Determination of anisotropy constants for monoclinic ferromagnetic compounds

There is much interest in the intrinsic magnetic properties of R3 T29 compounds (R - rare earth, T - transition metal) or the interstitially modified phases R3 T29 Nx. These phases reveal a monoclinic crystalline structure. Therefore, contrary to the case of uniaxial (i.e. tetragonal, hexagonal or rhombohedral) materials, two anisotropy constants are necessary to describe the magnetocrystalline anisotropy energy already in lowest order in a series expansion of direction cosines. Furthermore, the discussion of the origin of the magnetic anisotropy in R-T compounds showed, that both these constants have to be expected to have the same order of magnitude. Thus, the well established methods to determine the second and fourth order anisotropy constants K1 and K2 for uniaxial compounds from demagnetization curves had to be completely revised for the 3:29 compounds. We developed a fit-procedure which enables the determination of the two anisotropy constants (of lowest order) in monoclinic phases from the demagnetization curves of polycrystalline samples, measured in the range of reversible rotational processes. The procedure has been applied to R3(Fe, Ti)29 with R= Sm, Nd, Pr and Ce and to the interstitially modified nitrides R3 T29 Nx (x ∼ 4) with R= Sm, Nd and Pr. (author)