Yutaka Shimojo

Magnetic properties of the antiferromagnetic double perovskite Ba2PrRuO6

The ordered perovskite compound Ba2PrRuO6 is prepared and its magnetic properties are investigated. The Rietveld analysis of the neutron diffraction profiles measured at 150 K shows that the Pr3+ and Ru5+ ions are arranged with regularity over the six-coordinate B sites of the perovskite ABO3 and that Ba2PrRuO6 belongs to space group P21/n, with a = 6.0063(5), b = 5.9863(4), c = 8.4677(7) A and 90.04(2)°. The magnetic susceptibility and the heat capacity measurements show that this compound transforms to an antiferromagnetic state below 117 K. From the neutron diffraction patterns measured at 7 K, the magnetic structure is determined to be of Type I and the magnetic moments of Pr3+ and Ru5+ are estimated to be 2.2(1) and 2.0(2) µB, respectively. Their values are discussed on the basis of theoretical calculations for the crystal field splitting.

Study on the crystal and magnetic structures of and by powder neutron diffraction

We prepared oxygen stoichiometric and in which tetravalent terbium ions are stabilized at the B sites of the perovskite . Their crystal structures at room temperature and at 10 K were determined from both x-ray and neutron diffraction measurements. Both and have an orthorhombic perovskite-type structure with space group Pnma (No 62). Magnetic susceptibility measurements have been performed for both the compounds in the temperature range between 4.5 K and room temperature. Both the compounds show the antiferromagnetic transition at . The temperature-dependent magnetic susceptibilities were measured with zero-field-cooled (ZFC) and field-cooled (FC) conditions at an applied field of 1000 G. A dramatic difference between ZFC and FC was observed below the Neel temperatures for both the compounds, which shows the onset of a ferromagnetic moment below those temperatures. To determine the magnetic structures at the antiferromagnetic state, powder neutron diffraction measurements have been performed at 10 K and room temperature. Both the compounds have the G-type magnetic structure in which terbium atoms are antiferromagnetically coupled with the six neighbouring terbium atoms.

Structural properties of the copper oxide carbonate Ba4CaCu2O6+δCO3 (δ≃0)

Abstract The structure parameters of Ba4CaCu2O6 + δCO3 were refined by Rietveld analysis of angle-dispersive neutron powder diffraction data. The stoichiometric metal composition was confirmed by X-ray microanalysis. Iodometry showed that the amount of excess oxygen, δ, was nearly zero. The carbon content and infrared absorption spectrum of the compound gave evidence for the inclusion of CO32− ions in its crystal lattice. Ba4CaCu2O6CO3 is tetragonal with the P4/mmm space group and lattice parameters of a = 5.7879(2) A and c = 8.1409(3) A . Ba atoms occupy positions corresponding to the A site in ABO3 whereas Ca, Cu and C atoms are located at positions corresponding to the B site. Two copper sites are contained in the structure of Ba4CaCu2O6CO3: Cu(1) and Cu(2). If weak bonds between the Cu atoms and O atoms in the CO32− ion are neglected, Cu(1) and Cu(2) are taken as coordinated to four O(1) atoms and two O(2) atoms, respectively. Bond-valence sum calculations showed that the oxidation state of Cu is 2.48 for Cu(1) and 1.66 for Cu(2). The splitting and large thermal parameters of O atoms contained in the CO32− ion revealed its highly disordered orientation.

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.

Hexagonal ZrNiAl alloy and its hydride (deuteride) with the Fe2P-type structure

Abstract ZrNiAl alloy was found to absorb hydrogen up to a composition of ZrNiAlH0.53 in the measurement of a pressure-composition isotherm at 313 K. The structure parameters of the alloy and its hydride (deuteride) were refined by the Rietveld method using X-ray and neutron diffraction data. Both the alloy and deuteride have the Fe2P-type structure (space group: P62m; a = 6.9152(6)A and c = 3.4703(4)A for the alloy; a = 6.7225(7)Aandc = 3.7713(6)A for the deuteride). Hydrogenation leads to the lattice-contraction of the a axis by 2.8% and the lattice-expansion of the c axis by 8.7%. Neutron Rietveld refinement revealed that deuterium occupies a trigonal-bipyramidal site surrounded by three Zr and two Ni atoms.

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.

Crystal distortion and magnetic structure of γ-Mn(Au) alloys

Abstract γ-Mn alloys containing Au have been examined by magnetic measurements and X-ray and neutron diffraction experiments. The 9 at% Au alloy has a face centered orthorhombic lattice with a = 3.853, b = 3.794 and c = 3.731 A at 11 K, and shows a non-collinear antiferromagnetic structure with 4 sublattices; the three-axis components of the magnetic moments are as follows: μ a = 0, μ b = 1.10 and μ c = 1.91 μ B . A revised phase diagram for γ-Mn(Au) alloy system with 8–16 at% Au is proposed.

Magnetic and neutron diffraction studies on potassium uranate KUO3

Abstract The magnetic properties of KUO 3 with the cubic perovskite structure have been studied. It shows an antiferromagnetic-type of transition at ca. 17 K in the magnetic susceptibility vs. temperature curve. Magnetic hysteresis is observed at 4.5 K, but not observed at 20 K. Neutron diffraction measurements have been performed on the powdered KUO 3 below and above the transition temperature. The neutron diffraction pattern measured at 10 K shows no appreciable difference from that measured at 50 K. A small ordered magnetic moment of U 5+ ion will make it very difficult to observe magnetic diffractions, even if a magnetic ordering occurs. If the magnetic spin alignment occurs in a small domain, no magnetic diffraction will be found in the neutron experiments. On the other hand, the magnetic phenomena of KUO 3 have been analyzed on the basis of an octahedral crystal field model.

Neutron diffraction study on hp 13 type M7-xMnxGe6 (M = Co, Fe)

Abstract We have made neutron diffraction experiments for Fe 7- x Mn x Ge 6 with x = 2 and 4 and Co 7- x Mn x Ge 6 with x = 3.25, which have the hexagonal hp 13-type structure. It is determined by the Rietvelt analysis for the nuclear reflection that the 1T 1 site is entirely occupied by Mn atoms and the 6T 2 site by Fe or Co atoms and excess Mn atoms. The magnetic reflection of Fe 3 Mn 4 Ge 6 corresponds to the collinear antiferromagnetism with alternating ferromagnetic layers in which the magnetic moments of the 1T 1 and 6T 2 sites are 2.5 and 1.8 μ B /(Mn or Fe) atom, respectively. Magnetic structures of the other alloys are quite complicated.