The 57Fe Mössbauer-effect spectra of the series of hard magnetic materials, R2Fe14C, where R is Nd, Gd, Tb, Dy, Ho, and Lu, have been measured at 295 K. All of these carbides exhibit uniaxial magnetic anisotropy. The spectra resemble those obtained for the related R 2Fe14B compounds and have been fit with the model used earlier for Nd2Fe14B. The magnitude of the hyperfine field on each site, as a function of rare earth, parallels the Curie temperature; the maximum hyperfine fields and the maximum Curie temperature are observed for Gd2Fe14C. A linear correlation is observed between the hyperfine fields on the six sites in the analogous borides and carbides; however, these fields are systematically smaller in the carbides. The decrease in the tetragonal unit cell c-axis length in the carbides apparently reduces the exchange interactions between the 8j and 16k iron layers and hence reduces the moments. The isomer shift on each site decreases as the atomic number of the rare earth increases, whereas the quadrupole interactions are independent of rare earth.
G. J. Long et al., "A Mössbauer-Effect Study of a Series of R2Fe14C Hard Magnetic Materials," Journal of Applied Physics, vol. 69, no. 8, pp. 6040-6042, American Institute of Physics (AIP), Apr 1991.
The definitive version is available at http://dx.doi.org/10.1063/1.347763
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