Electron spin resonance studies on the frustrated tripod-Kagome material Mg${}_2$Gd${}_3$Sb${}_3$O${}_{14}$

As an example of a class of geometrically frustrated magnetic systems, the so-called tripod Kagome materials consisting of a modified pyrochlore lattice with nonmagnetic interlayers have been suggested as an interesting target of experimental investigation. Since the Kagome planes in these compounds are well separated from each other, two-dimensional magnetic behavior is expected. In our work we performed high-field electron spin resonance measurements on a powder sample of Mg${}_2$Gd${}_3$Sb${}_3$O${}_{14}$, a representative of a classical Heisenberg magnet, in which the magnetic Gd${}^{3+}$ centres are devoid of spin-orbit coupling. Measurements were conducted over a frequency range of 70-420 GHz and temperatures ranging from 3-50 K. The Gaussian shape of the spectra is consistent with a model where dipolar spin-spin interaction plays a dominant role, while the growing asymmetry of the lineshape upon decrease of temperature signifies an effective internal field building up, an indication of increasing short-range spin-spin-correlations. Furthermore, temperature dependent critical broadening of the linewidth and increase of the internal field strength provide insights into the dimensionality of the spin-spin correlations.