arXiv subjects

Franziska Walther

Publications and source records attributed to Franziska Walther.

4 recordsLinked to original sources

arXiv2026

Influence of the Pd-Si ratio on the valence transition in EuPd$_2$Si$_2$ single crystals

Single crystals of intermediate valent EuPd$_2$Si$_2$ were grown from an Eu-rich melt by the Bridgman as well as the Czochralski technique. The chemical and structural characterization of an extracted single crystalline Czochralski-grown specimen yielded a slight variation of the Si-Pd ratio along the growth direction and confirms the existence of a finite Eu(Pd$_{1-m}$Si$_m$)$_2$Si$_2$ homogeneity range. The thorough physical characterization carried out on the same crystal showed that this tiny variation in the composition affects the temperature $T_v$ at which the valence transition occurs. These experiments demonstrate a strong coupling between structural and physical properties in the prototypical valence-fluctuating system EuPd$_2$Si$_2$ and explain the different reported values of $T_v$.

cond-mat.str-el↗

arXiv2026

Competing magnetic order in EuPd$_3$Si$_2$

Single crystals of EuPd$_3$Si$_2$ were grown using a high-temperature EuPd-flux method. The material was structurally and chemically characterized by single-crystal x-ray diffraction, powder x-ray diffraction, Laue method and energy-dispersive x-ray spectroscopy. The structural analysis confirmed the orthorhombic crystal structure (space group $Imma$) but revealed differences in the lattice parameters and bond distances in comparison to previous work by Sharma et al.. The composition is close to the ideal 1:3:2 stoichiometry with an occupation of 7 % of the Si sites by Pd. The heat capacity, electrical resistivity, and magnetic susceptibility show two magnetic transitions indicating magnetic ordering below $T_{\rm N1}= 61\,\rm K$ and a spin reorientation at $T_{\rm N2}= 40\,\rm K$. The orthorhombic material shows magnetic anisotropy with field applied along the three main symmetry axes, which is summarized in the temperature-field phase diagrams. The susceptibility data hint to an alignment of the magnetic moments along $[100]$ between $T_{\rm N1}$ and $T_{\rm N2}$. Below $T_{\rm N2}$ the magnetic structure changes to an arrangement with moments canted away from $[100]$. In contrast to published work by Sharma et al., the single crystals investigated in this study are suggested to show AFM order below $T_{\rm N1}$ instead of ferromagnetism that sets in at higher $T_{\rm C1}=78\,\rm K$ which might originate from certain differences in the structure, composition or defects that have an impact on the dominant coupling constants of the RKKY interaction.

cond-mat.str-el↗

arXiv2026

Single crystal growth and properties of Au- and Ge-substituted EuPd$_2$Si$_2$

We report on the single crystal growth of Eu(Pd$_{1-x}$Au$_x$)$_2$Si$_2$, $0< x\leq 0.2$, from a levitating Eu-rich melt using the Czochralski method. Our structural analysis of the samples confirms the ThCr$_2$Si$_2$-type structure as well as an increase of the room temperature $a$ and $c$ lattice parameters with increasing $x$. Chemical analysis reveals that, depending on the Au concentration, only about 25-35\% of the amount of Au available in the initial melt is incorporated into the crystal structure, resulting in a decreasing substitution level for increasing $x$. Through Au substitution, chemical pressure is applied and large changes in valence crossover temperatures are already observed for low substitution levels $x$. In contrast to previous studies, we do not find any signs of a first-order transition in samples with $x_{\rm nom}=0.1$ or AFM order for higher $x$. Furthermore, we observe the formation of quarternary side phases for a higher amount of Au in the melt. In addition, cubic-mm-sized single crystals of EuPd$_2$(Si$_{1-x}$Ge$_x$)$_2$ with $x_{\rm nom}=0.2$ were grown. The analysis of the X-ray fluorescence revealed that the crystals exhibit a slight variation in the Ge content. Such tiny compositional changes can cause changes in the sample properties concerning variations of the crossover temperature or changes of the type of the transition from crossover to magnetic order. Furthermore, we report on a new orthorhombic phase EuPd$_{1.42}$Si$_{1.27}$Ge$_{0.31}$ that orders antiferromagnetically below $17\,\rm K$.

cond-mat.str-el↗

arXiv2025

Towards a critical endpoint in the valence fluctuating Eu(Rh$_{1-x}$Co$_{x}$)$_2$Si$_2$ system

We report on the successful single crystal growth of pure EuRh${_2}$Si${_2}$ and of Eu(Rh$_{1-x}$Co$_{x}$)$_2$Si$_2$ with $x\leq0.23$ by the flux method. Through Co substitution, EuRh$_2$Si$_2$ can be tuned from stable antiferromagnetism via a valence-transition state towards the valence-crossover regime. From magnetization measurements, we constructed a $B - T$ phase diagram for EuRh${_2}$Si${_2}$ comprising multiple magnetic phases and showing a sizable magnetic anisotropy within the basal plane of the tetragonal unit cell. This indicates a complex antiferromagnetic ground state for $x=0$. By applying positive chemical pressure through the substitution series Eu(Rh$_{1-x}$Co$_{x}$)$_2$Si$_2$, a sharp temperature-induced first-order phase transition is observed in magnetization, resistivity and heat capacity for 0.081 $\leq$ $x$ $\leq$ 0.119. The critical end point of this valence transition is located in the phase diagram in the vicinity of 0.119 $<x_{\rm EDX}<$ 0.166. At higher substitution level, the system reaches a valence-crossover regime. The obtained results are presented in a temperature-substitition phase diagram.

cond-mat.str-el↗