Qiwei Yan

Structure and magnetocrystalline anisotropy of R2Fe17−xGax compounds with higher Ga concentration

The effect of Ga substitution for Fe in R2Fe17 (R=Y, Sm, Gd, Tb, Dy, Ho, Er, and Tm) compounds on the structure and magnetocrystalline anisotropy has been studied by means of x‐ray diffraction and magnetization measurements. Both iron sublattice anisotropy and rare earth sublattice anisotropy are found to be modified by the introduction of the gallium atoms. A uniaxial anisotropy is shown in R2Fe17−xGax (for R=Y, Gd, Tb, Dy, Ho, Er, and Tm) compounds with high Ga concentration, whereas a reversal change in the easy magnetization direction is observed in the samples for R=Sm. The contributions to the uniaxial orientation of the magnetization in these compounds result from not only the rare earth sublattice, but also the iron sublattice.

Magnetic and transport properties of layered La1.2Sr1.8Mn2 - xTxO7 (T = Fe, Co, Cr)

The magnetic and transport properties of layered manganese oxides La1.2 Sr1.8 Mn2 - x Tx O7 (T = Fe, Co, Cr) are reported. The undoped oxide La1.2 Sr1.8 Mn2 O7 is ferromagnetic (FM) below 125 K where an insulating-metallic (I-M) transition occurs. Fe and Co doping have similar effects on the properties of La1.2 Sr1.8 Mn2 O7 , resulting in quick weakening of FM ordering, occurrence of a cluster-glass or spin-glass state for x > 0.07, immediate disappearance of the I-M transition and enhancement of low-temperature magnetoresistance. But a different effect is observed for Cr doping. In La1.2 Sr1.8 Mn2 - x Crx O7 , although the I-M transition also disappears quickly, FM ordering is maintained even for x = 0.5. These doping effects could be understood by considering the different exchange interactions between Mn and T (Fe, Co, Cr) and the corresponding change of the double-exchange interaction in La1.2 Sr1.8 Mn2 - x Tx O7 .

Effect of Fe doping on magnetic properties and magnetoresistance in La1.2Sr1.8Mn2O7

We report the effect of Fe doping on magnetic properties and magnetoresistance (MR) in the layered perovskite La1.2Sr1.8Mn2O7. Fe doping results in the weakening of ferromagnetic (FM) ordering, and the occurrence of a low-temperature spin-glass state in La1.2Sr1.8Mn2−xFexO7. Resistivity increases sharply with increasing Fe concentration. The metal–insulator transition disappears at a very low doping level (x=0.01), but the low-temperature MR effect is enhanced. These effects result from the replacement of Mn3+ by the doped Fe ions, which interrupts the path of double–exchange interaction and destroys the FM metallic state. Due to the anisotropic interaction in the layered perovskite, the magnetic properties and MR effect are more sensitive to Fe doping than those in ABO3-type perovskites.

The magnetic structure of Nd6Fe13Si

The magnetic structure of Nd6Fe13 Si has been studied by magnetization measurement, the singular point detection technique and neutron powder diffraction. It was found that the Nd6Fe13Si is ferrimagnetic with a compensation temperature of 357 K and a Curie temperature of 441 K. The spontaneous magnetization values are 12.9 J T-1 kg-1 at 5 K and 7.4 J T-1 kg-1 at 300 K. There are two values B0cr1 and B0cr2 of the magnetic phase transition field below 225 K: B0cr1=6.2 T and B0cr2=8.2 T at 77 K and B0cr=5.3 T at 300 K. The atomic magnetic moments are ordered in an antiparallel manner, and the two magnetosublattices are MI up arrow (8f(Nd), 16l(Nd), 4d(Fe), 16l2(Fe)) and Mn down arrow (16k(Fe), 161(Fe)).

A high-resolution neutron study of at 77 K including magnetic properties

The crystallographic and magnetic structures of at 77 K have been refined by Rietveld analysis of the high-resolution neutron powder diffraction data. The analysis indicates that has -type structure (). The Cr atoms occupy 12j, 6g and 4f sites with occupancies 0.12, 0.10 and 0.50 respectively, but Cr atoms are absent at 12k sites. The magnetic moments of all of the magnetic atoms lie in the plane perpendicular to the sixfold axes and exhibit planar magnetic anisotropy. The relations between the interesting abnormal magnetic properties and the structure are discussed.

EFFECTS OF GA SUBSTITUTION ON STRUCTURE AND MAGNETOCRYSTALLINE ANISOTROPY OF TM2FE17

A detailed investigation of the structure and magnetic properties of Tm2Fe17−xGax (x=0, 1, 2, 3, 4, 5, 6, 7, and 8) compounds has been performed by means of x-ray-diffraction, neutron-diffraction, magnetization, and ac-susceptibility measurements. Crystal-structure studies have shown that the prepared samples are single phase with the hexagonal Th2Ni17 for x⩽3 and the rhombohedral Th2Zn17 structure for x⩾5. In Tm2Fe13Ga4 the Th2Zn17 structure coexists with the Th2Ni17 structure. Substitution of Ga for Fe in Tm2Fe17 leads to an increase of the unit-cell volume, which is linear with the Ga concentration. In Tm2Fe17−xGax, the saturation magnetization at 1.5 K decreases linearly with increasing Ga content with a rate of 2.3 μB per substituted Ga atom. The Curie temperature is found first to increase with increasing Ga content, going through a maximum value of 485 K at about x=3, then to decrease. Between x=6 and 7, a minimum value of TC is reached and for higher x values TC increases again. X-ray-diffraction ...

Effects of Ga substitution in Y2Fe17 compounds on the magnetocrystalline anisotropy

The heating effects on the structure and fine structure of Cu-11.9Al-5Ni-1.6Mn-1Ti (wt%) shape memory alloy have been studied by means of transmission electron microscopy and microscopic compositional analysis. With the increase of the heating temperature and time, the stabilized M18R(1) martensite, transformed from the parent phase of L2(1) structure type, underwent the following structural variations: M18R(1) --> N18R(1) --> disorder N9R. Disorder N9R bainite precipitates and retained parent phases were observed in specimens heated at 573 and 623 K for 7.2 ks or longer. When the alloy was heated at 673 K for 133.2 ks, equilibrium alpha, gamma(2) and Ni,Al-rich phases were formed without any retained beta(1) parent phase. While the size of the X(s) particles decreased in the specimen heated at 623 K for 7.2 ks and they disappeared completely in the specimen heated at 673 K, the X(L) particles were coarsened after heating. With the increase of the heating temperature and time the growth of the antiphase domains was observed.

Magnetic anisotropy of Dy2Fe17−xGax compounds

Abstract The single-phase compounds of Dy2Fe17−xGax (x = 0, 1, 2, 3, 4, 5, 6, 7 and 8) were prepared by arc melting. The substitution of Ga in the Dy2Fe17 compound is found to have an important effect on their structure and magnetic properties. Dy2Fe17 sample has the hexagonal Th2Ni17-type structure and the Ga-substituted samples crystallize in the rhombohedral Th2Zn17-type structure. The unit cell volumes increase linearly with increasing gallium concentration. The Curie temperature is found first to increase and then to decrease with increasing gallium content x, attaining a maximum value of 557 K at about x = 3, which is 187 K higher than that of Dy2Fe17. The saturation magnetization decreases linearly with increasing gallium content from 15.13 μB/f.u. for x = 0 to −4.27 μB/f.u. for x = 8. For x ≈ 6, the Fe sublattice moment is found to be about equal to the Dy sublattice moment. X-ray diffraction measurements on magnetically aligned powder samples reveal a change in easy magnetization direction, and the samples with x ≤ 5 exhibit easy plane anisotropy while the samples with x ≥ 6 exhibit easy c-axis anisotropy at room temperature.

Effect of Ga substitution on the structure and magnetic properties of Ho2Fe17−xGax (x=0–8) compounds

The Rietveld analysis of x-ray diffraction data shows that Ho2Fe17−xGax (x=0–8) solid solutions crystallize with the Th2Ni17 structure for x⩽2, the Th2Zn17 structure for x⩾4, and the two coexisting phases for x=3. The unit-cell volume increases linearly with a slope of 8.7 A3 per Ga atom. At lower gallium concentrations, Ga atoms occupy the 18f, 18h sites in the Th2Zn17 structure (or 12j, 12k sites in the Th2Ni17 structure) and avoid the 6c, 9d sites. For higher Ga content (x⩾6) Ga atoms still avoid the 9d site, but preferentially occupy 6c and 18f sites for x=6–8 while the occupancy factor of the 18h site decreases. Gallium substitution decreases the saturation magnetization linearly with a slope of 2.5μB. The compounds Ho2Fe17−xGax (x=7,8) possess uniaxial magnetocrystalline anisotropy at room temperature. Doping first increases, then decreases the Curie temperature until this finally rebounds for x>6. The “anomalous” enhancement of the Curie temperature for x=7, 8 may be correlated with the variation o...

A high-resolution neutron study of

The crystallographic and magnetic structures of (x = 5,7) compounds at room temperature have been refined by Rietveld analysis of the high-resolution neutron powder diffraction data. The analysis indicates that (x = 5,7) compounds have -type structures (R3m). The Ga atoms only occupy preferentially 18h and 18f sites in compounds, but Ga atoms occupy preferentially 18h, 18f and 6c sites in compounds. The magnetic moments of all of the Fe atoms of compounds display ferromagnetic alignment, lie in the plane perpendicular to the sixfold axis and exhibit planar magnetic anisotropy. In contrast, the magnetic moments of all of the Fe atoms of compounds lie parallel to the sixfold axis and exhibit easy-axis magnetic anisotropy.