Zhi-gang Sun

Structure and magnetic properties of Pr2Fe17-xMnx (x=0-9) compounds

The influence of Mn substitution for Fe on the structure and magnetic properties of Pr2Fe17−xMnx compounds with 0⩽x⩽9 was investigated. X-ray diffraction indicates that all samples are single phase with the rhombohedral Th2Zn17-type structure. The unit cell volume V remains nearly constant with increasing manganese content up to x=2, then increases linearly at a rate of about 2.5 A3 per Mn atom up to x=8 and there is a large increase of cell volume at x=9. The Curie temperature increases a little from 298 K at x=0 to 308 K at x=1, and then decreases to 37 K at x=9 quickly. The saturation magnetization at 5 K was found to decrease monotonously with increasing Mn concentration. The thermal magnetization curves M(T) of the compounds with x=1–9 show a strong decrease below TC with decreasing temperature. Also it presents considerable magnetic hardness at low temperature. This can be attributed to the presence of narrow Bloch walls.

Structure and magnetic properties of SM2Fe17-xMnx compounds

The effect of Mn substitution for Fe in Sm2 Fe17-x Mnx compounds on the structure and magnetocrystalline anisotropy was studied by x-ray diffraction and magnetization measurements. The compounds prepared have a rhombohedral Th2 Zn17 -type structure single phase except for a small amount of -Fe for x = 1-4, while x = 5 has Nd3 (Fe,Ti)29 -type monoclinic structure. The Curie temperature TC is found to increase to 430 K for x = 1, then decrease to 255 K for x = 5. The saturation magnetization at 5 K decreases with increasing Mn concentration. Room temperature anisotropy changes from easy planar type to cone type and to easy c -axis type with increasing Mn concentration for x = 1, 2 and 3 respectively. The anisotropy field for x = 3 is about 1 T at 100 K and decreases to 0.4 T at room temperature.

Structure and magnetic properties of Pr2Co17−xMnx compounds

The structure and magnetic properties of Pr2Co17−xMnx (x=0–14) compounds were studied. A single phase with the rhombohedral Th2Zn17-type structure was obtained from x-ray diffraction patterns for x=0–11. The unit-cell volumes were found to increase linearly at a rate of about 5.7 A3 per Mn atom. Both the Curie temperature and saturation magnetic moment at 5 K decrease monotonously with increasing Mn concentration. The spin reorientation was found in Pr2Co17−xMnx compounds for x=1–5. The magnetic phase diagram of the compounds was given. A transition from ferromagnetic to antiferromagnetic for x=8–9 was observed due to the Mn substitution. At high Mn concentration (x=12,13,14), a rare-earth intermetallic 3:29 phase was found. This kind of 3:29 phase shows a paramagnetic character when the temperature is above 5 K.

The hard magnetic properties of nanocomposite Nd3.6Pr5.4Fe83Co3B5 ribbons prepared by melt spinning

Abstract Nanocomposite Nd 3.6 Pr 5.4 Fe 83 Co 3 B 5 ribbons were prepared by direct melt spinning at different wheel speeds. The hysteresis loop of the ribbons prepared at wheel speed V=20 m/s shows a single hard magnetic behavior with high coercivity. The values of remanence M r =11.3 kG s , intrinsic coercivity i H c =6.0 kOe and energy product ( BH ) max =17.2 MG Oe are obtained at room temperature. Transmission electron microscopy and magnetic force microscopy have been employed to image the microstructure and magnetic domains in the ribbons. Due to the unnegligible inter-grain exchange coupling, interaction domains are observed. The shape of the demagnetization curve in the second quadrant at different temperature gives more information about inter-grain exchange coupling. The coercivity mechanism is discussed.

Magnetohistory effect of Pr2Fe17-xMnx compounds

In this paper, the magnetohistory effect of Pr2Fe17-xMnx (x=1-9) compounds was studied. The zero-field cooling thermomagnetic curves M-ZF(T) of the compounds show a strong decrease below T-C with decreasing temperature. The peak temperature T-P decreases nearly linearly with increasing Mn substitution. Considerable magnetic hardness is also present at low temperature, which can be attributed to the presence of narrow Bloch walls. The coercivity mechanism is due to domain wall pinning effect, which is demonstrated through the initial magnetization curves. The temperature dependence of H-c is represented quite satisfactorily by a formula derived by Egami. The deduced domain wall energy density gamma and domain wall width delta are 19.2X10(-3) J/m(2) and 14.4 Angstrom, respectively

Magnetic properties, domain structure, and microstructure of anisotropic SmCo6.5Zr0.5 ribbons with C addition

The magnetic properties and the domain structure of anisotropic melt-spun SmCo6.5Zr0.5 alloys with C addition was investigated by means of x-ray diffraction (XRD), magnetic measurement, and magnetic force microscopy. The XRD analyses showed that the addition of a few percent of C led to a significant increase in the coercivity and simultaneously affected the characterization of crystalline texture of the ribbons. The easy magnetization c axis changed from parallel to the ribbon plane for SmCo6.5Zr0.5 ribbons to normal to the ribbon plane for SmCo6.5Zr0.5C0.25-0.75 ribbons. An optimal coercivity of 0.92 T was obtained for the SmCo6.5Zr0.5C0.5 ribbon spun at 5 m/s. The corresponding remanence measured normal or parallel to the ribbon plane was 7.1 kGs or 3.1 kGs, respectively. The domain structure was studied by magnetic force microscopey, A strip-shaped domain was observed on the surface of the SmCo6.5Zr0.5 ribbons and the walls lay straight and parallel. For C-doped ribbons, the domain walls formed a maze domain pattern of grains with c axis normal to the ribbon plane, Scanning electron micrographs showed that a dendrite structure was present in the SmCoZr ribbon surface, and C addition caused the above-mentioned dendrite to diminish.

The structure and magnetic properties of Gd2Co17-xMnx (x=0-4) compounds

Abstract X-Ray diffraction (XRD) and magnetization measurements were employed to investigate the effect of substitution of Mn for Co on the structure and magnetic properties of Gd2Co17−xMnx (x=0–4) compounds. XRD patterns show that all samples are single phase with rhombohedral Th2Zn17-type structure. The substitution of Mn for Co leads to a monotonic increase in unit cell volume. The saturation magnetization increases slightly for x≤2, then decreases slowly. The Curie temperature TC is found to decrease monotonically with increasing Mn concentration. The samples with x=1–4 exhibit a uniaxial anisotropy at room temperature as determined from the XRD measurement on magnetically aligned samples. The magnetocrystalline anisotropy field HA increases with increasing Mn concentration, attaining a maximum value of 43.7 kOe at x=4. Spin reorientation phenomena are observed in Gd2Co17 and off-stoichiometric Gd2Co16 compounds, which may be due to the different temperature dependence of the anisotropy of the Co sites.

Structure and magnetic properties of Tb2Co17-xMnx compounds

X-ray diffraction (XRD) and magnetization measurements were employed to investigate the effects of Mn substitution for Co on the structure and magnetic properties of Tb2Co17−xMnx compounds with x=0–7. XRD patterns show that all samples are single phase except the samples with x=6 and 7 which contain a small amount of impurity. The substitution of Mn for Co leads to a monotonic increase in unit cell volume. The saturation magnetization at 5 K remains nearly unchanged upon Mn substitution, while the Curie temperature decreases monotonically. XRD measurements on magnetically aligned powders with x=0–7 exhibit an easy-plane type of magnetic anisotropy at room temperature. For x=2, 3, and 4, spin reorientation transitions above room temperature are observed in the M–T curves. The magnetic phase diagram is given.

Magnetic entropy change and magnetoresistance in the LaFe11.375Al1.625 compound

Large magnetic entropy change |ΔS| with a nearly temperature-independent magnitude over a wide temperature range (about 70 K span from ∼140 K to 210 K) was observed in an Fe-based NaZn13-type compound LaFe11.375Al1.625. Such a behavior of magnetic entropy change is ascribed to two closely spaced magnetic transitions. One at 181 K (TN) with second-order nature is from the paramagnetic to antiferromagnetic state; another at 140 K (TO) with first-order nature, temperature hysteresis ∼5 K, is from antiferromagnetic to ferromagnetic state. At the antiferromagnetic to ferromagnetic transition a large change of resistance was found, which can be induced as a function of temperature as well as field. The magnetoresistence under a field of 1 T reaches 3.4%.

Honeycomb domain structures in amorphous TbFe thin films

The magnetic properties and domain structure of amorphous TbFe thin films were studied by magnetic measurement and magnetic force microscope. Honeycomb domain structures were found in the as-deposited amorphous film. The domain structures were composed of many small white round dots embedded in the black matrix, which formed an irregular hexagonal pattern with some deformation. The average dot size was about 450 nm, with an average separation of 610 nm. The derived domain wall energy density γ and the exchange constant A were 0.95×10−2 and 1.79×10−11 J/m, respectively.The magnetic properties and domain structure of amorphous TbFe thin films were studied by magnetic measurement and magnetic force microscope. Honeycomb domain structures were found in the as-deposited amorphous film. The domain structures were composed of many small white round dots embedded in the black matrix, which formed an irregular hexagonal pattern with some deformation. The average dot size was about 450 nm, with an average separation of 610 nm. The derived domain wall energy density γ and the exchange constant A were 0.95×10−2 and 1.79×10−11 J/m, respectively.