Magnetische Anisotropie und Quantenphasenübergang in CeTi_(1-x)V_(x)Ge_(3)

In der vorliegenden Arbeit habe ich ausgehend von der Verbindung CeTiGe_(3) die Substitutionsreihe CeTi_(1-x)V_(x)Ge_(3) untersucht. Hierbei wurden sowohl Polykristalle als auch Einkristalle hergestellt. Bei CeTiGe_(3) handelt es sich um einen stark anisotropen Ferromagneten mit T_(C) = 14.3 K. Wird ein Teil des Ti durch V ersetzt, fällt T_(C). Damit ist CeTi_(1-x)V_(x)Ge_(3) ein möglicher Kandidat für einen ferromagnetischen QKP

Magnetische Anisotropie und Quantenphasenübergang in CeTi_(1-x)V_(x)Ge_(3)

In the present work the substitution series of CeTi_(1-x)V_(x)Ge_(3) is examined. Within the framework of this thesis, several polycrystals and singlecrystals have been made. CeTiGe_(3) is a strong anisotropic ferromagnet with a T_(C) = 14.3 K. When Ti is partially substituted by V, T_(C) is reduced. So CeTi_(1-x)V_(x)Ge_(3) is a potential candidate for a ferromagnetic QCP

Anomalous Hall effect in the noncollinear antiferromagnet Mn5Si3

Metallic antiferromagnets with noncollinear orientation of magnetic moments provide a playground for investigating spin-dependent transport properties by analysis of the anomalous Hall effect. The intermetallic compound Mn5Si3 is an intinerant antiferromagnet with collinear and noncollinear magnetic structures due to Mn atoms on two inequivalent lattice sites. Here, magnetotransport measurements on polycrstalline thin films and a single crystal are reported. In all samples, an additional contribution to the anomalous Hall effect attributed to the noncollinear arrangment of magnetic moments is observed. Furthermore, an additional magnetic phase between the noncollinear and collinear regimes above a metamagnetic transition is resolved in the single crystal by the anomalous Hall effect

CePdAl - a Kondo lattice with partial frustration

Magnetic frustration, which is well-defined in insulating systems with localized magnetic moments, yields exotic ground states like spin ices, spin glasses, or spin liquids. In metals magnetic frustration is less well defined because of the incipient delocalization of magnetic moments by the interaction with conduction electrons, viz., the Kondo effect. Hence, the Kondo effect and magnetic frustration are antithetic phenomena. Here we present experimental data of electrical resistivity, magnetization, specific heat and neutron diffraction on CePdAl, which is one of the rare examples of a geometrically frustrated Kondo lattice, demonstrating that the combination of Kondo effect and magnetic frustration leads to an unusual ground state.Comment: 8 pages, 6 figure

Switching of a large anomalous Hall effect between metamagnetic phases of a non-collinear antiferromagnet

The anomalous Hall effect (AHE), which in long-range ordered ferromagnets appears as a voltage transverse to the current and usually is proportional to the magnetization, often is believed to be of negligible size in antiferromagnets due to their low uniform magnetization. However, recent experiments and theory have demonstrated that certain antiferromagnets with a non-collinear arrangement of magnetic moments exhibit a sizeable spontaneous AHE at zero field due to a non-vanishing Berry curvature arising from the quantum mechanical phase of the electron’s wave functions. Here we show that antiferromagnetic Mn5Si3 single crystals exibit a large AHE which is strongly anisotropic and shows multiple transitions with sign changes at different magnetic fields due to field-induced rearrangements of the magnetic structure despite only tiny variations of the total magnetization. The presence of multiple non-collinear magnetic phases offers the unique possiblity to explore the details of the AHE and the sensitivity of the Hall effect on the details of the magnetic texture

Switching of a large anomalous Hall effect between metamagnetic phases of a non-collinear antiferromagnet

The anomalous Hall effect (AHE), which in long-range ordered ferromagnets appears as a voltage transverse to the current and usually is proportional to the magnetization, often is believed to be of negligible size in antiferromagnets due to their low uniform magnetization. However, recent experiments and theory have demonstrated that certain antiferromagnets with a non-collinear arrangement of magnetic moments exhibit a sizeable spontaneous AHE at zero field due to a non-vanishing Berry curvature arising from the quantum mechanical phase of the electron’s wave functions. Here we show that antiferromagnetic Mn5Si3 single crystals exibit a large AHE which is strongly anisotropic and shows multiple transitions with sign changes at different magnetic fields due to field-induced rearrangements of the magnetic structure despite only tiny variations of the total magnetization. The presence of multiple non-collinear magnetic phases offers the unique possiblity to explore the details of the AHE and the sensitivity of the Hall effect on the details of the magnetic texture

Strategien für die Melissezüchtung (Melissa officinalis)

Es wurden 120 Melisseherkünfte in Feldversuchen evaluiert. In diesem Material wurde die Variabilität für Winterhärte, Gehalt und Zsammensetzung des ätherischen Öls, Rosmarinsäuregehalt und eingeschränkt Blattertrag beschrieben. Die beschriebene Variabilität ermöglichte die Entwicklung homozygoter Linien mit hoher Eigenleistung für die genannten Zuchtziele bis zur I4-Inzuchtgeneration. Die Kreuzung definierter Linien ermöglichte die Schaffung eines neuen Genpools als Ausgansmaterial für die Entwicklung weiterer aussichtsreicher Linien. Stichwörter: Melisse, Melissa officinalis L., Winterhärte, ätherisches Öl, Rosmarinsäure, ZüchtungBreeding strategies for lemon balm (Melissa officinalis)Evaluation was carried out in field experiments with 120 accessions of lemon balm. This material was characterized for winter hardiness, amount and composition of essential oil, amount of rosmarinic acid and, to a certain degree, for yield of leaves. The characterized variability opened the possibility to develop homozygous lines for the mentioned breeding goals up to inbreed generation I4. Crossing of defined lines created a new gene pool of basic material for development of new promising lines. Keywords: lemon balm, Melissa officinalis L., winter hardiness, essential oil, rosmarinic acid, breedin