Magnetic structures of GdMn₆Ge₆- a nuclear magnetic resonance analysis

Abstract

The origin of the interesting magnetic properties of GdMn6 Ge6 in the low-temperature, low-field phase is a spiral arrangement of the magnetic moments. This has been established by pulsed nuclear magnetic resonance experiments. Spin-echo spectra taken in an external magnetic field, and the observed enhancement of the radio-frequency field, suggest the presence of a spiral structure. This information is crucial for a quantitative analysis of the complicated 55 Mn spectra. The anisotropy of the hyperfine field at the 55 Mn site is about 10% and the enhancement has been found to be highly anisotropic, as well. Comparing the temperature dependencies of the Zeeman splitting at the individual lattice sites, Mn has been identified as the source of the transferred hyperfine fields at the 73 Ge nuclei. An analysis of the 73 Ge and 155/157 Gd spectra yields the size and relative orientation of the hyperfine fields and electric field gradients at the nuclei in agreement with 155 Gd Mössbauer spectroscopy results.

High temperature calorimetric examination of enthalpies of mixing in liquid (gadolinium–germanium–manganese) alloys

“…The values of D f H 298. 15 for Gd 2 Ge 3 and Gd 3 Ge 5 are close to the values of D mix H of liquid alloys [43], while D f H of refractory germanides Gd 5 Ge 3 , Gd 5 Ge 4 and GdGe are more negative than D mix H. The position of the D mix H extreme corresponds to that of the Gd 5 Ge 4 stoichiometry and is close to the stoichiometry of Gd 5 Ge 3 and GdGe (figure 1). This indicates that strong interaction between Gd and Ge atoms in gadolinium germanides remains at the transition into the liquid phase with possible formation of isostoichiometric clusters.…”

“…Consequently, the results for x Gd > 0.5 have been omitted from further calculations. The Q j coefficients of the equations (15) and (16), which approximate the D mix H Gd and D mix H for the compositions studied, are summarised in table 4. As can be seen from figure 5(a) and (b), the experimental results for sections of the ternary system are in good agreement with the literature results for the (Gd-Ge) and (GdMn) boundaries.…”

“…The values of D mix H Gd and D mix H calculated by equations (15) and (16) with confidence intervals are listed in table 5. The equation (17), which interpolates the D mix H by the method (I), assumes the following form: …”

“…The standard enthalpies of formation (D f H 298. 15 ) of gadolinium germanides have been measured using an electromotive force method (e.m.f.) with chloride electrolyte [43,44] and calculated by the Miedema model [45].…”

“…Rare-earth intermetallic compounds GdMnGe [1], REMn 2 Ge 2 [2][3][4][5][6][7][8][9][10][11], RE 3 Mn 4 Ge 4 [12] and REMn 6 Ge 6 [13][14][15][16][17][18] attract considerable attention due to their unusual electronic and magnetic properties. The intermetallic compounds containing gadolinium exhibit antiferromagnetic character of ordering and are able to transform into ferrimagnetic, paramagnetic and even to ferromagnetic state under the influence of temperature and/or magnetic field [3,5,8,11] or with the substitution of the Mn, Gd or Ge by TR, IIIa or IVa group elements [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34].…”