Masaru Mita

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.

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.

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.

Superconductivity and Magnetic Properties of YBa2(Cu1-xFex)3O7-y

Superconductivity and magnetic properties of YBa 2 (Cu 1- x Fe x ) 3 O 7- y with x =0-0.1 are investigated by the measurements of static magnetic susceptibility, electrical resistance, weight change and lattice parameters. Substitution of Fe atoms for Cu atoms causes orthorhombic to tetragonal phase transition at about x =0.035 and depresses critical temperature T c from 95 K to 32 K at x =0.1. The effective magnetic moment per Fe, about 5.5 µ B below x =0.01 decreases to 3.6 µ B at x =0.1. The removal of oxygen atoms in the specimens of superconducting tetragonal phase with x =0.04 by quenching brings about remarkable expansion of c -axis and decreases T c from 74 K to below 4.2 K. The effective moment per Fe was found to decrease from 4.4 µ B to 3.3 µ B with increase of oxygen deficiency due to quenching. Causes of reduced iron effective moments due to increase of iron concentration and oxygen deficiency are discussed in consideration of superexchange interaction between Fe and Cu spins.

Two-Magnon Ferrimagnetic Resonance Linewidth of Hexagonal Ferrite Zn2Y

The linewidth of resonance absorption of microwave power in a hexagonal ferrite, Zn 2 Y, induced by surface imperfections is discussed on the basis of two-magnon relaxation mechanism. Two maxima of the linewidth observed when direction angle θ H of the applied dc field with respect to the crystallographic c axis is changed are analyzed by a theoretical calculation. It is predicted from the theory that the angular position θ H E corresponding to the maximum at small angle is independent of the size of surface imperfections and θ H B to the other maximum is dependent on the size of surface imperfections. These results well coincide with the experimental results. Some information about an effective exchange constant and a parameter in scattering Hamiltonian are also obtained.

High Power Behavior and Spin-wave Spectrum in a Hexagonal Ferrite with Large Planar Anisotropy

Anisotropy of the absorption saturation of ferromagnetic resonance under a high r f -field was measured in a spherical sample of single crystal Zn 2 Y by the parametric excitation method. The measured absorption consists of three parts: a main mode and two subsidiary absorptions. To analyse the high power behaviors of these absorption peaks, an anisotropic dispersion relation of spin waves is derived from a phenomeno-logical treatment. The first and the second order non-linear behaviors are distinguished clearly in agreement with theory. Details of two subsidiary peaks accompanying with the main mode resonance are explained in terms of the dissipation processes due to the excitation of the spin wave corresponding to the obtained spectrum.

Magnon Analysis of Ferromagnetic Resonance in a Planer Ferrite, Zn2Y

The low power ferromagnetic resonance behavior at room temperature was measured on a magnetically anisotropic material, Zn 2 Y , with the object of studying relaxation processes on the basis of magnon manifold. The line-width of monocrystalline Zn 2 Y under a uniform mode resonance condition exhibits four kinds of maxima with increasing angle θ H of the applied d c field with respect to the crystallographic c axis. The first maximum is at θ H =0° and is small. The second maximum is the largest and extends over the entire region of θ H . The third and fourth maxima are small and attend on the larger angular tail of the second maximum. It may be concluded that the second maximum is due to the two-magnon decay of the uniform mode and the third due to the three-magnon decay of the uniform mode.

Magnetic properties and superconductivity of GdBa2(Cu1−xFex)3O7−y

Abstract In order to investigate magnetic interaction and its effect on superconductivity in GdBa 2 (Cu 1−x Fe x ) 3 O 7−y , critical temperature Tc, lattice parameters, d.c. susceptivility, Gd-ESR and Neel temperature T N are measured. We found tha ESR linewidth δH pp increases but T N decreases from 2.3 K to 2.0 K with increasing x up to 0.19. This indicates that there exists some magnetic interaction between Gd and Fe atoms even in superconducting state.

Helical spin ordering and magnetic constants of (Sr0.8Ba0.2)2Zn2Fe12O22

On Hexagonal ferrite (Sr0.8Ba0.2)2Zn2Fe12O22 with proper‐helix type spin ordering, the difference of Fourier transforms of exchange energy, J(?)−J(0) and J(Q)−J(2W), and uniaxial anisotropy constants, K1 and K2, are determined, where the Q is the propagation vector of helix. Nagamiya’s parameters (Pgq, ξ1 and ξ2 depending on the external magnetic field are defined.The magnetization in the experiment is clearly explained in complete agreement with the theory in terms of ϑ, ξ1 and ξ2. Neutron diffraction pattern changing with field is attempted to analyze by the use of ϑ, ξ1 and ξ2.