R. Verhoef

Strength of the rare-earth-transition-metal exchange coupling in hard magnetic materials, an experimental approach based on high-field magnetisation measurements: Application to Er2Fe14B

Abstract A new experimental technique is presented to determine the intersublattice molecular-field coefficient, n RT , in heavy rare-earth-transition-metal intermetallic compounds. The technique is based on high-field magnetisation measurements on finely powdered polycrystalline material that is free to rotate in the sampleholder. Experimental results are reported for a number of Er 2 Fe 14− x Mn x B compounds. The strength of the RT exchange coupling is not affected by the Mn substitution, and a value of 0.445 Tkg/Am 2 has been deduced for the coefficient n RT .

Moment reduction in RFe12-xTx compounds (R=Gd, Y and T=Ti, Cr, V, Mo, W)

Abstract We have investigated the magnetic properties of several ternary compounds of the type RFe 12- x T x , where R represents Y or Gd and T=Ti, Cr, V, Mo, W. For all compounds investigated we have determined the saturation magnetization at 4.2 K, the latter being derived from magnetic isotherms measured in fields up to 21 T. It is shown that the Fe moment in these materials varies with the T component in a manner which can qualitatively be understood on the basis of Friedels model. We also found that the Fe sublattice anisotropy is strong in all these compounds (in the Y compounds the anisotropy field B A ≈5T and in the Gd compounds B A ≈7 T), except for the compounds based on Mo.

Magnetic properties of Nd2Fe14C and some related pseudoternary compounds

Abstract We have investigated the magnetic properties of Nd2Fe14C and of several pseudoternary compounds of the type (Nd1−xRx)2Fe14C, where R represents Dy or Lu. For all compounds investigated we have determined the Curie temperatures and the saturation magnetization at 4.2 K, the latter being derived from magnetic isotherms measured in fields up to 35 T. The compounds Nd2Fe14C and Ho2Fe14C show spin reorientations at about 120 and 35 K, respectively, below which temperature the easy magnetization direction deviates from the c-axis. At 4.2 K we found indications for a FOMP transition near Hcr = 23 T in the Nd rich Nd1−xDyxFe14C compounds.

Magnetic properties of Er2Fe14−xMnxC

Abstract The magnetic properties of the compounds Er 2 Fe 14− x Mn x have been determined by means of X-ray diffraction, magnetic measurement and 57 Fe Mossbauer spectroscopy. Magnetization measurements made in fields up to 38 T showed that the saturation moment exhibits a minimum at a Mn concentration corresponding to about x =2, due to the antiparallel coupling between the R and 3d sublattice magnetizations the latter becoming strongly reduced with increasing Mn concentration. The reduction of the 3d-sublattice magnetization is accompnied by a corresponding reduction in the 57 FE hyperfine fields and by a lowering of the Curie temperature and the spin orientation temperature. Most of the compounds investigated have a break in the magnetization curves measured at 4.2 K which is interpreted as the onset of decoupling between the antiparallel rare earth and 3d sublattices. A mean field analysis was used to derive the intersublattice molecular field coefficient n RT .

The strength of the R-T exchange coupling in R2Fe14B compounds

Abstract The R-T exchange-coupling parameter of the ferrimagnetic R 2 Fe 14 B compounds (R = Gd, Tb, Dy, Ho, Er, Tm) has been deduced from high-field magnetisation measurements at 4.2 K on finely powdered Mn-doped samples of which the powder particles are free to orient themselves in the applied magnetic field. Values ranging from 0.954×10 -22 to 1.29×10 -22 J have been derived.

Resistivity of the heavy-fermion U(Pt,Pd)3 alloys

Abstract Electrical resistivity measurements have been performed on a series of mono- and polycrystalline U(Pt1-xPdx)3 compounds (x ⩽ 0.15) in the temperature range 1.4-300 K. On alloying with Pd the spin-fluctuation-like resistivity of pure UPt3 transforms into a more complex curve for x = 0.02 and x = 0.05 revealing a transition at 3.3 K and 5.6 K, respectively. At higher Pd concentrations (x = 0.10,0.15) the resistivity curves change to a Kondo-type of behaviour. In the same concentration range a second phase appears in the X-ray patterns.

High-field study of R2Fe17C compounds

Abstract Magnetically-aligned samples of ferrimagnetic compounds of the R 2 Fe 17 C series with the heavy rare earths Gd, Tb, Dy, Ho, Er and Tm have been studied at 4.2 K in magnetic fields up to 35 T. The exchange field of 225 T and the spin-exchange coupling J Dy-Fe / k = -7.2 K have been derived for Dy 2 Fe 17 C and full magnetization curves have been calculated.

Magnetic interactions in 3d-4f compounds

Abstract Values of the exchange field obtained from high-field magnetization, inelastic-neutron-scattering, specific heat and from values for T c are found to be consistent for a number of different 3d-4f series.

Magnetisation curves of single-crystalline Tb2Fe17

Abstract Magnetization measurements in fields up to 38 T have been performed on single-crystalline Tb2Fe17 at 4.2 K. Tb2Fe17 is confirmed to be an easy-plane ferrimagnet. Along the hard c-axis a transition is observed at 3.9 T. The data have been analysed within a one- and a two-sublattice model.

Crystal growth of R2T17 and R2Fe14B intermetallics (R = rare earth, T = Co, Fe)

Abstract Bulk single crystals of R2Co17 (R = Nd, Pr, Gd, Tb), R2Fe17 (R = Y, Dy, Er) and R2Fe14B (R = Y, Nd) have been grown from the melt using a modified “tri-arc” Czochralski method. The crystals were characterized using standard X-ray techniques. The measured densities were compared with the calculated ones obtained from the lattice parameters. High-field magnetization measurements were performed on some of the as-grown crystals.