Synthesis and anisotropic magnetism of singlecrystalline GdPt2Si2

TL;DR

This study reports the successful growth of high-quality single crystals of GdPt$_2$Si$_2$ via Sn flux, confirming a non-centrosymmetric CaBe$_2$Ge$_2$-type structure. Magnetic, thermodynamic, ESR, and transport measurements reveal a double AFM transition at $T_N \approx 8.4$ K and $T_0 \approx 6.9$–7.0 K, with an amplitude-modulated AFM state above $T_0$ that evolves into an equal-moment AFM ground state; field effects include a metamagnetic transition for $H \parallel a$ and suppression of $T_0$. ESR indicates FM polarization of conduction electrons at high temperature and enhanced magnetic fluctuations below $\sim$120 K, while magnetic entropy approaches $R\ln 8$ consistent with Gd$^{3+}$ moments. The results establish a comprehensive baseline for the magnetism in the RPt$_2$Si$_2$ series and related non-centrosymmetric systems, highlighting anisotropic spin rearrangements and potential noncollinear AFM contributions.

Abstract

Single crystals of GdPt$_2$Si$_2$ were grown using the Sn flux method, crystallizing in the CaBe$_2$Ge$_2$-type tetragonal structure with space group $P4/nmm$. Electrical resistivity, specific heat, and magnetization data revealed the presence of a double magnetic transition with $T_N \approx 8.4$~K and $T_0 \approx 6.8$~K. Analysis of the specific heat data suggest amplitude-modulated and equal-moment antiferromagnetic orderings, respectively. Field-induced magnetization and magnetic susceptibility data show a metamagnetic transition in the $H \parallel a$ direction at 2~K, as well as the suppression of the magnetic transition located at $T_0$ with increasing external magnetic field. Electron Spin Resonance (ESR) shows the Gd$^{3+}$ resonance followed by a small second resonance. Peak-to-peak linewidth ($ΔH_{pp}$) analysis reveals slight broadening at $T \sim 120$~K, indicating an increase in magnetic fluctuations at high temperatures. Ferromagnetic (FM) local polarization at high temperatures is also observed through the $g$-factor analysis, which shows a notable positive shift ($Δg$). Our results establish the fundamental physical properties of this material to aid in further understanding of the magnetism in the RPt$_2$Si$_2$ series and related non-centrosymmetric systems.

Figures (7)

• Figure 1: a) Crystal structure representation of GdPt$_2$Si$_2$ and b) its $bc$-plane projection where the absence of inversion symmetry of the Gd-ion is evidenced.
• Figure 2: Powder XRD pattern at room temperature. The solid black lines represent the Rietveld refinement fit, the solid blue line represents the difference between the observed and calculated profile, and the vertical green lines shows the Bragg positions.
• Figure 3: Inverse magnetic susceptibility for the main crystallographic directions (red and blue symbols). The black dotted line is a linear fit of the high-temperature region, from which the effective magnetic moment and the Weiss temperature were determined. The inset highlights the orientation dependence of the magnetic susceptibility ($\chi$) in the double magnetic transition region, plus the calculated polycrystalline average (green dashed line).
• Figure 4: a) and c) displays the magnetic susceptibility as a function of temperature and in the insets the $M(H)~vs.~H$ for $H \parallel a$, and $H \parallel c$ respectively. b) and d) show the magnetic phase diagram for the two main crystallographic directions obtained by magnetic susceptibility and heat capacity measurements.
• Figure 5: ESR spectra of Gd$^{3+}$ at $T=230$ K, $\nu = 9.4$ GHz and 6.3 mW (red symbols) together with the fitting using a Lorentzian equation (black line). The upper inset shows the temperature dependence of the linewidth and $g$-shift values obtained from the Lorentzian fits of the full spectra. The lower inset shows zooms in upon the region where a smaller resonance is observed.