Interplay of rare-earth and transition-metal subsystems in $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$

We present the synthesis and the experimental and theoretical study of the new member of the francisite family, $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$. The compound reaches an antiferromagnetic order at $T_{\mathrm{N}}=36.7\mathrm{K}$ and experiences first-order spin-reorientation transition to weakly ferromagnetic phase at $T_{\mathrm{R}}=8.7\mathrm{K}$ evidenced in specific heat $C_{\mathrm{p}}$ and magnetic susceptibility χ measurements. Distinctly different magnetization loops in $T<T_{\mathrm{R}}$ and $T_{\mathrm{R}}<T<T_{\mathrm{N}}$ temperature ranges reflect the interplay of rare-earth and transition-metal subsystems. At low temperatures, the saturation magnetization $M_{\mathrm{s}}\sim 5.2{\mu }_{\mathrm{B}}$ is reached in pulsed magnetic-field measurements. The electron spin resonance data reveal the complicated character of the absorption line attributed to response from both copper and ytterbium ions. Critical broadening of the linewidth at the phase transitions points to quasi-two-dimensional character of the magnetic correlations. The spectroscopy of $\mathrm{Y}{\mathrm{b}}^{3+}$ ions evidences splitting of the lowest-energy Kramers doublet of ${}^2{F}_{5/2}$ excited multiplet at $T_{\mathrm{R}}<T<T_{\mathrm{N}}$ while the ground Kramers doublet splits only at $T<T_{\mathrm{R}}$. We describe the magnetic properties both above and below the spin-reorientation transition in the framework of a unified approach based on the mean-field approximation and crystal-field calculations.

Figure 1

The Rietveld plot for $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$ francisite.

Figure 2

The temperature dependencies of reduced magnetization $\chi =M/B$ in $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$ at various magnetic fields. The inset shows this dependence at $B=1\mathrm{T}$ and its reciprocal.

Figure 3

The magnetization loops in $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$ at various temperatures. The upper inset represents the pulsed field magnetization at $T=2.4\mathrm{K}$. The lower inset represents the schematic phase diagram.

Figure 4

The temperature dependence of specific heat $C_{\mathrm{p}}$ in $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$. The lower inset represents the hysteresis of singularity at $T_{\mathrm{R}}$. The upper inset shows the magnetic field's evolution of singularity at $T_{\mathrm{N}}$.

Figure 5

The ESR spectra for $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$ at various temperatures. The circles are experimental data, the dashed lines are resolved components, and the solid lines are their summation.

Figure 6

The temperature dependencies of the effective $g$ factors and the linewidths for resolved components of ESR spectra. Inset: enlarged scale for the $\mathrm{\Delta }{B}_2\left(T\right)$ dependence.

Figure 7

The scheme of level splitting in $\mathrm{Y}{\mathrm{b}}^{3+}$ ions at various temperature ranges (a). The infrared transmission spectra in $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$ at several temperatures (b).

Figure 8

The infrared transmission spectra of $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$ at several temperatures in the spectral region of IA (a) and IB (b) transitions and corresponding color maps (b),(d).

Figure 9

The temperature evolution of infrared spectra of $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$ in the vicinity of $T_{\mathrm{R}}$ as transmission spectra (a) and color map (b). The intensity of the spectral line at $10353\mathrm{c}{\mathrm{m}}^{-1}$ as the function of temperature (c).

Figure 10

The schemes of orientations of the magnetic moments within copper ${\mathbf{M}}_i^{\mathrm{Cu}1,2}$ and rare-earth ${\mathbf{m}}_i^{\mathrm{Yb}}$ sublattices used in the calculation of the magnetic parameters of $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$ (the axis $a$ is oriented perpendicular to the plane).

Figure 11

The calculated (lines) and experimental (symbols) temperature dependencies of reduced magnetization $\chi =M/B$ in $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$ at various magnetic fields. The inset shows calculated and experimental temperature dependencies of specific heat $C_{\mathrm{p}}/T\left(T\right)$ in $\mathrm{C}{\mathrm{u}}_3\mathrm{Yb}{\left(\mathrm{Se}{\mathrm{O}}_3\right)}_2{\mathrm{O}}_2\mathrm{Cl}$ at $B=0$. Curve 1 represents the results of calculation for the scheme shown in Fig. 10; curve 2 corresponds to the scheme shown in Fig. 10.

Figure 12

The calculated (lines) and experimental (symbols) magnetization curves at $T=2\mathrm{K}$. The resulting calculated curve $M$($B$) and its components $M_{a,b,c}\left(B\right)$ (for down sweep of the magnetic field) are shown. Calculated contributions of the Cu subsystem ${\mathbf{M}}_{a,b,c}^{\mathrm{Cu}}\left(\mathrm{B}\right)$ to the total magnetization are shown by dashed curves.