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A flop of electric polarization from P‖c (Pc) to P‖a (Pa) is observed in MnTiO3 as a spin-flop transition is triggered by a c-axis magnetic field, H‖c=7 T. The critical magnetic field H‖c for Pa is significantly reduced in Mn1-xNixTiO3 (x=0.33). Pa and Pc have been observed with both H‖c and H‖a. Neutron diffraction measurements revealed similar magnetic arrangements for the two compositions where the ordered spins couple antiferromagnetically with their nearest intra- and interplanar neighbors. In the x=0.33 system, the uniaxial and planar anisotropies of Mn2+ and Ni2+ compete and give rise to a spin reorientation transition at TR. A magnetic field, H‖c, aligns the spins along c for TR

We report a single-crystal neutron diffraction study of the layered Sr2IrO4. This work unambiguously determines the magnetic structure of the system and reveals that the spin orientation rigidly tracks the staggered rotation of the IrO6 octahedra in Sr2IrO4. The long-range antiferromagnetic order has a canted spin configuration with an ordered moment of 0.208(3) μB/Ir site within the basal plane; a detailed examination of the spin canting yields 0.202(3) and 0.049(2) μB/site for the a axis and the b axis, respectively. It is intriguing that forbidden nuclear reflections of space group I41/acd are also observed in a wide temperature range from 4 K to 600 K, which suggests a reduced crystal structure symmetry. This neutron-scattering work provides a direct, well-refined experimental characterization of the magnetic and crystal structures that are crucial to the understanding of the unconventional magnetism exhibited in this unusual magnetic insulator. [ABSTRACT FROM AUTHOR]

A publisher's note is presented.

We have combined single-crystal neutron and x-ray diffractions to investigate the magnetic and crystal structures of the honeycomb lattice Na2lrO3. The system orders magnetically below 18.1(2) K with Ir4+ ions forming zigzag spin chains within the layered honeycomb network with an ordered moment of 0.22(1)µB/lr site. Such a configuration sharply contrasts with the Néel or stripe states proposed in the Kitaev-Heisenberg model. The structure refinement reveals that the Ir atoms form a nearly ideal two-dimensional honeycomb lattice while the IrO6 octahedra experience a trigonal distortion that is critical to the ground state. The results of this study provide much needed experimental insights into the magnetic and crystal structure that are crucial to the understanding of the exotic magnetic order and possible topological characteristics in the 5d-electron-based honeycomb lattice. [ABSTRACT FROM AUTHOR]

We have investigated magnetic orders and excitations in a Y-type hexaferrite BaSrCo2Fe11AlO22 (BSCoFAO), which was reported to exhibit spin-driven ferroelectricity at room temperature [S. Hirose, K. Haruki, A. Ando, and T. Kimura, Appl. Phys. Lett. 104, 022907 (2014)]. By means of magnetization, electric polarization, and neutron-diffraction measurements using single-crystal samples, we establish a H-T magnetic phase diagram for magnetic field perpendicular to the c axis (H⊥c). This system exhibits an alternating longitudinal conical (ALC) magnetic structure in the ground state, and it turns into a non-co-planar commensurate magnetic order with spin-driven ferroelectricity under H⊥c. The field-induced ferroelectric phase remains as a metastable state after removing magnetic field below ~250 K. This metastability is the key to understanding of magnetic field reversal of the spin-driven electric polarization in this system. Inelastic polarized neutron-scattering measurements in the ALC phase reveal a magnetic excitation at around 7.5 meV, which is attributed to spin components oscillating in a plane perpendicular to the cone axis. This phasonlike excitation is expected to be an electric-field active magnon, i.e., electromagnon excitation, in terms of the magnetostriction mechanism. [ABSTRACT FROM AUTHOR]

Using ambient pressure x-ray and high pressure neutron diffraction, we studied the pressure effect on structural and magnetic properties of multiferroic Mn1-xCoxWO4 single crystals (x=0, 0.05, 0.135, and 0.17) and compared it with the effects of doping. Both Co doping and pressure stretch the Mn-Mn chain along the c direction. At high doping level (x=0.135 and 0.17), pressure and Co doping drive the system in a similar way and induce a spin-flop transition for the x=0.135 compound. In contrast, magnetic ground states at lower doping level (x=0 and 0.05) are robust against pressure but experience a pronounced change upon Co substitution. As Co introduces both chemical pressure and magnetic anisotropy into the frustrated magnetic system, our results suggest the magnetic anisotropy is the main driving force for the Co induced phase transitions at low doping level, and chemical pressure plays a more significant role at higher Co concentrations. [ABSTRACT FROM AUTHOR]