[Show abstract][Hide abstract] ABSTRACT: The influence of coprecipitated barium ferrite (BaF) on the magnetic and mechanical properties of natural rubber–ferrite composites (RFCs) has been studied. Unusual characteristics of the BaF particles were revealed by a scanning electron microscope. The results show that the saturation magnetisation increases with increasing the ferrite content even for the considerably high BaF loading samples, whereas the coercivity is almost unchanged. The present RFCs recorded relatively low density 1·95 g cm?3 with high stored energy 1·26 MGOe at the maximum BaF loading of 220 phr. Both of the tensile strength and the elongation at break decrease with increasing BaF content. Evaluation of the swelling ratio was carried out to have an insight into the change in the mechanical properties of the RFCs at high BaF loading.
Plastics Rubber and Composites 09/2009; 38(7):297-301. · 0.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Epitaxially-grown BFZO thin films with various amounts of Zr content were successfully fabricated on (0 0 1) Nb doped-SrTiO3 substrates using the pulsed laser-beam deposition technique. The Zr substitution caused a substantial decrease in the leakage current density of the films. According to the analysis of the origin of the leakage current behaviour, the samples with x values smaller than 0.7 were found to show Poole-Frenkel (PF) type leakage properties at high electric fields, and the samples with larger x values exhibited Schottky-type behaviour. Regarding the x = 0.7 sample, it was considered that the currents of the PF- and Schottky-type behaviours determined the leakage properties of the samples, resulting in an intermediate state. The observed mechanism change is discussed in conjunction with the electronic band structure change, which may be caused by the increase in the relative amount of Zr ions, as well as by the change in the valence state of the Fe ions associated with Zr substitution.
Journal of Physics D Applied Physics 10/2007; 40(19):6066-6070. · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The structural, dielectric and magnetic properties of single crystalline Ba1−xBixFe0.3Zr0.7O3−δ (x=0.0–0.29) thin films have been studied. The pseudotetragonal epitaxial thin films were obtained by pulsed laser-beam deposition (PLD) on (001) SrTiO3 (STO) single-crystal substrates. The Bi substitution for the Ba ions up to an extent of x=0.18 caused a slight improvement in the leakage current properties, as well as an enhancement of the apparent dielectric constant. The saturation magnetization of the films was significantly decreased following Bi substitution. These changes were thought to be related to the increase in oxygen deficiencies in the films. The effect of the Bi substitution on the dielectric and magnetic properties was analyzed in conjunction with the change in valence value of the Fe ions.
Journal of Physics and Chemistry of Solids 08/2007; 68(8):1515-1521. · 1.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The structural, magnetic and electric properties of the Ba(Co1-xMnx)O3 oxides with x=0.00-0.25 were investigated. The samples with x=0.15,0.20, and 0.25 were found to be composed of the almost single phase of the 10H-type perovskite related crystal structure. The electric resistivity of the samples was significantly changed at around 50 K, and they had a dielectric characteristic below that temperature. In addition, the samples also showed the ferromagnetic behavior below. We will discuss the origin of the magnetism observed in the samples, in conjunction with the valence state of the transition metal ions.
IEEE Transactions on Magnetics 10/2005; 41:3496-3498. · 1.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: [PtMnSb15nm/Si10nm]*7 ferromagnet/semiconductor multilayered films were synthesized by solid-state reaction of [(Pt0.69nm/Mn0.44nm/Sb0.37nm)*10/Si10 nm]*7 elemental multilayers. Two different thermal treatments, i.e. the post-annealing and the simultaneous annealing (substrate heating during deposition) were employed to control the interdiffusion and the compound phase formation. Structural characterizations revealed that these films were composed of the PtMnSb, amorphous Si and interdiffusion layers. Moreover, the films produced by simultaneous annealing had the relatively thick interdiffusion layers rather than the films by the post-annealing. According to the magnetization measurements, we obtained the larger value of saturation magnetization for the simultaneous annealed film rather than that for the post-annealed one. We will discuss the structural and magnetic properties of the samples in conjunction with the extent of the interdiffusion as well as the crystallinity of the magnetic compound.
[Show abstract][Hide abstract] ABSTRACT: The effect of Zr substitution on the magnetic and dielectric properties of the BaFe1−xZrxO3−δ epitaxial grown films was investigated. The Zr substitution significantly improved the dielectric properties of the films. In addition to this, the saturation magnetization for the x = 0.7 sample was determined to be 0.98 μB/Fen+, in contrast to 0.09 μB/Fen+ for the x = 0.5 sample. This implies that the magnetic ordering for the x = 0.7 sample has been greatly enhanced, possibly due to the ferromagnetic spin alignment of Fe ions. We will discuss the magnetization behavior in conjunction with the valence state of the Fe ions in the samples.
Journal of Applied Physics 05/2005; 97(10). · 2.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A novel synthesis method of Ba–Ga–Ge type-I clathrates is proposed. It enables us to use BaCO3 for one of the starting materials in place of Ba metals, which should be the greatest advantage of handling the materials, from the viewpoint of possible industrial application in the near future. By using this method, we have successfully produced the Ba8Ga16Ge30 compounds from the starting materials BaCO3, Ge and Ga. The synthesis reaction should occur simultaneously with the reduction reaction of BaCO3, which requires rather high reaction temperature beyond 1573K. However, the resulting reactant still contains additional phases, such as Ge and Ba–Ga–O phases. The samples exhibited a positive value of the Seebeck coefficient from room temperature to 973K, in spite of the fact that the Ba–Ga–Ge type-I clathrates were usually reported to show negative Seebeck coefficient.
Journal of Alloys and Compounds 04/2005; 391(1):284-287. · 2.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: High coercivity barium ferrite (BaFe12O19) powders have been prepared by a coprecipitation method. After removing fine powders, they were incorporated into a natural rubber matrix with different loading levels up to 120 phr (part per hundred rubber). The variations in characteristics of rubber–ferrite composites (RFCs) were evaluated as a function of ferrite loading. The results showed that the coercivity is improved and the saturation magnetization is linearly dependent on the mass fraction of the filler, while the tensile strength, strain at break and modules are highly influenced by the size, shape and volume fraction of ferrite particles. The present RFCs showed a typical characteristic of low density (2.2 g/cm3), high stored energy (BHmax = 1.18 MG Oe) and flexibility (resilience = 0.844) at 120 phr of ferrite, which are relatively high when compared to previous works.
Journal of Materials Processing Technology 03/2005; · 2.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on the synthesis of the magnetoelectric BaFe1−xZrxO3−δ (x = 0.5 and 0.7) single-crystalline films whose magnetic and leakage properties have been greatly improved. The films were found to be excellent insulators, up to the leakage current density of about 1.1×10−5 A/cm2 at the bias electric field of 150 kV/cm for the x = 0.7 sample. This is much less than 10−2 of that for the BaFeO3−δ single-crystalline film, which means that the leakage current properties have been distinctly improved by zirconium substitution. As for the magnetic properties, the hysteresis loops measured at 5 K for the x = 0.7 samples apparently show huge saturation magnetization of 0.98 μB/Fe ion, in contrast to 0.09 μB/Fe ion for the x = 0.5 sample. This implies that the magnetic ordering for the x = 0.7 sample has been greatly enhanced, possibly due to the ferromagnetic spin alignment of Fe ions.
[Show abstract][Hide abstract] ABSTRACT: The structural, magnetic and electric properties of calcinated BaCo1-xMnxO3 (x = 0.0-0.25) oxides are investigated by X-ray diffraction (XRD) and transmission electron microscopy, SQUID measurements, and conventional four-probe technique, respectively. XRD data show a 2H-type perovskite at x = 0.0, 10H-type crystal structure at x = 0.15, and mixed phases (2H- and 10H-types) at x = 0.05 and 0.10. The magnetisation-temperature curves reveal the antiferromagnetic phase of the 2H single phase and ferromagnetic behavior (brought by the observed hysteresis and remanent magnetization) at 5 K of the 10H-type structure. A transition from ferromagnetic to paramagnetic state is also observed with a transition temperature of around 47 K. Around this temperature region, specifically at 50 K, a semiconductor-insulator transition is found with a dielectric constant ε = 1.13. These results suggest that the 10H-type structure around the obtained transition temperature is a possible candidate for device applications of ferromagnetic oxides with dielectric properties.
[Show abstract][Hide abstract] ABSTRACT: BaFeO3 (BFO) epitaxial thin films on  SrTiO3 substrates have been successfully produced by pulsed laser beam deposition. The epitaxially grown BFO was found to have tetragonal crystal structure with some amount of oxygen deficiencies. The magnetic susceptibilities of the samples strongly depended on the (hkl) directions of BFO varied in accordance with the crystalline directions, i.e., χ(100). The magnetic spin structure of the epitaxially grown BFO was speculated to be conventional antiferromagnetic. The remanent magnetization of the samples was found to depend on the amount of oxygen deficiencies significantly. This implies that the 180° superexchange interaction of Fe4+-O2--Fe4+ may possibly produce some kinds of ferromagnetic ordering.
IEEE Transactions on Magnetics 01/2004; 40(4):2736-2738. · 1.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The growth of single crystalline oxides on silicon substrates still remains to be a significant technological subject, since the fruitful achievements can be expected for various silicon device technologies. We have ever examined the possibility of BaZrO3 crystallization at low temperature and at low oxygen partial pressure, by a pulsed laser beam deposition technique. We confirmed that the BaZrO3 films on SrTiO3 (001) substrate could be epitaxially grown at the temperature as low as 500°C, and that the excellent crystallinity of BaZrO3 can be obtained in the film grown at the low oxygen partial pressure, such as 2.0×10−8Torr. However of this, the epitaxially grown of BaZrO3 thin films on Si (001) have not been obtained even at such a low oxygen partial pressure during deposition. This is considered to be due to the formation of the interfacial layer, which is amorphous SiO2 or crystallized SiC depending upon the substrate temperature.
Journal of Crystal Growth 08/2002; 243(1):164-169. · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have proposed that solid-state reaction (SSR) of compositionally modulated thin multilayered films, can be one of the profitable structural control techniques for synthesizing novel nano-structured thin film materials. This is because the SSR process should not only be dominated by total composition of multilayered films, but also by local composition at the interfaces of the multilayers, through the nucleation and growth process of reacted compounds. In this paper, we discuss a phase prediction method by SSR of multilayered films based on the modified effective heat of formation rule. In addition, some experimental results on the fabrication process of nano-structured films by the SSR technique are also described.
Journal of Crystal Growth 04/2002; 237:1946-1950. · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Antimony-doped MnPt3 thin films have been successfully fabricated by solid-state reaction of thin multilayered Mn/Sb/Pt films. It was found that the (100) preferential orientation of the MnPt3 phase was developed with increasing antimony content. In addition to this, an anomalous crystalline growth with (100) oriented grains was observed, which resulted in a wide distribution of the grain size of the annealed samples. This behavior is considered to be secondary grain growth, which is usually caused by a surface free energy minimization rule. However, the (100) planes of MnPt3 do not have the lowest surface free energy. We discuss the mechanism of this anomalous grain growth from the view-point of strain energy minimization, in conjunction with the anisotropy in the strain energy density for each crystallographic plane of MnPt3.
Journal of Alloys and Compounds 07/2001; 325(1):160-166. · 2.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have successfully produced LaCoO3 thin films by ion-beam sputtering and subsequent heat treatment. The compacts of La2O3 and CoO powder mixture were used for the targets. The films were mainly composed of the LaCoO3 phase, with a very small amount of an unidentified second phase. The resistivity at room temperature for the annealed 50 at.% La sample was determined to be 51 Ω m, whereas at high temperature, the resistivity was found to be same order of that for bulk LaCoO3, that is, comparable to the resistivity for metals. The possibility of a metal–insulator transition is described.
Thin Solid Films 06/2001; 388(1):183-188. · 1.87 Impact Factor