D.B. de Mooij

Meltspun permanent magnet materials containing Fe3B as the main phase

Abstract A novel type of permanent magnet material was obtained by annealing amorphous melt spun flakes of the approximate composition Nd 4 Fe 78 B 18 . The annealing process consists of two steps. At first, at a temperature T 1 , the metastable compound Fe 3 B crystallizes while, at a higher temperature T 2 , the hard magnetic phase Nd 2 Fe 14 B is formed. This phase comprises only 15% of the alloy. Nevertheless, materials in which the latter reaction has taken place show remarkable isotropic hard magnetic properties. The remanence μ 0 M r is 1.2 T, while intrinsic coercive fields μ 0 H c of almost 0.4 T have been attained, with ( BH ) max =95 kJ/m 3 . In this paper the preparation of these materials, the compositional dependence of the magnetic properties and a possible explanation for the high isotropic remanence are presented.

Magnetic properties of ternary rare-earth compounds of the type R2Fe14B

Abstract Ternary tetragonal compounds of the composition R 2 Fe 14 B were observed for R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. The lattice constants and the X-ray density of these compounds were determined. Also determined were the magnetic properties, comprising the temperature dependence of the magnetization in the range 4.2–700 K and the field dependence of the magnetization at 4.2 K in fields up to 20 T. These latter measurements were made in two mutually perpendicular directions, making it possible to determine the anisotropy fields. The magnetocrystalline anisotropy was found to consist of contributions due to the Fe and rare-earth sublattice, respectively.

Some novel ternary ThMn12-type compounds

Abstract Ternary compounds based on the tetragonal ThMn 12 structure are formed when rare earth. elements (R) are combined with iron and elements M (M ≡ Si, Ti, V, Cr, Mo or W). A structure determination was made for NdFe 10 Mo 2 , showing that the molybdenum atoms occupy only one of the three available crystallographic sites in this structure type. Detailed investigations of the systems YFe 12 − x V x showed that there is a substantial range of solid solubility extending approximately from x = 1.5 to x = 3. Curie temperatures were determined for the two series YFe 10 M 2 and GdFez 10 M 2 and were found to depend strongly on the component M.

Formation and magnetic properties of the compounds R2Fe14C

Abstract It was shown by X-ray diffraction that rare earth compounds of the type R2Fe17 can dissolve appreciable amounts of carbon up to x = 0.6 in R2Fe17Cx at 900 °C. The increase in the lattice constants is accompanied by a strong increase in Curie temperature. From a structure determination (R = 7%) it was found that the carbon atoms dissolve interstitially and occupy the 9e position in the Th2Zn17 structure type (R3m). This ternary carbide is present as the main phase when compounds of the type R2Fe14C are heated above their decomposition temperatures. The decomposition proceeds by means of a solid state transformation and the corresponding transformation temperatures Tt vary strongly with the R component. In several of the light rare earth systems Tt becomes rather low and makes an annealing treatment ineffective with regard to the formation of R2Fe14C phases. The magnetic properties of the R2Fe14C phases are compared with those of R2Fe14B. It is shown that the former follow the magnetic behaviour of the latter almost completely.

Magnetic properties of a series of novel ternary intermetallics (RFe10V2)

Abstract We have studied the magnetic properties of a series of novel ternary compounds of the composition RFe 10 V 2 (R ≡ Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y). X-ray diffraction showed that these materials crystallize in the tetragonal ThMn 12 structure. The Curie temperature falls into the range 483 to 616 K. From high-field magnetic measurements made at 4.2 K on aligned powders it was derived that the iron sublattice anisotropy is about 4 T, while the rare earth sublattice anisotropy is comparatively low in most of the compounds studied.

Structure and magnetic properties of R2Fe17Nx compounds

Abstract We have shown that ternary rare earth nitrides of the approximate composition R2Fe17N2.5 can be prepared by the reaction of R2Fe17 with nitrogen gas at 500°C for all members of this series. The crystal structure and lattice constants of these compounds have been determined and are discussed in terms of volume increase and nitrogen site occupation. The N2 uptake was found to be accompanied by strong increases of the Curie temperature and room temperature magnetization. From the results it was derived that the N2 uptake may lead to substantial changes in the RFe coupling strength.

Magnetic and crystallographic properties of ternary rare earth compounds of the type R2Co14B

Abstract Ternary tetragonal compounds of the composition R 2 Fe 14 C were observed for R = Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu. The lattice constants of these compounds were determined. Also determined were the magnetic properties, comprising the temperature dependence of the magnetization in the range 4.2–700 K and the field dependence of the magnetization at 4.2 K in fields up to 35 T. These latter measurements were made on magnetically-a ligned powders with the field parallel and perpendicular to the alignment direction, making it possible to determine the anisotropy fields. The magnetocrystalline anisotropy, consisting of contributions due to the Fe and rare-earth sublattice, was found to be of comparable magnitude in R 2 Fe 14 C and R 2 Fe 14 B.

Properties of metastable ternary compounds and amorphous alloys in the Nd-Fe-B system

Abstract We have studied the crystallization behaviour of numerous amorphous alloys of iron-rich composition in the Nd-Fe-B system. Increasing the boron(iron) concentration leads to an increase (decrease) of the thermal stability. Increasing the neodymium concentration gives rise to a strong initial increase in the thermal stability but leads to a decrease at higher neodymium concentrations. Two novel ternary compounds were observed in the iron-rich corner of the Nd-Fe-B system. The compound Nd2Fe23B3 is cubic and orders magnetically at 655 K. The compound NdFe12B6 is hexagonal and its Curie temperature is 230 K. Both compounds are metastable and transform to equilibrium phases at temperatures near or above 1000 K.

Magnetic properties of ternary Fe-rich rare earth intermetallic compounds

The crystal structure and the magnetic properties are determined for several novel ternary intermetallic compounds of the type RFe/sub 10/T/sub 2/, where R represents Ti, V, Cr, Mo, W, or Si. All these compounds show a strong ferromagnetic behavior, with Curie temperatures in the range 350 K to 600 K. The magnetic and crystallographic properties of the RFe/sub 10/T/sub 2/ compounds are discussed together with the properties of 3d-rich ternary compounds of different composition and structure. Special attention is paid to the magnetocrystalline anisotropy of these materials, consisting of contributions of the R sublattice and the Fe sublattice. Detailed information on the crystal-field-induced contribution of the former sublattice is derived from /sup 155/Gd Mossbauer spectroscopy performed on the Gd compounds of these series, since the /sup 155/Gd nucleus can be regarded as a sensitive probe of the electric field gradient at the nuclear site produced by the electric charges of the surrounding ions. It can be shown that this electric field gradient is proportional to the second order crystal field parameter A/sup 0//sub 2/, which in turn determines the magnetocrystalline anisotropy of the R sublattice. >

Metastable ferromagnetic materials for permanent magnets

Abstract It is shown that novel starting materials for permanent magnets can be prepared from amorphous alloys after controlled crystallization. The magnetic properties of several novel intermetallic rare earth compounds of a metastable nature that are absent in the corresponding phase diagram are described. We also discuss the importance of the possibility of generating specific microstructures of multiphase alloys by starting from the amorphous state. Such specific microstructures may have hard magnetic properties far superior to those attainable by normal casting and annealing procedures. Data are presented for the controlled crystallization of amorphous rare earth-iron-boron alloys close in composition to Fe 3 B.