of cobalt-based oxypnictides SmCoAsO are investigated by measuring magnetization,magnetoresistance and specific heat.The compound undergoes a ferromagnetic(FM) transition around Tc of 80 K,and a ferromagnetic to antiferromagnetic(AFM) transition below TN1 of about 45 K,and finally an AFM order of Sm ion at TN2 of 5.6 K.The weak FM order should originate from the itinerant 3d electrons of Co ions in the CoAs layers.We propose that the magnetic structure should be A-type AFM,which means that the FM order remains within the CoAs layer and the magnetic coupling between the CoAs layers becomes AFM below TN1 of 45 K.The AFM coupling between the CoAs layers should be very weak.A magnetic field μ0H of about 2 T may cause an AFM-FM metamagnetic transition.A rich magnetic phase diagram is established and the interplay between the 3d electrons of Co ions and 4f electrons of Sm ions is discussed.展开更多
Materials with strongly coupled magnetic and electronic degrees of freedom provide new possibilities for practical applications.In this paper,we have investigated the structure,magnetic property,and magnetodielectric(...Materials with strongly coupled magnetic and electronic degrees of freedom provide new possibilities for practical applications.In this paper,we have investigated the structure,magnetic property,and magnetodielectric(MD) effect in Ho_(2)Cu_(2)O_(5) and Yb_(2)Cu_(2)O_(5) poly crystalline samples,which possess a non-centrosymmetric polar structure with space group Pna2_(1).In Ho_(2)Cu_(2)O_(5),Ho^(3+) and Cu^(2+) sublattices order simultaneously,exhibiting a typical paramagnetic to antiferromagnetic transition at 13.1 K.While for Yb_(2)Cu_(2)O_(5),two magnetic transitions which originate from the orderings of Yb^(3+)(7.8 K) and Cu^(2+)(13.5 K) sublattices are observed.A magnetic field induced metamagnetic transition is obtained in these two cuprates below Neel temperature(T_(N)).By means of dielectric measurement,distinct MD effect is demonstrated by the dielectric anomaly at T_(N.)Meanwhile,the MD effect is found to be directly related to the metamagnetic transition.Due to the specific spin configuration and different spin evolution in the magnetic field,a positive MD effect is formed in Ho_(2)Cu_(2)O_(5),and a negative one is observed in Yb_(2)Cu_(2)O_(5).The spontaneous dielectric anomaly at T_(N) is regarded as arising from the shifts in optical phonon frequencies,and the magnetoelectric coupling is used to interpret the magnetic field induced MD effect.Moreover,an H-T phase diagram is constructed for Ho_(2)Cu_(2)O_(5) and Yb_(2)Cu_(2)O_(5) based on the results of isothermal magnetic and dielectric hysteresis loops.展开更多
Crystal structure, magnetic properties and magnetocaloric effects （MCE） of La1-xBixFe1 1.4Si1.6 （x=0.0 and 0.1） compounds were investigated by X-ray diffraction and magnetization measurements. The La1-xBixFe11.4Si...Crystal structure, magnetic properties and magnetocaloric effects （MCE） of La1-xBixFe1 1.4Si1.6 （x=0.0 and 0.1） compounds were investigated by X-ray diffraction and magnetization measurements. The La1-xBixFe11.4Si1.6 compounds presented a cubic NaZnx3 type structure. First, the magnetization behavior and the magnetic transition were analyzed in terms of Landau theory. Then, Bi substitution for La in La1-xBixFe11.4Si1.6 compounds led to a decrease in magnetic entropy change （-△SM^max） but an increase in Curie temperature （Tc） significantly. The significant increase of Tc by Bi substitution from 202.5 to 256 K for x=0.0 and x=0.1 respectively was attributed to an increase in the Fe-Fe exchange interactions. Moreover, magnetocaloric effect was calculated in terms of isothermal magnetic entropy change. The maximum values of （-△SM^max ） of La1-xBixFe11.4Si1.6 for x=-0.0 and 0.1 compounds were found to be, respectively, 22.56 and 4.36 J/（kg.K） under an applied magnetic field change of 5 T. For the same applied magnetic field （μ0H=5 T）, the relative cooling power （RCP） values were found to vary between 487 and 296 J/kg.展开更多
The magnetic properties and magnetocaloric effects （MCE） of HoNiGa compound are investigated systematically. The HoNiGa exhibits a weak antiferromagnetic （AFM） ground state below the Neel temperature TN of 10 K, a...The magnetic properties and magnetocaloric effects （MCE） of HoNiGa compound are investigated systematically. The HoNiGa exhibits a weak antiferromagnetic （AFM） ground state below the Neel temperature TN of 10 K, and the AFM ordering could be converted into ferromagnetic （FM） ordering by external magnetic field. Moreover, the fie/d-induced FM phase exhibits a high saturation magnetic moment and a large change of magnetization around the transition temperature, which then result in a large MCE. A large -△SM of 22.0 J/kg K and a high RC value of 279 J/kg without magnetic hysteresis are obtained for a magnetic field change of 5 T, which are comparable to or even larger than those of some other magnetic refrigerant materials in the same temperature range. Besides, the μ0H2/3 dependence of ｜△SPKM｜ well follows the linear fitting according to the mean-field approximation, suggesting the nature of second-order FM-PM magnetic transition under high magnetic fields. The large reversible MCE induced by metamagnetic transition suggests that HoNiGa compound could be a promising material for magnetic refrigeration in low temperature range.展开更多
The magnetic phase transition and magnetocaloric effects in Fe-doped MnNiGe alloys are investigated. The substitution of Fe for Ni decreases the structural transition temperature remarkably, resulting in the magnetost...The magnetic phase transition and magnetocaloric effects in Fe-doped MnNiGe alloys are investigated. The substitution of Fe for Ni decreases the structural transition temperature remarkably, resulting in the magnetostructural transition occurring between antiferromagnetic and ferromagnetic states in MnNil_χFexGe alloy. Owing to the enhanced ferromagnetic coupling induced by the substitution of Fe, metamagnetic behaviour is also observed in TiNiSi-type phase of MnNil-xFezGe alloys at temperature below the structural transition temperature.展开更多
文摘 Bi Mn过共晶合金分别从3个不同状态凝固,合金中MnBi析出相均在磁场作用下以晶体的c轴平行磁场取向,形成规则排列组织,并且所得材料的剩磁都具有明显的各向异性。合金从低于355℃的固液两相区凝固时,铁磁性MnBi析出相在1.0T磁场中迅速形成均布的织构组织,并能在无磁场条件下保持稳定,材料无需热处理就有很好的剩磁性能。因此,磁场凝固技术能够高效率地、直接制备出性能优良的MnBi/Bi磁性功能复合材料。
基金supported by the National Natural Science Foundation of China (90922006)Natural Science Foundation of Jiangsu Province (BK2009009)NSFC for Creative Research Group (20721002)
文摘The reactions of 6-phosphononicotinic acid (pnaH3) and metal salts result in three new compounds, namely, M(pnaH)-(H2O)3·H2O [M = Co(Ⅱ) (1), Ni(Ⅱ) (2), Zn(Ⅱ) (3)]. These compounds are isostructural and contain 21 helical chains made up of corner-sharing {MO5N} octahedra and {PO3C} tetrahedra. The chains are further connected by extensive hydrogen bonds to form a three-dimensional supramolecular structure. Magnetic studies reveal that dominant antiferromagnetic interactions are mediated in both 1 and 2. Interestingly the dehydrated compound 1 shows metamagnetic behavior at low temperature.
文摘The dynamic magnetic behavior of the kinetic metamagnetic spin-5/2 Blume-Capel model is examined, within a mean-field approach, under a time-dependent oscillating magnetic field. To describe the kinetics of the system, Glauber- type stochastic dynamics has been utilized. The mean-field dynamic equations of the model are obtained from the Master equation. Firstly, these dynamic equations are solved to find the phases in the system. Then, the dynamic phase transition temperatures are obtained by investigating the thermal behavior of dynamic sublattice magnetizations. Moreover, from this investigation, the nature of the phase transitions （first- or second-order） is characterized. Finally, the dynamic phase diagrams are plotted in five different planes. It is found that the dynamic phase diagrams contain the paramagnetic （P）, antiferromagnetic （AF5/2, AF3/2, AF1/2） phases and five different mixed phases. The phase diagrams also display many dynamic critical points, such as tricritical point, triple point, quadruple point, double critical end point and separating point.
基金supported by the National Natural Science Foundation of China (90922006)the Natural Science Foundation of Jiangsu Province (BK2009009)
文摘Two manganese phosphonates Mn3（4-piH）2（H2O）3·H2O （1） and Mns（4-piH）2（4-piH2）2（phen）2（H2O）4 （2） （4-pill4 = 4-phosphonoisophthalic acid, phen = 1,10-phenanthroline） have been synthesized under hydrothermal conditions in the pres- ence of organic co-ligand. Both compounds exhibit layer structures but with different topologies. In compound 1, a complicated ＂ladder-like＂ chain of {Mn3O3}O2 which contains three- and six-member rings made up of triangular shaped {Mn3O3} tri- mers is found. The chains are linked by the PO3C groups to form an inorganic layer. The phenyl and protonated carboxylate groups are pendent between the layers with extensive hydrogen bonds. In compound 2, tetramers of {MnnO6 } are connected by the { MnO6 } octahedra through corner-sharing to form an infinite chain, which is further bridged by 4-pill3- ligands into a thick hybrid layer. Magnetic measurements reveal that antiferromagnetic interactions are dominant in both compounds. Metamag- netism is observed in compound 1 at low temperature, while no long range ordering is found in compound 2 down to 1.8 K.
基金supported by the National Natural Science Foundation of China (21201028, 21421005, 21322103, 91422302, 91122031)
文摘A cyanide-bridged Fei^III2Coll double zigzag chain, { [Fen1（bipy）（CN）4]2Con（btab）2}n [bipy=2,2＇-bipyridine, btab=4,4＇-（1,3-phen- ylene）-bis-4H-1,2,4-triazole] （1）, was obtained with tetracyanometalate precursors and Con ions. The chains were further linked by the ditopic btab ligands to a layer. Magnetic property studies demonstrate that 1 shows both metamagnetism with a critical field He=400 Oe and single-chain magnet behavior.
基金Project supported by the National Natural Science Foundation of China （Grant No 50571112）, the National Basic Reseaxch Program of China （Grant No 2006CB601101） and the Program of Chinese Academy of Sciences （Grant No KJCX2-YW-W02）.
文摘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.
基金supported by the National Key Research and Development Program of China (2021YFB3501204)the National Science Foundation for Excellent Young Scholars (52222107)+2 种基金the National Science Foundation for Distinguished Young Scholars (51925605)the National Natural Science Foundation of China (52171195)Projects of Ganjiang Innovation Academy,Chinese Academy of Sciences (E055B002)。
文摘The magnetic properties,magnetic phase transition and magnetocaloric effects(MCE) of Er_(3)Si_(2)C_(2) compound were investigated based on theoretical calculations and experimental analysis.Based on the first principles calculations,the antiferromagnetic(AFM) ground state type in Er_(3)Si_(2)C_(2) compound was predicted and its electronic structure was investigated.The experimental results show that Ei_(3)Si_(2)C_(2) compound is an AFM compound with the Neel temperature(T_(N) of 7 K and undergoes a field-induced firstorder magnetic phase transition from AFM to ferromagnetic(FM) under magnetic fields exceeding 0.6 T at 2 K.The magnetic transition process of Er_(3)Si_(2)C_(2) compound was investigated and discussed.The values of the maximum magnetic entropy change(-ΔS_(M)^(max)) and the refrigeration capacity(RC) are 17 J/(kg·K)and 193 J/kg under changing magnetic fields of 0-5 T,respectively.As a potential cryogenic magnetic refrigerant,the Er_(3)Si_(2)C_(2) compound also provides an interesting research medium to study the magnetic phase transition process.
基金Project supported by the Key Project of National Natural Science Foundation of China(51176065)
文摘The FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were prepared by hot pressing(HP). The microstructure,corrosion behavior and magnetocaloric effect(MCE) of FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were investigated systematically. The results show that the corrosion resistance of FeNi coated LaFe_(11.6)Si_(1.4)Sn composites is better than that of LaFe_(11.6)Si_(1.4)/Sn composites in deionized water. The maximum magnetic entropy change((-△S_M)^(max)) and relative cooling power(RCP) of FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites are 13.30 J/(kg-K) and 146.25 J/kg, respectively, which are larger than that((-△S_M)^(max), 10.65 J/(kg·K) and RCP, 106.53 J/kg) of LaFe_(11.6)Si_(1.4)/Sn composites in a low magnetic field change of 2 T. FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites possess a more negative slope. The improvement of magnetic properties is due to high permeability FeNi permalloy(1 J85) which improves the itinerant-electron metamagnetic(IEM) transition. So, the method of coating FeNi can provide a new idea for enhancing the corrosion resistance and magnetocaloric effect of La(Fe_xSi_(1-x))_(13)-based materials.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10931160425 and 10634030)the Natural Science Foundation of Zhejiang Province (Grant No. Y6090564)
文摘The magnetic properties of cobalt-based oxypnictides SmCoAsO are investigated by measuring magnetization,magnetoresistance and specific heat.The compound undergoes a ferromagnetic(FM) transition around Tc of 80 K,and a ferromagnetic to antiferromagnetic(AFM) transition below TN1 of about 45 K,and finally an AFM order of Sm ion at TN2 of 5.6 K.The weak FM order should originate from the itinerant 3d electrons of Co ions in the CoAs layers.We propose that the magnetic structure should be A-type AFM,which means that the FM order remains within the CoAs layer and the magnetic coupling between the CoAs layers becomes AFM below TN1 of 45 K.The AFM coupling between the CoAs layers should be very weak.A magnetic field μ0H of about 2 T may cause an AFM-FM metamagnetic transition.A rich magnetic phase diagram is established and the interplay between the 3d electrons of Co ions and 4f electrons of Sm ions is discussed.
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.11704091)the Open Project of Guangxi Key Laboratory of Nuclear Physics and Nuclear Technology(Grant No.NLK2021-10)the Open Project of Key Laboratory of Novel Materials for Sensor of Zhejiang Province,China(Grant No.ZJKLNMS2021010)。
文摘Materials with strongly coupled magnetic and electronic degrees of freedom provide new possibilities for practical applications.In this paper,we have investigated the structure,magnetic property,and magnetodielectric(MD) effect in Ho_(2)Cu_(2)O_(5) and Yb_(2)Cu_(2)O_(5) poly crystalline samples,which possess a non-centrosymmetric polar structure with space group Pna2_(1).In Ho_(2)Cu_(2)O_(5),Ho^(3+) and Cu^(2+) sublattices order simultaneously,exhibiting a typical paramagnetic to antiferromagnetic transition at 13.1 K.While for Yb_(2)Cu_(2)O_(5),two magnetic transitions which originate from the orderings of Yb^(3+)(7.8 K) and Cu^(2+)(13.5 K) sublattices are observed.A magnetic field induced metamagnetic transition is obtained in these two cuprates below Neel temperature(T_(N)).By means of dielectric measurement,distinct MD effect is demonstrated by the dielectric anomaly at T_(N.)Meanwhile,the MD effect is found to be directly related to the metamagnetic transition.Due to the specific spin configuration and different spin evolution in the magnetic field,a positive MD effect is formed in Ho_(2)Cu_(2)O_(5),and a negative one is observed in Yb_(2)Cu_(2)O_(5).The spontaneous dielectric anomaly at T_(N) is regarded as arising from the shifts in optical phonon frequencies,and the magnetoelectric coupling is used to interpret the magnetic field induced MD effect.Moreover,an H-T phase diagram is constructed for Ho_(2)Cu_(2)O_(5) and Yb_(2)Cu_(2)O_(5) based on the results of isothermal magnetic and dielectric hysteresis loops.
文摘Crystal structure, magnetic properties and magnetocaloric effects （MCE） of La1-xBixFe1 1.4Si1.6 （x=0.0 and 0.1） compounds were investigated by X-ray diffraction and magnetization measurements. The La1-xBixFe11.4Si1.6 compounds presented a cubic NaZnx3 type structure. First, the magnetization behavior and the magnetic transition were analyzed in terms of Landau theory. Then, Bi substitution for La in La1-xBixFe11.4Si1.6 compounds led to a decrease in magnetic entropy change （-△SM^max） but an increase in Curie temperature （Tc） significantly. The significant increase of Tc by Bi substitution from 202.5 to 256 K for x=0.0 and x=0.1 respectively was attributed to an increase in the Fe-Fe exchange interactions. Moreover, magnetocaloric effect was calculated in terms of isothermal magnetic entropy change. The maximum values of （-△SM^max ） of La1-xBixFe11.4Si1.6 for x=-0.0 and 0.1 compounds were found to be, respectively, 22.56 and 4.36 J/（kg.K） under an applied magnetic field change of 5 T. For the same applied magnetic field （μ0H=5 T）, the relative cooling power （RCP） values were found to vary between 487 and 296 J/kg.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51671022 and 51427806)the Beijing Natural Science Foundation,China(Grant No.2162022)the Fundamental Research Funds for the Central Universities,China(Grant No.FRF-TP-15-002A3)
文摘The magnetic properties and magnetocaloric effects （MCE） of HoNiGa compound are investigated systematically. The HoNiGa exhibits a weak antiferromagnetic （AFM） ground state below the Neel temperature TN of 10 K, and the AFM ordering could be converted into ferromagnetic （FM） ordering by external magnetic field. Moreover, the fie/d-induced FM phase exhibits a high saturation magnetic moment and a large change of magnetization around the transition temperature, which then result in a large MCE. A large -△SM of 22.0 J/kg K and a high RC value of 279 J/kg without magnetic hysteresis are obtained for a magnetic field change of 5 T, which are comparable to or even larger than those of some other magnetic refrigerant materials in the same temperature range. Besides, the μ0H2/3 dependence of ｜△SPKM｜ well follows the linear fitting according to the mean-field approximation, suggesting the nature of second-order FM-PM magnetic transition under high magnetic fields. The large reversible MCE induced by metamagnetic transition suggests that HoNiGa compound could be a promising material for magnetic refrigeration in low temperature range.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.50701022 and 50831006)
文摘The magnetic phase transition and magnetocaloric effects in Fe-doped MnNiGe alloys are investigated. The substitution of Fe for Ni decreases the structural transition temperature remarkably, resulting in the magnetostructural transition occurring between antiferromagnetic and ferromagnetic states in MnNil_χFexGe alloy. Owing to the enhanced ferromagnetic coupling induced by the substitution of Fe, metamagnetic behaviour is also observed in TiNiSi-type phase of MnNil-xFezGe alloys at temperature below the structural transition temperature.
