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 Cu3Au-type structure compound, whereas complete disorder produces an A75B25 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.

Mossbauer and AC susceptibility experiments on HoCo12B6 (Fe-57) show that the Fe atoms exhibit a strong preferential occupation of the 18h site. HoCo12B6 undergoes an axis to plane spin reorientation at T-sr = 75(2) K.

The magnetic properties of rare-earth intermetallic compounds R3Co29Si4B10 (R = La, Gd, Tb, Er, Tm) have been investigated by magnetization. All the compounds exhibit paramagnetism at room temperature, and magnetic ordering from 154 to 206 K. The magnetic moments of the Co sublattice and rare-earth sublattice couple ferrimagnetically for the heavy rare-earth compounds R3Co29Si4B10 (R = Gd, Tb, Er, Tm). The saturation magnetic moment derived from La3Co29Si4B10 for the Co sublattice is similar to0.4 mu (B)/Co. (C) 2001 Elsevier Science B.V. All rights reserved.

. Magnetic properties of the series of ThMn,,-structure intermetallic compounds R(Fe,,Ti) 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 cu,(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(Fe,,Ti) 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 R2Fe,4B, the iron anisotropy in R(Fe,,Ti) is greater, and the rare-earth anisotropy is much weaker at low temperature, with the opposite sign for the rare-earth crystal-field coefficient Azo. The average iron moment is 1.7 pB in R(Fe,,Ti) 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 Fe-57 Mossbauer study has been conducted on the Fe-57 doped novel rare-earth intermetallic compounds R3T29Si4B10 (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu, T = Ni, Co). The Fe-57 Site assignment has been investigated by Fe-57 Mossbauer spectroscopy combined with thermodynamic analysis and crystal field estimation. The investigation demonstrated that Fe-57 atoms preferentially occupy the 2c crystallographic site with (4) over bar m2 local symmetry in the R3T29Si4B10 compounds. Sequentially, the 8j1, 8j2 and 8i2 crystallographic sites are the second preferentially occupied and 8i3 and 16 K sites are the third preferential occupancy group of iron atoms. The magnetic hyperfine interaction at 4.2 K demonstrates the effect of a spin-induced Co magnetic moment.

A series of quaternary rare-earth transition-metal intermetallic compounds based around the composition Nd3T29Si4B10 (T=Co, Ni) has been synthesised successfully, although it is found that the compound does not form for T=Fe. The new phase is designated by Nd3(T1−xSix)33B10 (0.115≤x≤0.150) and has a tetragonal structure with space group P4/nmm (No. 129). The Nd3Ni29Si4B10 compound has close links with the ternary compounds NdNi9Si2 and NdNi12B6.

A set of eight tetragonal La1-xYxMn2Si2 compounds doped with 57Fe and covering the entire range 0 x1 have been investigated by Mössbauer effect spectroscopy over the temperature range 4.2-520 K. Distinct changes in the quadrupole splitting (QS) and magnetic hyperfine field (µ0Hhf) values were observed around critical concentrations of xc~0.15 (4.2 K) and xc~0.2 (room temperature; RT) as the antiferromagnetism of the Y-rich compounds gives way to the predominant ferromagnetism of the La-rich compounds. The temperature dependences of QS and µ0Hhf for the La-rich compounds (x0.25) also show distinct changes in the range ~285-470 K which we relate to the reported magnetic phase transitions occurring in these critical regions. The magnetic phase diagram which we have derived for the La1-xYxMn2Si2 series from our Mössbauer measurements is in excellent agreement with the recent findings of neutron diffraction investigations. We show that analyses of both the Mössbauer and neutron data on LaMn2Si2 give a fully consistent account of the temperature dependent canting of the magnetic structure. Finally, consistent with earlier magnetization measurements, we suggest that a magnetically frustrated state, possibly a spin glass, may exist within the boundary regions of these magnetic phase transitions.

DyCo10Mo2−xVx compounds (x=0, 0.5, 1.0, 1.5, 2.0) with the ThMn12 structure were prepared by means of arc-melting and subsequent vacuum annealing. The magnetic properties were investigated by X-ray diffraction on fixed aligned powder samples and by magnetization measurements. The lattice constants decrease linearly with increasing x, according to Vegard's law. The easy magnetization direction of all samples is parallel to the c-axis at room temperature. The magnetization hysteresis loops of the aligned sample at a very low temperature after this sample was cooled under an applied field and zero field are different. It results from the large coecivity at low temperature and magnetization reversal when passing the compensation temperature in the cooling process. After analyses, it is found that the samples are not magnetized to full saturation at 10K due to the relatively small applied fields from −5 to 5T. At least two or three types of particles with much different coercivity coexist in every sample, and the maximum coercivity for at least one of the types is larger than 5T. The smaller the value of x, the larger the coercivity in the DyCo10Mo2−xVx compounds. Temperature dependence of the magnetization indicates that a spin reorientation transition occurs, and the transition temperature increases from ∼30K (for x=0) to ∼40K (for x=2). The influence of substitution of Mo and V in Co positions of the 1:12 structure on the magnetic coupling constant and crystalline electric field parameter is discussed.

We have successfully prepared a Y3(Fe0.93V0.07)29 single crystal by the Czochralski method followed by an appropriate annealing procedure. The spontaneous magnetization lies in the (1 0 2)-plane over the investigated temperature range of 5–300 K. The Curie temperature is Tc = 439 K. The saturation magnetization at 5 K is Ms = 48.3 μB/f.u. which corresponds to an average Fe magnetic moment of 1.79 μB. The uniaxial anisotropy K1* of Fe-sublattice at T = 5 K is — 2.25 MJ/m3. We observed no easy magnetization direction within the (1 0 2)-plane which may be due to the coexistence of Y3(Fe,V)29 crystallites, oriented to each other at a relative angle of θ = 60° about the [1 0 2] axis. This feature has been well explained with a six-domain model in terms of the anisotropy constants Ki(T) of the iron sublattice of the monoclinic 3 : 29 structure.

The formation of a sizeable single crystal of the Nd3(Fe,Ti)29-type phase, namely Y3(Fe0.933V0.067)29 is reported. It was prepared by the solid-state transformation of a Y2(Fe,V)17 single crystal whose chemical composition is Y3(Fe,V)29. Initial disagreement between powder and single-crystal X-ray data has been resolved by performing magnetization measurements on single crystal. These measurements show a peculiar behaviour and have been quantitatively analysed by considering that the crystal is actually twinned. Refinement of the single-crystal data is then re-examined and confirms the monoclinic structure already reported for this system.

The novel quaternary rare-earth transition-metal intermetallic compound Nd3Ni29Si4B10 of space group P4/nmm (No. 129) has been synthesised and its structure determined. The crystal structure has been investigated by scanning electron microscopy, X-ray and neutron powder diffraction measurements. Rietveld refinements of the powder X-ray and neutron diffraction patterns reveal a tetragonal structure of lattice parameters a=b=11.2327(7) Å, c=7.8754(3) Å with two formula units of Nd3Ni29Si4B10 per unit cell. The structure contains two rare-earth crystallographic sites of high symmetry, four B sites, seven transition metal sites and one Si site. The Ni atoms at the 2c 4 mm crystallographic site have a quasi-spherical polyhedral coordination.

The effects of Tb substitution on the magnetic structure of LaMn2Si2 have been investigated by neutron powder diffraction. Measurements were performed between 4 K and 550 K on two representative compounds, LaMn2Si2, 10% and 30% Tb. Both crystallize in the ThCr2Si2 structure (I-4/mmm). For La0.9Tb0.1Mn2Si2, magnetic lines superimposed on nuclear lines are observed. A canted ferromagnetic structure is inferred at temperatures below 305 K whilst between 305 and 440 K, a planar structure with antiferromagnet coupling within Mn-Mn layers is proposed. For La0.7Tb0.3Mn2Si2, additional (111), (113)and (201) lines, not present in the 10% Tb compound, appear at low temperatures. This indicates the existence of a structure consisting of ferromagnetic (001) Mn planes coupled antiferromagnetically along the c-axis at low temperatures.

Interstitial rare-earth iron-rich Sm3(Fe,Cr)29Xy (X=N, C) compounds with the monoclinic Nd3(Fe,Ti)29 structure have been successfully synthesized by gas–solid reaction. An intrinsic coercivity μ0iHc of ∼0.80 T at 293 K has been attained for both the nitride and carbide prepared by ball-milling. The intrinsic coercivity μ0iHc of the nitride powder increases with decreasing average particle size d and exhibits a maximum at d=0.4 μm, then decreases slowly for smaller d values. Our results suggest that the coercivity of the Sm3Fe24Cr5Ny powder is mainly controlled by a nucleation mechanism as observed in the Sm3(Fe,Ti)29Ny and 2:17:N nitrides. A remanence of Br=O.87 T has been achieved at 293 K for Sm3Fe24Cr5Ny which gives an energy product of (BH)max=l04.8 kJ/m3. Similar hard magnetic properties were observed for the carbide powder. The temperature coefficient of the remanence of the carbide is worse than that of Nd–Fe–B, although it has a better temperature coefficient of coercivity. Both the nitride and carbide powders have better corrosion resistance than commercial Nd–Fe–B powder.

The magnetic behaviour of a novel quaternary rare-earth compound Nd3Co29Si4B10 has been investigated by AC magnetic susceptibility and Fe-57 Mossbauer effect spectroscopy measurements. The Nd3Co29Si4B10 compound exhibits a magnetic transition around T-c1 similar to 200 K with a second magnetic transition occurring around T-c2 similar to 43 K. Addition of similar to 0.5 wt% Fe-57 is found to decrease the magnetic ordering temperatures to T-c1 similar to 167 K and T-c2 similar to 38 K. Similar to other Co-rich, light rare-earth compounds, Nd3Co29Si4B10 is likely to exhibit ferromagnetic ordering below T-c1. (C) 1998 Elsevier Science B.V. All rights reserved.

A systematic investigation of structure and intrinsic magnetic properties of the novel compounds R3(Fe, T)29 (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy; T=V and Cr) has been performed. The lattice constants and unit cell volume decrease with increasing the rare-earth atomic number from R=Nd to Dy, except for Ce, reflecting the lanthanide contraction. The Curie temperature increases from R=Ce to Gd and decreases from Gd to Dy, respectively, with increasing atomic number and Gd3Fe29−xTx has the highest Curie temperature for each series of R3Fe29−xTx (T=V or Cr) compounds. The saturation magnetization of R3Fe29−xTx at 4.2 K decreases gradually from R=Nd to Dy with increasing atomic number, except for Ce, in each series of R3Fe29−xTx. It is suggested that the Ce ion in Ce3Fe29−xTx is valence fluctuated which leads to the unusual magnetic properties. The spin reorientations of the easy magnetization direction of R3Fe29−xTx are observed at around 230, 230, and 160 K for R=Nd, Sm, and Tb when T=V, and at around 230 and 180 K for R=Nd and Tb when T=Cr, respectively. First order magnetization processes are observed around 5.7 T for Sm3Fe26.7V2.3 and 4 T for Sm3Fe24.0Cr5.0 at 4.2 K, 2.0 T for Tb3Fe28.0V1.0, and 2.3 T for Tb3Fe28.0Cr1.0 at room temperature. A phenomenological analysis shows that the saturation magnetization of R3Fe29−xTx compounds with a low T concentration can be roughly calculated based on a combination of those of the 2:17R and 1:12 units in a ratio of 1:1.

The novel ternary rare-earth iron-rich interstitial compounds R3(Fe,Cr)29Xy (R=Nd, Sm and X=N, C) with the monoclinic Nd3(Fe,Ti)29 structure have been successfully synthesized. Introduction of the interstitial nitrogen and carbon atoms led to a relative volume expansion ΔV/V of about 6% and an enhancement of Curie temperatures Tc about 268 K for the nitride and about 139 K for the carbide, respectively. The Nd3Fe24.5Cr4.5Xy compounds have a planar anisotropy at room temperature. A first-order magnetization process (FOMP) with critical field Bcr=4.4 T and 3.1 T at room temperature were observed for the Nd-nitride and carbide compounds, respectively. The Sm3Fe24Cr5Xy compounds were found to have a large uniaxial anisotropy of about 18 T at 4.2 K and about 11 T at 293 K. A FOMP with Bcr=2.3 T was also observed in the Sm-nitride compounds at 4.2 K. Magnets with coercivity of μOjHc∼0.8 T at 293 K has been successfully developed from the Sm3Fe24Cr5Xy (XN and C) phases.

The novel compound has been successfully synthesized. Its x-ray pattern can be indexed with a monoclinic symmetry and the space group. Thermomagnetic analysis gives a magnetic ordering temperature of 400 K. The saturation magnetization of at 4.2 K and room temperature are and and the anisotropy fields at 4.2 K and room temperature are 5.2 T and 1.7 T, respectively. A systematic analysis of the magnetic properties of novel compounds (R = Y, Ce, Pr, Nd, Sm, Gd, or Tb) at 4.2 K has been performed on the basis of their saturation magnetization. This suggests that the saturation magnetization of compounds with a low stabilizing element concentration can be calculated roughly from a combination of those of the rhombohedral or hexagonal and tetragonal units in a ratio of 1:1.

Be-substituted Nd/sub 2/(Fe/sub 14-x/Be/sub x/)B compounds have been successfully prepared. The observed linear reduction of unit cell volume with Be substitution indicates that the Be atoms enter almost exclusively the Fe sites. Both the Curie temperature and magnetization are weakened upon Be substitution; the reduction in T/sub c/ is about 26 K/Be atom and the reduction in the average Fe moment is about 0.26 /spl mu//sub B//Be atom, respectively. The fits to room temperature Mossbauer spectra of Nd/sub 2/(Fe/sub 13/Be)B give an average hyperfine field of 23.7 T. The room temperature anisotropy of Be substituted Nd/sub 2/(Fe/sub 14-x/Be/sub x/)B compounds is around 8 T which is nearly unchanged, compared to the parent Nd/sub 2/Fe/sub 14/B compound. Moreover, the Be substitution leads to an increase in the canting angle at 10 K, from 28/spl deg/ to /spl sim/36/spl deg/, and a decrease in the spin-reorientation temperature from 131 K to 123 K for Be/sub 0.5/ and 112 K for Be/sub 1.0/ substitution, respectively. These effects indicate a weakened A/sub 20/ value and/or an enhanced A/sub 40/ value for Nd atoms.