Pressure dependence of the magnetic ground state in CePtSi2

TL;DR

This study investigates the magnetic structure of CePtSi2 under pressure, revealing incommensurate magnetic order at ambient conditions and its disappearance below the superconducting transition, implying other factors influence superconductivity.

Contribution

The paper provides detailed neutron diffraction data showing pressure effects on magnetic order in CePtSi2, highlighting the magnetic order's suppression at lower pressures than superconductivity onset.

Findings

Incommensurate magnetic peaks observed below 1.25 K at ambient pressure.

Magnetic order disappears around 1.0 GPa, below the superconducting critical pressure.

Magnetic fluctuations may not be the primary driver of superconductivity.

Abstract

CePtSi2 was reported to exhibit an antiferromagnetic order below T*=1.8 K at ambient pressure, a valence state change at ~1.2 GPa, and superconductivity in the range between 1.4 and 2.1 GPa with the maximum transition temperature of 0.14 K [T. Nakano et al., Phys. Rev. B 79, 172507 (2009)]. We have performed polycrystalline and single crystal neutron diffraction experiments to determine the magnetic structure under ambient and high pressures. We found that incommensurate magnetic peaks with the magnetic propagation vector of (0.32, 0, 0.11) at ambient pressure below T_{SDW}~1.25 K. Those magnetic peaks which originate from a spin-density-wave order with the easy axis along the c axis and an averaged ordered moment of 0.45(5) mu_B, suggesting that there may be an intermediate phase between T* and T_{SDW}. Applying pressures, the magnetic propagation vector shows no change and the magnetic order disappears around 1.0 GPa, which is much lower than the critical pressure for the superconducting phase. The results suggest that other than magnetic fluctuations may play a primary role in the superconducting pairing mechanism.