Kenichi Oikawa

Analysis of crystal structure and phase transition of LaCrO3 by various diffraction measurements

Abstract Crystal structure and structural phase transition of LaCrO3 have been investigated by using various diffraction technique. X-ray diffraction at high temperature revealed that the crystal structure of LaCrO3 below 240°C and above 280°C is orthorhombic- and rhombohedral-distorted perovskite, respectively. The discrete volume compression was observed at the phase transition from orthorhombic to rhombohedral phase. The space group of LaCrO3 below 240°C was determined to be Pbnm (No. 62), whereas that above 280°C was R 3 c (No. 167) by using selected area electron diffraction and convergent-beam electron diffraction. The Rietveld refinement of neutron diffraction patterns of LaCrO3 at various temperatures was carried out using the space group determined by the electron diffraction. It was revealed that the volume compression at the phase transition was principally due to the shrinkage of the [CrO6] octahedra. DSC-XRD simultaneous measurements indicated that the phase transition started at about 250°C and was completed at about 268°C with heating rate of 5°C/min involving absorption of heat. No intermediate phase other than orthorhombic or rhombohedral was observed at the phase transition.

Magnetic and neutron diffraction study on the ordered perovskite Sr2HoRuO6

Magnetic properties of an ordered perovskite compound Sr2HoRuO6 have been reported. Powder neutron diffraction measurements at 10xa0K, 25xa0K and room temperature were performed to investigate the crystal and magnetic structures of Sr2HoRuO6. As a result of the refinement of the data collected at room temperature, it was found that the crystal structure of this compound is a distorted perovskite [a = 5.7710(3)xa0A, b = 5.7801(3)xa0A, c = 8.1640(4)xa0A and β = 90.200(3)°] with space group P21/n and a 1∶1 ordered arrangement of Ru5+ and Ho3+ over the six-coordinate B sites. Data collected at 10 and 25xa0K show that Sr2HoRuO6 has a long range antiferromagnetic ordering involving both Ru5+ and Ho3+. The direction of the magnetic moments is along the c-axis. Each of these orders in a type I arrangement and these magnetic moments are antiparallel in the ab-plane with each other. Magnetic susceptibility measurements from 5 to 300xa0K showed the existence of a magnetic transition at 36xa0K and divergence between zero-field and field cooled conditions below this temperature. The field-dependence of the magnetization was measured and a small magnetic hysteresis loop was found below the divergence temperature indicating the existence of a weak ferromagnetic moment associated with the antiferromagnetism.

Magnetic and neutron diffraction studies of the ordered perovskite Ba2NdRuO6

The magnetic properties of the ordered perovskite compound Ba2NdRuO6 are reported. Powder neutron diffraction measurements were performed at 100, 35 and 7xa0K to determine its crystal structure and magnetic properties. Refinement of the data collected at 100xa0K showed that this compound has monoclinic symmetry, space group P21/n with a = 5.9888(2), b = 5.9916(2), c = 8.4667(2)xa0A and β = 90.026(3)°, and that the structure is that of a perovskite with a 1∶1 ordered arrangement of Ru5+ and Nd3+ over the 6-coordinate sites. From the data collected at 35 and 7xa0K, it was found that there is a long range antiferromagnetic ordering in the Ba2NdRuO6. The magnetic structure is of type I and the magnetic moments of Nd3+ and Ru5+ ions are in the same direction in the ab plane.

Crystal and magnetic structures of the antiferromagnetic manganese sulfide BaLa2MnS5 by powder neutron diffraction measurements

Powder neutron diffraction measurements were performed on an antiferromagnetic manganese sulfide BaLa2MnS5 at 7 and 100xa0K. This sulfide has a tetragonal nuclear structure with space group I/mcm. The neutron diffraction data at 7xa0K show a collinear antiferromagnetic structure (space group I) with a propagation vector k = (1/2, 1/2, 1/2). The magnetic moment of Mn2+ is estimated to be 4.21 μB and determined to lie in a parallel direction with the c-axis. The magnetic exchange constants, (2J1 + J2)/kB andJ3/kB, are estimated to be −6.6xa0K and 0.80xa0K, respectively, from the molecular field approximation.

Magnetic properties and crystal structures of ordered perovskites Sr2TbRu1 −xIrxO6

We have performed powder neutron diffraction measurements for Sr2TbRuO6 at 10xa0K and room temperature. It has been found that the crystal structure of this compound is a distorted perovskite (a = 5.7932(2)xa0A, b = 5.8107(1)xa0A, c = 8.2011(3)xa0A and β = 90.249(2)°) with the space group P21/n (No.14) and a 1 ∶ 1 ordered arrangement of Ru5+ and Tb3+ over the 6-coordinate B sites. Data collected at 10xa0K show that Sr2TbRuO6 has long range antiferromagnetic ordering involving both Ru5+ and Tb3+. Each of these ions orders in a type I arrangement. The direction of the magnetic moments is canted by ca. 20° from the c axis. The magnetic susceptibility and specific heat measurements show the existence of magnetic transitions at 32xa0K and 41xa0K. n The magnetic properties of Sr2TbRu1 − nxIrxO6 (0 < x < 1) are also reported in this paper. The structural data and the value of the effective magnetic moment indicate that these compounds adopt the valence configuration of Sr2Tb3+(Ru1 − nxIrx)5+O6 (x = 0.0–0.7) or Sr2Tb4+(Ru1 − nxIrx)4+O6 (x = 0.85–1.0). Evidence for the presence of a mixed valence state was not found. The magnetic transition temperature for Sr2Tb3+(Ru1 − nxIrx)5+O6 decreases with increasing x. On the other hand, that for Sr2Tb4+(Ru1 − nxIrx)4+O6 increases with x.

Magnetic and neutron diffraction study on ordered perovskites Sr2LnRuO6 (Ln=Tb, Ho)

Abstract Magnetic properties of ordered perovskite-type compounds Sr 2 LnRuO 6 (Ln=Tb, Ho) are reported. Powder neutron diffraction measurements at 10 K, 25 K and room temperature were performed to investigate their crystal and magnetic structures. Both of these compounds are distorted perovskites with space group P 2 1 / n and a 1:1 ordered arrangement of Ln 3+ and Ru 5+ over the six-coordinate sites. Data collected at 10 K and 25 K show that they have a long range antiferromagnetic ordering involving both Ln 3+ and Ru 5+ . Each of these ions orders in a Type I arrangement. The direction of the magnetic moments is along the c -axis for Sr 2 HoRuO 6 , while it is canted by ca. 20° from the c -axis for Sr 2 TbRuO 6 . The magnetic susceptibility and specific heat measurements show the existence of magnetic transitions at 41 K for Sr 2 TbRuO 6 and at 36 K for Sr 2 HoRuO 6 . The field-dependence of the magnetization was measured and a small hysteresis loop was found below magnetic transition temperatures, indicating the existence of a weak ferromagnetic moment associated with the antiferromagnetism.

Studies on magnetic properties of La0.95Sr0.05CrO3 and La0.85Sr0.15CrO3 by means of powder neutron diffraction

The magnetic properties of the perovskite-type compounds La1-xSrxCrO3 (x = 0.05 and 0.15) have been investigated. In the magnetic susceptibility measurements, three magnetic anomalies have been observed for La0.95Sr0.05CrO3 (at 21 K, 85 K and 280 K) and for La0.85Sr0.15CrO3 (at 26 K, 160 K and 267 K). Powder neutron diffraction measurements on these two compounds indicate that the anomaly found at ≈20 K in their susceptibility-temperature curves is not ascribable to the magnetic transition. Heat capacity measurements also show that two anomalies have been found at 90 K and 280 K for La0.95Sr0.05CrO3 and at 160 K, 190 K and 266 K for La0.85Sr0.15CrO3, and no anomaly has been found at ≈20 K. The magnetic structures for all the compounds have been determined to be of G type, in which Cr atoms are antiferromagnetically coupled with the six neighbouring Cr atoms at all of the temperatures. The magnetic moments of Cr atoms are directed parallel to the z-axis of an orthorhombic unit cell for La0.95Sr0.05CrO3 at 10 K and 50 K and for La0.85Sr0.15CrO3 at 10 K and 50 K; the Gz mode dominates. The Gy mode dominates for La0.95Sr0.05CrO3 at 125 K; i.e., a spin reorientation has occurred between 50 K and 125 K.

Physical characteristics of delay-line current-biased kinetic inductance detector

Our preceding works reported the development of a high spatial and temporal resolution imaging system by using a current biased kinetic inductance detector (CB-KID) with the use of a delay-line technique. We called this system as a delay-line CB-KID, and succeeded in imaging of neutron events caused by the nuclear reaction and hot spots produced by using the delay-line CB-KID system. It was essentially important for our proposal to use a superconducting stripline to guide the pulsed signal where the signal propagates at a constant fast velocity along the stripline. In the present study, we intend to measure a propagation velocity of the signal along the stripline precisely to compare with the theoretical prediction of the signal propagation, which was recently developed with a superconducting waveguide S-I-S model by Koyama and Ishida [11]. Our present measurements showed a good agreement between the theoretical predictions and the experimental results on the propagation velocity as a function of temperature.

Neutron signal features of Nb-based kinetic inductance detector with 10B convertor

In our preceding works, we demonstrated successful neutron detection using a superconducting current-biased kinetic inductance detector (CB-KID), which is composed of two Nb-based superconducting meanderlines and the 10B neutron absorption layer. The CB-KID with a 10B absorption layer outputs the voltage pulses when it is irradiated by pulsed neutrons. We expected that the voltage V is proportional to a product of the bias current I b and a time derivative of the local kinetic inductance dΔL k/dt, and a pair of signals propagate along the Nb stripline as an electromagnetic wave at a certain fraction of the light velocity c toward end electrodes. It still remains to be revealed why the signal voltage shows such a continuum in the histogram of the signal height even if the incident energy of the light ion is apparently monochromatic. In the present work, we investigated the distribution of the height and width of the signal. We found a clear correlation between height and width, which might be a key of understanding the operating principle of our detector. We consider that the origin of the signal distribution is due to the positional dependence of the light ion bombardment with respect to the meandering Nb nanowire.

Development of AC Magnetic Field Imaging Technique Using Polarized Pulsed Neutrons at J-PARC

We have been developing a quantitative magnetic field imaging technique at J-PARC. As was previously reported [1], we successfully quantified strength and direction of a static magnetic field by analyzing the wavelength dependence of polarization position by position for images, which were obtained using a time-of-flight (TOF) method of pulsed neutrons. Applying this method to observe a magnetic field in industrial products, such as voltage converters and motors, it is necessary to extend this technique to the AC magnetic field driving at a frequency of commercial power supply (50~60Hz). In this study, we attempted to measure an AC magnetic field quantitatively with the TOF method. Magnetic field imaging experiments were performed at the beam line of BL10 “NOBORU” in the Materials and Life science experimental Facility (MLF) of J-PARC. The experimental setup was the same as the previous experiment [1]. An AC magnetic field was produced by applying an AC electric current to a small solenoid coil with the diameter of 5 mm and length of about 50 mm. The frequency of applied field was set to 50.5 Hz, which is slightly higher than that of a two-fold repetition of the pulsed neutrons of J-PARC. Polarization images were obtained under applying the AC field in the coil and wavelength dependence of polarization in a selected area was analyzed, in which polarization changes due to the neutron spin rotation were observed. By fitting the results with a model assuming that only the magnetic field inside the coil contributed to the neutron spin rotation, the amplitude of applied AC field was estimated to be 3.22±0.14×10 A/m, which was corresponded to the designed value of 3.3×10 A/m. This work was supported by Photon and Quantum Basic Research Coordinated Development Program from the Ministry of Education, Culture, Sports, Science and Technology, Japan.