Abstract
We have performed inelastic neutron scattering measurements in the ferroelectric noncollinear- magnetic phase of CuFe1−xGaxO2 (CFGO) with x = 0.035 under applied uniaxial pressure. This system has three types of magnetic domains with three different orientations reflecting the trigonal symmetry of the crystal structure. To identify the magnetic excitation spectrum corresponding to a magnetic domain, we have produced a nearly ‘single-domain’ multiferroic phase by applying a uniaxial pressure of 10 MPa onto the [1 ̄10] surfaces of a single crystal CFGO sample. As a result, we have successfully observed the ‘single-domain’ spectrum in the multiferroic phase. Using the Hamiltonian employed in the previous inelastic neutron scattering study on the ‘multi-domain’ multiferroic phase of CFGO (x = 0.035) [Haraldsen et al. Phys. Rev. B 82 020404R (2010)], we have refined the Hamiltonian parameters so as to simultaneously reproduce both of the observed ‘single-domain’ and ‘multi-domaim’ spectra. Comparing between the Hamiltonian parameters in the multiferroic phase of CFGO and in the collinear four-sublattice magnetic ground state of undoped CuFeO2 [Nakajima et al, Phys. Rev. B 84 184401 (2011)], we suggest that the nonmagnetic substitution weakens the spin-lattice coupling, which often favors a collinear magnetic ordering, as a consequence of the partial release of the spin frustration.
