Berezinskii-Kosterlitz-Thouless Type Scenario in Molecular Spin Liquid AACr2_2O4_4

The spin relaxation in chromium spinel oxides $A$Cr$_{2}$O$_{4}$ ($A=$ Mg, Zn, Cd) is investigated in the paramagnetic regime by electron spin resonance (ESR). The temperature dependence of the ESR linewidth indicates an unconventional spin-relaxation behavior, similar to spin-spin relaxation in the two-dimensional (2D) chromium-oxide triangular lattice antiferromagnets. The data can be described in terms of a generalized Berezinskii-Kosterlitz-Thouless (BKT) type scenario for 2D systems with additional internal symmetries. Based on the characteristic exponents obtained from the evaluation of the ESR linewidth, short-range order with a hidden internal symmetry is suggested.Comment: 7 pages, 4 figure

Role of alkaline metal in the rare-earth triangular antiferromagnet KYbO2_2

We report crystal structure and magnetic behavior of the triangular antiferromagnet KYbO$_2$, the A-site substituted version of the quantum spin liquid candidate NaYbO$_2$. The replacement of Na by K introduces an anisotropic tensile strain with 1.6% in-plane and 12.1% out-of-plane lattice expansion. Compared to NaYbO$_2$, both Curie-Weiss temperature and saturation field are reduced by about 20% as the result of the increased Yb--O--Yb angles, whereas the $g$-tensor of Yb$^{3+}$ becomes isotropic with $g=3.08(3)$. Field-dependent magnetization shows the plateau at 1/2 of the saturated value and suggests the formation of the up-up-up-down field-induced order in the triangular AYbO$_2$ oxides (A = alkali metal), in contrast to the isostructural selenides that exhibit the 1/3 plateau and the up-up-down field-induced order

Electron Spin Resonance in Frustrated Two- and Three-Dimensional Chromium Magnets

The goal of the present work is the experimental investigation of spin correlations and corresponding magnetic properties in two- and three-dimensional Cr3+ based oxides, and chalcogenides by means of electron spin resonance spectroscopy. Due to only partially filled electronic 3d3 shells, the Cr3+ ions exhibit an electron spin S = 3/2 and the physics of these compounds is characterized by the exchange interaction between the chromium spins dependent on lattice geometry and dimensionality.Die Doktorarbeit befasst sich mit dem Thema "Elektronenspinresonanz in frustrierten zwei- und dreidimensionalen Chrom-Magneten". Die untersuchten Systeme haben interessante magnetische bzw. dielektrische Eigenschaften. Als Messmethode dient die Elektronenspinresonanz (ESR), die direkt an den magnetischen Momenten misst und somit eine mikroskopische Sonde für die lokalen elektronischen Eigenschaften und Wechselwirkungen darstellt. Die Untersuchungen zeigen, wie sich mit Hilfe der ESR magnetische Wirbel in frustrierten Schichten sowie dreidimensionalen Strukturen nachweisen lassen. In den frustrierten Schichten wird auch der Zusammenhang zwischen den magnetischen Wirbeln und der elektrischen Polarisation diskutiert

Probing the density of states in EuFe2−xRuxAs2

The evolution of the electronic density of states at the Fermi level of intermetallic EuFe2-xRuxAs2 in the whole concentration range ( 0 <= x <= 2) is reported. Systematic electron spin resonance investigations of the Korringa-type Eu spin relaxation in combination with the results of band-structure calculations and magnetic susceptibility measurements can provide a clear picture of how the density of states is reduced by substituting Fe with Ru in EuFe2As2. Moreover, the strength of the exchange coupling between the local Eu and the itinerant spin systems can be estimated consistently with the weak coupling expected for this class of layered compounds