In-plane Anisotropy of the Single-<i>q</i> and Multiple-<i>q</i> Ordered Phases in the Antiferromagnetic Metal CeRh<sub>2</sub>Si<sub>2</sub>

We performed magnetization, resistivity, and neutron diffraction measurements under uniaxial stress applied along [1-10] direction on the tetragonal magnet CeRh2Si2 with commensurate magnetic orders. CeRh2Si2 has two successive antiferromagnetic (AF) orders in zero magnetic field. The high temperature phase (AF1 phase) has the magnetic modulation wave vector of q = (1/2, 1/2, 0), and the low temperature phase (AF2 phase) is characterized by the four q-vectors of q = (1/2, ±1/2, 0), and (1/2, ±1/2, 1/2). By measuring the uniaxial stress dependence, we confirmed that the AF1(AF2) phase has the single-q(multi-q) magnetic order with two-fold(four-fold) rotational symmetry. We also performed inelastic neutron scattering measurement on the single crystal samples. We found a magnetic excitation at the transfer energy ħω ∼ 8 meV. By applying the linear spin-wave theory, we found that the nearest and the next-nearest neighbor exchange interactions on the ab-plane, J1 and J2, are dominant in the AF2 phase. However, the J1-J2 model cannot lift the degeneracy between the single-q (AF1) and multi-q (AF2) 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[10].