Effects of Biaxial Crystal Field on the Magnetic Properties on?a?Spin-1?Ising?System

Within the effective field theory (EFT) with a probability distribution technique that accounts for the self spin correlation functions, the magnetic properties such as the hysteresis loops, susceptibility and magnetization of a spin-1 Ising system with effects of a biaxial crystal field are studied. The effects of the biaxial crystal field on the magnetic properties are discussed and numerical calculations are performed and analyzed for the cases of the honeycomb lattice. A number of interesting phenomena such as the shape of the hysteresis loops and the susceptibility have been found.     

Magnetic and dielectric properties of HoMnO3 nanoparticles synthesized by the polymerized complex method

In this paper, we report on the magnetic and dielectric properties of HoMnO₃ nanoparticles with different size synthesized by a polymerized complex method have been investigated. The HoMnO₃ nanoparticles crystallized in hexagonal perovskite-type structure. The zero-field-cooled magnetic susceptibility curve of HoMnO₃ nanoparticles with averaged size of 30 nm shows that complicated magnetic transitions occurred in a temperature range from 2 to 100 K, which was confirmed by magnetic hysteresis loops. With increasing the particle size, the antiferromagnetic (AFM) transition temperature increases from 56 to 77 K, due to the reduced surface-to-volume ratio. Moreover, with a decrease in particle size, the Mn-spin reorientation temperature (T_SR) is enhanced from 44 to 48 K.     

Magnetic Properties of Oxygen Clusters

Magnetic properties of oxygen pair clusters are investigated theoretically for different geometries of clusters which can be realized by doping molecular cryomatrices with oxygen. Anomalous temperature and pressure behavior of the magnetic susceptibility, magnetic heat capacity and magnetic entropy is predicted. It is shown that the low-temperature magnetic susceptibility of these solid solutions is very sensitive to the orientational structure of impurity oxygen clusters, which makes it possible to use the susceptibility data for studying structural and dynamics properties of the host lattice, including high-pressure phases of simple molecular crystals.     

Magnetic Field for Radiating and Receiving Loops Placed on Parallel Planes

In the calibration of radio receivers and field-intensity meters, a radiating loop and a receiving loop under test are mainly located either in a coaxial or coplane to each other. A formula to obtain the average magnetic-field strength incident on a receiving loop is derived for the case where the radiating and receiving loop antennas have a certain deviation on a parallel plane from the coaxial or coplanar alignment of the loops. In order to expand the uniform region of the magnetic field around the test point, the distribution of the magnetic field is investigated by using this formula for some alignments where the four (or less) radiating loops and a receiving loop lie on parallel planes to each other. It is obvious that the uniform regions are improved by factors of about 10 or 16 by increasing a radiating loop to two or four loops, respectively.     

The Magnetic Properties of the Spin-1 Ising System with?the?Effect of the Transverse Crystal Field

Within the framework of the effective-field theory with a probability distribution technique which accounts for the self-spin correlations, we study the magnetic properties of the spin-1 Ising system with the transverse crystal field and the applied external magnetic field. The influence of the transverse crystal field on the phase diagrams, hysteresis loops and susceptibility is discussed in detail.     

Hysteresis properties of sintered Sm Co5permanent magnets

The magnetic properties of individual SmCo5particles have been extensively studied in the literature. In the present work, initial magnetization curves and hysteresis loops of sintered SmCo5magnets have been drawn with a hysteresigraph. The observed properties depend on the previous magnetic treatment of the sample. After thermal demagnetization, the initial susceptibility is very high; after dc field demagnetization, it is very weak. The inner hysteresis loops are often unsymmetrical. Results are interpreted by considering the magnets as particle assemblies related together by dipolar interactions.     

Calibration of Coercive and Stray Fields of Commercial Magnetic Force Microscope Probes

Variable-field magnetic force microscope (MFM) is introduced to characterize the magnetic behavior of commercially available MFM probes that is relevant to interpret MFM imaging. A Nanotec Electronica S.L. microscope has been conveniently modified to apply magnetic fields in axial direction (up to 1.5 kOe) and in-plane direction (up to 2.0 kOe). Axial and transeverse hysteresis loops of the probes have been generated by measuring the changes in the MFM contrast observed when the magnetic field is applied. The variation of the MFM signal is ascribed to the modification of the magnetic state of the tips. This is enabled by the large coercitivity (~1.7 kOe) of the checked longitudinal recording media. The properties of the probes depend on the coating material, the macroscopic tip shape, and tip radius. In only a few cases, the magnetization of the probe can be oriented along in-plane orientation. In addition, the stray field of the tips has been deduced by measuring the influence of the probe in the magnetic state of the checked samples.     

Effects of Mn and Gd Co-substituted into ZnO on Structural and Magnetic Properties

We have worked on the structural and magnetic properties of Zn_0.99?xMn_0.01Gd _x O _δ (for x = 0.02, 0.03, and 0.04) compounds prepared by using a sol–gel method. The x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy were used to understand the structural properties of the samples. We observed that co-substitution of Mn (1 %) and Gd (2–4 %) into the ZnO does not change the hexagonal structure. Scanning electron microscope (SEM) images show us that the grain size decreases with the increasing amount of the Gd into the ZnO matrix. The magnetic properties of the samples have been investigated by using magnetic hysteresis and DC susceptibility measurements. The ZMG1 sample shows a weak ferromagnetic behavior at room temperature, whereas the ZMG2 and ZMG3 samples exhibit a paramagnetic nature. Furthermore, it is also found that the magnetizations of the samples decrease with increasing Gd content in the ZnMnO system due to the enhancing interaction between Gd ³⁺ ions. We summarize that the co-substitution of Mn and Gd into the ZnO generates a room-temperature ferromagnetism, but it still needs more work to obtain strong and high coercivity magnetic loops for applications.     

Magnetic hysteresis properties of internally oxidised Ni-Si alloys

Results are presented of magnetic hysteresis measurement made on some internally oxidised Ni-Si alloys. The alloys investigated were originally of nominal composition 0.058, 0.48, 0.77 and 0.96 wt % Si in Ni. Hysteresis loops have been obtained for all the alloys in both unoxidised and several internally oxidised states using a standard technique. The effect of the internal oxide precipitation on the coercivity and remanence of the specimens is made clear by these measurements. The dependence of coercivity on precipitate morphology and alloy compositions is considered and results of the variation of coercivity with the temperature of measurement in the range 20 to 265° C are discussed.     

Magnetic damping force in electrodynamically suspended trains

A magnetic levitation system utilizing superconducting magnets is now being developed for a high speed ground vehicle. From a view point of ride quality, a damping force for the mechanical oscillation of a levitated vehicle is one of the most important problems in this levitation system. This paper presents the analysis of the magnetic damping force in a loop track magnetic levitaion system; the magnetic damping force is caused by track loops. It is theoretically pointed out that the magnetic damping force is "negative" except in an extremely low velocity range. The theory is applied to the estimation of the magnetic damping force in a train model of practical interest. The results of the estimation suggest that the negative magnetic damping force is considerably large in a median velocity range (100 ∼ 200 km/h). Passive damping has been also investigated; it is found that damper loops installed in the levitation cryostat is effective even in persistent mode operation. It is concluded that rather good ride quality will be obtained by use of the passive damping method.     

General Formulas for the Average Magnetic Field at a Receiving Circular-Loop Antenna Placed Arbitrarily to a Radiating Loop

For testing the sensitivity of receivers having loop antennas, radiating and receiving loops have been located either coplanar or coaxial to each other. Theoretical analyses of the magnetic fields have been carried out for such alignments of loops. It is often necessary in the actual tests to estimate the effects of deviations from these ideal arrangements of the loops. In this paper, the radiating and receiving circular loops are located arbitrarily in direction, and a formula is derived to obtain the average normal component of the magnetic-field strength incident on the receiving loop using the Eulerian angles. The theory is applied to the design of a generator in which a rotating field is used as the standard field. In this case, the calculated values of the magnetic field are in agreement with the measured ones to within ±0.1 dB.     

Nd_2Fe_(14)B/α-Fe交换耦合双层薄膜磁性能

利用微磁学理论模拟计算了Nd2Fe14B/α-Fe交换耦合双层膜的磁滞回线,并对双层膜体系的剩磁、矫顽力、最大磁能积与软磁层厚度的关系进行了研究。结果显示,软磁层厚度小于临近尺寸时,磁滞回线为矩形,双层膜完全耦合;软磁层厚度与磁性能的关系表明,随着软磁层厚度的增加,剩磁和最大磁能积先增大后减小,而矫顽力单调下降。     

Tweezing of Magnetic and Non‐Magnetic Objects with Magnetic Fields

Although strong magnetic fields cannot be conveniently “focused” like light, modern microfabrication techniques enable preparation of microstructures with which the field gradients – and resulting magnetic forces – can be localized to very small dimensions. This ability provides the foundation for magnetic tweezers which in their classical variant can address magnetic targets. More recently, the so‐called negative magnetophoretic tweezers have also been developed which enable trapping and manipulations of completely nonmagnetic particles provided that they are suspended in a high‐magnetic‐susceptibility liquid. These two modes of magnetic tweezing are complimentary techniques tailorable for different types of applications. This Progress Report provides the theoretical basis for both modalities and illustrates their specific uses ranging from the manipulation of colloids in 2D and 3D, to trapping of living cells, control of cell function, experiments with single molecules, and more.     

Magnetic properties of some rare earth ferrites

The tetragonal SrEu₂Fe₂O₇ and BaEu₂Fe₂O₇ have been investigated using Mössbauer spectroscopy and magnetic susceptibility techniques. The measurements of magnetic susceptibility have been carried out in the temperature range 100 to 700°K. The data have been fitted to Curie-Weiss law $\text{χ =}\text{C}\text{T}\text{+ θ +}\text{A}$ using a non-linear least square curve fitting procedure. These ferrite compounds are paramagnetic above 534°K and 537°K respectively, with antiferromagnetic ordering below these temperatures.     

Magnetic field dependence of the Leggett angle,the susceptibility,and the longitudinal nuclear magnetic resonance of3He-B

The magnetic field dependences of the Leggett angle, the susceptibility, the free energy, and the longitudinal NMR frequency of³He-B are calculated from a generalized weak coupling theory. Employing the experimental values for the Landau parametersF ₀ ^a andF ₂ ^a , reasonable agreement with the susceptibility data measured recently by Hoyt, Scholz, and Edwards is obtained. Substantial field dependence of the Leggett angle and the longitudinal NMR frequency is predicted.     

Magnetic properties of textured CoPd nanocrystalline thin films

CoPd is an important nanomaterial for magnetic and magneto-optic storage of information. In this work, CoPd alloyed thin films are grown via radio frequency magnetron sputtering on silicon, glass and polyimide substrates in a vacuum chamber with base pressure of 5 x 10(-8) mbar. The films are nanocrystalline with grain size between 4 and 80 nm. The magnetic properties of thoroughly textured CoPd alloyed thin films are compared to random polycrystalline ones. Magnetization hysteresis loops recorded under fields up to 12 kOe via a home-made magneto-optic Kerr-effect magnetometer reveal strong tendency for perpendicular magnetic anisotropy for the textured film. This anisotropy leads to the formation of well-defined stripe or labyrinthine ferromagnetic domains with the local spins oriented perpendicular to the film plane. The domain patterns and the hysteresis loops are simulated with micromagnetic calculations. Finally, an induced magnetic moment of 0.44 microB/atom is measured for Pd via X-ray magnetic circular dichroism and it is separated into spin and orbital magnetic moment contributions.     

Magnetic properties of thin-film Co/Fe/Ni magnetic systems

The magnetic properties of Co/Fe/Ni thin-film structures grown by magnetron sputtering have been studied using magnetooptical techniques. The results of x-ray diffraction measurements showed that all samples possessed a nanocrystalline structure. The magnetization curves and hysteresis loops were measured using the equatorial Kerr effect for two orientations of the external magnetic field. It is established that the Co/Fe/Ni thinfilm structures exhibit a planar magnetic anisotropy. The magnetic behavior of each layer in the initial inhomogeneous Co/Fe/Ni structure is substantially influenced by stray fields of the adjacent layers. This circumstance accounts for the complex shapes of hysteresis loops. The annealing in vacuum at T = 500°C renders Co/Fe/Ni thin-film structures magnetically hard compared to the initial state. The experimental results are explained by certain features of the microstructure of samples.     

AC Magnetic Technique to Measure Specific Absorption Rate of Magnetic Nanoparticles

The electrodynamic method is applied to determine the specific absorption rate (SAR) of an assembly of superparamagnetic nanoparticles as a function of frequency and magnetic field amplitude. The home made frequency-adjustable electromagnet is used to create a nearly uniform magnetic field in a core gap of a volume 1×3×3 cm³ in the frequency range f=10–150 kHz and for magnetic field amplitudes up to H ₀=250 Oe. Two oppositely connected pick-up coils are used to record the electromotive force signal (EMF) generated by magnetic nanoparticles. By integrating the EMF signal one can determine the low-frequency hysteresis loops of the assembly and the assembly SAR. Using this method the measurement of SAR has been carried out for magnetite nanoparticles with an average diameter D=25 nm. The electrodynamic method is shown to be capable of measuring a small amount of magnetic nanoparticles, up to 5×10^?5 g, dispersed in a solid matrix. The maximal SAR ～?80 W/g has been obtained for the magnetite nanoparticle assembly investigated.     

Surface Morphology, Structural and Magnetic Properties of Electrodeposited NiFeCu/Cu Films

The magnetic and structural properties of the NiFeCu/Cu films electrodeposited on polycrystalline titanium (Ti) substrates and their characterizations were studied. The structural analysis by X-ray diffraction (XRD) has revealed that all films have face-centred cubic (FCC) structure. On the other hand, the XRD analysis showed that the degree of (111) texture is dependent on the Cu content within the film. The composition analysis was carried out by energy-dispersive X-ray spectroscopy (EDX). The result of EDX indicated that the Cu content within the film increases with increasing of non-magnetic Cu layer thickness. The hysteresis loops of the films measured by vibrating sample magnetometer (VSM) showed that all films have a small coercivity typical for soft magnetic materials. The surface morphological structure of the films was investigated by atomic force microscopy (AFM). AFM images indicated that all films have main grains (globular islands) and smaller secondary grains on the main grains with different sizes. The differences observed in the magnetic properties of the films were attributed to the Cu content within the films.     

Irreversible Magnetic Properties of Ceramic Hgba2Ca2Cu3O8 at Very High Pulsed Magnetic Fields

The magnetic properties of ceramic HgBa₂Ca₂Cu₃O₈ have been investigated using pulsed magnetic fields up to 50 tesla. The irreversibility line H _irr (T) and the magnetic critical current J _c,m (H,T) have been extracted from the high field hysteresis loops. Irreversibility fields exceed available fields at temperatures below 15 K. The magnetic critical current J _c,m is strongly dependent on the granular structure of the ceramic superconductor. This is reflected in the moderate value of the critical current density and its significant field dependence.