Guo Huiqun

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.

A new permanent magnetic materials crystallized from amorphous Co84-xBxZr16 alloys

The crystallization of amorphous Co84-xBxZr16 alloys and the influence of heat treatment on its hard magnetic properties are studied. The dependence of B-content on crystallization temperature of the samples is determined from differential scanning calorimetric (DSC) traces. The intrinsic coercivities iHc are found to increase with increasing annealing temperature and go through a maximum then to lower values. A coercivity of 2.7kOe and an energy product of 4.0MGOe are obtained at room temperature in Co82B2Zr16 alloy annealed at 660°C for a short time. These alloys would be expected as an applicable material for permanent magnet.

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.

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.

Magnetic Hardening of Rapidly Quenched Co-M-Zr (M=B, Fe) Alloys

Effects of the quenching rate and annealing temperature on hard magnetic properties of rapidly quenched Co84-x BxZr16 and Co82-x FexZr18 alloys were studied. The B- or Fe-content dependence of room temperature coercivity Hc, remanence Br and maximum energy product (BH)max are obtained. The Hc is suggested to originate from the microstructure with the optimal grain size.

Magnetic properties and crystallization of the rapidly quenched (Fe1-xNdx)81.5B18.5 alloys

Magnetic properties and crystallization behaviors of amorphous (Fe1-xNdx)81.5B18.5 alloys were studied. The crystallization temperature is found to rise at first and then drop monotonically with x, having a maximum value of 976 K at x = 0.11 (9 at% Nd). The (Fe1-xNdx)81.5B18.5 alloys prepared at a quenching rate of vs = 6.6 m/s are amorphous, and exhibit good glass formability. Both the coercive field Hc and energy product (BH)max depend strongly on Nd concentration. Amorphous (Fe1-xNdx)81.5B18.5 alloys with higher Nd concentration have a high coercive field at low temperature, due to the large random uniaxial anisotropy of Nd. The room-temperature Hc and (BH)max obtained on optimal annealing conditions show two maxima as a function of Nd concentration x. The highest room-temperature coercive field Hc = 22 kOe within the Nd concentrations around x = 0.368 and the maximum energy product (BH)max = 13.3 MG Oe at x = 0.055 are observed. The hard magnetic properties of these crystallized samples are related to the presence of the hard magnetic Nd2Fe14B phase.

Curie temperature, magnetic moment, and high-field susceptibility of amorphous Fe90-XSiXZr10 alloys

The magnetization curves at 1.5K and thermomagnetization curves in the fields of about 450e for amorphous Fe90-XSiXZr10 (x = 0, 4, 7 and 10) alloys prepared by the drum spinning technique are measured with an extracting sample magnetometer. At low Si concentration the amorphous Fe90-XSiXZr10 alloys exhibit a large value of the high-field susceptibility, but the average magnetic moment per Fe atom μFe, and the Curie temperature, Tc, are quite small, compared with amorphous Fe87-XSiXB13 alloys. This unusual behavior could be explained in terms of the presence of the antiferromagnetic states.

Martensitic transformation, thermomagnetic properties and electronic resistivity of amorphous alloys (Fe1-xNix)84B16 after crystallization

In the reduced curves of electronic resistivity and thermomagnetic measurement of the amorphous alloys, (Fe1-xNix)84B16 with 0.02<x<0.08, preheated to a temperature higher than that of crystallization, an anomalous abruption at about 150°C was observed. The results of differential thermal analysis (DTA) and of x-ray diffraction show that after crystallization of the amorphous alloys (Fe1-xNix)84B16 the anomalous abruption can be attributed to the martensitic transformation of γFe(Ni) to αFe(Ni).