CrFe2Ge2: Investigation of novel ferromagnetic material of Fe13Ge8-type crystal

TL;DR

This study introduces CrFe$_2$Ge$_2$, a novel Fe$_{13}$Ge$_{8}$-type intermetallic, and characterizes its structure, magnetism, and transport. Structural analysis (single-crystal XRD) and Mössbauer spectroscopy reveal two Fe sublattices and a Cr substitution pattern consistent with Cr-rich/Cr-poor subunits, while magnetic and thermodynamic measurements establish ferromagnetic ordering near $T_C \approx 200$ K. A non-mean-field critical behavior is extracted from modified Arrott plots, giving $\beta \approx 0.392$, $\gamma \approx 1.309$, and $\delta \approx 4.34$, corroborated by Widom scaling and scaling analyses; renormalization-group calculations place CrFe$_2$Ge$_2$ in a 3D isotropic long-range exchange regime with $J(r) \approx r^{-4.86}$. Rhodes–Wohlfarth analysis yields a ratio of ~3, indicating itinerant ferromagnetism, while low-temperature transport shows electron-magnon scattering and a Debye-like lattice contribution to heat capacity. Overall, CrFe$_2$Ge$_2$ provides insight into Fe-Ge intermetallic magnetism, highlighting the impact of multi-sublattice structure and long-range exchange on critical behavior and transport.

Abstract

We successfully synthesized a novel intermetallic compound $\rm CrFe_2Ge_2$ with the $\rm Fe_{13}Ge_{8}$-type crystal structure. A structural study is presented combining single-crystal X-ray diffraction and Mössbauer spectroscopy analysis, confirming the presence of two distinct Fe sublattices. $\rm CrFe_2Ge_2$ exhibits a metallic ferromagnetic state with $T_C \approx \rm 200~K$. This material does not follow the usual $M^2 \propto H/M$ Arrott law, rather a modified Arrott law is obeyed in this material. The critical exponents determined from detailed analysis of modified Arrott plots were found to be $β= 0.392$, $γ= 1.309$ and $δ= 4.26$ obtained from the critical isotherm at $ T_{\rm C} =\rm 200~K$. Self-consistency and reliability of the critical exponent analysis were verified by the Widom scaling law and scaling equations. Using the results from renormalization group calculation, the critical behavior of $\rm CrFe_2Ge_2$ is akin to that of a $d=3, n=3$ ferromagnet in which the magnetic exhange distance is found to decay as $J(r) \approx r^{-4.86}$ with long-range magnetic coupling. The evaluated Rhodes-Wohlfarth ratio of $\sim 3$ points to an itinerant ferromagnetic ground state. Low-temperature measurements of resistivity, $p(T)$, and specific heat, $C_P(T)$, reveal a pronounced contribution from electron-magnon scattering.

Figures (8)

• Figure 1: Crystal structure of CrFe$_{2}$Ge$_{2}$ projected along the c axis (a) and a axis (b).
• Figure 2: PXRD $\rm CrFe_2Ge_2$ Rietveld refinement. Blue tick marks indicate X-ray diffraction peaks of $\rm CrFe_2Ge_2$.
• Figure 3: Mössbauer 295 K and 80 K spectra of CrFe$_{2}$Ge$_{2}$ system. The calculated lines over the experimental points are the sum of two doublets and three sextets, respectively (see Table \ref{['tab:mossb']}), shown slightly shifted for clarity.
• Figure 4: (a) Magnetization as function of temperature M(T) of $\rm CrFe_2Ge_2$ and $dM/dT$ in the inset. (b) Temperature dependence of inverse magnetic susceptibility for $\rm CrFe_2Ge_2$.The solid lines indicate the fit with the modified Curie–Weiss law. (c) Isothermal magnetization curves M(H) at various temperatures at magnetic field H of up to 9 T. (d) $M^2$ vs. $H/M$ plots (Arrott plot) for various temperature for $\rm CrFe_2Ge_2$.
• Figure 5: Temperature-dependent entropy changes for CrFe$_{2}$Ge$_{2}$