Home >  About ISSP >  Publications > Activity Report 2018 > Xxxx Xxxx

Single-q and Multi-q Magnetic Orders in the Collinear Commensurate Antiferromagnet CeRh2Si2

Nakajima Group

Since the discovery of magnetic skyrmion lattice (SkL) in MnSi[1], magnetic orders described by multiple magnetic modulation wave vectors (q-vectors), which are referred to as multi-q magnetic orders, have been attracting remarkable attention. In the early stage of the magnetic skyrmon studies, the Dzyaloshinskii-Moriya (DM) arising from the broken inversion symmetry of the crystal structure was considered to be one of the most important ingredients for realizing the SkL states. Thus, non-centrosymmetric magnets were intensively investigated. This trend has changed since the discovery of the SkL state with a large topological Hall effect in Gd2PdSi3 [2], which has the centrosymmetric crystal structure. It was also theoretically pointed out that the biquadratic interaction term derived from the perturbative expansion for the Kondo lattice Hamiltonian can stabilize a variety of multi-q states even in centrosymmetric systems [3]. In the present study, we applied this model to the centrosymmetric collinear-commensurate antiferromagnet CeRh2Si2 [4].

CeRh2Si2 has a ThCr2Si2-type centrosymmetric tetragonal crystal structure and is known to have two antiferromagnetic phases at low temperatures in zero magnetic field [5]. Both magnetic phases are characterized by commensurate q-vectors. Specifically, the high-temperature phase (AF1) has a single q-vector of q = (1/2,1/2,0). This q-vector breaks the fourfold rotational symmetry of the crystal structure, and thus results in two magnetic domains characterized by q = (1/2,1/2,0) and (1/2,-1/2,0). On the other hand, the low-temperature phase (AF2) is characterized by four q-vectors of q = (1/2,1/2,0), (1/2,-1/2,0), (1/2,1/2,1/2), and (1/2,-1/2,1/2). In contrast to the AF1 phase, AF2 phase was reported to be a multi-q phase, i.e., the magnetic structure is described by a superposition of the four magnetic modulations. This means that the AF2 phase retrieves the fourfold rotational symmetry of the crystal, although it was lost in the high-temperature AF1 phase. This distinct change in symmetry should be seen in bulk properties such as magnetization, resistivity etc. as well as the neutron diffraction intensities. However, they were not observed because the AF1 phase exhibits a multi-domain state, in which the two single-q magnetic domains coexist. The intrinsic anisotropy of the magnetic order and associated physical properties were not macroscopically observed.

We thus applied a weak uniaxial stress to a single crystal of CeRh2Si2, and performed magnetization, resistivity and neutron diffraction measurements. The direction of the uniaxial stress was selected to be the [1-10] direction of the crystal to lift the degeneracy between the two magnetic domains. In Fig. 1, we show temperature variations of magnetization and resistivity measured at ambient pressure and under uniaxial stress of 20 MPa. In both the measurements, the applications of the uniaxial stress induced the difference in magnetization and resistivity only in the AF1 phase. We also performed neutron diffraction measurements with uniaxial stress. We measured temperature variations of the magnetic Bragg peaks at (1/2,1/2,0) and (1/2,1/2,1), which correspond to the two q-vectors of (1/2,1/2,0) and (1/2,-1/2,0) respectively. Similarly to the magnetization and resistivity measurements with the uniaxial stress, we observed significant uniaxial-stress dependence of the intensity only in the AF1 phase. Specifically, the magnetic scattering corresponding to the q-vector of (1/2,-1/2,0) completely suppressed by the application of uniaxial stress, demonstrating that the system exhibits a single-domain AF1 phase under uniaxial stress. Interestingly, the magnetic Bragg peak at (1/2,1/2,1) reappeared in the AF2 phase even in the finite uniaxial stress. In addition, the temperature dependence of the magnetic peak at (1/2,1/2,1/2), which is characteristic of the AF2 phase, was not affected by the uniaxial stress. These observations mean that the AF2 phase indeed has the multi-q magnetic order with fourfold symmetry. This is also consistent with the fact that the bulk properties of the AF2 phase are insensitive to the uniaxial stress. We also performed neutron inelastic scattering experiments and determined the exchange interactions between the magnetic moments. We calculated the exchange energies for the AF1 and AF2 phases and found that they are equal. By introducing the biquadratic interaction term mentioned above, the degeneracy is lifted, and the multi-q state is stabilized as the ground state. The present results demonstrated that the biquadratic term, which was originally introduced to explain the SkLs in centrosymmetric magnets, is also applicable to collinear commensurate multi-q orders. We also emphasize here that an application of uniaxial stress is quite useful to investigate magnetic materials exhibiting both single-q and multi-q orders.


References
  • [1] S. Mühlbauer et al., Science 323, 915 (2009).
  • [2] T. Kurumaji et al., Science 365, 914 (2019).
  • [3] S. Hayami et al., Phys. Rev. B 95, 224424 (2017).
  • [4] H. Saito et al., Phys. Rev. B 108, 094440 (2023).
  • [5] S. Kawarazaki et al., Phys. Rev. B 61, 4167 (2000).
Authors
  • H. Saito, F. Kona, H. Hidakaa, H. Amitsukaa, C. Kwangheeb, M. Hagihalab, T. Kamiyamab, S. Itohb, and T. Nakajima
  • aHokkaido University
  • bKEK-IMSS