Zhao Jian-gao

Magnetic properties of metastable R2Fe23B3 compounds with R-Ce, Pr and Nd

Abstract Amorphous ribbons with composition R 2 Fe 23 B 3 (R-Ce, Pr and Nd) were prepared by a single roller quenching apparatus. When the samples were annealed at 630°C for 10 min, they crystallize to the metastable R 2 Fe 23 B 3 single phase. A detailed study of the phase structure and magnetic properties of the metastable R 2 Fe 23 B 3 compounds has been made by using X-ray diffraction and magnetization measurements.

Magnetic moment, Curie temperature, and coercive field for amorphous (Fe1−xNdx)81.5B18.5 alloys

Abstract The magnetization data under high magnetic field and Curie temperature of amorphous (Fe1−xNdx)81.5B18.5 alloys were measured. Their spontaneous magnetization is explained by a non-collinear structure. The average magnetic moment μ Nd per neodymium atom is assumed to be constant for all x; however, the average magnetic moment μ Fe per iron atom decreases monotonically with increasing x, and becomes more rapid when x > 0.4. The neodymium concentration dependence of the Curie temperature Tc shows a monotonic decrease. This behavior can be attributed to the decrease in FeFe spacing and the number of FeFe atom pairs with increasing x. The highest coercive field of 22 kOe at 1.5 K has been observed in amorphous Fe31.5Nd50B18.5 alloy. Such a high coercive field at low temperature results from the large random uniaxial anisotropy of neodymium.

Magnetic hardening of rapidly quenched Co100−xZrx alloys

Abstract Influence of quenching rate and heat treatment on the magnetic properties of rapidly quenched Co100−x alloys were studied. The room-temperature coercive field is found to increase with increasing vs at vs ⩽ 47 m/s. Annealing at about 650°C gives a highest coercive field of each composition. With increasing Zr concentration x, the room-temperature coercive field obtained under optimal annealing conditions is found to increase from 1.0 kOe for x = 12 to 3.0 kOe for x = 20, but the magnetization decreases monotonically. The highest room-temperature coercive field Hc = 3.0 kOe and energy product (BH)max = 4.2 MGOe measured in a field of 8 kOe are obtained in the annealed Co82Zr18 and Co84Zr16 alloys, respectively X-ray diffraction and thermomagnetic measurements show that the hard magnetic properties of the as-quenched and annealed Co100−xZrx alloys are associated with the presence of majority phase with Tc = 800 K.

Magnetic Anisotropy in the Radula of Chiton

Radular teeth of chitons were studied by using magnetic torque-meter and transmission electron microscopy (TEM). The magnetic torque curves give clear evidence of presence of strong uni-axial magnetic anisotropy. The easy axis is along the length direction of tongue-like radula. The TEM pattern shows that long chip-like magnetite nano-scaled particles packed in the radular teeth with both uni-axial shape anisotropy and magneto-crystalline anisotropy.

Magnetic properties and crystallization of amorphous Co100−x−yBxZry alloys

Abstract The magnetic properties and crystallization behavior of amorphous Co 100− x − y B x Zr y (0 ⩽ x ⩽ 25; y = 10, 16) alloys were studied. In amorphous Co 90− x B x Zr 10 alloys the average magnetic moment per cobalt atom and Curie temperature are found to decrease monotonically with increasing boron concentration x , and the crystallization temperature increases linearly. The crystallized Co 90− x B x Zr 10 alloys have a small coercive field. However, high coercive fields are observed in the crystallized Co 84− x B x Zr 16 alloys. The room-temperature coercive field H c in the optimal heat-treated samples is found to increase monotonically with increasing x from 2.2 kOe for x = 0 to 4.7 kOe for x = 16. The remanent magnetization B r (at H = 8 kOe) and the energy product ( BH ) max for the Co 84 Zr 16 alloy annealed at 660 °C for a short time are obtained to be 6.1 kG and 4.2 MGOe, respectively.

MAGNETISM OF RAPIDLY QUENCHED (FE1-XNDX)75B25 ALLOYS

Effects of heat treatment on hard magnetic properties of rapidly quenched (Fe1-xNdx)75B25 (0 less-than-or-equal-to x less-than-or-equal-to 0.223) alloys were studied. The coercive field increases with increasing x at first, goes through a maximum value at x = 0.053 to lower value, then rises rapidly again. For x = 0.223, the room temperature coercive field is found to be 21 kOe. The as-quenched samples are amorphous. The Curie temperature and saturation magnetization are found to decrease monotonically with increasing x. The maximum of the crystallization temperature is 955 K at Nd concentration of x = 0.093. The crystalline phases were identified by X-ray diffraction and thermomagnetic measurements.

Evidence for the reversible structural transformation in amorphous Fe18Co72Zr10

The temperature cyclical scanning of magnetic anisotropy with temperature from room temperature to 620 K has been investigated for Fe18Co72Zr10. The sample shows a thermomagnetic hysteresis in magnetic anisotropy which, together with the differential scanning calorimetry and the observation of the temperature dependence of field-induced anisotropy, provides the evidence for a first-order reversible structural transformation. Two short-range orders (SRO) with h.c.p.-like and f.c.c.-like symmetry have been proposed to explain the observations.

Magnetic Mössbauer and structural characterization of Re2Fe14B (RE=Nd,Y,Tb,Gd)single crystals

Abstract Magneto-structural refinement studies (lattice parameters, atomic positions and Mossbauer hyperfine parameters) for RE 2 Fe 12 B single crystals with RE = Nd, Y, Gd, Tb, grown by a modified Czochralski technique are reported. A small planar contribution to the anistropy in Gd 2 Fe 14 B at 77 K was observed.

Origin of ultraviolet photovoltaic effect in Fe3O4 thin films

We have investigated the transport and ultraviolet photovoltaic properties of Fe3O4 thin films grown on glass substrates by facing-target sputtering technique. The nonlinear dependence of current-density on voltage suggests that the transport process is most likely the tunnelling process and grain boundaries act as barriers. Furthermore, nonequilibrium electron-hole pairs are excited in the grains and grain boundary regions for Fe3O4 film under ultraviolet laser, since the energy gap of Fe3O4 is smaller than the ultraviolet photon energy. And then the built-in electric field near the grain boundaries will separate carriers, leading to the appearance of an instant photovoltage.

Nano-magnetic material in the radula teeth of chiton Acanthochiton rubrolinestus Lischke

In this note, relationships among the components, structure distribution and easy magnetization direction, structure of magnetic domain of nano-magnetic material in the major mature lateral radula teeth of chiton A. rubrolinestus Lischke are probed by using the high resolution transmission electron microscope (HRTEM), the scanning electron microscope (SEM), the magnetic force microscope (MFM) and the super-conducting quantum interference device (SQUID) magnetometer from the point of view of magnetism to provide a basis for comprehending biologic function of the magnetic radula.