No abstract

MnP, a superconductor under pressure, exhibits a ferromagnetic order below TC~290 K followed by a helical order with the spins lying in the ab plane and the helical rotation propagating along the c axis below Ts~50 K at ambient pressure. We performed single crystal neutron diffraction experiments to determine the magnetic ground states under pressure. Both TC and Ts are gradually suppressed with increasing pressure and the helical order disappears at ~1.2 GPa. At intermediate pressures of 1.8 and 2.0 GPa, the ferromagnetic order first develops and changes to a conical or two-phase (ferromagnetic and helical) structure with the propagation along the b axis below a characteristic temperature. At 3.8 GPa, a helical magnetic order appears below 208 K, which hosts the spins in the ac plane and the propagation along the b axis. The period of this b axis modulation is shorter than that at 1.8 GPa. Our results indicate that the magnetic phase in the vicinity of the superconducting phase may have a helical magnetic correlation along the b axis.Comment: 5 pages, 4 figure

We have investigated magnetic orders and excitations in a Y-type hexaferrite BaSrCo 2 Fe 11 AlO 22 (BSCoFAO), which was reported to exhibit spin-driven ferroelectricity at room temperature [Hirose et al., Appl. Phys. Lett. 104, 022907 (2014)]. By means of magnetization, electric polarization and neutron diffraction measurements using single-crystal samples, we establish 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-coplanar 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 phason-like excitation is expected to be electric-field-active magnon, i.e., electromagnon excitation, in terms of the magnetostriction mechanism.