MAGNETIZATION BEHAVIOUR FOR TEXTURED BULK YBaCuO POLYCRYSTALLINE SUPERCONDUCTORS

In present paper, study of magnetization behaviour was carried out for textured bulk YBaCuO polycrystalline superconductors synthesized by MTG process. The magnetization behaviour apparently different from that of sintered samples was observed. Magnetization hysteresis measurements were performed for the textured YBaCuO superconductors at 77K in± 10kOe magnetic field range. Based on the results of magnetization hysteresis, the magnetic field dependence of critical current density (Jc) at 77K was evaluated for the textured YBaCuO samples. The magnetic flux penetration in textured bulk YBaCuO polycrystalline superconductors was investigated at 77K through the magnetization hysteresis measurements under various maximum applied magnetic fields (HM) and reasonable discussion for the phenomena was conducted in terms of Bean's critical state model. The enhancement of magnetic properties for textured hulk YBaCuO polycrystalline superconductors is presumably attributed to the improvement of microstructure in these samples.

A Sensitivity Mapping Technique for Tensile Force and Case Depth Characterization Based on Magnetic Minor Hysteresis Loops

In the nondestructive testing and evaluation area,magnetic major hysteresis loop measurement technology are widely applied for ferromagnetic material evaluation.However the characterization ability of major hysteresis loop measurement technology greatly varies as the evaluated target properties.To solve this limitation,magnetic minor hysteresis loops,which reflect the responses of ferromagnetic material magnetization in a systematic way,is recommend.Inspired by plenty of information carried by the minor loops,the sensitivity mapping technique was developed to achieve the highest sensitivity of minor-loop parameters to the nondestructively evaluated targets.In this study,for the first time,the sensitivity mapping technique is used to measure the tensile force in a steel strand and evaluate the effective case depth in induction-hardened steel rods.The method and procedures for the sensitivity mapping technique are given before experimental detection.The obtained experimental results indicate that the linear correlation between the induced voltage(or the magnetic induction intensity)and the tensile force(or effective case depth)exists at most of the locations in the cluster of minor loops.The obtained sensitivity maps can be used to optimize the applied magnetic field(or excitation current)and the analyzed locations at the minor loops for achieving the highest sensitivity.For the purpose of tensile force measurement,it is suggested that the strand should be firstly magnetized to the near-saturation state and then restored to the remanent state.In this way,the highest sensitivity is obtained as about 15.26 mV/kN.As for the induction-hardened steel rods,the highest sensitivity of magnetic induction intensity to the effective case depth occurs under low magnetic field conditions and the absolute value of the highest sensitivity is about 0.1110 T/mm.This indicates that if the highest sensitivity is required in the case depth evaluation,the induction-hardened steel rods are only required to be weakly magnetized.The proposed sensitivity mapping technique shows the good performance in the high-sensitivity evaluation of tensile force and case depth in ferromagnetic materials and its application scope can be extended to other nondestructive detection fields.

Magnetostrictive and Kinematic Model Considering the Dynamic Hysteresis and Energy Loss for GMA

Due to the influence of magnetic hysteresis and energy loss inherent in giant magnetostrictive materials （GMM）, output displacement accuracy of giant magnetostrictive actuator （GMA） can not meet the precision and ultra precision machining. Using a GMM rod as the core driving element, a GMA which may be used in the field of precision and ultra precision drive engineering is designed through modular design method. Based on the Armstrong theory and elastic Gibbs free energy theory, a nonlinear magnetostriction model which considers magnetic hysteresis and energy loss characteristics is established. Moreover, the mechanical system differential equation model for GMA is established by utilizing D＇Alembert＇s principle. Experimental results show that the model can preferably predict magnetization property, magnetic potential orientation, energy loss for GMM. It is also able to describe magnetostrictive elongation and output displacement of GMA. Research results will provide a theoretical basis for solving the dynamic magnetic hysteresis, energy loss and working precision for GMA fundamentally.

Magnetic hysteresis, compensation behaviors, and phase diagrams of bilayer honeycomb lattices

Magnetic behaviors of the Ising system with bilayer honeycomb lattice（BHL） structure are studied by using the effective-field theory（EFT） with correlations. The effects of the interaction parameters on the magnetic properties of the system such as the hysteresis and compensation behaviors as well as phase diagrams are investigated. Moreover, when the hysteresis behaviors of the system are examined, single and double hysteresis loops are observed for various values of the interaction parameters. We obtain the L-, Q-, P-, and S-type compensation behaviors in the system. We also observe that the phase diagrams only exhibit the second-order phase transition. Hence, the system does not show the tricritical point（TCP）.

Effects of the Mn/Co ratio on the magnetic transition and magnetocaloric properties of Mn_(1+x)Co_(1-x)Ge alloys

We have investigated the magnetic transition and magnetocaloric effects of Mn1＋xCo1-xGe alloys by tuning the ratio of Mn/Co. With increasing Mn content, a series of first-order magnetostructural transitions from ferromagnetic to paramagnetic states with large changes of magnetization are observed at room temperature. Further increasing the content of Mn （x = 0.11） gives rise to a single second-order magnetic transition. Interestingly, large low-field magnetic entropy changes with almost zero magnetic hysteresis are observed in these alloys. The effects of Mn/Co ratio on magnetic transition and magnetocaloric effects are discussed in this paper.

Influence of rare-earth ions on structural and magnetic properties of CdFe_2O_4 ferrites

Nano-sized powders of rare-earth ions added CdFe2O4 ferrites were synthesized by oxalate co-precipitation method.The influence of R ions（R = Sm3＋, Y3＋, and La3＋） on the microstructure and magnetic properties of CdFe2O4 ferrites was studied.XRD, SEM, FTIR, and magnetic hysteresis loops were used for analyzing the samples.The addition of R ions alters the structure of the powders and decreases the crystalline size, lattice constant, and grain size.The magnetic properties such as saturation magnetization, remanent magnetization, and magnetic moment increased due to addition of rare-earth ions in CdFe2O4 ferrite.The formation of secondary phase on the grain boundaries supports the abnormal growth.FTIR spectra show two absorption bands.Results suggest that the magnetic properties depend on the particular method of preparation and additives.

Magnetocrystalline anisotropy and dynamic spin reorientation of half-doped Nd_(0.5)Pr_(0.5)FeO_(3)single crystal

The single crystals of Nd_(0.5)Pr_(0.5)FeO_(3)were successfully grown by optical floating zone method.Room temperature x-ray diffraction and Laue photograph declared the homogeneity and high quality of the crystal.The significant magnetic anisotropy and multiple magnetic transitions illustrate the complex magnetic structure.At high temperatures(T>66 K),it shows the typical characteristics ofΓ_(4)(G_(x),A_(y),F_(z))state.With the decrease of the temperature,it undergoes a first-order spin reorientation transition fromΓ_(4)(G_(x),A_(y),F_(z))toΓ_(2)(F_(x),C_(y),G_(z))state in the temperature window of 45-66 K under an applied magnetic field of 0.01 T.As the temperature drops to~17 K,a new magnetic interaction mechanism works,which results in a further enhancement of magnetization.The T-H phase diagram of Nd_(0.5)Pr_(0.5)FeO_(3)single crystal was finally constructed.

Size-dependent exchange bias in single phase Mn_3O_4 nanoparticles

Glassy magnetic behavior and exchange bias phenomena are observed in single phase Mn3O4 nanoparticles.Dynamics scaling analysis of the ac susceptibility and the Henkel plot indicate that the observed glassy behavior at low temperature can be understood by taking into account the intrinsic behavior of the individual particles consisting of a ferrimagnetic（FIM） core and a spin-glass surface layer.Field-cooled magnetization hysteresis loops display both horizontal and vertical shifts.Dependence of the exchange bias field（HE） on the cooling field shows an almost undamped feature up to 70 kOe,indicating the stable exchange bias state in Mn3O4.HE increases as the particle size decreases due to the higher surface/volume ratio.The occurrence of the exchange bias can be attributed to the pinning effect of the frozen spin-glass surface layer upon the FIM core.

Mechanical and magnetic hysteresis as indicators of the origin and inception of fatigue damage in steel

N2 and N3 are known as the transition points of the three principal stages of fatigue: initial accommodation, accretion of damage and terminal fatigue. Many experiments show that the ratios of N2/Nf and N3/Nf tend to be stable even though the specific N2 and N3 values may fluctuate widely. The primary goal of this research is to study the piezomagnetic field surrounding AISI 1018 steel specimen under repeated loads and to find the ratio values of N2/Nf and N3/Nf by analyzing 11 sets of low-cycle fatigue data. An MTS-810 testing system with a peak capacity of 222 kN was used to obtain the data which consisted of stress, strain, and piezomagnetic field. A computer program was constructed to track the evolution of the piezomagnetic field and re- gression analysis was carried out to determine N2 and N3 values. It was observed that there exists a consistent relationship between N2 and Nf. The apparent invariance of the ratio N2/Nf implies that N2 may be identified as an index of performance in the early loading response of a specimen that forecasts its fatigue life, Nf. It has been demonstrated that measurements of the magnetic and mechanical hysteresis can yield significant insights into the various stages of the development of a fatigue critical microstructure which culminates in complete rupture of the material.

Study of magnetic hysteresis effects in a storage ring using precision tune measurement

With the advances in accelerator science and technology in recent decades, the accelerator commumty has focused on the development of next-generation light sources, for example diffraction-limited storage rings （DLSRs）, which require precision control of the electron beam energy and betatron tunes. This work is aimed at understanding magnet hysteresis effects on the electron beam energy and lattice focusing in circular accelerators, and developing new methods to gain better control of these effects. In this paper, we will report our recent experimental study of the magnetic hysteresis effects and their impacts on the Duke storage ring lattice using the transverse feedback based precision tune measurement system. The major magnet hysteresis effects associated with magnet normalization and lattice ramping are carefully studied to determine an effective procedure for lattice preparation while maintaining a high degree of reproducibility of lattice focusing. The local hysteresis effects are also studied by measuring the betatron tune shifts which result from adjusting the setting of a quadrupole. A new technique has been developed to precisely recover the focusing strength of the quadrupole by hysteresis effect. returning it to a proper setting to overcome the local

Dynamic magnetic hysteresis in a liquid suspension of acicular maghemite particles

This paper presents theoretical and experimental studies on the magnetodynamics and energy absorption in a dilute suspension of small ferromagnetic particles with magnetic hysteresis and mechanical mobility in an AC magnetic field. Experiments with 0.1% suspensions of acicular particles of gamma ferric oxide in solid and liquid matrices, subjected to a 430 Hz magnetic field with an intensity of up to 1200 Oe, revealed important role of particle mobility. The main qualitative and quantitative features of the phenomenon are in agreement with a model of joint magneto-mechanical dynamics of particles with a chain-of-spheres mode of incoherent magnetic reversal.

Magnetic Properties and Kinetics Parameters of Electroless Magnetic Loss CoFeB Films

Electroless CoFeB films with good soft magnetic properties were fabricated on polyester plastic substrate from sodium tartarate as a complexing agent.The plating rate of electroless CoFeB films is a function of concentration of sodium tetrahydroborate,pH of the plating bath,plating temperature and the metallic ratio.The estimated regression coefficient b0-b3 confidence interval,residual error r and confidence interval rint were confirmed by a computer program.The optimal composition of the plating bath was obtained and the dynamic electromagnetic parameters of films were measured in the 2-10 GHz range.At 2 GHz,the μ＇,μ″ of the electroless CoFeB films were 304 and 76.6,respectively,as the concentration of reducer is 1 g/L.Magnetic hysteresis loop of the deposited CoFeB films show a remanence close to the saturation magnetization and coercivity of about 55.7-127.4 A/m.The loops along the hard axis display low anisotropic field Hk of 2 388-3 582 A/m.

Effect of Particle Size on the Hysteretic Behavior and Magnetocaloric Effect of La_(0.5)Pr_(0.5)Fe_(11.4)Si_(1.6) Compound

Bulk Lao.sPro.sFe11.4Sil.6 compound exhibits a large magnetic-entropy change ASm of 28.1 J/（kg K） for a magnetic-field change from 0 to 1.5 T at the Curie temperature, Tc of 186 K, accompanied by a large magnetic hysteresis of 56 J/kg and a noticeable thermal hysteresis of about 1 K. If the bulk sample is ground into middle-size particles （30-60 tm）, then the thermal hysteresis is almost eliminated and the magnetic hysteresis loss is decreased by 29%, while the large ASm maintains. Especially, fine powder with an average size of 2 tm shows the same Tc as the bulk and does not lose stability. Meanwhile, a comparatively large ASm of 13.9 J/（kg K） and a hysteresis reduction of 70% are attained. The hysteresis reduction can be ascribed to the decrease of internal strains and to the improvement of heat transfer due to the increase of the ratio of the surface area to the volume.

Research on Magnetomechanical Coupling Effect of Q235 Steel Member Specimens

In this study,magnetomechanical coupling tests were performed on Q235 solid round steel model specimens in NIM-200HF magnetomechanical coupling equipment.Hysteresis loops were obtained in different magnetic fields and stresses.Magnetization curves were also achieved at different stresses.Influence of the applied stresses on the hysteresis loops was investigated.The stress sensitive region and linear stress sensitive region of magnetic induction were determined for the model specimen according to the experimental data.The dependence relation of magnetic induction versus applied stresses was established,and the optimum magnetic field was determined in the stress sensitive range of magnetic induction,which builds a basis for nondestructive testing(NDT) of stress with the total magnetic flux for steel structure.Based on modified Jiles-Atherton's model of magnetic hysteresis,the hysteresis loop for Q235 steel 4-mm diameter model specimen was numerically simulated,which was well consistent with the experimental results.

Study of cobalt ferrite nanosuspensions for low-frequency ferromagnetic hyperthermia

High-coercive cobalt ferrite nanoparticles were synthesized and studied for magnetic hyperthermia by direct injection of their suspension into a tumor and application of a strong audio-frequency magnetic field for heating. Physical （dynamic magnetic hysteresis and heat generation in both liquid and solid dispersions）, biological （toxicity and penetration of particles in therapeutic quantities into mouse tumor tissue） as well as other properties of the particles were studied. A model was developed to describe the magnetodynamics in suspensions of magnetic nanoclusters with an account for both Brownian and regular rotations, to provide understanding of observed phenomena. The experimental and theoretical techniques developed have formed a basis for controllable synthesis of the magnetic nanoparticles for low-frequency heat generation in medical and other applications.

Influence of partial substitution of cerium for lanthanum on magnetocaloric properties of La_(1–x)Ce_xFe_(11.44)Si_(1.56) and their hydrides

The structure and magnetocaloric properties of La1–xCexFe11.44Si1.56 and their hydrides La1–xCexFe11.44Si1.56Hy（x=0, 0.1, 0.2, 0.3, 0.4） were investigated.The samples crystallized mainly in the cubic Na Zn13-type structure with a small amount of α-Fe phase as impurity.The lattice constants and Curie temperature presented the same change tendency with increasing of Ce content.For the hydrides, the influence of Ce content on lattice constants was weakened and the values of H concentration y were approximate to be 1.56.The La1–xCexFe11.44Si1.56 compounds exhibited large values of isothermal entropy change –ΔSm around the Curie temperature TC under a low magnetic field change of 1.5 T.The value of –ΔSm increased and then decreased with increasing Ce content, reached the maximum, 26.07 J/kg·K for x=0.3.TC increased up to the vicinity of room temperature by hydrogen absorption for the Ce substituted compounds, but TC only slightly decreased with increasing Ce content.The first-order metamagnetic transition was still kept in the hydrides and the maximum values of –ΔSm were lower than those of the La1–xCexFe11.44Si1.56 compounds, but still remained large values, about 10.5 J/kg K under a magnetic field change of 1.5 T.The values of –ΔSm were nearly independent of the Ce content and did not increase with increasing x for the hydrides.The La1–xCexFe11.44Si1.56Hy（x=0–0.4） hydrides exhibited large magnetic entropy changes, small hysteresis loss and effective refrigerant capacity covered the room temperature range from 305 to 317 K.These hydrides are very useful for the magnetic refrigeration applications near room temperature under low magnetic field change.

Microstructure and Magnetic Property Variation with Addition of Rare Earth Element Dy in Co-Ni-Al Ferromagnetic Shape Memory Alloy

The influence of rare earth element Dy on martensitic transformation and magnetic properties of Co-Ni-Al alloy was studied.The results showed that the microstructure of the sample has a dual-phase structure（γ-phase and martensite）.The rare earth element Dy was segregated in Co-richγ-phase and took the place of Co after its addition into the Co-Ni-Al alloy.As Dy content increased to over 0.5at.%,the grain was refined and the rare earth intermetallic compounds Co5 Dy were precipitated inγ-phase.Meanwhile,one-step thermo-elastic martensitic transformation occurred in the sample,wherein the phase transformation temperature significantly increased with rising Dy content.The martensite had a tetragonal L10 structure with a（111）twinning plane.Furthermore,the sample exhibited obvious hysteresis behaviors in the magnetic hysteresis loops.In addition,the saturation magnetization,coercivity,retentivity and magnetocrystalline anisotropy were significantly enhanced owing to the bigger radius of Dy which took the place of Co in the alloy.

Intrinsic ferromagnetism in CoBr2 nanolayers:a DFT+U and Monte Carlo study

The intrinsic ferromagnetism of CoBr2 bulk was investigated using DFT(density functional theory)combined with the full potential linear augmented plane wave method and Monte Carlo simulations.The ground state of CoBr2 exhibits ferromagnetic behavior and a semiconductor character.We used the generalized gradient approximation(GGA)and GGA+U(Hubbard correction)approximations to determinate the magnetic moment.The magnetic moment reached the experimental value and was in good agreement with the other theoretical values.The value obtained was used as an input to a Monte Carlo study to calculate the thermal magnetization and magnetic hysteresis cycles.Ferromagnetic behavior was observed and was found to be due to an positive exchange interaction.These results lead us to believe that this material could be a promising spintronic material.

Influence of High-Pressure Nitrogenation on the Structural,Magnetic and Magnetocaloric Properties of La_(0.5)Pr_(0.5)Fe_(11.4)Si_(1.6)

Nitrogenation of La0.5Pr0.5Fe11.4Si1.6 with a particle size of 100-150 μm was performed in a high-purity N2 atmosphere of 40 MPa. La0.5Pr0.5Fe11.4Si1.6N0.3 nitrogenated at 480 ℃ exhibits an increase in the Curie temperature Tc from 187 to 195 K. Moreover, for a field change from 0 to 1.5 T, the maximum hysteresis loss at Tc is remarkably reduced from 53 to 3 J kg^-1 and a large magnetic-entropy change ASm of over 10 J kg^-1 K^-1 is maintained. For a La0.5Pr0.5- Fe11.4Si1.6N1.2 sample, nitrogenated at 550 ℃, the XRD pattern clearly exhibits two 1：13 phases and, accordingly, the thermal magnetic curves exhibit two transitions, at 210 and at 295 K. The two transitions lead, for a field change of 5 T, to a ASm larger than 2 J kg^-1 K^-1 over a large temperature range from 200 to 310 K with a maximum value of 5.3 J kg^-1 K^-1 at 225 K. Upon further increase in the nitrogenation temperature to 650 ℃, the amount of the nitrogen- poor phase strongly decreases and a large amount of α-Fe precipitates, resulting in a large reduction in the MCE.