Browsing by Author "Manna, Kaustuv"
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- ItemEvidence for a percolative Mott insulator-metal transition in doped Sr2IrO4(College Park, MD : APS, 2021) Sun, Zhixiang; Guevara, Jose M.; Sykora, Steffen; Pärschke, Ekaterina M.; Manna, Kaustuv; Maljuk, Andrey; Wurmehl, Sabine; van den Brink, Jeroen; Büchner, Bernd; Hess, ChristianDespite many efforts to rationalize the strongly correlated electronic ground states in doped Mott insulators, the nature of the doping-induced insulator-to-metal transition is still a subject under intensive investigation. Here, we probe the nanoscale electronic structure of the Mott insulator Sr2IrO4−δ with low-temperature scanning tunneling microscopy and find an enhanced local density of states (LDOS) inside the Mott gap at the location of individual defects which we interpret as defects at apical oxygen sites. A chiral behavior in the topography for those defects has been observed. We also visualize the local enhanced conductance arising from the overlapping of defect states which induces finite LDOS inside of the Mott gap. By combining these findings with the typical spatial extension of isolated defects of about 2 nm, our results indicate that the insulator-to-metal transition in Sr2IrO4−δ could be percolative in nature.
- ItemLaser-Assisted Floating Zone Growth of BaFe2S3 Large-Sized Ferromagnetic-Impurity-Free Single Crystals(Basel : MDPI, 2021) Amigó, Maria Lourdes; Maljuk, Andrey; Manna, Kaustuv; Stahl, Quirin; Felser, Claudia; Hess, Christian; Wolter, Anja U.B.; Geck, Jochen; Seiro, Silvia; Büchner, BerndThe quasi-one-dimensional antiferromagnetic insulator BaFe2S3 becomes superconducting under a hydrostatic pressure of ∼10 GPa. Single crystals of this compound are usually obtained by melting and further slow cooling of BaS or Ba, Fe, and S, and are small and needle-shaped (few mm long and 50–200 μm wide). A notable sample dependence on the antiferromagnetic transition temperature, transport behavior, and presence of superconductivity has been reported. In this work, we introduce a novel approach for the growth of high-quality single crystals of BaFe2S3 based on a laser-assisted floating zone method that yields large samples free of ferromagnetic impurities. We present the characterization of these crystals and the comparison with samples obtained using the procedure reported in the literature.
- ItemA New Highly Anisotropic Rh-Based Heusler Compound for Magnetic Recording(Weinheim : Wiley-VCH, 2020) He, Yangkun; Fecher, Gerhard H.; Fu, Chenguang; Pan, Yu; Manna, Kaustuv; Kroder, Johannes; Jha, Ajay; Wang, Xiao; Hu, Zhiwei; Agrestini, Stefano; Herrero-Martín, Javier; Valvidares, Manuel; Skourski, Yurii; Schnelle, Walter; Stamenov, Plamen; Borrmann, Horst; Tjeng, Liu Hao; Schaefer, Rudolf; Parkin, Stuart S.P.; Coey, John Michael D.; Felser, ClaudiaThe development of high-density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat-assisted magnetic recording was developed, rapidly heating the media to the Curie temperature Tc before writing, followed by rapid cooling. Requirements are a suitable Tc, coupled with anisotropic thermal conductivity and hard magnetic properties. Here, Rh2CoSb is introduced as a new hard magnet with potential for thin-film magnetic recording. A magnetocrystalline anisotropy of 3.6 MJ m−3 is combined with a saturation magnetization of μ0Ms = 0.52 T at 2 K (2.2 MJ m−3 and 0.44 T at room temperature). The magnetic hardness parameter of 3.7 at room temperature is the highest observed for any rare-earth-free hard magnet. The anisotropy is related to an unquenched orbital moment of 0.42 μB on Co, which is hybridized with neighboring Rh atoms with a large spin–orbit interaction. Moreover, the pronounced temperature dependence of the anisotropy that follows from its Tc of 450 K, together with a thermal conductivity of 20 W m−1 K−1, make Rh2CoSb a candidate for the development of heat-assisted writing with a recording density in excess of 10 Tb in.−2. © 2020 The Authors. Published by Wiley-VCH GmbH