Investigation of the magnetic interactions in the tripod-Kagome compound Mg${}_2$Gd${}_3$Sb${}_3$O${}_{14}$ by electron spin resonance experiments

As an example of a class of geometrically frustrated magnetic systems, the so-called tripod Kagome materials have been suggested as an interesting target of experimental investigation due to the frustrated nature and the question of dimensionality of the magnetic interactions. 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 quasiclassical Heisenberg magnet, where the effect of spin-orbit coupling of Gd${}^{3+}$ ions vanishes to first order. Measurements were conducted over a frequency range of 70-420 GHz and temperatures ranging from 3-50 K. The Gaussian lineshape is consistent with a model of dominant dipolar spin-spin interactions, while the growing asymmetry of the lineshape upon decrease of temperature signifies an increase of an effective internal field, an indication of increasing short-range spin-spin-correlations. Such a behavior is typical for frustrated systems, making our studies one of the first to reveal such significant features in this family of materials. 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.