Phase formation and ferrimagnetism of GdCo₉Si₄

Abstract

The phase relations of the GdCo 13−x Si x system have been studied by means of scanning microscopy, microprobe analysis and x-ray diffraction. Single-phase samples GdCo 9±δ Si 4∓δ (structure type LaFe 9 Si 4 with space group I 4/mcm) are formed in a narrow composition range |δ| 0.2, where GdCo 9 Si 4 forms as a fully ordered ternary compound. The magnetic properties of GdCo 9 Si 4 have been investigated by ac susceptibility, magnetization, specific heat and resistivity measurements. These experiments reveal ferrimagnetism below about 47 K, which is analysed in terms of a two-sublattice molecular field model with a local moment Gd subsystem coupling antiparallel to the itinerant ferromagnetic Co 3d sublattice. The 3d-3d exchange of the latter is the driving force for the onset of long range magnetic order. The validity of the twosublattice model is demonstrated by high field measurements, showing that the ferrimagnetic coupling starts to break up at a lower critical field µ 0 H l 27 T. The magnetic ground state of GdCo 9 Si 4 has been analysed on a microscopic basis via LSDA electronic structure calculations.

High field investigation on the ferrimagnetic systems GdCo9−xSi4+x(−0.2 ⩽x⩽ 0.2) and TbCo9Si4

“…The magnetic properties of the stoichiometric GdCo 9 Si 4 were studied by means of ac susceptibility, magnetisation, specific heat and resistivity measurements reported in [9]. These experiments reveal ferrimagnetism below 47K, where the local moment Gd subsystem couples antiparallel to the itinerant ferromagnetic Co-3d sublattice which is the driving force for the onset of long range magnetic order.…”

“…According to the assumption, that the Gd and the Co-sublattice couple antiparallel in GdCo 9-x Si 4+x high field magnetisation measurements were performed. Applying a local moment molecular field model for two sublattices using Néel theory [11] for analysing the M(T) and M(H) data (measured in low fields) allows to estimate the strength of the intra-sublattice exchange coefficients γ CoCo = 90 Gmol emu −1 , γ GdGd = 0.3 Gmol emu −1 and the Gd-Co inter-sublattice exchange coefficient γ GdCo = −9.8 Gmol emu −1 [9]. The low temperature saturation magnetisation M Gd (T = 0) of the Gd sublattice where Gd is in a 8 S 7/2 state delivers a magnetization of 7 μ B /f.u.…”

“…To ensure homogeneity, the buttons were broken, flipped over and remelted another four times and finally, sealed in an evacuated quartz tube and annealed at 1050°C for one week. The structural sample characterisation as well as the investigation of the microstructure was described in [9]. All materials investigated within this work exhibit the tetragonal LaFe 9 Si 4 structure.…”

“…This may be related to structural problems because it was found that the crystal structure of these compounds varies significantly with increasing Si content, namely from a cubic NaZn 13 -type structure to a tetragonal CeNi 8.5 Si 4.5 -type structure with space group I4/mcm [8]. The stoichiometric compound GdCo 9 Si 4 is ferrimagnetic, where the antiparallel coupling can be broken up applying a sufficient high magnetic field as was shown recently [9]. Because the magnetic behaviour in these materials is on one side very dependent on the stoichiometry and on the other side a metamagnetic transition is observed, we report in this paper high field investigations on GdCo 9-x Si 4+x (-0.2 ≤ x ≤ 0.2).…”

Magnetic properties and magnetocaloric effects in GdCo9Si2 compound with multiple magnetic phase transitions

“…They have gained more attention as potential highly efficient magnetocaloric materials and giant isotropic magnetostriction materials. 10 This inspires us to investigate the magnetic behaviors of Co-rich compounds in the Gd-Co-Si system. However, except for above mentioned Gd-based compounds, only a few reports are available on the structure and magnetocaloric studies on this series.…”