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Register a new userPressure dependence of the magnetic ground states in MnP
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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.
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We report the discovery of superconductivity on the border of long-range magnetic order in the itinerant-electron helimagnet MnP via the application of high pressure. Superconductivity with Tsc~1 K emerges and exists merely near the critical pressure Pc~8 GPa, where the long-range magnetic order just vanishes. The present finding makes MnP the first Mn-based superconductor. The close proximity of superconductivity to a magnetic instability suggests an unconventional pairing mechanism. Moreover, the detailed analysis of the normal-state transport properties evidenced non-Fermi-liquid behavior and the dramatic enhancement of the quasi-particle effective mass near Pc associated with the magnetic quantum fluctuations.
We report a detailed $mu$SR study of the pressure evolution of the magnetic order in the manganese based pnictide MnP, which has been recently found to undergo a superconducting transition under pressure once the magnetic ground state is suppressed. Using the muon as a volume sensitive local magnetic probe, we identify a ferromagnetic state as well as two incommensurate helical states (with propagation vectors ${bf Q}$ aligned along the crystallographic $c-$ and $b-$directions, respectively) which transform into each other through first order phase transitions as a function of pressure and temperature. Our data appear to support that the magnetic state from which superconductivity develops at higher pressures is an incommensurate helical phase.
We have studied the Ce valence as a function of pressure in CeRhIn5 at 300 K and at 22 K using x-ray absorption spectroscopy in partial fluorescent yield mode. At room temperature, we found no detectable change in Ce valence greater than 0.01 up to a pressure of 5.5 GPa. At 22 K, the valence remains robust against pressure below 6 GPa, in contrast to the predicted valence crossover at P=2.35 GPa. This work yields an upper limit for the change in Ce-valence and suggests that the critical valence fluctuation scenario, in its current form, is unlikely.
The pressure dependence of superconducting transition temperature $T_{rm c}$ has been investigated through the DC magnetic measurements for FeSe$_{0.8}$ and FeSe$_{1.0}$. For both samples, with increasing pressure $P$, the $T_{rm c}$$-$$P$ curve exhibits a two-step increase, showing a local maximum of $sim$11 K at $P$$sim$1.0 GPa and a rapid increase with an extremely large pressure coefficient for $P$$>$1.5 GPa. $T_{rm c}$ saturates at $sim$25 K (21 K) in FeSe$_{1.0}$ (FeSe$_{0.8}$) for $P$$>$3 GPa. A rapid decrease in superconducting volume fraction is observed with an increase in $T_{rm c}$ above 1.5 GPa, suggesting the presence of electronic inhomogeneity.
We present neutron diffraction measurements on single crystal samples of non-superconducting Ba(Fe1-xCrx)2As2 as a function of Cr-doping for 0<=x<=0.47. The average SDW moment is independent of concentration for x<=0.2 and decreases rapidly for x>=0.3. For concentrations in excess of 30% chromium, we find a new G-type antiferromagnetic phase which rapidly becomes the dominant magnetic ground state. Strong magnetism is observed for all concentrations measured and competition between these ordered states and superconductivity naturally explains the absence of superconductivity in the Cr-doped materials.
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