The influence of Ga doping on magnetic properties, magnetocaloric effect, and electronic structure of pseudo-binary GdZn1-xGax (x = 0-0.1)

TL;DR

This study investigates Ga substitution in the pseudo-binary intermetallic GdZn$_{1-x}$Ga$_x$ ($x=0-0.1$) to understand how electron count tunes magnetic order and the magnetocaloric effect. The authors combine synthesis, structural and spectroscopic characterization, SQUID magnetometry, and magnetocaloric measurements with density functional theory (DFT) and a mean-field framework to connect electronic structure to exchange interactions. They find that $T_{ m C}$ decreases with Ga content while long-range ferromagnetism persists and critical behavior remains mean-field-like; Ga-doping also removes flat-band instabilities in GdZn, aligning theoretical predictions with experimental trends. The results illuminate the role of conduction electrons in mediating Gd–Gd exchange and offer a pathway to tune magnetism and MCE in lanthanide intermetallics through controlled electron-count adjustments.

Abstract

We explore the impact of introducing IIIA-group element Ga in place of IIB-group element Zn in binary intermetallic GdZn on its magnetic and magnetocaloric properties, as well as explicate the modified electronic band structure of the compound. The magnetic transition temperature of the compound decreases with the increase of Ga concentration in GdZn1-xGax (x = 0-0.1) while the crystal structure (CsCl-prototype) and lattice parameters remain unchanged. Our detailed analysis of magnetization and magnetocaloric data conclusively proves that long-ranged magnetic ordering exists in the sample, despite the magnetic interaction considerably weakening with the increase of Ga. The experimental data is rationalized using both theoretical machine learning model and first-principle density functional theory.The electronic band structure of GdZn is manifested with some unusual complex features which gradually diminish with Ga doping and conventional sinusoidal feature of Ruderman-Kittel-Kasuya- Yosida (RKKY)-type interactions also disappears. A mean-field theory model is developed and can successfully describe the overall magnetocaloric behavior of the GdZn1-xGax series of samples

Figures (12)

• Figure 1: (a--c) Room temperature powder x-ray diffraction data of GdZn$_{1-x}$Ga$_x$ for $x$ = 0, 0.05, and 0.10 samples, respectively, using Mo K$\alpha$ ($\lambda \approx$0.71 Å) radition. The elemental mapping at the selected areas on (d, e) $x =$ 0 and (f-h) $x =$ 0.10 samples using energy dispersive spectroscopy.
• Figure 2: (a, b) The XPS survey spectra, (c, d) Gd 3$d$ core-level, and (e, f) Zn 2$p$ core-level spectra of the GdZn$_{1-x}$Ga$_x$ for $x=0$ and 0.10, respectively. (g) Ga 2$p$ core-level spectra of $x =$ 0.10 sample.
• Figure 3: The temperature dependencies of ZFC and FC magnetization curves of GdZn$_{1-x}$Ga$_x$ for (a) $x=0$, (b) $x=0.05$, and (c) $x=0.1$. The measurements were conducted at $H = 500$ Oe. The Curie-Weiss fittings of $\chi_{dc}^{-1}$ vs. $T$ in the paramagnetic temperature range (data recorded in the presence of a 20 kOe magnetic field) for the samples are shown as insets in (a), (b), and (c). The temperature dependence of $dM/dT$ for the samples is shown in (d).
• Figure 4: M vs. H curves recorded at 5 K for GdZn$_{1-x}$Ga$_x$ for (a) $x=0$, (b) $x=0.05$, and (c) $x=0.1$. The expanded views of the curves in the low magnetic field region are shown in insets.
• Figure 5: (a--c) The normalized slopes (NS's) for different universality classes in the critical region for GdZn$_{1-x}$Ga$_x$ with $x= 0$, $0.05$, and $0.1$ respectively. (d-f): Modified Arrott plots using the correct critical exponents for the samples, where black circles, red, and blue lines represent the experimental data points, linear fit for $H > 10$ kOe, and the extrapolation of the linear fit at $T_C$ down to $H=0$.