磁铁矿和磁赤铁矿磁化率的温度和频率特性及其环境磁学意义

磁化率随温度和频率的变化特性(F-T)对于研究超顺磁和单畴磁性颗粒的磁学性质非常有效。文章结合饱和磁化强度和矫顽力随温度变化的特性,依据尼尔理论,探讨了磁性颗粒的粒径分布与其(F-T)特性的关系。结果表明,磁化率的最大值对应于其解阻温度,因此可以用来估算磁性颗粒的平均粒径。随温度变化的频率磁化率曲线可以转化为连续的粒径分布曲线。本方法可以用来模拟自然地质体(例如,火山灰、黄土沉积物)中磁性矿物的粒度分布。

稀土-铁-碳化合物磁性的理论分析

利用两个次晶格的分子场理论分析了稀土-铁-碳化合物的磁性,计算了分子场系数nFF,nRF,nRR以及自旋交换系数AFF,ARF,ARR,并对所得结果进行了讨论。

磁处理对南海原油凝点的影响规律研究

通过对原油进行磁处理,可以改善原油的流动性,降低其输送成本。通过控制磁化温度、磁化转速和磁化强度,对模拟南海原油油样进行磁处理后凝点变化规律进行了研究。结果表明:磁处理能降低南海原油的凝点,磁化温度、磁化转速和磁化强度对南海原油的凝点均有影响。在40~80℃的温度区间内,磁化温度越高,磁处理降凝效果越好;在0~100 mT的磁场强度范围内,随着磁化强度增加,凝点具有不断降低趋势;最优的磁化转速为1000 r/min,在此转速下,实验油样凝点降低了4.7%。

碎屑储集岩热磁特征与磁性矿物识别

对采自渤海湾盆地济阳坳陷孤南洼陷4口探井的22块古近系沙河街组碎屑储集岩标本进行了细致的磁化率-温度曲线、三轴饱和等温剩磁热退磁测试,研究不同含油级别的储集岩的热磁特征与磁性载体,结果表明:孤南洼陷沙河街组储集岩磁性矿物及其组合可以划分为3种类型:磁铁矿、针铁矿+磁黄铁矿+磁铁矿、赤铁矿+磁铁矿,岩石的磁性载体及其组合与岩石的颜色、岩性等沉积学特征密切相关,而与含油性关系不明显;在氩气环境中加热,含油标本中的磁铁矿Hopkinson峰低而宽,甚至不明显,居里温度附近曲线多呈锯齿状,冷却过程中,磁铁矿重现作用不明显,烃类有机质对碎屑储集岩中沉积成因磁铁矿的热磁行为具有一定的控制作用;烃类流体侵位,储集岩中的磁性矿物及其组合未发生明显变化,亦不存在某种演化序列或规律性,烃类流体化学重磁化不具普遍性。

土壤磁化率-温度(κ-T)曲线测定中的影响因素研究

土壤磁化率-温度曲线(κ-T)可用于鉴定土壤中磁性矿物类型。以水稻土、红壤、黄壤和砖红壤为对象,采用BaringtonMS2κ-T磁化率/温度系统,测定了不同土壤类型中磁性矿物种类。结果表明:水稻土κ-T曲线在300℃出现矿物相变点,黄壤、红壤和砖红壤在350℃出现相变点;水稻土和黄壤κ-T曲线呈现出磁铁矿的居里点(580℃),表明土壤磁性载体以磁铁矿为主;红壤和砖红壤的κ-T曲线呈现赤铁矿的居里点(680℃)。将水稻土和红壤分别制成2 mm、1 mm、0.30mm和0.15 mm的颗粒大小,称取相同质量土样(1 g)研究不同颗粒大小对土壤κ-T曲线测定的影响;称取过2 mm筛土样0.5 g、1 g、1.5 g和2 g,研究不同称样量对κ-T曲线测定的影响。结果表明:不同土壤类型,颗粒大小和称样量对κ-T曲线的测定有一定影响,但不会改变土壤中磁性矿物的相变点。它们对红壤和砖红壤的κ-T曲线测定影响甚少,对水稻土和黄壤的影响较大。实验证明在颗粒大小上选择过0.30 mm筛的土样,称样量上选择大于1 g的土样可以得到较明显的κ-T曲线,不会掩盖矿物的相变点。

Effects of intense magnetic field on digestion and settling performances of bauxite

The effects of magnetic field intensity, roasting temperature and roasting time on digestion rate and settling performance of bauxite with different iron contents were investigated systematically. The results indicate that such magnetic treatment can profoundly change the microstructure and digestion performance of bauxite. For the two samples carrying different iron contents, phase transformation of the aluminum oxide phase proceeds faster in the high iron bauxite than the low one. The optimal pretreatment conditions of low iron bauxite are roasting temperature 550 ℃ and magnetic field intensity 6 T, while for high iron bauxite are 500 ℃ and 9 T. The digestion rate of alumina can reach 95% and 92% at digestion temperature of 190 ℃ and 250 ℃. The settling performances of roasted ore by intense magnetic field after digestion are enhanced through pretreatment.

Effects of coal rank, Fe_3O_4 amounts and activation temperature on the preparation and characteristics of magnetic activated carbon

Coal-based Magnetic Activated Carbons （CMAC＇s） were prepared from three representative coal samples of various ranks： Baorigele lignite from Inner Mongolia; Datong bitumite from Shanxi province; and Taixi anthracite from Ningxia Hui Auto- nomous Region. Fe3O4 was used as a magnetic additive. A nitrogen-adsorption analyzer was used to determine the specific surface area and pore structure of the resulting activated carbons. The adsorption capacity was assessed by the adsorption of iodine and methylene blue. X-ray diffraction was used to measure the evolution behavior of Fe304 during the preparation process. Magnetic properties were characterized with a vibrating-sample magnetometer. The effect of the activation temperature on the performance of CMAC＇s was also studied. The results show that, compared to Baorigele lignite and Taixi anthracite, the Datong bitumite is more appropriate for the preparation of CMAC＇s with a high specific surface area, an advanced pore structure and suitable magnetic properties. Fe304 can effectively enhance the magnetic properties and control the pore structure by increasing the ratio of meso- pores. An addition of 6.0% Fe304 and an activation temperature of 880 ℃ produced a CMAC having a specific surface area, an iodine adsorption, a methylene blue adsorption and a specific saturation magnetization of 1152.0 m2/g, 1216.7 mg/g, 229.5 mg/g and 4.623 emu/g, respectively. The coal used to prepare this specimen was Datong bitumite.

Temperature Dependence of Exchange Bias and Coercivity in Ferromagnetic Layer Coupled with Polycrystalline Antiferromagnetic Layer

The temperature dependence of exchange bias and coercivity in a ferromagnetic layer coupled with an antiferromagnetic layer is discussed.In this model,the temperature dependence comes from the thermal instability of the system states and the temperature modulated relative magnetic parameters.Morever,the thermal fluctuation of orientations of easy axes of antiferromagnetic grains at preparing has been considered.From the present model,the experimental results can be illustrated qualitatively for available magnetic parameters.Based on our discussion,we can conclude that soft ferromagnetic layer coupled by hard antiferromagnetic layer may be very applicable to design magnetic devices.In special exchange coupling,we can get high exchange bias and low coercivity almost independent of temperature for proper temperature ranges.

Temperature dependence of magnetization reversal mechanism in CoNi/CoO bilayers

Exchange coupling and magfietization reversal mechanism in two series of CoxNil-x/CoO （30 nm） （x=0.2 and 0.4） bilayers are studied by vector magnetometer. Two components of magnetization are measured parallel and perpendicular to the applied field. At low temperatures, coercivity Hc oc （tFM）^-n, n = 1.5 and 1.38 for x = 0.2 and 0.4, respectively, in agreement with the random field model. At room temperature, the coercivity is nearly proportional to the inverse FM layer thickness. In addition to the exchange field and the coercivity, the characteristic of the magnetization reversal mechanism was found to change with temperature. At temperatures below 180 K, magnetization reversal process along the unidirectional axis is accompanied only by nucleation and pinning of domain wall while magnetization rotation is also involved at high temperatures.

Phase evolution and room temperature ferroelectric and magnetic properties of Fe-doped BaTiO_3 ceramics

To make the ferroelectric BaTiO3 possess ferromagnetism simultaneously,magnetic Fe was doped into BaTiO3 ceramics at doping levels up to 10%(molar fraction).Both tetragonal and hexagonal phases coexisted in the Fe-doped BaTiO3 ceramics except at 1% doping level.X-ray diffraction analysis indicated that higher doping level of Fe,higher sintering temperature and longer sintering time promoted the formation of hexagonal phases in Fe-doped BaTiO3 ceramics.Ferroelectricity was observed in all samples at room temperature,but it was greatly depressed by Fe doping.Except at doping level of 1%,room-temperature ferromagnetism was observed in the BaTiO3 ceramics.The dependence of the saturation magnetization and coercivities of the Fe-doped BaTiO3 ceramics on doping level was systematically studied.Both the saturation magnetization and magnetic coercivities were found to be dependent on the doping level as well as the fraction of the hexagonal phase in the ceramics.

Fe48Co52 Alloy Nanowire Arrays： Effects of Magnetic Field Annealing

The effects of magnetic field annealing on the properties of Fe48Co52 alloy nanowire arrays with various interwire distances （Di=30-60 nm） and wire diameters （Dw=22-46 nm） were investigated in detail. It was found that the array＇s best annealing temperature and crys- talline structure did not show any apparent dependence on the treatment of applying a 3 kOe magnetic field along the wire during the annealing process. For arrays with small Dw or with large Di, the treatment of magnetic field annealing also had no obvious influence on their magnetic performances. However, such a magnetic field annealing constrained the shift of the easy magnetization direction and improved the coercivity and the squareness obviously for arrays with large Dw or with small Di. The difference in the intensity of the effective anisotropic field within the arrays was believed to be responsible for this different variation of the array＇s magnetic properties after magnetic field annealing.

Hydrogenation reaction characteristics and properties of its hydrides for magnetic regenerative material HoCu_2

The hydrogenation reaction characteristics and the properties of its hydrides for the magnetic regenerative material HoCu_2(CeCu_2-type) of a cryocooler were investigated. The XRD testing reveals that the hydrides of HoCu_2 were a mixture of Cu, unknown hydride Ⅰ, and unknown hydride Ⅱ. Based on the PCT(pressure-concentration-temperature) curves under different reaction temperatures, the relationships among reaction temperature, equilibrium pressure, and maximum hydrogen absorption capacity were analyzed and discussed. The enthalpy change ΔH and entropy change ΔS as a result of the whole hydrogenation process were also calculated from the PCT curves. The magnetization and volumetric specific heat capacity of the hydride were also measured by SQUID magnetometer and PPMS, respectively.

A δ-function-like peak in the specific heat of two-dimensional vortex lattice： Monte carlo study

A repulsive vortex\|vortex interaction model was used to numerically study the melting transition of the two\|dimensional vortex system with Monte Carlo method. Then a δ\|function\|like peak in the specific heat was observed and the internal energy showed a sharp drop at the melting temperature, which indicated that there exists a first\|order melting transition at finite temperatures. The Lindemann criterion was also investigated and valid, but different from previous simulation results.

Synthesis of Diphenyl Carbonate over the Magnetic Catalysts Pd/La_(1-x)Pb_xMnO_3 (x=0.2-0.7)

The magnetic perovskite-supported palladium catalysts Pd/Lal_xPbxMnO3 （x = 0.2-0.7） were prepared and used for the oxidative carbonylation of phenol to diphenyl carbonate. The synthesized catalysts were characterized by the X-ray diffraction （XRD）, surface area measurement BET, vibration sample magnetometer （VSM） and tem- perature-programmed reduction （TPR）. The experimental results demonstrated that the magnetic Pd/La1-xPbxMnO3 （x = 0.4-0.5） obtain relative better catalytic activity. It can be explained by higher concentration of oxygen vacan- cies, larger amount and better mobility of lattice oxygen of their support. Furthermore, these samples possess suffi- cient saturated magnetization. Thus, Pd/La1-xPbxMnO3 （x = 0.4-0.5） may be suitable for operation in the magneti- cally stabilized bed reactor.

Effects of Electric and Magnetic Fields on Pure Dephasing of Exciton Qubits

In a two-dimensional quantum dot （QD） with parabolic confinement potential, we investigate pure dephasing due to deformation potential exciton-bulk longitudinal acoustic phonons （LAP） interaction for exciton qubits under the influence of external static electric and magnetic fields by adopting the full quantum-mechanical method of Kunihiro Kojima and Akihisa Tomita. The wave function is found and the dependence of the pure dephasing factor on the confinement length of the QD and time and temperature is discussed. We find the external electric and magnetic fields have important effects on pure dephasing of exciton qubits because exciton-LAP interaction increases, leading to more pure dephasing.

块状铁矿石竖炉磁化焙烧的工艺优化

竖炉磁化焙烧是处理难选红铁矿较有效的方法。通过对弱磁块矿竖炉磁化焙烧的试验研究,提出了更加科学、高效的竖炉磁化焙烧理论,在现有鞍山式竖炉的基础上,通过高效控制铁矿石竖炉磁化焙烧还原气氛,对竖炉磁化焙烧工艺进行了优化。结果表明：还原气体H2体积分数提高到12%±1%,同时降低CO体积分数,提高块矿焙烧还原温度,可获得最佳的磁化焙烧效果;通过独立设置铁矿石磁化焙烧还原煤气系统与加热煤气系统,可实现还原煤气的成分、流量、压力灵活调节;通过减少还原煤气总量,将矿石还原煤气量降低至1 400~1 600m3/h,降低竖炉的生产成本;通过独立的还原煤气系统,提高还原煤气中焦炉煤气比例,将H2体积分数控制在12%±1%,矿石磁化率控制在2.33左右,降低了竖炉磁化焙烧煤气消耗,提高矿石磁化焙烧质量;为保证还原煤气降低用量后的压力和喷出的均匀性,将还原煤气喷出塔的出口面积缩小50%,使矿石能够充分、均匀地完成还原。

First-and second-order phase transitions in RE_(6)Co_(2)Ga(RE=Ho,Dy or Gd)cryogenic magnetocaloric materials

Rare-earth(RE)rich intermetallics crystallizing in orthorhombic Ho_(6)Co_(2)Ga-type crystal structure exhibit peculiar magnetic properties that are not widely reported for their magnetic ordering,order of magnetic phase transition,and related magnetocaloric behavior.By tuning the type of RE element in RE_(6)Co_(2)Ga(RE=Ho,Dy or Gd)compounds,metamagnetic anti-to-paramagnetic(AF to PM)phase transitions could be tuned to ferro-to-paramagnetic(FM to PM)phase transitions.Furthermore,the FM ground state for Gd_(6)Co_(2)Ga is confirmed by density functional theory calculations in addition to experimental observations.The field dependence magnetocaloric and Banerjee’s criteria demonstrate that Ho_(6)Co_(2)Ga and Dy_(6)Co_(2)Ga undergo a first-order phase transition in addition to a second-order phase transition,whereas only the latter is observed for Gd_(6)Co_(2)Ga.The two extreme alloys of the series,Ho_(6)Co_(2)Ga and Gd_(6)Co_(2)Ga,show maximum isothermal entropy change(|ΔS_(iso)^(max)(5T)|)of 10.1 and 9.1 J kg^(-1)K^(-1)at 26 and 75 K,close to H_(2)and N_(2)liquefaction,respectively.This outstanding magnetocaloric effect performance makes the RE6 Co_(2)Ga series of potential for cryogenic magnetic refrigeration applications.

A Novel Magnetic Separation Oxygen-enriched Method and the Influence of Temperature and Magnetic Field on Enrichment

A novel oxygen-enriched method is presented. Using two opposite magnetic poles of two magnets with certain distance forms a magnetic space having a field intensity gradient near its borders. When air injected into the magnetic space outflows from the magnetic space via its borders, oxygen molecules in air will experience the interception effect of the gradient magnetic field, but nitrogen molecules will outflow without hindrance. Thereby the continuous oxygen enrichment is realized. The results show that the maximum increment of oxygen concentration reaches 0.49% at 298 K when the maximum product of magnetic flux density and field intensity gradient is 563T^2/m. The enrichment level is significantly influenced by the gas temperature and the magnetic field. The maximum increment of oxygen concentration drops to 0.16% when the gas temperature rises to 343 K, and drops to 0.09% when the maximum product of magnetic flux density and gradient is reduced to 101 T^2/m from 563 T^2/m.

Reversible magnetocaloric effect and refrigeration capacity enhanced by two successive magnetic transitions in DyB2

A large and reversible magnetocaloric effect is found in the compound DyB2, which is associated with two successive mag- netic transitions： a spin-reorientation-like transition followed by a ferromagnetic-paramagnetic transition. These two transitions appreciably enlarge the magnetic-refrigeration temperature window and yield a huge refrigeration capacity of 610 J kg^-1, with a maximum magnetic entropy change -ASmax of 17 J kg^-1K^-1, at a magnetic-field change of 5 T. The corresponding values for low magnetic-field change of 2 T are 193 J kg^-1 and 7.4 J kg-lK^-1, respectively.

Diffusion in Two-dimensional Magnetized Dusty Plasmas

A molecular dynamical simulation method is used to investigate the diffusion of the two-dimensional magnetized dusty plasmas. The effects of charge and mass of the particles, as well as the external magnetic field are discussed in detail It is shown that, relative to the mass of particulate, the charge and magnetic field have a more considerable effect on the diffusion process, particularly on the resulting structure of the system. The dependence of diffusion coecient on the temperature is shown to be linearly changed over a wide range of temperature.