Baisheng Zhang

Magnetic and crystallographic properties of novel Fe‐rich rare‐earth nitrides of the type RTiFe11N1−δ (invited)

We succeed in inserting a number of nitrogen atoms into the RTiFe11 intermetallics. The nitrides retain the ThMn12‐type structure, but with an increase in the unit cell volume. The crystallographic sites located by nitrogen atoms are determined by using neutron diffraction techniques. The nitrogen atoms are found to have an effect of increasing Curie temperature and saturation magnetization. Moreover, an essential change in magnetocrystalline anisotropy is observed upon nitrogenation. By all of these effects, the NdTiFe11N1−δ compounds have excellent intrinsic magnetic properties favorable for permanent magnet applications.

NEUTRON DIFFRACTION STUDY OF THE NITRIDE YTIFE11NX

Abstract A neutron diffraction study was carried out on a powder sample of the composition YTiFe 11 N 0.5 at 300 K. Neutron diffraction measurements not only confirm that the nitride maintains the tetragonal structure of its virginal compound YTiFe 11 ( ThMn 12 - type , I 4/ mmm ), but also indicate that the nitrogen atoms occupy the interstitial 2b sites. A detailed analysis of the crystallographic and magnetic structure is presented, and the relationship of the magnetic properties to the crystallographic structure is discussed in this paper.

Neutron diffraction study of ternary nitrides of the type R2Fe17Nx

We have carried out neutron diffraction measurements on powder samples of Nd2Fe17Nx and Y2Fe17Nx at room temperature. The refinements of the neutron data indicate that the nitrogen atoms occupy the 9e interstices in the nitride Nd2Fe17Nx (Th2Zn17 type, R3m) or the 6h interstices in the nitride Y2Fe17Nx (Th2Ni17 type, P63/mmc), respectively. At room temperature, both Nd2Fe17Nx and Y2Fe17Nx adopt a magnetic structure in which the easy magnetization direction is perpendicular to the c axis. Using the above results, we have briefly discussed the effect of a nitrogenation on the magnetocrystalline anisotropy of the Sm sublattice of Sm2Fe17Nx.

Neutron powder diffraction study on the structures of LaNi5−xAlxDy compounds

Abstract The structures of LaNi5−xAlxDy ( x=0.75, 0.25, y=1.01, 1.10, 1.91 and 3.1) were systematically investigated by neutron and X-ray diffraction. D atoms are found to enter the 6m site of the α-phase but not the reported 12n site, while the 6m and 12n sites of the β-phase. In the case of LaNi4.75Al0.25Dy with lower Al content and symmetry, D atoms do not enter the α-phase but occupy the 4h site besides the 6m and 12n sites of the β-phase. The relationship between structures and properties is also discussed.

Neutron diffraction study of Y2Fe14BN1−δ

Abstract The studies of the crystallographic and magnetic properties of R2Fe14BN1−δ, where R represents Nd and Y, have been carried out by neutron diffraction techniques and magnetic measurements. Upon nitrogenation, the tetragonal structure of R2Fe14B is retained, but the unit cell volume is slightly increased. The refinement of neutron data indicates the nitrogen atoms occupy the 4f interstices in the nitrite of Y2Fe14B. In the consequence of filling these interstices, the Curie temperatures of these nitrides are increased about 60 K, wheres, their saturation moments and anisotropy fields are a little inferior to their virginal counterparts. In order to explain the changes of the magnetic properties, we give a brief discussion about the relationship between the magnetic properties and the crystallographic structure of these nitrides.

A study on the effect of hydrogen in the compounds with -type structure

The structural and magnetic properties of hydrides with -type structure have been studied by means of magnetic measurements, the neutron powder diffraction technique and self-consistent spin-polarized band calculations (LMTO-ASA). We found that the hydrides retain the -type structure, but with an increase of unit-cell volume. The neutron diffraction results indicate that hydrogen atoms occupy the interstitial 2b sites. Magnetic measurements carried out on , and their hydrides show that both the Curie temperature and the saturation magnetization can be enhanced by introducing interstitial hydrogen atoms. Band-structure calculations and spin-fluctuation theory give a fair description of the enhancement of the magnetization and Curie temperature.

Neutron diffraction study of substituted YBa2Cu2.85M0.15O7-δ

Abstract Samples of YBa2Cu2.85M0.15O7-δ (M=Ti, Mn, Fe, Co) have been prepared. A decrease of Tc value with increase of 3d electron number of the substituting element was observed. Neutron diffraction studies on the samples were carried out to learn the relationship between Tc and site occupation of the substituting atoms. The results show that Ti and Fe prefer to substitute for 2q-Cu, while Mn and Co prefer to substitute for 1a-Cu. Primary discussion was made.

Neutron diffraction study of Y(TiFeC)12

Abstract Structure measurements on the carbide Y(TiFeC)12 prepared by arc-melting were carried out by means of powder neutron diffraction. Data analysis by profile technique showed that the carbon atoms occupy the 8i sites in the ThMn12 type structure, substituting for some Fe atoms. The large electronegativity of carbon on the 8i sites explains the observed effect of carbon on the intrinsic magnetic properties of RTiFe11, which is completely different from that of the interstitial nitrogen.

Structure and magnetic properties of a solution of carbon in prepared by arc melting

The structural and magnetic properties of a solution of carbon in prepared by arc melting have been studied by means of magnetic measurements and the neutron powder diffraction technique. It was found that the carbides retain the -type structure but with an increase of unit-cell volume. The neutron diffraction results indicate that most of the carbon atoms occupy the interstitial 2b sites and the others occupy the substitutional 8i sites. According to the magnetic measurements, both the Curie temperature and the saturation magnetization are found to increase with the carbon concentration x in the series, and the magnetocrystalline anisotropy is also affected by the carbon atoms.

The modulation principle of vacuum on the superconductivity of YBCO

Abstract By neutron diffractions, and other experiments we have found that oxygen ions in YBCO can diffuse out of the sample in vacuo at room and low temperature, while the T c decreases greatly. We have also found that if the vacuum-deoxidation process lasts for several days there will be a damping oscillation of T c with time ( t ), and higher vacuum corresponds to a greater amplitude and a shorter period. We tentatively think that T c should satisfy the following function: T c0 ∞ T c e −βt cos (ω t +ϕ); it may be due to the diffusion of oxygen and the saturation of the valence state.