The Curie Temperature of Magnetically Inhomogeneous Amorphous Fe-Zr-B Alloys

The Curie temperature of amorphous Fe-Zr-B alloys was determined by both the Mossbauer thermal scan and a modified Arrott-plots methods. For amorphous Fe_(Zr_B_x)_8 alloys, the two methods make a difference between the values of T_c. On the other hand, for amorphous Fe_(Zr_B_x)_ alloys, the results of the two methods agree with each other within limits of the experimental error. It is found that the magnetic inhomogeneity often causes the difficulty in the determination of T_c and the measurement of T_c necessitating external fields is accompanied by a serious problem in the case of the magnetically inhomogeneous materials. Since no external field is necessary, the Mossbauer thermal scan method is very useful for determining T_c of amorphous alloys containing Fe atoms

Hybrid inorganic–organic superlattice structures with atomic layer deposition/molecular layer deposition

A combination of the atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques is successfully employed to fabricate thin films incorporating superlattice structures that consist of single layers of organic molecules between thicker layers of ZnO. Diethyl zinc and water are used as precursors for the deposition of ZnO by ALD, while three different organic precursors are investigated for the MLD part: hydroquinone, 4-aminophenol and 4,4′-oxydianiline. The successful superlattice formation with all the organic precursors is verified through x-ray reflectivity studies. The effects of the interspersed organic layers/superlattice structure on the electrical and thermoelectric properties of ZnO are investigated through resistivity and Seebeck coefficient measurements at room temperature. The results suggest an increase in carrier concentration for small concentrations of organic layers, while higher concentrations seem to lead to rather large reductions in carrier concentration.Peer reviewe

Competition between intragranular and intergranular tunneling magnetoresistance in polycrystalline Sr2FeMoO6

Polycrystalline Sr2FeMoO6 (SFMO) samples with various grain sizes and densities of Fe/Mo disorder defects were synthesized from sol-gel-derived precursors by means of a sample-encapsulation technique. The samples with perfect Fe/Mo ordering exhibited metallic transport behavior and a large magnetoresistance (MR) effect, whereas the samples with a high-disorder density and small grain size showed a metal-insulator transition and lower MR values. It is suggested that a competition between intragranular and intergranular tunneling MR effects exists in the SFMO system. To confirm this competition, homocomposite samples consisting of two or three single-phase SFMO components with different grain sizes were designed. Large enhancement in low-field magnetoresistance (LFMR) was observed in the homocomposites, which could be attributed to the enhanced intergranular effect. It is thus concluded that the intergranular effect is more important to the LFMR than the intragranular effect.Peer reviewe

Atomic layer deposition of Al-doped ZnO thin films

Atomic layer deposition has been used to fabricate thin films of aluminum-doped ZnO by depositing interspersed layers of ZnO and Al 2O3 on borosilicate glass substrates. The growth characteristics of the films have been investigated through x-ray diffraction, x-ray reflection, and x-ray fluorescence measurements, and the efficacy of the Al doping has been evaluated through optical reflectivity and Seebeck coefficient measurements. The Al doping is found to affect the carrier density of ZnO up to a nominal Al dopant content of 5 at. %. At nominal Al doping levels of 10 at. % and higher, the structure of the films is found to be strongly affected by the Al 2O3 phase and no further carrier doping of ZnO is observed.Peer reviewe

Structural transformation and magnetic competition in Yb(Mn1-xFex)O3

Structural and magnetic properties of the Yb(Mn1−xFex)O3 (0⩽x⩽1) system have been systematically investigated. Initial samples were prepared via a sol-gel method. A pure hexagonal phase was only obtained for samples with x⩽0.5. With high-pressure annealing, a pure orthorhombic perovskite phase was achieved for all the compositions. The Fe57 Mössbauer spectrum for x=0.5 shows that only Fe3+ ions exist in the system; there was no evidence of chemical inhomogeneities. With increasing x, the Néel temperature TN increases for both hexagonal and orthorhombic phases. The orthorhombic Yb(Mn0.5Fe0.5)O3 shows an interesting weak ferromagnetic state in the temperature range of 239–298K, the ferromagnetism disappearing abruptly on cooling below Tt=239K. The transition at Tt appears to be a reorientation of the spin axis of a type-G antiferromagnetic order from the orthorhombic a axis to the b axis in the (010) plane.Peer reviewe

Characterization of magnetic properties of Sr2CuWO6 and Sr2CuMoO6

In this work we examine the low-temperature magnetic properties of the two double-perovskite compounds Sr2CuWO6 and Sr2CuMoO6 using magnetic susceptibility, muon spin rotation and relaxation, and neutron powder diffraction measurements. Additionally, the most relevant spin exchange interaction constants are derived from ab initio electronic structure calculations, aided by x-ray absorption spectroscopy. The compounds exhibit quasi-two-dimensional magnetic properties, with broad maxima at Tmax = 83 and 95 K for Sr2CuWO6 and Sr2CuMoO6, respectively. However, three-dimensional long-range order takes place below TN = 24(1) and 28(2) K for Sr2CuWO6 and Sr2CuMoO6, respectively. Our results show that the low-dimensional magnetic correlations are mainly due to the significant next-nearest-neighbor interactions in the ab plane of the double-perovskite structure, whereas three-dimensional long-range magnetic order is caused by weaker next-nearest-neighbor interactions along the c axis. Next-nearest-neighbor interactions are also slightly frustrated by weaker nearest-neighbor interactions within the ab plane. Based on these results we predict the low-temperature magnetic structure in these compounds to be type-II antiferromagnetic order of the double-perovskite lattice.Peer reviewe

Magnetic Properties of Ternary DyMn_2X_2 Compounds (X=Si and Ge)(Magnetism)

Magnetic properties of DyMn_2Si_2, DyMn_2Ge_2 and their mixed compounds DyMn_2(Si_Ge_x)_2, which display a variety of interesting magnetic behaviors originating in competing magnetic interactions and anisotropy, have been investigated systematically by magnetization mesurements ^Dy Mossbauer spectroscopy and neutron diffraction experiments. This report presents a review of the results mainly obtained by the magnetization measurements

VLBI Detections of Parsec-Scale Nonthermal Jets in Radio-Loud Broad Absorption Line Quasars

We conducted radio detection observations at 8.4 GHz for 22 radio-loud broad absorption line (BAL) quasars, selected from the Sloan Digital Sky Survey (SDSS) Third Data Release, by a very-long-baseline interferometry (VLBI) technique. The VLBI instrument we used was developed by the Optically ConnecTed Array for VLBI Exploration project (OCTAVE), which is operated as a subarray of the Japanese VLBI Network (JVN). We aimed at selecting BAL quasars with nonthermal jets suitable for measuring their orientation angles and ages by subsequent detailed VLBI imaging studies to evaluate two controversial issues of whether BAL quasars are viewed nearly edge-on, and of whether BAL quasars are in a short-lived evolutionary phase of quasar population. We detected 20 out of 22 sources using the OCTAVE baselines, implying brightness temperatures greater than 10^5 K, which presumably come from nonthermal jets. Hence, BAL outflows and nonthermal jets can be generated simultaneously in these central engines. We also found four inverted-spectrum sources, which are interpreted as Doppler-beamed, pole-on-viewed relativistic jet sources or young radio sources: single edge-on geometry cannot describe all BAL quasars. We discuss the implications of the OCTAVE observations for investigations for the orientation and evolutionary stage of BAL quasars.Comment: 10 pages, no figure, 3 tables, accepted for publication in PAS