Gu Benxi

Magnetic properties of rapidly quenched NdFeB alloys with lower Nd concentration

Abstract The room temperature hysteresis loops of rapidly quenched M1−xT1x(M = Fe3B,Fe2B,T1 =Nd2Fe14B; 0≤×≤1.0) alloys at different annealing temperatures and times were measured. The phase components of M1−xT1x alloys a crystallized from amorphous were obtained by X-ray diffraction and thermomagnetization measurements. The concentration dependence of the intrinsic coercivity iHc and magnetic energy product (BH)max are found to have a maximum value for the heat treated (Fe3B)1−x(Nd2Fe14B)x alloys. A coercivity of 3 KOe and an energy product of 13 MGOe in Nd4Fe77.5B18.5 alloys are obtained at room temperature by annealing at 670 °C for a short time. These NdFeB alloys containing a few percent Nd could be used as inexpensive bonded magnets, due to their higher values of Br and (BH)max.

Magnetic properties and Mössbauer spectra of X type hexagonal ferrites

Abstract The process of formation and the chemical instability of Ba2Fe22+Fe283+O46 were studied by magnetic and X-ray analyses. The magnetic properties, resistivity and Mossbauer spectra were measured. A compound with X structure was also obtained by firing 1 2 yGd2O3 + (1 - y)BaO + 6Fe2O3(y ≤ 0.15) at 1400°C in air. It was found that the uniaxial anisotropy constant K1 increased with y at 293 K.

Exchange coupled Nd2Fe14B/α-Fe nanocomposite magnets with fine α-Fe grains obtained by low wheel speed spinning

Abstract Exchange coupled Nd2Fe14B/α-Fe nanocomposite magnets have been synthesized by melt-spinning. The effect of wheel speed on the magnetic properties and microstructure has been studied. The results show that a uniform Nd2Fe14B/α-Fe nanocomposite structure with fine α-Fe grains can be developed at an optimum wheel speed of about 12 m/s. After a low temperature annealing, the magnetic properties can reach maximum values: iHc=432.2 kA/m, Jr=1.08 T, (BH)max=115 kJ/m3. With further increasing the wheel speed, the volume fraction of an amorphous phase increases. The microstructure of the ribbons becomes nonuniform after a subsequent high temperature crystallization, and several α-Fe grains abnormally grow to about 100 nm, deteriorating the magnetic properties of the ribbons.

Magnetic properties of heat treated Nd3Fe81B16 alloy

The hysteresis loop and Mossbauer spectrum of the heat treated Nd3Fe81B16 alloy ribbons annealing at 660° C for 10min. have been measured. A coercive field of about 2kOe and an energy product of about 8MGOe are obtained at room temperature. X-ray diffraction and Mossbauer spectrum analyses show that the high coercivity may originate from the Fe3B phase containing Nd. The value of remanence and energy product in this alloy are much higher than those of anisotropic BaFe12O19 ferrite. It may be used as a cheap permanent magnet.

Formation of Co3O4Nanotubes and the Magnetic Behaviour at Low Temperature

Tubular Co3O4 nanostructures were prepared from cobalt nanowires embedded in an anodic alumina template. The morphologies of nanowires/nanotubes were studied by transmission electron microscopy, and x-ray diffraction was used in the analysis of the nanostructures and phases. A possible formation mechanism of the process from nanowires to nanotubes is discussed. The vibrating sample magnetometer measurements show anomalous magnetic behaviour of the cobalt oxide nanotubes at low temperature.

Magnetic Properties and Low-Field Magnetoresistance of Pr0.7Pb0.3MnO3 Single Crystals

The magnetic properties and magnetoresistance of Pr0.7Pb0.3MnO3 single crystals have been studied. At low temperature, the temperature dependence of magnetization can be represented as M(T) = M(0)(1-BT3/2). A large B value was observed. The spontaneous magnetic moment is slightly larger than the spin-only value for Mn3+ and Mn4+ ions. Above the Curie temperature, the susceptibility obeys the Curie-Weiss Law and the resistivity R can fit well with R0exp (T0/T)1/4. It is found that the effective paramagnetic moment obtained from the Curie constant is larger than the theoretical value. The large effective paramagnetic moment may originate from the magnetic clusters. A large low-field magnetoresistance of ΔR/R(0) = -50% is observed at 230 K in 1 T.

Magnetic Properties and Intergranular Action in Bonded Hybrid Magnets

Abstract Magnetic properties and intergranular action in bonded hybrid magnets, based on NdFeB and strontium ferrite powders were investigated. The long-range magnetostatic interaction and short-range exchange coupling interaction existed simultaneously in bonded hybrid magnets, and neither of them could be neglected. Some magnetic property parameters of hybrid magnets could be approximately obtained by adding the hysteresis loops of two magnets pro rata.

Magnetic properties of rapidly quenched (Nd2Fe14B)1−x(N d1.1Fe4B4)x alloys

Abstract Amorphous ribbons with the formal composition (T 1 ) 1− x (T 2 ) x (i.e. Nd 12±ϵ Fe 88 − y B y ) with T 1 = Nd 2 Fe 14 B and T 2 = Nd 1.1. Fe 4 B 4 and 0≤ x ≤1.0 were prepared by a single roller quenching apparatus. The Curie temperature T c and crystalliz ation temperature T cr of the samples and the effects of heat treatment on their magnetic properties and microstructure were studied. The concentration dependence of T c is found to have a maximum value of 505 K and about x = 0.19 ( y = 13). The T cr increases rapidly with increasing x , goes through a maximum to lower values, then rises again. The X-ray diffraction measurements show that the crystallized samples consist of T 1 and T 2 . In the electron diffraction microscope we see well defined grains of T 1 and T 2 which have an average size of about 650 A for T 1 and about 1500 A for T 2 after annealing at 700–800°C. The coercivity under optimal annealing condition is found to be approximately constant with increasing concentration x of the nonmagnetic T 2 phase. An intrinsic coercivity of 8.6 kOe and an energy product of 12 MGOc in Nd 2 Fe 14 B are obtained at room temperature by annealing at 800°C for 10 min.

Anisotropic Magnetization in Arrays of Coupled Ni Nanowires

Arrays of Ni nanowires with different wire diameters were prepared by electrodepositing the corresponding material into cylindrical pores of anodic alumina templates. A transition of the easy magnetization direction has been observed from the wire axis to the transverse direction when the wire diameter increases. It is analytically obtained that this phenomenon is mainly originated from the competition of shape anisotropy and the magnetostatic coupling among the Ni wires. Based on dipolar interaction model, numerical calculation is performed to study the interaction among the nanowires, and the result is in agreement with the experimental data.

Structure and Magnetic Properties of Sputtered Bi2DyFe5O12 Films

The effects of the annealing temperature and time on the structure and magnetic properties of the sputtered BiDy-iron garnet films were investigated. X-ray diffraction analysis shows that the as-sputtered films are amorphous. After annealing at about 550°C, amorphous films crystallize into the garnet phase and an unknown phase. The intensity of the unknown phase decreases with increasing annealing temperature and time and vanishes at 650°C for 30 min. It is found that the unknown phase has a large influence on the half-width of the (420) x-ray diffraction peak. The as-sputtered films have a very small magnetization of about 1 emu/g at room temperature. When films are annealed above 570°C, the magnetization increases rapidly with increasing annealing temperature and time.