RESUMO
The n-type HgCr_{2}Se_{4} exhibits a sharp semiconductor-to-metal transition (SMT) in resistivity accompanying the ferromagnetic order at T_{C}=106 K. Here, we investigate the effects of pressure and magnetic field on the concomitant SMT and ferromagnetic order by measuring resistivity, dc and ac magnetic susceptibility, as well as single-crystal neutron diffraction under various pressures up to 8 GPa and magnetic fields up to 8 T. Our results demonstrate that the ferromagnetic metallic ground state of n-type HgCr_{2}Se_{4} is destabilized and gradually replaced by an antiferromagnetic, most likely a spiral magnetic, and insulating ground state upon the application of high pressure. On the other hand, the application of external magnetic fields can restore the ferromagnetic metallic state again at high pressures, resulting in a colossal magnetoresistance (CMR) as high as â¼ 3×10^{11}% under 5 T and 2 K at 4 GPa. The present study demonstrates that n-type HgCr_{2}Se_{4} is located at a peculiar critical point where the balance of competition between ferromagnetic and antiferromagnetic interactions can be easily tipped by external stimuli, providing a new platform for achieving CMR in a single-valent system.
RESUMO
High-pressure neutron diffraction (HPND) experiments in extended pressure and temperature ranges can provide invaluable information for understanding many pressure-induced emergent phenomena, such as unusual phase transitions and quantum critical behavior involving spin, orbital, charge and structural degrees of freedom, in strongly correlated materials. Many apparatuses for different purposes of HPND experiments have been developed in several laboratories. Recently, a clamp-type cubic anvil high pressure cell that can generate pressure over 7 GPa at 3 K was developed for low-temperature HPND measurements. In this paper, characteristics of the clamp-type cubic anvil high pressure cell are presented and its performances are demonstrated by measuring magnetic neutron scattering under pressure on MnP single crystal samples.
RESUMO
An inelastic neutron scattering study has been performed in an S = 3/2 bilayer honeycomb lattice compound Bi3Mn4O12(NO3) at ambient and high magnetic fields. Relatively broad and monotonically dispersive magnetic excitations were observed at ambient field, where no long-range magnetic order exists. In the magnetic-field-induced long-range ordered state at 10 T, the magnetic dispersions become slightly more intense, albeit still broad as in the disordered state, and two excitation gaps, probably originating from an easy-plane magnetic anisotropy and intrabilayer interactions, develop. Analyzing the magnetic dispersions using the linear spin-wave theory, we estimated the intraplane and intrabilayer magnetic interactions, which are almost consistent with those determined by ab initio density functional theory calculations [M. Alaei et al., Phys. Rev. B 96, 140404(R) (2017)], except the third and fourth neighbor intrabilayer interactions. Most importantly, as predicted by the theory, there is no significant frustration in the honeycomb plane but frustrating intrabilayer interactions probably give rise to the disordered ground state.
RESUMO
Strain, magnetization, dielectric relaxation, and unpolarized and polarized neutron diffraction measurements were performed to study the magnetic and structural properties of spinel Co_{1-x}V_{2+x}O_{4}. The strain measurement indicates that, upon cooling, ΔL/L in the order of â¼10^{-4} starts increasing below T_{C}, becomes maximum at T_{max}, and then decreases and changes its sign at T^{*}. Neutron measurements indicate that a collinear ferrimagnetic order develops below T_{C} and upon further cooling noncollinear ferrimagnetic ordering occurs below T_{max}. At low temperatures, the dielectric constant exhibits a frequency dependence, indicating slow dynamics. These results indicate the existence of an orbital glassy state at low temperatures in this nearly metallic frustrated magnet.