Zhao Jian-Gao

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 phase components in amorphous (Fe1−xNdx)81.5B18.5 alloys after crystallization

Abstract Magnetic properties and phase components for amorphous (Fe1−xNdx)81.5B18.5 alloys after crystallization were studied systematically. The crystallization temperature of the amorphous alloys is found to increase first with increasing Nd concentration x, goes through a maximum at x=0.11, then decreases. The crystalline phases of the samples annealed at different temperature were identified by X-ray diffraction and thermomagnetic measurements. It is observed that the crystallized (Fe1−xNdx)81.5B18.5 alloys with 3–6 at% Nd additions consist of Nd2Fe14B, Fe3B and αFe. The concentration dependence of the intrinsic coercivity iHc and maximum energy product (BH>)max are found to have a maximum at the concentration near x=0.055. A room temperature coercive field of 2.9 kOe and an energy product of 13.3 MGOe are obtained in Fe77Nd4.5P18.5 alloy annealed at 670°C for a short time. These FeNdB alloys with fewer Nd concentration would be used as an inexpensive bonded magnets, due to its higher values of Br and (BH)max.

Magnetic properties of amorphous (Fe1 - xCox)77.5Nd4B18.5 alloys and the effects of heat treatment on its hard magnetic properties

Abstract The magnetic moment and Curie temperature of amorphous (Fe 1 - x Co x ) 77.5 Nd 4 B 18.5 (0 ≤ x ≤ 0.4; 1.0) alloys and the effects of heat treatment on its hard magnetic properties were studied. The Nd magnetic moment in the amorphous samples are present as a speromagnetic structure. The Fe atom moment is found to increase from 2.0μ B for x = 0 to 2.27μ B for x = 0.4, as the Co atom moment is assumed to keep a value of 1.21μ B over the whole concentration. The Curie temperature of these amorphous alloys increases remarkably with increasing Co concentration. This behavior is due to the stronger exchange interactions between Fe-Co atoms than that of Fe-Fe and Co-Co atoms. The intrinsic coercive field i H c and maximum energy product ( BH ) max obtained under optimal annealing conditions are found to decrease monotonically with increasing Co concentration, but appear at higher values of 2.3–3.0 kOe and 11.6–13.5 MGOe for x ≤ 0.2, respectively. The hard magnetic properties in the crystallized FeCoNdB alloys are proved to be due to the presence of some hard magnetic 2:14:1 phase. The Co substitution for Fe results in an increase in T c of the 2:14:1 phase, improving the thermostability of these materials.

NMR-STUDY OF CHEMICAL SHORT-RANGE ORDER IN FE-B METALLIC GLASSES

11B NMR study in glassy Fe100−xBx (12 ⩽ x ⩽ 24) suggests that B atoms will be fitted into some larger holes of Bernal polyhedrals only for x < 18, as the Polk model described. But for x ⩾ 18, B atoms will occupy some positions of vertex sites of some polyhedras besides filling more larger holes until all of the larger holes are filled, like the Gaskell model pointed. Using this pattern, the big changes of the concentration dependence of some properties such as magnetic moments and Curie temperature at x = 18 can be interpreted.

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.

Crystallization of amorphous Fe62Co15.5Nd4B18.5 alloy and its influence on hard magnetic properties

Magnetic properties and crystallization of amorphous Fe62Co15.5Nd4B18.5 alloy are studied. The Curie temperature of the present sample is 127K higher than that of amorphous Fe77.5Nd4B18.5 alloy, but their crystallization temperature is compatible with each other. A coercive field of 2.34kOe, a remanence of 12.3kG and an energy product of 11.6MGOe are obtained at room temperature in the Fe62Co15.5Nd4B18.5 alloy annealed at 650? C. The 15.5at.%-Co substitution for Fe results in an increase of about 110K in Tc of 2:14:1 phase.

THE SCATTERING MECHANISM OF RESISTIVITY IN AMORPHOUS FE90-XCOXZR10 ALLOYS

Abstract The reduced resistivities of amorphous Fe90−xCoxCr10 alloys have been studied in the temperature ranges 4.2–300 K and 300–900 K by the fourprobe method. The magnetization was measured with an extracting-sample magnetometer and the Curie temperatures were measured with a magnetic balance. In the low cobalt concentration range 0 ⩽ x ⩽ 20, the resistivity curves exhibit a minimum around the Curie temperature TC, which can be explained by the coherent exchange scattering model. In the high cobalt concentration range 20 ⩽ x ⩽ 90, a Kondo-like resistivity minimum is observed at very low temperatures. At higher temperatures (T ⩽ Tcr − 100) there exists a change from Ziman behaviour ϱ ∞ T to ϱ ∞ T 1 2 for 0 ⩽ x ⩽ 90, which can be considered to be the result of scattering by phonons, when the wavelength of the phonon is greater than the electron mean free path.

Magnetic properties of melt-spun (Nd-Fe)-B alloys

The magnetic properties of melt-spun (Fe1-xNdx)94B6 alloys (x=0.07-0.90) are reported. Their spontaneous magnetizations are interpreted on the basis of a sperimagnetic structure with Nd and Fe cones. The highest coercivity at room temperature is 8 kOe for this as-quenched amorphous alloy system.

Oscillatory interlayer coupling with Cu and Zr underlayer thickness for Co/Cu multilayers

Oscillatory behavior (with a period of about 9 nm) of antiferromagnetic coupling with the thicknesses of Cu and Zr underlayers is reported for sputtered Co(1 nm)/Cu(2.3 nm) multilayers. The related oscillation of magnetoresistance is also observed. Based on the analysis of x-ray diffraction patterns, the variation of crystallographic orientation and modulation period is proved not responsible to the phenomenon. But the underlayer strongly affects the growth orientation of multilayer.

Negative Magnetoresistance Effect in La-Pb-Mn-O Bulk Manganese Oxides

The structure, magnetic and magnetotransport properties of La1-xPbxMnO bulk manganese oxides prepared by the standard ceramic techniques were investigated by XRD, VSM, ESM and MR measurements. The sintering condition and the hole doped concentration x have a strong influence on the magnetic properties and magnetoresistance effect. The maximum MR, 20% at room temperature under a field of 2 T, was obtained for x = 0.4 and the sintered temperature Ts = 1260°C. The correlation among the structure, magnetic and MR is discussed.