In-plane anisotropy of single-q and multiple-q ordered phases in the antiferromagnetic metal CeRh2Si2

We performed magnetization, resistivity, and neutron diffraction measurements under uniaxial stress applied along the [11 over bar 0] direction on the tetragonal magnet CeRh2Si2 with commensurate magnetic orders. CeRh2Si2 has two successive antiferromagnetic (AFM) orders in zero magnetic field. The high temperature phase (AFM1 phase) has the magnetic modulation wave vector of q = (12, 12, 0), and the low temperature phase (AFM2 phase) is characterized by the four q-vectors of q=( 1 2 , 12, 0), (12, 1 2 ,0),( 1 2 ,2 1 , 21), and (12, 12, 21). By measuring the uniaxial stress dependence of the magnetization, resistivity and the intensities of magnetic Bragg reflections, we confirmed that the AFM1 phase has the single -q magnetic order with twofold rotational symmetry and the AFM2 phase has the multi -q magnetic order with fourfold rotational symmetry. To understand the origin of multi -q order of CeRh2Si2, we also performed inelastic neutron scattering measurement on the single crystal samples. We found a magnetic excitation at the transfer energy h over bar omega similar to 8 meV. By applying the linear spin-wave theory, we found that the nearest-and next-nearest neighbor exchange interactions on the ab plane, J1 and J2, are dominant in the AFM2 phase. However, the J1 -J2 model cannot lift the degeneracy between the single -q (AFM1) and multi -q (AFM2) phases. We suggest that it can be lifted by taking into account the biquadratic interaction derived from the perturbative expansion for the Kondo lattice Hamiltonian [S. Hayami et al., Phys. Rev. B 95, 224424 (2017)].