Hong-Shuo Li

Intrinsic magnetic properties of the iron-rich ThMn12-structure alloys R(Fe11Ti); R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu

Magnetic properties of the series of ThMn12-structure intermetallic compounds R(Fe11Ti) have been determined for rare earths from Nd to Lu plus Y. The highest Curie temperature (607 K) is for R=Gd, and R-Fe exchange interactions are much stronger for light rare earths than for heavy ones. The temperature dependence of the iron sublattice magnetisation and anisotropy are determined for the Y and Lu compounds. Spin reorientation transitions are found as a function of temperature for the rare earths with a negative second-order Stevens coefficient alpha J(Nd, Tb, Dy), and a set of crystal-field parameters is derived to account for the transitions in a consistent way. A sharp increase in magnetisation observed for Sm(Fe11Ti) below 130 K in a field of about 10 T applied perpendicular to the easy direction indicates that J-mixing may be important for Sm3+. Compared with R2Fe14B, the iron anisotropy in R(Fe11Ti) is greater, and the rare-earth anisotropy is much weaker at low temperature, with the opposite sign for the rare-earth crystal-field coefficient A20. The average iron moment is 1.7 mu B in R(Fe11Ti) at 4.2 K; Mossbauer spectra are analysed to yield the average moments on each site. Limits set by the intrinsic magnetic properties on the performance of magnets made from these families of alloys are discussed.

A 5e Mossbauer study of a new series of rare-earth iron nitrides: R2Fe17N3- delta

57Fe Mossbauer spectra have been obtained at room temperature and at 15 K for R2Fe17 and R2Fe17N3- delta ( delta approximately=0.4) with R identical to Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y. The easy direction of magnetization of the R2Fe17 compounds can be identified by analysis of the hyperfine field and quadrupole interactions. For rare-earth elements with J>3, the sixth-order crystal-field parameter B66 determines the easy magnetization direction in the basal plane. In the nitrides, the average hyperfine field at 15 K increases by approximately 13% above the value in the parent compounds, from about 31 to 35 T, and it is anisotropic, being greatest when the magnetization lies along the c-axis. There is also an increase in the isomer shift of 0.12(2) mm s-1. Spin reorientation transitions occur in the nitrides of Er and Tm; only the samarium nitride has an easy c-axis at room temperature, but Sm, Er and Tm all have easy c-axis magnetic structures at 15 K.

Relationship between ThMn12 and Th2Ni17 structure types in the YFe11−xTix alloy series

A series of YFe11−xTix alloys with x=0.10, 0.25, 0.40, 0.50, 0.70, 1.00, 1.25, 1.50, and 2.00 have been investigated using x‐ray diffraction, thermomagnetic analysis, the singular point detection technique, and 57Fe Mossbauer spectroscopy. A pure ThMn12 ‐type phase was observed when 0.7≤x≤1.25. It has Curie temperature of 524 K, anisotropy field of 2.3 T, and average iron magnetic moment of 1.47 μB at room temperature. The relationship between the CaCu5 and the Th2Ni17 or ThMn12 structure types is discussed in terms of substitution of transition‐metal dumbbells on Ca sites, and a structural explanation is given for the directions of the iron anisotropy in the 2:17 and 1:12 compounds.

3d magnetism in R2Fe14B compounds

Abstract An investigation of the magnetic properties of R 2 Fe 14 B compounds with R = Y, La, Ce, Gd, Lu and Th has been carried out. In all compounds the value of the Fe moment is in the range 2.0–2.2μ B , close to that of metallic Fe. This shows that effects of electron transfer and hybridization are weaker than in binary R-Fe compounds. The variations of the Curie temperatures of the different compounds is interpreted in terms of the dependence of the magnetic interactions on distance and on R. In all compounds, except Th 2 Fe 14 B, the temperature dependence of the anisotropy exhibits a maximum at T / T c ≃ 0.4. This effect is ascribed to competition between contributions from different Fe atomic sites and/or to a change in the crystal field interactions associated with the magnetovolume anomaly which occurs in R 2 Fe 14 B compounds below T c .

Magnetic properties of Y2Fe17Cx

Abstract The Curie temperature of Y2Fe17Cx increases linearly with carbon content in the hexagonal phase, 0 ⩽ × ⩽ 1. It saturates at 520 K for x ⩾ 1.1, where the phase becomes rhombohedral. The iron moment and magnetization for Y2Fe17C at T = 0 K and 290 K respectively are 2.08 microB and 1.56 T, 1.65 microB and 1.25 T. Thermopiezic analysis shows that the carbide absorbs hydrogen at 250 °C at 1 bar. Hydrogenated carbides show a further increase in Tc.

Magnetic properties of new ternary R6Ga3Fe11 compounds

Three new rare earth–iron ternary compounds with the La6Ga3Co11 structure (I4/mcm), Pr6Ga3Fe11, Nd6Ga3Fe11, and Sm6Ga3Fe11, are found to be ferromagnetic with Curie temperatures of 320, 397, and 462 K, respectively. Large anisotropies have been observed from the magnetization curves and the anisotropy field is larger than 7 T at room temperature. First‐order magnetization processes were observed for all samples throughout the temperature range of 4.2–300 K. Point charge calculations give A20=1070 K a−20 at the 16l site and −283 K a−20 at the 8f site.

Spin reorientation transitions in R2Fe17N3−δ; R = Er, Tm

Abstract Spin reorientations from the c-axis at low temperatures to the c-plane at higher temperatures are observed at 120 K in Er 2 Fe 17 N 2.7 and at 200 K in Tm 2 Fe 17 N 2.7 . The corresponding crystal field parameters B 20 are -0.117(12) K/ion and -0.357(35) K/ion espectively, and the average effective crystal field coefficient A 20 is -59(7) Ka 0 -2 . Implications for the anisotropy of Sm 2 Fe 17 N 3−δ are discussed.

Spin reorientation transitions and crystal field interactions in the R(Fe10V2) series

Abstract Spin reorientation transitions to a ground state where the magnetization is not parallel to c-axis, are observed below room temperature in R(Fe 10 V 2 ), R = Nd , Dy , Ho and Er . These are quantitatively explained by using a set of five crystal-field coefficientsd derived from the fit of the magnetization curves of a Dy(?Fe 11 Ti) crystal. An explanation is given of why first-order spin reorientation transitions are found in Ho(fe 10 V 2 ) and Ho(Fe 10 No 2 ), but not in Ho(Fe 11 Ti).

R-T and R-R exchange interactions in the rare-earth (R)-transition-metal (T) intermetallics : an evaluation from relativistic atomic calculations

Intra-atomic exchange integrals J4f-5d, J4f-6s and J4f-6p for rare-earth trivalent ions were obtained from relativistic self-consistent field atomic calculations, using the local-density approximation for exchange and correlation potential. The effective (molecular-field) exchange coefficients nRT between rare-earth and transition-metal ions and nRR between rare-earth ions were obtained based on a simplified three-sublattice (4f, 3d and conduction electron) mean-field model. Quantitative results show a decrease in magnitude of nRT across the rare-earth series, which agrees well with values observed in many rare-earth-transition-metal intermetallic series. It is shown that the 4f-5d exchange interaction is far more important than the 4f-6s and 4f-p interactions, as expected from the Campbell model for the exchange interactions occurring in rare-earth-transition-metal intermetallics.

Chapter 1 Magnetic properties of ternary rare-earth transition-metal compounds

Publisher Summary This chapter discusses the magnetic properties of ternary rare-earth transition-metal compounds. The magnetism of pure elements concerns the properties of about 20 metals, mostly from the 3d or 4f series. Binary intermetallic compounds are much more numerous. Magnetic binaries may involve one or both elements with magnetic moments. Composition adds a further dimension, with many binary diagrams exhibiting ranges of solid solubility and a number of intermetallic phases, each with its particular structure. Sometimes, the distinction is a matter of site preference, such as ordered substitution of one quarter of the sites of the fcc structure leads to a Cu 3 Au-type structure compound, whereas complete disorder produces an A 75 B 25 fcc solid solution. The magnetic properties of binary intermetallic compounds, usually involving a 3d or 4f element, and sometimes both, are reviewed in the chapter. The order of decreasing transition-metal content the magnetic properties of ternaries with structures related to a binary structure type is discussed. The true ternary compounds are also discussed in the chapter.