The effects of Ce-doping on the phase transition of the orbital/spin ordering （OO/SO） are studied through the structural, magnetic, and electrical transport measurements of perovskite vanadate Sm1 x Ce x VO 3 . The ...The effects of Ce-doping on the phase transition of the orbital/spin ordering （OO/SO） are studied through the structural, magnetic, and electrical transport measurements of perovskite vanadate Sm1 x Ce x VO 3 . The measurements of structure show that the cell volume decreases as x≤ 0.05, and then increases as Ce-doping level increases further. The OO state exists but is suppressed progressively in the sample with x≤0.2 and disappears as x0.2. The temperature at which the C-type SO transition is present increases monotonically with Ce-doping level increasing. The temperature dependence of resistivity for each of the samples shows a semiconducting transport behavior and the transport can be well described by the thermal activation model. The activation energy first decreases as x ≤0.2, and then increases for further doping. The obtained results are discussed in terms of the mixed-valent state of the doped-Ce ions.展开更多
The magnetic and electronic properties of the geometrically frustrated triangular antiferromagnet CuCrO2 are investigated by first principles through density functional theory calculations within the generalized gradi...The magnetic and electronic properties of the geometrically frustrated triangular antiferromagnet CuCrO2 are investigated by first principles through density functional theory calculations within the generalized gradient approxi- mations （GGA）＋U scheme. The spin exchange interactions up to the third nearest neighbours in the ab plane as well as the coupling between adjacent layers are calculated to examine the magnetism and spin frustration. It is found that CuCrO2 has a natural two-dimensional characteristic of the magnetic interaction. Using Monte Carlo simulation, we obtain the Neel temperature to be 29.9 K, which accords well with the experimental value of 24 K. Based on non- collinear magnetic structure calculations, we verify that the incommensurate spiral-spin structure with （110） spiral plane is believable for the magnetic ground state, which is consistent with the experimental observations. Due to intra-layer geometric spin frustration, parallel helical-spin chains arise along the a, b, or a＋ b directions, each with a screw-rotation angle of about I20°. Our calculations of the density of states show that the spin frustration plays an important role in the change of d-p hybridization, while the spin-orbit coupling has a very limited influence on the electronic structure.展开更多
Conical spin order, where the spin components along the conical axis form magnetization while the spiral parts induce ferroelectric polarization, possesses multiferroicity with inherent magnetoelectric coupling. A Mon...Conical spin order, where the spin components along the conical axis form magnetization while the spiral parts induce ferroelectric polarization, possesses multiferroicity with inherent magnetoelectric coupling. A Monte Carlo simulation performed using a classical Heisenberg spinel （AB2O4） model reveals a multiple conical spin order, i.e., three modulations with different cone angles and wavelengths on A sites and two alternate B sites. The spin order not only exists as the ground state but also survives locally stably in a larger parameter region. The whole existence range can be effectively expanded by anisotropy to cover the cases of CoCr2O4 and MnCr2O4. The multiple conical spin order is well maintained and finely tuned by frustration and anisotropy over the whole existence range, and the magnetic and ferroelectric properties are influenced correspondingly.展开更多
The influences of W doping at Mn site on the charge order and spin order were studied by measuring M-T curves, M-H curves and ESR spectra of La0.3Ca0.7Mn1?xWxO3 (x = 0.00, 0.04, 0.08, 0.12, 0.15) system. The results s...The influences of W doping at Mn site on the charge order and spin order were studied by measuring M-T curves, M-H curves and ESR spectra of La0.3Ca0.7Mn1?xWxO3 (x = 0.00, 0.04, 0.08, 0.12, 0.15) system. The results showed that: When 0.00≤ x≤0.08, the system exhibits charge ordering (CO) phase, and its spin order experiences the change of paramagnetism (PM)-charge ordering (CO)-antiferro- magnetism (AFM) with decreasing temperature; when x≥0.12, the charge ordering (CO) phase melts, part of charge ordering (CO)phase remains in the paramagnetism (PM)background, the spin order of the system is mainly paramagnetism (PM), and ferromagnetic (FM) clusters appear at low tem- perature.展开更多
Magnetic properties of Nd_(0.5)Sr_(0.5)Mn_(1-x)(Ga_x, Ti_x)O_3 system (0.04≤x≤0.4) were inves- tigated through magnetization and electron spin resonance (ESR) measurements. It was observed that a small amount of Ti ...Magnetic properties of Nd_(0.5)Sr_(0.5)Mn_(1-x)(Ga_x, Ti_x)O_3 system (0.04≤x≤0.4) were inves- tigated through magnetization and electron spin resonance (ESR) measurements. It was observed that a small amount of Ti substitution for Mn will destroy the charge-ordering (CO) phase completely and induce the cluster-spin-glass phase in the system, which displays a procedure of collapse of CO and of an enhancement of spin ordering (SO) phase. In contrast, the Ga substitution for Mn induces a melt- ing of CO phase in the system. It was observed that with substitution the CO phase is suppressed gradually and the remanent CO phase is retained all the while, and withal, there is a co-existence of AFM CO phase and FM SO at low temperature. In addition, an abrupt rise of magnetization was observed in M-T curves. We attributed this abnormal phenomenon to a transition from canted AFM SO to FM SO in CO region.展开更多
An attitude controller using the second order sliding mode control methodology with a backstepping approach（SOSMCB）is designed and implemented for a spinning missile with two internal moving mass blocks.The system c...An attitude controller using the second order sliding mode control methodology with a backstepping approach（SOSMCB）is designed and implemented for a spinning missile with two internal moving mass blocks.The system consists of a rigid body and two radial internal moving mass blocks and its mathematical model is established based on Newtonian mechanics.The control scheme integrates a second order sliding mode control algorithm into the last step of the backstepping approach,and its stability is proved by means of a Lyapunov function.The performance of the controller is demonstrated by numerical simulations,the results show that the attitude controller is stable and effective.展开更多
In order to understand the properties of the spin system with orbital degeneracy, we first study the ground state of the SU(4) spin-orbital model on a square lattice. The mean-field results suggest that for a small Hu...In order to understand the properties of the spin system with orbital degeneracy, we first study the ground state of the SU(4) spin-orbital model on a square lattice. The mean-field results suggest that for a small Hund's interaction, the flavor liquid state is stable against the solid state, but with sufficient deviation from the SU(4) limit the long-range order may be attained in 2D system. Furthermore, we employ a variational approach to calculate the phase diagram of the ground state and the temperature-dependent susceptibility by taking into account the Hund's interaction and the anisotropy in orbital wavefunctions. Finally, the implications for the experimental observations on the material, , are discussed.展开更多
Polycrystalline samples of La0.4Cao.6Mn1-xCrxO3 （x = 0.00, 0.02, 0.04, 0.06） were prepared by the solid state reaction method. The influence of Cr3＋ substitution for Mn3＋ on the magnetic property and charge orderi...Polycrystalline samples of La0.4Cao.6Mn1-xCrxO3 （x = 0.00, 0.02, 0.04, 0.06） were prepared by the solid state reaction method. The influence of Cr3＋ substitution for Mn3＋ on the magnetic property and charge ordering phase of La0.4Ca0.6MnO3 was studied through the measurements of X-ray diffraction （XRD）, magnetization-temperature （M-T） curves and electron spin resonance （ESR） spectra. The experimental results indicate that the mother＇s body of La0.4Ca0.6MnO3 has very complicated magnetic structure, exhibits charge ordering phase at 258 K, and shows long-range strongly correlated charge ordering-antiferromagnetism （CO-AFM） phase from 175 to 50 K. Spin glass state appears when the temperature decreases to about 41 K. When the Cr substitution amount is x = 0.06, the charge ordering phase of the mother＇s body is de-stroyed, because the Cr3＋ substitution for Mn3＋ destroys the spin order of CE-type antiferromagnetism, and thus leads to the melting of charge ordering. It is verified experimentally that the strong coupling between charge order and spin order exists in the charge order system of CE-type antiferromagnetism.展开更多
Elastic neutron diffraction measurements were performed on single crystals to study the ground state below the mysterious exotic transition temperature 0.86 K. An antiferromagnetic order with a tiny moment of 0.027 μ...Elastic neutron diffraction measurements were performed on single crystals to study the ground state below the mysterious exotic transition temperature 0.86 K. An antiferromagnetic order with a tiny moment of 0.027 μB per formula is formed as the ground state for CeOs4Sb12 below the transition point. Our neutron data gives the evidence of spin density wave state for CeOs4Sb12 in this work.展开更多
The coexistence of superconductivity and spin density wave in SmO1-xFxFeAs is theoretically studied using the model Hamiltonian which contains BCS type superconductivity and spin density wave terms. Employing green fu...The coexistence of superconductivity and spin density wave in SmO1-xFxFeAs is theoretically studied using the model Hamiltonian which contains BCS type superconductivity and spin density wave terms. Employing green function formalism, the expression for the spin density wave order parameter (M) and expression for spin density wave transition temperature TSDW is obtained. The interplay between the superconductivity and spin density wave is examined in these parameters and the coexistence of the two states is established in the order parameter range of 0.1≤MmeV≤0.13 which is seen to be in broad experimental agreement.展开更多
通过电阻率-温度(temperature dependence of resistivity,ρ-T)曲线、磁化强度-温度(temperature depen-dence of magnetization,M-T)曲线、ESR谱线的测量,研究了La0.45Ca0.55MnO3样品的电磁特性。结果表明,样品在整个测量温区呈现绝...通过电阻率-温度(temperature dependence of resistivity,ρ-T)曲线、磁化强度-温度(temperature depen-dence of magnetization,M-T)曲线、ESR谱线的测量,研究了La0.45Ca0.55MnO3样品的电磁特性。结果表明,样品在整个测量温区呈现绝缘体行为,输运机制满足可变程跃迁模型。样品存在电荷有序(charge ordering,CO)相,相变温度TCO≈240K,并随温度降低发生顺磁(paramagnetism,PM)→电荷有序(CO)→反铁磁(antiferromagnetism,AFM)变化。值得注意的是,由于样品低温下存在多种复杂的磁相互作用,在40K发生自旋玻璃转变,表现为再入型自旋玻璃行为。展开更多
基金Project supported by the National Key Basic Research Program of China (Grant No. 2011CBA00111)the National Natural Science Foundation of China(Grant Nos. 10974205, 11104273, and 11004193)
文摘The effects of Ce-doping on the phase transition of the orbital/spin ordering （OO/SO） are studied through the structural, magnetic, and electrical transport measurements of perovskite vanadate Sm1 x Ce x VO 3 . The measurements of structure show that the cell volume decreases as x≤ 0.05, and then increases as Ce-doping level increases further. The OO state exists but is suppressed progressively in the sample with x≤0.2 and disappears as x0.2. The temperature at which the C-type SO transition is present increases monotonically with Ce-doping level increasing. The temperature dependence of resistivity for each of the samples shows a semiconducting transport behavior and the transport can be well described by the thermal activation model. The activation energy first decreases as x ≤0.2, and then increases for further doping. The obtained results are discussed in terms of the mixed-valent state of the doped-Ce ions.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10874021)
文摘The magnetic and electronic properties of the geometrically frustrated triangular antiferromagnet CuCrO2 are investigated by first principles through density functional theory calculations within the generalized gradient approxi- mations （GGA）＋U scheme. The spin exchange interactions up to the third nearest neighbours in the ab plane as well as the coupling between adjacent layers are calculated to examine the magnetism and spin frustration. It is found that CuCrO2 has a natural two-dimensional characteristic of the magnetic interaction. Using Monte Carlo simulation, we obtain the Neel temperature to be 29.9 K, which accords well with the experimental value of 24 K. Based on non- collinear magnetic structure calculations, we verify that the incommensurate spiral-spin structure with （110） spiral plane is believable for the magnetic ground state, which is consistent with the experimental observations. Due to intra-layer geometric spin frustration, parallel helical-spin chains arise along the a, b, or a＋ b directions, each with a screw-rotation angle of about I20°. Our calculations of the density of states show that the spin frustration plays an important role in the change of d-p hybridization, while the spin-orbit coupling has a very limited influence on the electronic structure.
文摘Conical spin order, where the spin components along the conical axis form magnetization while the spiral parts induce ferroelectric polarization, possesses multiferroicity with inherent magnetoelectric coupling. A Monte Carlo simulation performed using a classical Heisenberg spinel （AB2O4） model reveals a multiple conical spin order, i.e., three modulations with different cone angles and wavelengths on A sites and two alternate B sites. The spin order not only exists as the ground state but also survives locally stably in a larger parameter region. The whole existence range can be effectively expanded by anisotropy to cover the cases of CoCr2O4 and MnCr2O4. The multiple conical spin order is well maintained and finely tuned by frustration and anisotropy over the whole existence range, and the magnetic and ferroelectric properties are influenced correspondingly.
基金supported by the National Natural Science Foundation of China(Grant No.19934003)the State Key Project of Fundamental Research of China(No.001CB610604)
文摘The influences of W doping at Mn site on the charge order and spin order were studied by measuring M-T curves, M-H curves and ESR spectra of La0.3Ca0.7Mn1?xWxO3 (x = 0.00, 0.04, 0.08, 0.12, 0.15) system. The results showed that: When 0.00≤ x≤0.08, the system exhibits charge ordering (CO) phase, and its spin order experiences the change of paramagnetism (PM)-charge ordering (CO)-antiferro- magnetism (AFM) with decreasing temperature; when x≥0.12, the charge ordering (CO) phase melts, part of charge ordering (CO)phase remains in the paramagnetism (PM)background, the spin order of the system is mainly paramagnetism (PM), and ferromagnetic (FM) clusters appear at low tem- perature.
基金Supported by the National Natural Science Foundation of China (Grant No.10334090)National Basic Research Program of China (Grant No.001CB610604)the Natural Science Foundation of Zhejiang Province, China (Grant No.Y606128)
文摘Magnetic properties of Nd_(0.5)Sr_(0.5)Mn_(1-x)(Ga_x, Ti_x)O_3 system (0.04≤x≤0.4) were inves- tigated through magnetization and electron spin resonance (ESR) measurements. It was observed that a small amount of Ti substitution for Mn will destroy the charge-ordering (CO) phase completely and induce the cluster-spin-glass phase in the system, which displays a procedure of collapse of CO and of an enhancement of spin ordering (SO) phase. In contrast, the Ga substitution for Mn induces a melt- ing of CO phase in the system. It was observed that with substitution the CO phase is suppressed gradually and the remanent CO phase is retained all the while, and withal, there is a co-existence of AFM CO phase and FM SO at low temperature. In addition, an abrupt rise of magnetization was observed in M-T curves. We attributed this abnormal phenomenon to a transition from canted AFM SO to FM SO in CO region.
基金Supported by the National Natural Science Foundation of China(11202023)
文摘An attitude controller using the second order sliding mode control methodology with a backstepping approach（SOSMCB）is designed and implemented for a spinning missile with two internal moving mass blocks.The system consists of a rigid body and two radial internal moving mass blocks and its mathematical model is established based on Newtonian mechanics.The control scheme integrates a second order sliding mode control algorithm into the last step of the backstepping approach,and its stability is proved by means of a Lyapunov function.The performance of the controller is demonstrated by numerical simulations,the results show that the attitude controller is stable and effective.
文摘In order to understand the properties of the spin system with orbital degeneracy, we first study the ground state of the SU(4) spin-orbital model on a square lattice. The mean-field results suggest that for a small Hund's interaction, the flavor liquid state is stable against the solid state, but with sufficient deviation from the SU(4) limit the long-range order may be attained in 2D system. Furthermore, we employ a variational approach to calculate the phase diagram of the ground state and the temperature-dependent susceptibility by taking into account the Hund's interaction and the anisotropy in orbital wavefunctions. Finally, the implications for the experimental observations on the material, , are discussed.
基金supported by the Key Program of the National Natural Science Foundation of China (No.19934003)the Key Program of Natural Science Research of Anhui Education Department (No.KJ2011A259+3 种基金 KJ2008A34ZC)the Natural Science Research Programs of Anhui Education Department, China (No.KJ2010B229No.KJ2010B228No.KJ2009B281Z)
文摘Polycrystalline samples of La0.4Cao.6Mn1-xCrxO3 （x = 0.00, 0.02, 0.04, 0.06） were prepared by the solid state reaction method. The influence of Cr3＋ substitution for Mn3＋ on the magnetic property and charge ordering phase of La0.4Ca0.6MnO3 was studied through the measurements of X-ray diffraction （XRD）, magnetization-temperature （M-T） curves and electron spin resonance （ESR） spectra. The experimental results indicate that the mother＇s body of La0.4Ca0.6MnO3 has very complicated magnetic structure, exhibits charge ordering phase at 258 K, and shows long-range strongly correlated charge ordering-antiferromagnetism （CO-AFM） phase from 175 to 50 K. Spin glass state appears when the temperature decreases to about 41 K. When the Cr substitution amount is x = 0.06, the charge ordering phase of the mother＇s body is de-stroyed, because the Cr3＋ substitution for Mn3＋ destroys the spin order of CE-type antiferromagnetism, and thus leads to the melting of charge ordering. It is verified experimentally that the strong coupling between charge order and spin order exists in the charge order system of CE-type antiferromagnetism.
文摘Elastic neutron diffraction measurements were performed on single crystals to study the ground state below the mysterious exotic transition temperature 0.86 K. An antiferromagnetic order with a tiny moment of 0.027 μB per formula is formed as the ground state for CeOs4Sb12 below the transition point. Our neutron data gives the evidence of spin density wave state for CeOs4Sb12 in this work.
文摘The coexistence of superconductivity and spin density wave in SmO1-xFxFeAs is theoretically studied using the model Hamiltonian which contains BCS type superconductivity and spin density wave terms. Employing green function formalism, the expression for the spin density wave order parameter (M) and expression for spin density wave transition temperature TSDW is obtained. The interplay between the superconductivity and spin density wave is examined in these parameters and the coexistence of the two states is established in the order parameter range of 0.1≤MmeV≤0.13 which is seen to be in broad experimental agreement.
文摘通过电阻率-温度(temperature dependence of resistivity,ρ-T)曲线、磁化强度-温度(temperature depen-dence of magnetization,M-T)曲线、ESR谱线的测量,研究了La0.45Ca0.55MnO3样品的电磁特性。结果表明,样品在整个测量温区呈现绝缘体行为,输运机制满足可变程跃迁模型。样品存在电荷有序(charge ordering,CO)相,相变温度TCO≈240K,并随温度降低发生顺磁(paramagnetism,PM)→电荷有序(CO)→反铁磁(antiferromagnetism,AFM)变化。值得注意的是,由于样品低温下存在多种复杂的磁相互作用,在40K发生自旋玻璃转变,表现为再入型自旋玻璃行为。
