Nobuyuki Momozawa

Field-Induced Commensurate Intermediate Phases in Helimagnet (Ba1-xSrx)2Zn2Fe12O22(x=0.748)

Neutron diffraction and magnetization measurements have been made on single crystal specimens of hexagonal-ferrite helimagnet (Ba 1- x Sr x ) 2 Zn 2 Fe 12 O 22 ( x =0.748) in a field applied perpendicular to the c -axis. Two types of intermediate phases, intermediate-I and -II, are successively induced by a field, and their magnetic structures are determined by using the Fourier series expansion method. In each phase, the moments order in fanlike oscillatory structures in which there are large and small spin-bunches perpendicular to the c -axis. The magnetization curve and the turn angle of the helix are discussed from exchange interactions.

Magnetic Structure of (Ba1-xSrx)2Zn2Fe1 2O22 (x=0-1.0)

Neutron and X-ray diffraction studies and magnetization measurements were carried out on single crystals of (Ba 1- x Sr x ) 2 Zn 2 Fe 12 O 22 . The substitution of Ba by Sr produces two effects on the crystal structure: a lattice deformation around the Sr ions and a redistribution of the Zn and Fe ions in the tetrahedral sites. The magnetic structure is analyzed in consideration of these effects: Spins are bunched in the form of ferrimagnet in the every (T 1/2 ST 1/2 ) block and the bunched spins make an angle φ 0 between the adjacent (T 1/2 ST 1/2 ) blocks. At 294 K, the turn angles φ 0 s are found to be 0^° (ferromagnetic), 0^°<φ 0 <180^° (helical) and 180° (antiferromagnetic) for 0≤ x ≤0.5, 0.5< x <0.8 and \(0.8{\lesssim}x{\leq}1.0\), respectively. A brief discussion on the exchange interaction of this spin system is given.

Magnetic structure change in Ba2Mg2Fe12O22

Neutron diffraction study was carried out on a single crystal of Ba 2 Mg 2 Fe 12 O 22 . The magnetic structure of Ba 2 Mg 2 Fe 12 O 22 changes at 195 K, collinear ferrimagnet above 195 K and proper helix below 195 K. The helix is propagated along the c -axis by rotations of the large and small spin-bunches. The turn angle of the helix is 59.6° at 77 K and rapidly decreases as the temperature approaches 195 K. Results are discussed from a point of view of the exchange interactions.

Superexchange Interactions of (Ba1-xSrx)2Zn2Fe12O22 System Studied by Neutron Diffraction

Neutron diffraction experiments were carried out on single crystals of (Ba 1- x Sr x ) 2 Zn 2 Fe 12 O 22 at 8 K, where x is the Sr concentration ranging from 0 to 1.0. Competition of three superexchange interactions exists among Fe magnetic moments present in the 4th, 5th, and 8th layers of Sr-rich crystals. This competition leads to a distorted helimagnetic structure consisting of large and small ferrimagnetic bunches. The relations between exchange integrals J 45 , J 48 , and J 58 are determined by using the molecular field approximation as J 45 / J 58 =0.365 7 +0.019 0 x +0.061 7 x 2 and J 48 / J 58 =0.504 7 +0.010 4 x +0.011 6 x 2 at 8 K. These relations provide a clear interpretation for the magnetic structure of the (Ba 1- x Sr x ) 2 Zn 2 Fe 12 O 22 system. Zn ion distributions in the tetrahedral sites and a local lattice deformation around Sr ions are also discussed in detail.

Single crystal growth of (Ba1−xSrx)2Zn2Fe12O22 from high temperature solution

Abstract Single crystals of (Ba 1− x Sr x ) 2 Zn 2 Fe 12 O 22 , 0≤ x ≤0.84, up to 27 mm in diameter and 3.6 mm thick, were successfully grown from Na 2 O-Fe 2 O 3 flux. The starting composition in molar % is 19.69 BaO(SrO), 19.69 ZnO, 53.61±0.75 Fe 2 O 3 and 7.01±0.31 Na 2 O. Temperature cycling in the first stage of slow cooling is required to remove by-products. The nucleation temperature ranges between 1111 and 1243°C, depending strongly on the solubilities of BaO and SrO in the flux. The X-ray diffraction and chemical analysis studies give evidence that (Ba 1− x Sr x ) 2 Zn 2 Fe 12 O 22 crystallizes as a homogeneous solid-solution system.

Cation Distribution and Helimagnetic Structure of the Ba2(Zn1-xMgx)2Fe12O22 System as Revealed by Magnetization Measurements and Neutron Diffraction

Magnetization measurements and neutron diffraction experiments were carried out on single crystals of Ba 2 (Zn 1- x Mg x ) 2 Fe 12 O 22 , where x is the Mg concentration ranging from x =0 to 1.0. T...

Modification of Helix in (Ba1-xSrx)2Zn2Fe12O22 Due to Applied Magnetic Field

Magnetization measurements and neutron diffraction experiments were carried out on (Ba 1- x Sr x ) 2 Zn 2 Fe 12 O 22 in a field applied parallel to the c -plane. Spins in the (T 1/2 ST 1/2 ) block are observed to be bunched in the form of ferrimagnet. Five magnetic phases appear with increasing field : helix with a small ferromagnetic component, intermediate (1) having a period of four (T 1/2 ST 1/2 ) blocks, intermediate (2) and (3) having a period of two ( T 1/2 ST 1/2 ) blocks and ferromagnetic. A crossing angle between the adjacent (T 1/2 ST 1/2 ) spin blocks is almost equal to the turn angle of the helix in the first three phases, rapidly decreases in intermediate (3) phase and becomes zero in ferromagnetic phase.

Photocatalytic activity of TiO2 particulate films prepared by depositing TiO2 particles with various sizes

TiO2 particles of various sizes were prepared by grinding in cyclohexanone, and TiO2 particulate films were obtained by depositing these TiO2 particles with various sizes onto a glass or quartz substrate. The effect of the particle size and thickness on the photocatalytic properties of the films was evaluated via oxidative degradation of gaseous 2-propanol. The initial rate of 2-propanol degradation under UV light irradiation for the films deposited with 30nm TiO2 particles increased with increasing film thickness up to 600nm, and reached a saturated value above this film thickness. Photocatalytic activity for the films with thickness below 600nm was larger when smaller TiO2 particles were deposited onto the substrate, due to the increase in the surface area of the particulate films. Furthermore, saturated values of the photocatalytic activity for thick films were smaller for the films deposited with smaller particles, which is mainly attributed to the change in crystal form of the particles during the grinding treatment.TiO2 particles of various sizes were prepared by grinding in cyclohexanone, and TiO2 particulate films were obtained by depositing these TiO2 particles with various sizes onto a glass or quartz substrate. The effect of the particle size and thickness on the photocatalytic properties of the films was evaluated via oxidative degradation of gaseous 2-propanol. The initial rate of 2-propanol degradation under UV light irradiation for the films deposited with 30 nm TiO2 particles increased with increasing film thickness up to 600 nm, and reached a saturated value above this film thickness. Photocatalytic activity for the films with thickness below 600nm was larger when smaller TiO2 particles were deposited onto the substrate, due to the increase in the surface area of the particulate films. Furthermore, saturated values of the photocatalytic activity for thick films were smaller for the films deposited with smaller particles, which is mainly attributed to the change in crystal form of the particles during the grinding treatment.

Neutron diffraction study of helimagnet (Ba1−xSrx)2Zn2Fe12O22

Neutron diffraction experiments were carried out on a single crystal of (Ba 1- x Sr x ) 2 Zn 2 Fe 12 O 22 , x =0.748, at 77 and 296 K. The turn angle of the helix, φ 0 , is 81.6° at 77 K and 135° at 296 K. The helix consists of large and small ferrimagnetic spin-bunches separated by an angle of φ 0 / 2 in the c -plane. Their magnitudes are 4.32 µ and 0.32 µ, respectively. Here, µ is the magnetic moment per Fe ion: µ= 4.66 µ B at 77 K and µ= 1.86 µ B at 296 K. These results are discussed from a point of view of the super-exchange interaction.

Polarization Analysis of X-Ray Diffraction Peaks from a Hexagonal Ferrite –Anomaly of Forbidden Reflections—-

X-ray polarization analyses were carried out for allowed and forbidden (00 l ) reflections as well as a magnetic scattered satellite peak of a hexagonal ferrite (Ba 1- x Sr x ) 2 Zn 2 Fe 12 O 22 using synchrotron radiation. Polarization mixing was observed in both forbidden reflections and the magnetic scattered satellite peak. Magnitudes of the components of the structure factor tensor for the forbidden reflection are determined.