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Elastoresistance describes the resistance change induced by an elastic deformation. In the well-known compound BaFe₂As₂ with clear nematicity, a diverging elastoresistance has been taken as a measure of the nematic susceptibility [1]. In contrast to BaFe₂As_2, the related CaK(Fe,Ni)₄As₄ orders antiferromagnetically as a so-called spin-vortex crystal (SVC) [2], which does not entail any nematicity. Here, we have determined the elastoresistance of CaK(Fe_1-xNi_x)₄As₄ (x=0-0.05), spanning the phase diagram from a superconducting sample with T_c=35 K and no magnetic order, to a sample with magnetic order at a high T_N=51 K having T_c=10 K. The nematic susceptibility for SVC order is analyzed theoretically via a Ginzburg-Landau expansion and compared with the elastoresistance data. Implications on the place of CaK(Fe,Ni)₄As₄ in the wider material class and the factors contributing to elastoresistance are discussed.
[1] Chu et al., Science 337, 710 (2012)
[2] Meier et al., npj Quantum Materials, 3, 5, (2018)