Electronic structure and magnetism in doped semiconducting half-Heusler compounds

We have studied in details the electronic structure and magnetism in M (Mn and Cr) doped semiconducting half-Heusler compounds FeVSb, CoTiSb and NiTiSn (XM$_{x}$Y$_{1-x}$Z) in a wide concentration range using local-spin density functional method in the framework of tight-binding linearized muffin tin orbital method(TB-LMTO) and supercell approach. Our calculations indicate that some of these compounds are not only ferromagnetic but also half-metallic and may be useful for spintronics applications. The electronic structure of the doped systems is analyzed with the aid of a simple model where we have considered the interaction between the dopant transition metal (M) and the valence band X-Z hybrid. We have shown that the strong X-d - M-d interaction places the M-d states close to the Fermi level with the M-t$_{2g}$ states lying higher in energy in comparison to the M-e$_{g}$ states. Depending on the number of available d-electrons, ferromagnetism is realized provided the d-manifold is partially occupied. The tendencies toward ferromagnetic(FM) or antiferromagnetic(AFM) behavior are discussed within Anderson-Hasegawa models of super-exchange and double-exchange. In our calculations for Mn doped NiTiSn, the strong preference for FM over AFM ordering suggests a possible high Curie temperature for these systems.Comment: 14 pages, 6 figure

Time for pulse traversal through slabs of dispersive and negative (ϵ\epsilon, μ\mu) materials

The traversal times for an electromagnetic pulse traversing a slab of dispersive and dissipative material with negative dielectric permittivity ($\epsilon$) and magnetic permeability ($\mu$) have been calculated by using the average flow of electromagnetic energy in the medium. The effects of bandwidth of the pulse and dissipation in the medium have been investigated. While both large bandwidth and large dissipation have similar effects in smoothening out the resonant features that appear due to Fabry-P\'{e}rot resonances, large dissipation can result in very small or even negative traversal times near the resonant frequencies. We have also investigated the traversal times and Wigner delay times for obliquely incident pulses and evanescent pulses. The coupling to slab plasmon polariton modes in frequency ranges with negative $\epsilon$ or $\mu$ is shown to result in large traversal times at the resonant conditions. We also find that the group velocity mainly contributes to the delay times for pulse propagating across a slab with n=-1. We have checked that the traversal times are positive and subluminal for pulses with sufficiently large bandwidths.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.

EKSPERIMENTASI MEDIA PEMBELAJARAN BERBASIS RPG (ROLE PLAYING GAME) DENGAN MENGGUNAKAN METODE INSTRUCTIONAL GAMES DAN TEAMS GAMES TOURNAMENTS PADA PEMBELAJARAN IPA SISWA KELAS VII SMPN 2 TUNTANG KABUPATEN SEMARANG

Penelitian ini bertujuan untuk mengetahui ada tidaknya perbedaan kemampuan kognitif antara siswa yang diajar dengan penggunaan media pembelajaran game edukasi berbasis Role Playing Game (RPG) dengan metode Instructional Games dan Teams Games Tournaments materi Kalor dan Perpindahannya pada siswa SMP kelas VII. Metode penelitian yang digunakan adalah metode eksperiment. Penelitian ini dilaksanakan di SMP N 2 Tuntang. Populasi dalam penelitian ini adalah semua siswa kelas VII SMP N 2 Tuntang Tahun Ajaran 2015/2016 yang terdiri dari 7 kelas. Teknik pengambilan sampel yang digunakan adalah cluster random sampling. Sampel yang digunakan dalam penelitian ini sebanyak 2 kelas, yaitu kelas VIIA dan VIIB, yang masing-masing terdiri dari 32 siswa. Teknik pengambilan data dilakukan dengan teknik dokumentasi dan tes. Teknik dokumentasi digunakan untuk memperoleh data keadaan awal siswa yang diambil dari nilai Fisika hasil tes tengah semester I, sedangkan teknik tes untuk memperoleh data kemampuan kognitif IPA siswa pada pokok bahasan Kalor dan Perpindahannya. Teknik analisis data yang digunakan dalam penelitian ini adalah dengan uji t-test satu ekor. Dari analisis data diperoleh hasil terdapat perbedaan rerata kemampuan kognitif antara penggunaan media pembelajaran game RPG(Roleplaying Game) pada metode Instructional Games dan Teams Games Tournaments pada materi Kalor dan Perpindahannya siswa kelas VII SMPN 2 Tuntang. Hal ini ditunjukkan oleh nilai signifikansi 0,002 (<0,05). Kata kunci: Game edukasi, Instructional Games, Teams Games Tournaments, Kalor dan Perpindahannya, RP

Electronic structure of half-metallic magnets

We have analyzed the electronic structure of half-metallic magnets based on first principles electronic structure calculations of a series of semi-Heusler alloys. The characteristic feature of the electronic structure of semi-Heusler systems is a d-d gap in the density of states lying at/close to the Fermi level depending on the number of valence electrons. We have employed various indicators of chemical bonding to understand the origin of the gap in these systems, which is crucial for their half-metallic property. The density of states of other half-metallic magnets also supports a gap and it is a generic feature of these systems. We have discussed in some details the origin of magnetism, in particular, how the presence of the gap is crucial to stabilize half-metallic ferro and ferri magnetism in these systems. Finally, we have studied the role of magnetic impurities in semiconducting semi-Heusler systems. We show with the aid of model supercell calculations that these systems are not only ferromagnetic but also half-metallic with possibly high Curie temperature.Comment: 7 pages, 6 figure

Sintesis dan Karakterisasi Serbuk SiO2 dengan Variasi PH dan Molaritas Berbahan Dasar Pasir Bancar, Tuban

Dalam Tugas Akhir ini telah disintesis serbuk silika dengan variasi konsentrasi larutan Sodium Hidroxyde (NaOH) dan pH akhir kopresipitasi. Bahan dasar yang digunakan adalah pasir silika dari pantai Bancar, Tuban, Jawa Timur, Indonesia yang sudah dimurnikan menggunakan metode leaching, NaOH, HCl, dan aquades. Karakterisasi struktur SiO2 menggunakan X-Ray Diffractometer (XRD) dengan fasilitas software High Score Plus (HSP). Berdasarkan hasil analisis, ditunjukkan bahwa SiO2 yang terbentuk amorf kemurnian Si pada serbuk silika meningkat dibandingkan dengan pasir alam

DNase I nick translation in situ on meiotic chromosomes of the mouse, Mus musculus

DNase-I-sensitive sites have been located on the meiotic chromosomes of the mouse, Mus musculus, by the in situ DNase I nick-translation method. We find that: (1) of all the cell types studied, pachytene nuclei are the most sensitive to DNase I; (2) in diplotene the nicks occur preferentially in the vicinity of chiasmata; (3) the sex chromosomes are also sensitive to the enzyme despite their transcriptional quiescence; and (4) in the sex bivalent the nicks are primarily observed in the putative region of recombination. We conclude that, in addition to discriminating between the transcriptionally active and inactive states of chromatin, DNase I identifies recombination-specific chromatin changes in meiotic prophase