Magnetization Studies of Mercury-Cuprates and Its Precursors

The mercury-cuprates such as (Hg, Cr)/Sr-1201 and (Hg, Re)/Sr-1201 were synthesized byencapsulation-technique at 880–920°C for 12–16 h, and characterized by power XRD,M(T) andM(H). All the precursors (Sr₂CuO₃, Cr_0.30Sr₂CuO _y or Re_0.10Sr₂CuO_y) were found to be non-superconducting. The samples with optimal composition (Hg_0.70Cr_0.30)Sr₂CuO_4+δ [(Hg, Cr)/Sr-1201] and (Hg_0.90Re_0.10)Sr₂CuO_4+δ [(Hg, Re)/Sr-1201] are superconducting withT _c ^onset ∼ 58 and ∼ 54 K, respectively. At low temperatures (below 10 K), on cooling in D.C.-magnetic field of 4 kOe, the sample (Hg, Re)/Sr-1201 shows a dramatic decrease in diamagnetic signal. Further, this effect is also faintly reflected in theM(H) curve. Such a behaviour was not observed in the (Hg, Cr)/Sr-1201 cuprates. We ascribe this effect to a field enhanced paramagnetic contribution possibly arising from mixed valent (6+, 7+ dominant) Re ions in the (Hg, Re)/Sr-1201 cuprates.     

Impedance and Magnetization Studies of Ultrafine Ni-Zn Ferrite

Ultrafine Ni0.5Zn0.5 Fe2O4 powder was prepared by PVA aided chemical method. The powder and sintered pellets were characterised by X-ray diffraction (XRD), vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA) and complex impedance (Cl) analysis. The particles are found to be in the size range of 15 to 26 nm for various annealing temperatures. The coercivity, saturation magnetisation, Neel temperature and electrical conductivity are found to vary with sintering time at 800℃ for the pellet samples. The variations in the above intrinsic properties are explained qualitatively     

Magnetization Studies of Field-Induced Transitions by Using a Single-Turn Coil Technique

Some technical improvements for magnetization measurements using a vertical-type single-turn coil (V-STC) method have been attempted. We have chosen LaCoO₃, RbCoBr₃ and SrCu₂(BO₃)₂ that show interesting field induced magnetic transitions, as test materials. Intriguing features were clearly observed in magnetic fields of up to 100 T. The quality of the data is of comparable to those obtained by a conventional non-destructive pulse magnet.     

Exchange Bias and Its Phase Reversal in Zero Magnetization Admixed Rare-Earth Intermetallics

The exchange bias effect—an important attribute in many device applications— is traditionally discussed as a form of exchange anisotropy at the interface between the ferromagnetic/antiferromagnetic layers of two distinct systems. We report here on magnetically ordered alloys possessing the feature of unidirectional anisotropy that reverses its sign at a characteristic temperature. These alloys are admixed rare-earth (RE) intermetallics, comprising two dissimilar rare-earth ions, belonging to the two different halves of the $4f$ series. All $4f$ rare-earth ions exhibit ferromagnetic coupling between the spins of their ions and the conduction electrons. Magnetic moments of dissimilar RE ions in such admixed alloys, however, get antiferromagnetically coupled, and they display a magnetic compensation feature in which the field-induced reversal in the orientation of the magnetic moments of dissimilar rare-earth ions occurs at the compensation temperature $(T_{rm comp})$ . Above a threshold field, the conduction electron polarization also reverses its sign at $T_{rm comp}$. We suggest that this effect correlates with the observed phase reversal in the exchange bias field.      

电工钢片交流磁化曲线的计算机拟合及应用

本文介绍一种电工钢片交流磁化曲线的计算机拟合方法及其在磁测量计算过程中的运用     

MnFe2O4多晶微粉的共沉淀法制备及磁性研究

用化学共沉淀法制备了MnFe2O4铁酸盐多晶微粉,发现与NiFe2O4相比,MnFe2O4的制备有其独特之处:反应温度在80℃以上时,经沉淀洗涤后直接得到MnFe2O4纳米微粉,不需热处理过程;反应温度在80℃以下时,需要对沉淀洗涤后前驱体进行热处理才能得到MnFe2O4纳米微粉.利用振动样品磁强计测量了样品在室温下的磁性能;利用X射线衍射确定了粉体的组成、晶粒大小和晶格常数;利用扫描电子显微镜观察了颗粒的形貌.     

砝码磁化强度的测量结果不确定度分析

砝码是一种能复现给定质量值的实物量具，具有一定的物理特性和计量特性，本文详细介绍了砝码物理特性磁化强度的测量及测量结果不确定度分析。     

铁素体纤维的损伤与磁性

在铁素体纤维提取工艺理论分析的基础上,研究了提取过程中纤维的损伤机制,提出了提高纤维磁性的工艺措施。结果表明,纤维的损伤机制为氧化反应和置换反应,纤维中的氧、铜和吸附水导致其磁性下降。当mCr/m(Fe+Cr)在13%附近时,通过采取适当的工艺措施,纤维的比饱和磁化强度MS出现极大值(159 emu/g)。     

High-Sensitivity Magnetization Measurements

1. IntroductionThe increasing importance of thin-film magneticdevices, plus the continuing interest in weakly magnetic geological samples and high-temperature superconductors, has increased the need for accurate measurements of the magnetic properties of samples thatare physically small, or have small magnetization, orboth. Three measurement techniques are regularlyused for such measurements' the vibrating-samplemagnetometer (VSM), the alternating gradient-fieldmagnetometer (AGM or AGFM), …     

Magnetization Time Lag Caused by Eddy Currents and Its Influence on High-Speed Magnetic Flux Leakage Testing

In high-speed magnetic flux leakage (MFL) testing, the tested workpieces pass rapidly through magnetizers. Thus, the magnetization time for workpieces is short. Because of the eddy current effect, the magnetic field inside the workpieces cannot instantly reach equilibrium, and if the magnetizing time is insufficient for the field to reach equilibrium, the MFL signals will be changed because of incomplete magnetization. In this article, the magnetization time lag caused by eddy currents and the influence of this lag on high-speed MFL testing is investigated. The time required for magnetic field to reach equilibrium in specimens, including steel bars and pipes, is obtained by theoretical calculations, finite element simulations, and experiments. The results indicate that the time required for a magnetic field inside a specimen to reach equilibrium is in the range of 50–100 ms. Using conventional magnetizers, the defect signals at testing speed of 10 m/s change because the workpiece reaches the detection zone before the magnetic field inside reaches the stable state. A simple solution is to increase the axial length of the magnetizing coil. After this procedure, signals obtained at 0.1 m/s and 10 m/s are almost identical.     

Photoinduced Magnetization Rotation and Precessional Motion of Magnetization in Ferromagnetic (Ga,Mn)As

Dynamics of photoinduced magnetization have been studied in ferromagnetic semiconductor (Ga,Mn)As thin films by time-resolved polar Kerr rotation. Ultrafast (150 fs) magnetization rotation has been realized using both chirality of excitation light and p–d exchange interaction. We also report on the occurrence of photoinduced magnetization precession in longer time domain. This is initiated by a change in hole concentration and resultant change in magnetic anisotropy. The overall behaviors of these photoinduced magnetization dynamics are discussed.     

Stress Induced Enhancement of Magnetization Reversal Process of DyFeCo Films With Perpendicular Magnetization

A method to control magnetization reversal in magnetic films with perpendicular magnetic anisotropy was demonstrated in this study. Alloys of rare earth-transition metals (RE-TM) with their extremely large anomalous Hall coefficient and relatively large magnetostriction constants were suitable to observe the stress induced anisotropy using anomalous Hall effect. Stress applied to the RE-TM thin films significantly reduced the perpendicular coercivity and nucleation field of the film in comparison with that of the film in stress-free condition. Dy_x(Fe₉₀Co₁₀)_1-x thin films revealed large Hall voltage and remarkable change in the coercivity under the mechanical tensile stress     

Magnetization of dilute Al-Mn and Al-Fe alloys

The magnetization of very dilute Al-Mn and Al-Fe alloys was measured from 2 to 0.01 K in order to obtain a limit on how nonmagnetic such systems are. Results indicate that the impurity contribution to the magnetization is almost temperature independent and that the moment per impurity is less than 1.7 × 10^–2. The Al nuclear paramagnetism is mainly responsible for the uncertainty in this value.Supported by NSF grant DMR 76 21702.     

Effects of Substituting Se with Te in the FeSe Compound: Structural, Magnetization and M?ssbauer Studies

Polycrystalline samples of FeSe_1−x Te _x (x=0.00, 0.25, 0.50, 0.75 and 1.00) were synthesized by solid-state reaction to study the effects of substituting Se with Te in the system. The magnetization properties of the resulting compounds were investigated and the crystallographic structures of the samples analyzed through X-ray diffraction. M?ssbauer spectroscopy was used to determine the ionic state of the Fe ions and the hyperfine fields. The magnetic susceptibility curves of the samples with x=0.25, 0.50 and 0.75 show superconducting behavior. The lattice parameters and the cell volume increase monotonically with increasing Te concentration and the M?ssbauer spectra reveal the absence of internal magnetic hyperfine fields.     

Magnetization reversal in ferromagnets

Quantum and classical reversal of magnetization in ferromagnets are considered. Expressions for the tunnelling and thermal activation rates of the magnetization reversal with the effect of magnetoelastic dissipation to the lowest order are presented with the prefactors included. The results are given for low temperatures, near the cross-over temperature and for high temperatures, so that an experimental check would be possible to perform. The results are within the transition state theory.     

Magnetization and Susceptibility Studies on BaZrO3-Doped YBa2Cu3O7 − x Bulk Superconductors

We studied the YBa₂Cu₃O_{7 ? x} bulk superconductor doped with BaZrO₃ up to 50 wt.%, obtained by solid-state reaction powder technology. From DC magnetization loops and low frequency AC susceptibility measurements we determined the influence of the BaZrO₃ doping level on the critical temperature, critical current density, field for full penetration, and intergrain lower critical field. The results show that even high content of BaZrO₃ does not lead to degradation of the superconducting properties of bulk YBa₂Cu₃O_{7 ? x} .     

Relaxation and Magnetization Dynamics of Frustrated Spin-Chain Systems

A 3D model of the magnetization dynamics in frustrated triangular spin-chain systems Ca₃Co₂O₆ is proposed. This model is a generalization of the 2D model developed earlier. The spins are assumed to interact with the nearest neighbors and external agency (heat reservoir and external magnetic field) that causes them to change their states randomly with time. A probability of a single spin-flip process is assumed in a Glauber-like form. The 3D model allows describing the step-like behavior of a magnetization curves experimentally observed in a strong magnetic field.     

Thermodynamic Magnetization of Normal and Superfluid 3He

We have measured the thermodynamic magnetization in the various phases of normal and superfluid ³ He. The A-B discontinuity differs from that inferred from nuclear-specific (NMR) experiments. We offer reasons why this apparent disagreement can be consistent with our current picture of super-fluid ³ He. One consequence of this measurement is an improved set of values for the phenomenological Landau-Ginzburg free energy -parameters.     

Magnetization in Ni and Ni-Fe thin films

Nickel films have been deposited in conventional high vacuum, ultra-high vacuum, and in controlled contaminant, ultra-high vacuum environments. High field saturation magnetization Msmeasurements on the films made in high vacuum and an oxygen-contaminated ultra-high vacuum system show that they posses low values of Msfor film thicknesses of 1000 Å. The normal moments observed for ultra-high vacuum deposited films lead to the conclusion that the low Msvalues are associated with the oxygen and are caused by a true loss of effective magnetization rather than coupled superparamagnetism or a ripple blocking field. Supplementary torque and ferromagnetic resonance studies on the Ni and two different Ni-Fe compositions also show that the grain boundary perpendicular anisotropy models are not particularly relevant for films made under such nominal technical vacuum conditions.