KCuCl 3 is a three dimensionally coupled spin dimer system, which undergoes a pressure-induced quantum phase transition from a gapped ground state to an antiferromagnetic state at a critical pressure of P c ' 8:2 kbar. Magnetic excitations in KCuCl 3 at a hydrostatic pressure of 4.7 kbar have been investigated by conducting neutron inelastic scattering experiments using a newly designed cylindrical high-pressure clamp cell. A well-defined single excitation mode is observed. The softening of the excitation mode due to the applied pressure is clearly observed. From the analysis of the dispersion relations, it is found that an intradimer interaction decreases under hydrostatic pressure, while most interdimer interactions increase. For a system of isolated S ¼ 1=2 spin dimers with an antiferromagnetic (AF) intradimer exchange interaction J > 0, the triplet excitation is dispersionless and the excitation energy is given by h " !ðqÞ ¼ J. When a threedimensional interdimer exchange interaction J 0 is switched on, excited triplets can hop to neighboring dimers due to the transverse component of the interdimer interactionÞ so that the magnetic excitations become dispersive. With increasing ðJ 0 =JÞ, the dispersion range increases and the lowest excitation energy corresponding to the energy gap of the system decreases. At a quantum critical point ðJ 0 =JÞ c , the gap closes and the disordered ground state changes to the AF-ordered state. 1,2)The AF state stabilized for ðJ 0 =JÞ > ðJ 0 =JÞ c is described by the coherent superposition of the singlet j0; 0i and two triplet components j1; AE1i. Such a quantum phase transition (QPT) was first realized in TlCuCl 3 3-5) by the application of hydrostatic pressure. The critical pressures determined by magnetization measurement and neutron scattering experiment are P c ¼ 0:42 kbar 3) and 1.07 kbar, 5) respectively. There is a discrepancy between the critical pressures obtained from macroscopic and microscopic measurements.In this study, we investigate magnetic excitations in KCuCl 3 under hydrostatic pressure. The crystal structure (space group P2 1 =c) of KCuCl 3 is the same as that of TlCuCl 3 6,7) and is composed of planar dimers of Cu 2 Cl 6 . The dimers are stacked to form infinite double chains parallel to the crystallographic a-axis. These double chains are located at the corners and center of the unit cell in the bc-plane. A strong AF exchange interaction with J ¼ 4:34 meV in the planar dimer of Cu 2 Cl 6 dimerizes the spins of Cu 2þ . As shown in Fig. 1, neighboring spin dimers couple along the a-axis and in the ð1; 0; " 2 2Þ plane, in which the hole orbitals of Cu 2þ spread. [8][9][10][11][12] The lowest triplet excitation occurs at Q ¼ ð0; 0; 1Þ and its equivalent reciprocal points. The magnitude of the energy gap is Á ¼ 2:67 meV. 8,13,14) Consequently, KCuCl 3 is magnetically characterized as an interacting spin dimer system. KCuCl 3 undergoes a QPT under hydrostatic pressure, as observed in TlCuCl 3 .15) The critical pressure obtained through magnetization measurement ...

The capture cross sections and capture-ray spectra of 209 Bi were measured in a neutron energy region from 5 to 80 keV and at 520 keV, using pulsed keV neutrons from the 7 Li(p; n) 7 Be reaction and a time-of-flight method. The capture rays from a bismuth or standard gold sample were detected with a large anti-Compton NaI(Tl) spectrometer. The capture yield of the bismuth or gold sample was obtained by applying a pulse-height weighting technique to the corresponding capture-ray pulse-height spectrum. The derived capture cross sections from 5 to 80 keV were in good agreement with recent measurements, but that at 520 keV was about half of previous measurements. This large discrepancy at 520 keV was ascribed to the incorrect background-subtraction in the previous measurements from a comparison between the present and previous capture-ray spectra. Strong transitions from the capture states to low lying states of 210 Bi were observed in the present-ray spectra. The multiplicities of observed rays were obtained from the-ray spectra.

The capture cross sections and capture -ray spectra of 209 Bi were measured in a neutron energy region from 5 to 80 keV and at 520 keV, using pulsed keV neutrons from the 7 Li(p; n) 7 Be reaction and a time-of-flight method. The capture rays from a bismuth or standard gold sample were detected with a large anti-Compton NaI(Tl) spectrometer. The capture yield of the bismuth or gold sample was obtained by applying a pulse-height weighting technique to the corresponding capture -ray pulse-height spectrum. The derived capture cross sections from 5 to 80 keV were in good agreement with recent measurements, but that at 520 keV was about half of previous measurements. This large discrepancy at 520 keV was ascribed to the incorrect background-subtraction in the previous measurements from a comparison between the present and previous capture -ray spectra. Strong transitions from the capture states to low lying states of 210 Bi were observed in the present -ray spectra. The multiplicities of observed rays were obtained from the -ray spectra.

The wave vector Q ¼ ðh; 0; 2h À 1Þ shown in the left panel of Fig. 4(b) is incorrect. The correct wave vector is Q ¼ ðh; 0; À2h þ 1Þ.

Magnetic phase transitions under hydrostatic pressures in spin gap systems TlCu0.988Mg0.012Cl3 and KCu0.973Mg0.027Cl3 were investigated by magnetization measurements. The present doped systems exhibit impurity-induced magnetic orderings. With increasing pressure, ordering temperature TN increases. With a further increase in pressure, the present systems undergo phase transitions to uniform antiferromagnetic phases due to the closing of the triplet gap in the intact dimers. The crossover from the impurity-induced ordered phase to the uniform antiferromagnetic phase occurs at P ≃ 1.3 kbar for TlCu0.988Mg0.012Cl3. c 2017 Elsevier B.V. All rights reserved. Gapped ground states have been observed in many magnetic insulators. Most gapped ground states are composed of singlet spin dimers. Therefore, when a small number of nonmagnetic ions are substituted for magnetic ions, singlet spin dimers are partially broken, so that unpaired spins are produced near the nonmagnetic ions. Unpaired spins can interact through the effective exchange interaction J eff that is mediated by the triplet excitations in intact dimers [1,2]. This effective exchange interaction can cause the ordering of unpaired spins, which leads to the small staggered magnetic order in intact dimers. Such impurity-induced magnetic ordering is observed in many gapped spin systems doped with nonmagnetic impurities [3,4,5].The present study is concerned with impurity-and pressure-induced magnetic orderings in ACu 1−x Mg x Cl 3 with A= Tl and K. The parent compounds TlCuCl 3 and KCuCl 3 are S = 1/2 coupled spin dimer systems with antiferromagnetic intradimer exchange interactions J/k B = 65.9 K and 50 K, respectively [6,7]. The magnetic ground states are spin singlets with excitation gaps ∆/k B = 7.5 K and 30.5 K [8]. The gap decreases under hydrostatic pressure, and both systems undergo magnetic ordering [9,10]. The critical pressures for TlCuCl 3 and KCuCl 3 are P c = 0.42 kbar and 8.2 kbar, respectively. Because the effective interaction J eff between unpaired spins is enhanced * Corresponding author.Email address: tanaka@lee.phys.titech.ac.jp (H. Tanaka).as the gap decreases [1,2], we expect an increase in T N with pressure in ACu 1−x Mg x Cl 3 . To investigate the systematic change in the magnetic ordering in ACu 1−x Mg x Cl 3 , we carried out magnetization measurements under hydrostatic pressure.Doped ACu 1−x Mg x Cl 3 crystals were prepared by the vertical Bridgman method. The magnesium concentration x was analyzed by ICP−OES. In the present study, we used samples with x = 0.012 and 0.027 for A=Tl and K, respectively. The magnetizations were measured at temperatures down to 1.8 K under magnetic fields of up to 7 T using a SQUID magnetometer. Pressures of up to ∼9 kbar were applied using a cylindrical high-pressure cramp cell. A magnetic field was applied along the [2, 0, 1] direction. As pressure-transmitting fluid, a mixture of Fluorinert FC70 and FC77, and Daphne oil 7373 were used. The pressure was calibrated with the superconducting transition...