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We report experimental studies on ${\mathrm{Ru}}_{2\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{CrSi}$ focusing on properties related to antiferromagnetism in ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ and spin glass (SG) in ${\mathrm{Ru}}_{1.9}{\mathrm{Fe}}_{0.1}\mathrm{CrSi}$. By measuring the temperature dependence of magnetization $M(T)$, specific heat $C(T)$, electrical resistivity $\ensuremath{\rho}(T)$, and muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$), we observed that ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ exhibited an antiferromagnetic (AF) transition at a temperature ${T}_{N}$ of $\ensuremath{\sim}13$ K, and ${\mathrm{Ru}}_{1.9}{\mathrm{Fe}}_{0.1}\mathrm{CrSi}$ showed SG properties that could be interpreted as successive SG transitions, where the spin-freezing occurred at temperature ${T}_{g}$, and below that strong irreversibility in $M(T)$ and a gradual peak of $M(T)$ at ${T}^{*}\phantom{\rule{4pt}{0ex}}(g{T}_{g})$ appeared. When the data for $0\ensuremath{\le}x\ensuremath{\le}0.1$ were compared, by substituting Fe the AF order was rapidly destroyed and it appeared to change to two anomalies at ${T}^{*}$ and ${T}_{g}$. With increasing $x$, there was a slight change in ${T}_{g}$ from ${T}_{N}$ for $x=0$; however, ${T}^{*}$ increased, suggesting that the AF and the SG states are closely related. Furthermore, the results of specific heat, resistivity, and magnetization in high fields were presented and compared. For ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ in specific heat under high magnetic fields up to 14 T, the peak shape around ${T}_{N}$ and the ${T}_{N}$ value were constant. The resistivity and magnetization in pulsed fields suggested that ${T}_{N}$ of ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ was constant up to over 50 T. These results demonstrated the unusual robustness of the AF transition to magnetic fields. In ${\mathrm{Ru}}_{1.9}{\mathrm{Fe}}_{0.1}\mathrm{CrSi}$, unusual hysteresis in magnetoresistance was observed in static and pulsed magnetic fields, although their appearances differed. These hystereses were considered a manifestation of the curious properties of the SG state with strong irreversibility.

The effect of chemical substitution on the ground state of the geometrically frustrated antiferromagnet ${\mathrm{CsCrF}}_{4}$ has been investigated through a neutron powder diffraction experiment. Magnetic Fe-substituted ${\mathrm{CsCr}}_{0.94}{\mathrm{Fe}}_{0.06}{\mathrm{F}}_{4}$ and nonmagnetic Al-substituted ${\mathrm{CsCr}}_{0.98}{\mathrm{Al}}_{0.02}{\mathrm{F}}_{4}$ samples are measured, and magnetic Bragg peaks are clearly observed in both samples. Magnetic structure analysis revealed a ${120}^{\ensuremath{\circ}}$ structure having a magnetic propagation vector ${\mathbit{k}}_{\mathrm{mag}}=(0,0,1/2)$ in ${\mathrm{CsCr}}_{0.94}{\mathrm{Fe}}_{0.06}{\mathrm{F}}_{4}$. For ${\mathrm{CsCr}}_{0.98}{\mathrm{Al}}_{0.02}{\mathrm{F}}_{4}$, a quasi-${120}^{\ensuremath{\circ}}$ structure having ${\mathbit{k}}_{\mathrm{mag}}=(1/2,0,1/2)$ is formed. It is notable that the identified magnetic structure in ${\mathrm{CsCr}}_{0.94}{\mathrm{Fe}}_{0.06}{\mathrm{F}}_{4}$ belongs to a different phase of ground states from those in ${\mathrm{CsCr}}_{0.98}{\mathrm{Al}}_{0.02}{\mathrm{F}}_{4}$ and the parent ${\mathrm{CsCrF}}_{4}$. These results suggest that the Fe substitution strongly influences the ground state of ${\mathrm{CsCrF}}_{4}$.

Two series of Heusler compounds Ru 2 Cr 1− x X x Si ( X = V, Ti) are synthesized, and their magnetic and electrical properties are investigated. Overall, these two series of compounds are identical in numerous properties. The measurements of magnetic properties reveal that an antiferromagnetic transition observed for x = 0 becomes smeared and it changes into a spin-glass state with increasing x . Around x = 0.5 this behavior disappears and it becomes paramagnetic. High-field magnetization for x = 0.3 and 0.4 up to 62 T exhibits no sign of magnetic transition or saturation of the magnetization. In the temperature dependence of resistivity, the kink that indicates the antiferromagnetic transition observed for x = 0 becomes invisible even for x ∼ 0.1. This also exemplifies that the antiferromagnetic order is destroyed by the substitution and is replaced by the spin-glass state. Concerning the resistivity, these samples exhibit semiconducting behavior for small x , whereas with increasing x ≳ 0.5 they turn to show metallic behavior and Ru 2 VSi becomes a paramagnetic metal. Nevertheless, Ru 2 TiSi shows a tendency for semiconductivity again.

In this study, the temperature ( T) dependence of specific heat ( C p ) is investigated in an equilateral triangular spin tube CsCrF 4 above T = 0 . 38K under several magnetic fields ( B ). At B = 0 T, no λ -type anomaly of the temperature dependence [ C p ( T) ] appears over the entire temperature range. However, the DC and AC magnetic susceptibilities exhibit a small anomaly, which is interpreted as an antiferromagnetic phase transition at T N ∼4.5K. This difference may indicate that the large magnetic entropy at B = 0 T is spent far below T N , because a large fluctuated spin state due to geometrical spin frustration may have occurred at T = 0K. Under different magnetic fields, the C p ( T)/T curves present shoulders and/or broad peaks above B = 1 T. The electronic specific heat coefficient decreases with increasing B indicating that the magnetic ground state consists of an antiferromagnetic ordered state with large spin fluctuations, rather than a gapless spin-liquid state, and their fluctuations are sensitively suppressed by the magnetic fields.

Magnetic birefringence under mechanical stress is useful for investigating antiferromagnetically ordered spins. Although the stress is expected to lead to a single magnetic domain, intrinsic distri...

In material science, half filled 3d orbital of transition metals is essentially an important factor controlling characteristics of alloys and compounds. This paper presents a result of the challenge of excitation of inner-core electron system with long lifetime of zinc films. The advanced zinc films with excited inner-core electron, 3dn (n = 9, 8). We report experimental results of XPS measurements of 9 points in the sample along vertical direction, respectively. The most pronounced futures are existence of satellites, which are about 4 eV higher than the main lines. According to the charge transfer mechanism proposed by A. Kotani and K. Okada, it was clarified that the origins of these peaks are c3d9L for the main peak and c3d9 for the satellite, respectively. From the energy difference, δEB, and peak intensity ratio, I+/I-, between c3d9 and c3d10L, the energy for charge transfer, Δ, and mixing energy, T, were estimated. In the region where the intensity of c3d10L becomes large, Δ becomes small, 1.2 Δdc = 5.5 eV and Udd = 5.5 eV. In the analysis along vertical direction, intensity profile of Zn3d9 showed odd functional symmetry and that of Zn3d10L showed even functional symmetry. Only the intensity profile of C1s (288 eV) showed the same spatial correlation with Zn3d9. In our experiment, the sample also showed high mobility of the constituting elements. These suggest that charge conservation in excited zinc atom suggests combination between Zn3d9 and C2-.

We performed X-ray diffraction, magnetic susceptibility, and magnetization experiments on nonequilateral triangular spin tubes composed of α-KCr1−x Fe x F4 (x = 0∼0.13), which consisted of one-dimensional Heisenberg antiferromagnets coexisting with geometrically-frustrated spin systems with bond randomness. The variation of lattice parameters with x may indicate that the Fe3+ ions constitute the low-spin state (S = 1/2). As a result of analyses of the frustration factor and the spin-flop transition field, we found that the effect of geometrical spin frustration was enhanced and that the magnetic anisotropy was weakened as x was increased. Because these results are remarkably similar to the previous results for α-KCr1−x Al x F4, the effect of the chemical impurity substitutions, whether they are magnetic or nonmagnetic ions, on α-KCrF4 is clearly understood.

We performed temperature (T) dependence experiments on the AC magnetic susceptibility of equilateral and non-equilateral triangular spin tubes CsCrF4 and α-KCrF4, respectively. In α-KCrF4, the linear (X0′) and the nonlinear (X2′) magnetic susceptibilities show sharp peaks at 4.0 K, which corresponds to an antiferromagnetic phase transition. On the other hand, in CsCrF4, broad and positive X0′ (T) peaks appear above f = 31 Hz at T ≃ 4 K, but no anomaly of X0′ (T) occurs at f = 31 Hz. Furthermore, the X2′ (T) curve at f = 977 Hz shows a broad and negative peak at T ∼3 K. We suspect that there is a gradual change in spin dynamics below T ≃ 4 K from the paramagnetic state at a high temperature to a slowly-fluctuating spin state without typical antiferromagnetic longrange order as one-dimensionality along the spin tubes coexists with geometrical spin frustration in the equilateral triangular planes.

We have performed multi-frequency electron spin resonance (ESR) and magnetization measurements on single crystals of the quasi one-dimensional magnet IPACu(Cl x Br1−x )3 (x=0.83) in magnetic fields H along the b-axis at temperatures below an antiferromagnetic long-range ordering temperature (T N ≅ 13 K). We observed some ESR branches for typical antiferromagnetic modes with biaxial anisotropy at 1.5 K (≪ T N). We have analyzed the magnetization curve and the ESR excitation modes for H∥b by using a two sub-lattice model and obtained good agreement between experiment and calculation. In addition, we show that the origin of a field-induced magnetization jump is a spin-flop transition. These results show that the phase at temperatures below T N in this Cl-Br mixed compound can be described as a simple two sub-lattice antiferromagnet.

${\mathrm{Fe}}_{2}\mathrm{MnSi}$ exhibits a ferromagnetic transition at ${T}_{C}\ensuremath{\sim}230$ K and another transition to a phase with antiferromagnetic components at ${T}_{A}\ensuremath{\sim}60$ K. By substituting V for Mn, so as to obtain ${\mathrm{Fe}}_{2}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{V}}_{x}\mathrm{Si}$, ${T}_{A}$ is revealed to decrease with $x$ and then vanish around $x\ensuremath{\sim}0.2$. In this study, the phase boundary of the transition at ${T}_{A}$ in the high-field range is found for $0\ensuremath{\le}x\ensuremath{\le}0.15$ with pulsed fields up to $\ensuremath{\sim}70$ T. The magnetization of ${\mathrm{Fe}}_{2}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{V}}_{x}\mathrm{Si}$ slowly increases even at the highest field of $\ensuremath{\sim}70$ T, though it occurs more gradually as $x$ increases. We compare the magnetization for $0\ensuremath{\le}x\ensuremath{\le}0.20$ at 62 T with the Slater-Pauling rule, which holds when a Heusler compound is a half-metal, and find fairly good agreement. This suggests an intimate relation between the high-field phase and the half-metallic electronic structure, and that at the high-field limit the phase approaches the half-metallic state, which has been predicted by band-structure calculations.

The ground state of the frustrated equilateral triangular spin tube CsCrF4 is still hidden behind a veil though NMR spectrum broaden into 2 T at low temperature. In order to investigate the spin structure in an ordered state by 19F-NMR, we have determined the anisotropic hyperfine coupling tensors for each three fluorine sites in the paramagnetic state. The measurement field was raised up to 10 T to achieve highest resolution. The preliminary analysis using the obtained hyperfine tensors has shown that the archetypal 120°-type structure in ab-plane does not accord with the NMR spectra of ordered state.

Optical birefringence imaging systems demonstrate a high potential for comprehensively investigating various phase transitions. To completely demonstrate such abilities, the temperature dependence of birefringence (Δn) was measured in Δn ≃ 0 materials (i.e., cubic crystals with imperfect crystallization) via a background subtraction method. As a result, highly accurate birefringence imaging at 384 × 288 pixels was obtained using phase transition processes as well as varying temperatures visually characterized by the spatial distribution of not only the retardance level but also the optical fast-axis azimuth.

In this paper we present experimental results with the ion recombination process in the vapor phase growth method. We consider the growth process of only one element case, Zinc, because of the clarification of the change of electron states in the element, not the entropy effect due to different elements. The advantages of using the ion recombination process are the following; 1) controllability of total energy, 2) the highest quenching rate, 3) locality of the collision. The total energy of the ion system was below 240 eV. Zn-ions exist on the growth front surface and Zn+ones impinge to the growth surface from the vapor phase. The crystal structures of deposited zinc films are measured with the XRD system. Very strong diffuse scattering intensity of x-ray diffraction was observed at 10 eV, 90 eV, 100 eV and 230 eV after seven months “annealing” in room temperature from the preparation. These experimental facts suggest the effectiveness of the application of the excitation process of the inner core electron system as a new advanced material process. In this process, the ion recombination process and the existence of a metastable state are essentially important factors.

It has been shown that Fe2MnSi exhibits a ferromagnetic transition at Tc and an antiferromagnetic transition at a lower temperature, TA, to a phase referred to as the AF phase. In a recent study on Fe1.3Mn1.7Si, another antiferromagnetic transition at a temperature lower than TA, defined as TA2, was found, with the phase below TA2 referred to as the AF2 phase. In this study, magnetic properties of Fe3-xMnxSi are investigated for an x range of 1.65 ≤ x ≤ 1.85 in order to study theses transitions with varying x. For x ≥ 1.75, a transition characterized by a rather rapid decrease in the temperature dependence of magnetization is observed at a temperature lower than TA at fields higher than ∼2 T. This implies the AF2-AF transition exists for x ≥ 1.75 as for x = 1.7. The magnetic field where the AF2-AF transition occurs increases with x, whereas at lower fields TA2 does not depend strongly on x. Meanwhile, at near zero field, the ferromagnetic transition and spontaneous magnetization disappears for x ≥ 1.75, in contrast to the case for x = 1.7. This implies that the transition from paramagnetism directly to the AF2 phase occurs at low fields. These results are summarized in the B-T magnetic phase diagram.

The properties of Heusler compounds Ru2−x Fe x CrGe are investigated and compared with those of Ru1.9Fe0.1CrSi. Ru2CrGe is confirmed to exhibit an antiferromagnetic transition with Neel temperature 13 K by magnetic susceptibility and specific heat measurements. When Fe is substituted for Ru, a peak in the magnetic susceptibility is observed, and in the lower temperature region irreversibility between temperature dependences of magnetization for zero-field-cooling and field-cooling conditions is found. Nevertheless, in specific heat of Ru1.9Fe0.1CrGe, there is no anomaly to indicate phase transition. The specific heat is almost identical to that for Ru1.9Fe0.1CrSi. The above results demonstrate that the magnetic states in the low temperature region of Fe-substituted samples are spin-glass-like states. Slight substitution of Fe for Ru destroys the long-range-order and lead to peculiar spin-glass-like states.

Fe2MnSi exhibits a ferromagnetic transition at TC and another transition to a phase with antiferromagnetic components at a low temperature of TA . By substituting V for Mn, so as to obtain Fe2Mn1−x V x Si, TA decreases with x and then vanishes around x ~ 0.2. In this study, the magnetic transitions are investigated by magnetization measurements for Fe2Mn1−x V x Si (y = 1, 0 ≤ x ≤ 0.2) in high magnetic fields up to ~70 T and for Fe1.5(Mn1−x V x )1.5Si (y = 1.5, 0 ≤ x ≤ 0.1) up to 5 T. For y = 1.5, with increasing x, TC increases and TA decreases as for y = 1, and the rate of the decrease in TA with x is slightly smaller than for y=1. In the low magnetic field region, TA for y = 1 does not significantly change due to the magnetic field but a distinct decrease is observed in high fields. The critical field at 0 K of this transition in Fe2MnSi is found to be larger than 70 T, and with increasing x, the critical field decreases corresponding to the decrease of TA at zero field.

We developed a suitable sample stage that is optimized for birefringence imaging measurements at high electric fields (E 5 kV/cm) and low temperatures (T 20 K) to directly observe electric-field-induced ferroelectric domains in SrTiO3. As a result, a huge retardance area corresponding to the ferroelectric domains appears at E ≥ 2 kV/cm and T ≤ 60 K even though the paraelectric domains partially remain. Furthermore, the fast-axis direction drastically rotates by 90° at the ferroelectric phase transition temperature because of an electrostrictive effect in ferroelectrics. The phase diagram of the critical electric fields and temperatures agrees with previous reports obtained from dielectric and neutron scattering measurements.

Magnetic torque τ and magnetostriction ΔL/L measurements were carried out in the spin gap system (CH3)2CHNH3CuCl3. The magnetic torque shows a cusp-like anomaly at the magnetic field Ha1with increasing the magnetic field, and the magnetostriction shows a kink at almost the same magnetic field. These results suggest that anomalous change in the magnetic torque is associated with the lattice distortion, and it is expected that the field-induced magnetic phase transition is not simple Bose-Einstein condensation in this system.

The isomorphous compounds A2CuF4 (A = K, Rb, Cs) are two-dimensional Heisenberg ferromagnets with the Curie temperatures of 6.25, 6.05 and 4.55 K, respectively. Previous studies showed that pressure-induced magnetic phase transitions occur in K2CuF4 and Rb2CuF4 at around 10 GPa, above which the ferromagnetic behaviour disappears as a result of the structural change from antiferrodistortive to ferrodistortive order of the CuF6 octahedra in the basal plane. For Cs2CuF4 it was revealed that the interlayer exchange interaction changes from ferromagnetic to antiferromagnetic at a certain pressure below 2.2 GPa. Motivated by this unexpected result, we have carried out magnetic measurements on Cs2CuF4 in a diamond-anvil cell at various pressures up to 26 GPa by using a superconducting quantum interference device vibrating coil magnetometer. It was found that the Neel temperature increases with pressure at a rate of 0.3 K GPa−1 up to 17 GPa, reaches a maximum of about 9 K at around 17 GPa and then decreases rapidly to zero. At pressures above 21 GPa the magnetic susceptibility decreases to the background level, strongly suggesting that a structural change similar to those observed for the other two compounds occurs for Cs2CuF4 at around this pressure.

The compound (CH 3 ) 2 CHNH 3 CuCl 3 consists of ferromagnetic and antiferromagnetic alternating Heisenberg chains with S =1/2; a pair of ferromagnetically coupled spins behaves as a spin with S =1. Consequently, it has the Haldane gap in its energy spectrum at T =0 K. We investigated an issue what will happen when Cl ions are randomly replaced by other kind of anions, for instance by Br ions. Performing experiments on single crystals of mixed compounds (CH 3 ) 2 CHNH 3 Cu(Cl x Br 1− x ) 3 in which Cl ions are randomly replaced by Br ions, we found that the energy gap disappeared over the region 0.44 x

Phase transitions in SrTiO3 between quantum paraelectric, coherent paraelectric, and electric-field-induced ferroelectric states are governed by tetragonal domains with quantum fluctuations. However, their characteristics are still unclear. To observe the electric-field-induced ferroelectric state using birefringence imaging techniques, we developed a suitable sample holder to apply high electric fields of up to \(E \simeq 5\) kV/cm and temperatures down to T = 20 K. From birefringence imaging measurements of the ferroelectric LiNbO3 with varying electric field, distributions of the electric field in the sample stage were found to be negligible. In SrTiO3, a huge-retardance area corresponding to the ferroelectric domains appears at E > 2 kV/cm and T ≤ 60 K even though the paraelectric domains partially remain. Furthermore, the fast-axis direction rotates by 90° at the ferroelectric phase transition because of an electrostrictive effect in ferroelectrics. The phase diagram of the critical electric field an...

In the layered compound (C3H7NH3)2CuCl4, both electrical and magnetic effects are impacted by rotations of CuCl6 octahedra and alkylammonium chains (C3H7NH3) at successive structural phase transiti...

The dependence of optical linear birefringence Δ n on temperature T was measured on a single crystal of (CH 3 ) 2 CHNH 3 CuCl 3 , which consists of ferromagnetic–antiferromagnetic (F–AF) alternating Heisenberg chains with S =1/2. The curve of dΔ n ( T )/d T showed a large peak near 25 K and a small shoulder near 45 K. The presence of these two anomalies is qualitatively similar to the theoretical curve of the magnetic specific heat in ferromagnetic-dominant F–AF chains.

Electron paramagnetic resonance measurements were performed at 24 GHz on the magnetic compound (CH 3 ) 2 CHNH 3 CuBr 3 , which consists of antiferromagnetic-antiferromagnetic alternating Heisenberg...

At ambient pressure, both the intralayer and the interlayer exchange interactions in the layered compound (CH 3 NH 3 ) 2 CuCl 4 are ferromagnetic. Magnetic susceptibility and neutron scattering experiments performed under pressures up to about 1 GPa revealed that the interlayer exchange interaction turns into an antiferromagnetic one at a pressure between 0.41 GPa and 0.61 GPa, while the intralayer exchange interaction remains ferromagnetic. The spin structure in the antiferromagnetic phase is still collinear at least up to 1.1 GPa.

In the two-dimensional Heisenberg antiferromagnet (C 2 H 5 NH 3 ) 2 CuCl 4 , the intralayer exchange interaction is ferromagnetic, whereas the interlayer exchange interaction, which is less than 10 -4 of the intralayer one, is antiferromagnetic, and the spins collinearly lie in each layer. To investigate the effect of pressure on its spin structure, magnetic susceptibility and neutron scattering measurements under pressures up to 2.5 GPa were performed. The magnetic susceptibility measurements revealed the appearance of a pressure-induced weak ferromagnetic moment along the c -axis around 0.6 GPa. The neutron scattering measurements clarified the noncollinear spin structure which causes the weak ferromagnetic moment mentioned above. That is, the ferromagnetically coupled spins in each layer cant from the layer, which brings about the weak ferromagnetic moment along the c -axis. The ferromagnetic coupling in each layer and the antiferromagnetic coupling among the nearest-neighboring layers are maintained a...

Measurements of macroscopic properties have indicated that the bond-disordered spin-gap system (CH3)2CHNH3-Cu(ClxBr1-x)3 is gapless when x is between 0.44 and 0.87. Using muon spin relaxation to investigate microscopic properties of sample with x=0.35, we observed a dynamical spin fluctuation, whose characteristic frequency decreases with decreasing temperature, indicating a magnetic ground state., 4 pages. Submitted to muSR2008(Tsukuba) and accepted for publication

Electron spin resonance experiments were performed on α'-NaV 2 O 5 , a possible spin-Peierls compound, at 9.3 and 23.5 GHz over 1.3–700 K. Analyzing all factors of the absorption line above T sp =34 K, such as the value and the angular dependence of the linewidth at high temperatures, the temperature dependence of both the linewidth and the resonance field, as well as the high temperature lineshape, we find that the exchange-narrowing theory closely explains these factors when a linear Heisenberg chain with S =1/2 along the b -axis is assumed, and the antisymmetric exchange interaction, ∑ i d i i +1 ·( S i × S i +1 ) with d i +1 // c -axis, between nearest-neighbor spins on the b -axis is adopted as the origin of line broadening. As long as the results of this study are concerned, the model of V 4+ magnetic chains separated by nonmagnetic V 5+ chains in the a b -plane above 34 K is acceptable. However, the results do not necessarily deny a V-O-V molecular spin model that has been proposed to account for a...

The compound (CH 3 ) 2 CHNH 3 CuCl 3 has recently been found to be an ideal ferromagnetic-antiferromagnetic alternating Heisenberg chain with the energy gap Δ/ k =17∼18 K [H. Manaka et al. : J. Phys. Soc. Jpn. 66 (1997) 564]. When an external field H is applied to this compound, the energy gap should vanish at the critical field H c1 = Δ/ g µ B . Just above H c1 , the three-dimensional magnetic long-range order is expected, if the interchain coupling exists. Motivated by this expectation, we performed specific heat measurements over a temperature range from 0.5 to 5 K applying H up to 12 T. As a result, we found a λ-type anomaly of specific heat over 10∼12 T, which indicates a transition to the three-dimensional long range order. The temperature at which the λ-type anomaly appears increases with increasing H . The critical field obtained by extrapolating the curve of the λ peak position versus H is 9.0 T, which is close to that obtained from a magnetization measurement.

Since the ferromagnetic intralayer exchange interaction in K 2 CuF 4 is due to the antiferrodistortive (AFD) orbital ordering of the 3d holes of Cu 2+ ions, we expect that the ferromagnetism of this compound to disappear when the AFD order of the distortion of CuF 6 octahedra collapses. Recent magnetic susceptibility measurements performed at high pressures on this compound actually confirmed the disappearance of the ferromagnetism above approximately 9 GPa [M. Ishizuka et al. : J. Phys. Soc. Jpn. 65 (1996) 1927]. To obtain evidence of the pressure-induced structural change which corresponds to the magnetic change mentioned above, we measured the pressure dependence of the phonon-Raman spectra of this compound. As a result, we found that the scattering lines relevant to the vibrational modes of CuF 6 octahedra ordered in the AFD fashion disappeared above 9∼10 GPa. This result is consistent with the structure above 9 GPa revealed by recent X-ray diffraction experiments that we performed.

We report that antiferromagnetic and antiferromagnetic (AF-AF) alternating Heisenberg chains with S =1/2 are formed in (CH 3 ) 2 CHNH 3 CuBr 3 , which is in contrast to the almost isomorphous compound (CH 3 ) 2 CHNH 3 CuCl 3 , because the Cl compound forms ferromagnetic-dominant ferromagnetic and antiferromagnetic (F-AF) alternating Heisenberg chains [H. Manaka et al. : J. Phys. Soc. Jpn. 66 (1997) 564]. From the analysis of the dependence of magnetic susceptibility on temperature, χ( T ), the two different antiferromagnetic exchange interactions defined in the Hamiltonian H = -2 J 1 ∑ S 2 i · S 2 i +1 -2 J 2 ∑ S 2 i · S 2 i -1 are determined to be J 1 / k =-61 K and J 2 / k =-33 K. Applying the low temperature experimental data to the formula χ( T )∝ T -1/2 exp (-Δ/ k T ), we estimate the energy gap Δ to be 98 K. We discuss why AF-AF and F-AF alternating chains are formed in the Br and the Cl compounds, respectively, in spite of their almost isomorphous crystal structures.

On measuring the dependence of the magnetic susceptibility of (CH 3 ) 2 CHNH 3 CuCl 3 on the temperature, we find that this compound forms ferromagnetic and antiferromagnetic alternating linear chains with S =1/2. The magnetic susceptibilities observed in external fields applied along three different surfaces of an as-grown single-crystal sample show broad peaks at around 24 K and steeply decrease to zero with further decreases in temperature toward 0 K. Two types of superexchange interactions defined in the Hamiltonian H = -2 J 1 ∑ S 2 i · S 2 i +1 - 2 J 2 ∑ S 2 i · S 2 i -1 are determined to be J 1 / k =-23.5 K and J 2 / k =+54.1 K, which indicates that a pair of ferromagnetically coupled spins behaves as a spin of S =1 and thus this compound is regarded as antiferromagnetic linear chains with S =1. The present system can therefore be discussed in terms of the Haldane conjecture for integer spins. The energy gap is estimated to be 17.1∼18.1 K.

Birefringence imaging microscopy is well suited for comprehensively investigating various structural phase transitions but its weak point is that it imposes an inherent limit on the maximum retardance that can be detected. To detect retardance above this limit, we performed simultaneous birefringence measurements at multiple wavelengths on (CnH2n+1NH3)2MnCl4 with \(n = 1,2,3\). For n = 1, we successfully detected large jumps in retardance (over six times greater than the limit) in the first-order phase transitions at Tc1 \( \simeq \) 88 K and Tc2 \( \simeq \) 251 K. For n = 2, a gradual change in retardance appears in the second-order phase transition at Tc = 214 K. High-definition images of optical fast-axis azimuths provided information on the misorientation of the alkylammonium chains. For n = 3, a retardance kink appears at Tc4 \( \simeq \) 152–155 K, and a retardance jump appears in the commensurate-incommensurate phase transition at Tc5 \( \simeq \) 96–99 K.

We have used a combination of neutron resonant spin-echo and triple-axis spectroscopies to determine the energy and linewidth of the magnon resonance in IPA-Cu(Cl$_{0.95}$Br$_{0.05}$)$_3$, a model spin-1/2 ladder antiferromagnet where Br substitution induces bond randomness. We find that the bond defects induce a blueshift, $\delta \Delta$, and broadening, $\delta \Gamma$, of the magnon gap excitation compared to the pure compound. At temperatures exceeding the energy scale of the inter-ladder exchange interactions, $\delta \Delta$ and $\delta \Gamma$ are temperature independent within the experimental error, in agreement with Matthiessen's rule according to which magnon-defect scattering yields a temperature independent contribution to the magnon mean free path. Upon cooling, $\delta \Delta$ and $\delta \Gamma$ become temperature dependent and saturate at values lower than those observed at higher temperature, consistent with the crossover from one-dimensional to two-dimensional spin correlations with decreasing temperature previously observed in pure IPA-CuCl$_3$. These results indicate limitations in the applicability of Matthiessen's rule for magnon scattering in low-dimensional magnets., Comment: 4 pages, 3 figures

We have used a combination of neutron resonant spin-echo and triple-axis spectroscopies to determine the energy, fine structure, and linewidth of the magnon resonance in the model spin-1/2 ladder antiferromagnet IPA-CuCl_3 at temperatures T << Delta_0 /k_B, where Delta_0 is the spin gap at T=0. In this low-temperature regime we find that the results deviate substantially from the predictions of the non-linear sigma model proposed as a description of magnon excitations in one-dimensional quantum magnets and attribute these deviations to real-space and spin-space anisotropies in the spin Hamiltonian as well as scattering of magnon excitations from a dilute density of impurities. These effects are generic to experimental realizations of one-dimensional quantum magnets., 4 pages, 4 figures

In this report we propose a new idea to improve electron configuration of an atom and show the first apparent experimental data, which applies long‐lifetime excited states of the inner‐core electron system of atoms. For the next material‐revolution from Carbon and Nuclear society to Hydrogen society, development of a high efficient and low cost hydrogen storage system is one of the most important key technologies. The surface reaction processes between hydrogen atoms and hydrogen storage alloys system are controlled by the number of d‐electrons of transition elements, that is, perfectly or partly occupied. We confirmed the idea to change the number of d‐electrons of zinc atoms by using the excitation of inner‐core electrons due to surface‐ion‐recombination (SIR) process. Average density of Zn− was controlled by the electrostatic potential energy of a sapphire substrate and that of Zn+ ions was controlled by the collision frequency between Zn atoms and incident electrons. After SIR process, unique excited ...

We carried out magnetization $M(T)$ and specific-heat ${C}_{P}(T)$ measurements of the new Heusler compounds ${\text{Ru}}_{2\ensuremath{-}x}{\text{Fe}}_{x}\text{CrSi}$ $(x=0.1,\text{ }0.3,\text{ }\text{and}\text{ }0.5)$, which exhibit spin-glass freezing. $M(T)$ has peak- and irreversibility-type anomalies. The temperatures at which these anomalies appear have magnetic field dependence described by the Gabay-Toulouse and de Almeida-Thouless lines in the low-field range. For the magnetic specific heat ${C}_{m}(T)$, we did not observe a discontinuity indicating long-range magnetic phase transition but a broad hump characteristic of spin-glass freezing. ${C}_{m}(T)$ in the low-temperature range is described as a combination of linear- and quadratic-$T$ terms. The quadratic-$T$ dependence of ${C}_{m}(T)$ is probably associated with excitation of the Ising component of the freezing spins.