J.S. Lord

The volume dependence of the magnetization and NMR of Fe4N and Mn4N

The forced volume magnetostriction and the NMR of ferromagnetic FeN and ferrimagnetic Mn4N have been measured in the ordered state. At 4.2 K the magnetization ( sigma ) per unit mass and the effective field (HI) at the nucleus of the Fe(I) site of Fe4N are found to change with pressure such that delta ln sigma / delta P approximately= delta ln mod HI mod / delta P 0. The result for Mn4N is interpreted as showing that the magnitude of the small (negative) moment on the Mn(II) site decreases more rapidly under pressure than does the large Mn(I) moment. The value of delta ln mod HI mod / delta P for Mn4N was found to be a strong function of temperature such that delta lnTN/ delta P approximately=5.2 Mbar-1. An analysis of the Mn4N NMR data suggests that the discrepancy between the calculated (spin) and measured moment at the Mn(I) site may be due to a small orbital moment at that site.

A ferromagnetic Kondo compound: CePdSb

Abstract The ferromagnetic ground state of CePdSb has been confirmed by neutron diffraction measurements and the observation of Sb-NMR in zero field. It is therefore one of the few ternary compounds to exhibit both Kondo lattice and ferromagnetic behaviour. Inelastic neutron scattering has allowed the crystal field parameters of the cerium ion to be determined. Under pressure the Curie point ( T c ≅ 17 K) of CePdSb was found to increase at the rate d ln T c /d P = 14 Mbar −1 .

NMR study of the Sm2Fe17 hydrides

Abstract The 147 Sm NMR spin echo spectra of the Sm 2 Fe 17 H x ( x =0, 2.9, 4.6) series at 4.2 K are presented. The observed quadrupole septets are assigned to the samarium 6c site with different numbers of neighbouring hydrogen atoms occupying the 9e and 18g interstitial sites. A significant influence of hydrogen at 18g sites on the electric field gradient is observed, but hydrogen at the 9e sites has little effect. The difference is discussed in terms of the distances between samarium and hydrogen 9e and 18g atoms in the structure. A relation of the corresponding electric field gradient to the Sm contribution to the magnetocrystalline anisotropy is given.

NMR of Nd and Sm in Nd/sub 2/Fe/sub 14/B and Sm/sub 2/Fe/sub 14/B

The spin-echo nuclear magnetic resonance (NMR) spectra of /sup 143/Nd, /sup 145/Nd, /sup 147/Sm and /sup 149/Sm in polycrystalline samples of Nd/sub 2/Fe/sub 14/B and Sm/sub 2/Fe/sub 14/B measured at 4.2 K are presented. Well resolved quadrupole subspectra are assigned to the rare earth sites 4f and 4g in the compounds. The corresponding values of the quadrupole splitting and hyperfine fields are analyzed in terms of the contributions, depending on the rare earth type, as well as local symmetry and environment of the sites. From the quadrupole splitting, the 4f and the lattice contributions to the electric field gradient at Nd and Sm nuclei are derived. On this basis, the crystal electric field coefficients A/sub 2//sup 0/ for both rare earth sites are obtained and compared to those obtained in other measurements. >

A nuclear magnetic resonance investigation of the ferromagnetic phase of CePdSb as a function of temperature and pressure

The ferromagnetic state of CePdSb below 17 K has been confirmed by zero-field Sb NMR. The effective field at the Sb nucleus at low temperature is +2.78 T and the quadrupole interaction is 3.8 (2.3) MHz for . The NMR spectra do not reflect reported magnetic behaviour at 6 K. The transition at this temperature is therefore thought to be due to a second phase. The value of is , which is similar to that of . The value of , which is estimated to be times the value expected for an isotropic elastic solid. The elastic properties of CePdSb are therefore predicted to be extremely anisotropic. The temperature dependence of was measured from 1.4 - 15 K but measurements are required to lower temperatures before it can be decided whether a 4.5 K gap exists in the spin-wave spectrum, as postulated from heat capacity measurements.

Nuclear magnetic resonance study of the Sm2Fe17 carbides

Abstract The 147 Sm and 149 Sm NMR spin echo spectra and the spin echo decays of Sm 2 Fe 17 C x for x = 0, 0.5, 1 and about 3 at 4.2 K are reported. The quadrupole septets in the spectra are assigned to the samarium 6c site with different numbers of carbon atoms occupying the neighbouring 9e interstitial sites. A significant influence of carbon neighbours on the Sm quadrupole splitting and hyperfine field is observed and is attributed to a strong change of the Sm valence electron distribution and polarisation caused by carbon neighbours. From the quadrupole splittings the values of the lattice electric field gradient and the corresponding crystal electric field coefficient A 2 0 are derived. For the Sm sites with 0 (3) carbon nearest neighbours the A 2 0 value of −66 K a 0 −2 (−350 K a 0 −2 is obtained.

Pressure dependence of magnetic properties of Fe4N and Mn4N

Abstract The value of the magnetization of ferromagnetic Fe 4 N is found to decrease under pressure while that of ferrimagnetic Mn 4 N increases. The magnitude of the effective field at the 55 Mn nucleus of the Mn(I) site of Mn 4 N also increases under pressure. It is deduced that the magnitude of the moment at the Mn(II) site decreases under pressure, while that of the Mn(I) site is independent of pressure, in agreement with the model of covalent magnetism for Mn 4 N.

Evidence for a magnetic moment at the Lu site of LuFe2

Abstract High pressure 175 Lu NMR measurements of LuFe 2 at 4.2 K suggest that Lu, like Y and Zr, carries a negative magnetic moment, in agreement with self-consistent energy band calculations. The observed spectrum is more complicated than would be expected for a Laves phase compound.

Nuclear magnetic resonance study of Nd2Fe17Nx

Abstract The 145Nd nuclear magnetic resonance spin echo spectra of Nd2Fe17 and Nd2Fe17N3 at 4.2 K are presented. A single quadrupole septet observed in the spectra of both compounds is assigned to the Nd site with no nitrogen neighbours in Nd2Fe17, and with three nitrogen neighbours in Nd2Fe17N3. A drastic reduction in the quadrupole splitting with nitriding is attributed to a huge increase in the “lattice” electric field gradient at the Nd site caused by nitrogen neighbours. The corresponding change of the crystal electric field parameter A20 caused by the three N neighbours amounts to −282Ka0−2, very close to that in the isostructural Sm2Fe17Nx series.

Nuclear magnetic resonance of neodymium in NdFe11TiNx

Abstract The 143 Nd and 145 Nd nuclear magnetic resonance spin-echo spectra of NdFe 11 Ti and NdFe 11 TiN x at 4.2 K are measured. For the host compound a single broad line pattern is observed and assigned to the Nd 2a sites. A narrow line at higher frequencies appearing in the spectra of NdFe 11 TiN x for both isotopes is attributed to the Nd sites with nitrogen as the nearest neighbour. Its very small linewidth is assigned to a large reduction in the quadrupole splitting caused by a huge increase in the ‘lattice’ electric field gradient at the Nd site produced by nitrogen. The corresponding change in the crystal electric field parameter A 2 0 caused by nitrogen of 185 Ka 0 −2 is obtained.