Hydrogen-induced reduction of electric field gradient in La2Fe14BHx studied by NMR on 139La

The 139La NMR spin-echo spectra of La2Fe14BHx are reported. Since lanthanum has no 4f electrons, the observed quadrupole splittings are directly proportional to the lattice part of the electric field gradient, Vzzlat. This quantity decreases as the content of interstitial hydrogen x grows. To describe the fall-off of Vzzlat, a dimensionless function f2(x) is introduced, normalised so that f2(0)=1. Analysis of the new and earlier published data obtained by several experimental techniques demonstrates that the reduction of both the second-order crystal field parameter A20 and the lattice electric field gradient Vzzlat is described by the same function f2(x) in all R2Fe14BHx. The only distinction that needs to be made is between R being a light and a heavy rare earth.