Magnetic Fluctuation and First-Order Transition in Trillium Lattice of EuPtSi Observed by 151Eu Mossbauer Spectroscopy

We report the results of Eu-151 Mossbauer spectroscopy on EuPtSi with a chiral structure belonging to the P2(1)3 (#198) space group at zero magnetic field. The paramagnetic single absorption forms a magnetic splitting profile directly below T-N = 4.0 K and the spectrum at 3.9 K consists of the sum of the paramagnetic single absorption and the magnetic splitting absorption, which indicates a first-order transition at T-N = 4.0 K. The temperature dependence of the effective hyperfine fields H-hf at the Eu nucleus follows a power law of H-hf = H-0(1 - T/T-N)(beta) with H-0 = 25.6 +/- 0.4T and beta = 0.16 +/- 0.01 indicates a full moment of Eu2+ ions. The relative integral intensity I of the Eu-151 Mossbauer spectroscopy for EuPtSi is enhanced using a Debye calculation below T-0 similar or equal to 15 K, which indicates the development of magnetic correlations. The line width Gamma of the (151) Eu Mossbauer spectra increases below T-FD (similar or equal to 8K) close to the Weiss temperature theta(p) and shows a sharp peak at T-N. The magnetic behavior of EuPtSi can be divided into three magnetic regions: the paramagnetic (PM) phase, the fluctuation-disordered (FD) phase and the antiferromagnetic phase with fluctuation disordering (AF with FD). The magnetic fluctuation is realized around the first-order transition between the paramagnetic and helimagnetic states in EuPtSi.