Variation of the magnetic ordering in $\text{Gd}{T}_2{\text{Zn}}_{20}$ ($T=\text{Fe}$, Ru, Os, Co, Rh and Ir) and its correlation with the electronic structure of isostructural $\text{Y}{T}_2{\text{Zn}}_{20}$

Magnetization, resistivity, and specific heat measurements were performed on solution-grown single crystals of six $\text{Gd}{T}_2{\text{Zn}}_{20}$ ($T=\text{Fe}$, Ru, Os, Co, Rh, and Ir) compounds, as well as on their Y analogs. For the Gd compounds, the Fe column members manifest a ferromagnetic (FM) ground state (with an enhanced Curie temperature $T_C$ for $T=\text{Fe}$ and Ru), whereas the Co column members manifest an antiferromagnetic (AFM) ground state. Thermodynamic measurements on $\text{Y}{T}_2{\text{Zn}}_{20}$ revealed that the enhanced $T_C$ for ${\text{GdFe}}_2{\text{Zn}}_{20}$ and ${\text{GdRu}}_2{\text{Zn}}_{20}$ can be understood within the framework of Heisenberg moments embedded in a nearly ferromagnetic Fermi liquid. Furthermore, electronic structure calculations indicate that this significant enhancement is due to a large transition metal partial density of states at the Fermi level that places these compounds close to the Stoner FM criterion. The change from FM to AFM ordering (between the Fe and Co column materials) is associated with the filling of electronic states with two additional electrons/f.u. The degree of this sensitivity is addressed by the studies of the pseudoternary compounds $\text{Gd}{\left({\text{Fe}}_x{\text{Co}}_{1-x}\right)}_2{\text{Zn}}_{20}$ and $\text{Y}{\left({\text{Fe}}_x{\text{Co}}_{1-x}\right)}_2{\text{Zn}}_{20}$, which clearly reveal the effect of $3d$-band filling on their magnetic properties.

Figure 1

(Color online) The lattice constants $\left(a\right)$ of $\text{Gd}{T}_2{\text{Zn}}_{20}$ and $\text{Y}{T}_2{\text{Zn}}_{20}$ versus the Goldschmidt radius $\left(r\right)$ of the transition metal with coordination number 12 (Ref. 22)

Figure 2

(Color online) Temperature dependent magnetization of $\text{Gd}{T}_2{\text{Zn}}_{20}$ divided by the applied field $H=1000\text{Oe}$.

Figure 3

(Color online) Field dependent magnetization of $\text{Gd}{T}_2{\text{Zn}}_{20}$ at 1.85 K for an applied magnetic field along all three principal directions: [100], [110], and [111].

Figure 4

(Color online) Applied field $\left(H=1000\text{Oe}\right)$ divided by the magnetizations of $\text{Gd}{T}_2{\text{Zn}}_{20}$ as a function of temperature. The solid line represents the high-temperature CW fit for ${\text{GdFe}}_2{\text{Zn}}_{20}$.

Figure 5

(a) Temperature dependent magnetization $\left(M\right)$ of ${\text{GdFe}}_2{\text{Zn}}_{20}$ divided by the applied field $\left(H=1000\text{Oe}\right)$, (b) specific heat $\left(C_p\right)$, and (c) resistivity $(\rho )$ and its derivative with respect to temperature $\left(d\rho /dT\right)$. Inset in (b): The magnetic part of specific data estimated as $\Delta C_p=C_p\left({\text{GdFe}}_2{\text{Zn}}_{20}\right)-C_p\left({\text{LuFe}}_2{\text{Zn}}_{20}\right)$ near $T_C$. Inset in (c): $\rho$ over the whole temperature range of 2–300 K.

Figure 6

Arrott plot of magnetic isotherms for ${\text{GdFe}}_2{\text{Zn}}_{20}$.

Figure 7

(a) Temperature dependent $M/H$ for ${\text{GdRu}}_2{\text{Zn}}_{20}$ $\left(H=1000\text{Oe}\right)$, (b) $C_p$, and (c) $\rho$ and $d\rho /dT$. Inset in (b): The magnetic part of specific data estimated as $\Delta C_p=C_p\left({\text{GdRu}}_2{\text{Zn}}_{20}\right)-C_p\left({\text{LuRu}}_2{\text{Zn}}_{20}\right)$. Inset in (c): $\rho$ over the whole temperature range.

Figure 8

Arrott plot of magnetic isotherms for ${\text{GdRu}}_2{\text{Zn}}_{20}$.

Figure 9

(a) Temperature dependent $M/H$ for ${\text{GdOs}}_2{\text{Zn}}_{20}$ $\left(H=1000\text{Oe}\right)$, (b) $C_p$, and (c) $\rho$ and $d\rho /dT$. Inset in (c): $\rho$ over the whole temperature range.

Figure 10

Arrott plot of magnetic isotherms for ${\text{GdOs}}_2{\text{Zn}}_{20}$. The demagnetizing field $D_m$ cannot be ignored for this low $T_C$ and was estimated from the geometric factor of the sample $\left(D\sim 0.03\right)$.

Figure 11

(a) Temperature dependent susceptibility $\left(\chi \right)$ and $d\left(\chi T\right)/dT$ of ${\text{GdCo}}_2{\text{Zn}}_{20}$, (b) $C_p$ and $C_p/T$, and (c) $\rho$ and $d\rho /dT$. Inset in (c): $\rho$ over the whole temperature range.

Figure 12

(a) Temperature dependent $\chi$ and $d\left(\chi T\right)/dT$ of ${\text{GdRh}}_2{\text{Zn}}_{20}$, (b) $C_p$ and $C_p/T$, and (c) $\rho$ and $d\rho /dT$. Inset in (c): $\rho$ over the whole temperature range.

Figure 13

(a) Temperature dependent $\chi$ and $d\left(\chi T\right)/dT$ of ${\text{GdIr}}_2{\text{Zn}}_{20}$, (b) $C_p$, and (c) $\rho$ and $d\rho /dT$. Inset in (c): $\rho$ over the whole temperature range.

Figure 14

(Color online) Pressure dependent $T_{10\%}$ (a caliper of $T_C$) of ${\text{GdFe}}_2{\text{Zn}}_{20}$ and ${\text{GdRu}}_2{\text{Zn}}_{20}$. The dash lines are the linear fits of the data.

Figure 15

(Color online) Temperature dependent magnetization of $\text{Y}{T}_2{\text{Zn}}_{20}$ under applied field $H=50\text{kOe}$.

Figure 16

(Color online) Field dependent magnetization of $\text{Y}{T}_2{\text{Zn}}_{20}$ at 1.85 K.

Figure 17

(Color online) Low-temperature specific heat of $\text{Y}{T}_2{\text{Zn}}_{20}$.

Figure 18

(Color online) The DOS of ${\text{YFe}}_2{\text{Zn}}_{20}$ (in St/eV cell) and partial DOS (in St/eV cell). $E_F$ corresponds to zero energy. The red solid line in (a) corresponds to the total DOS and the blue dashed line to the PDOS of Y atoms. The red solid line in (b) corresponds to the PDOS of Zn and the blue dashed line to the PDOS of Fe atoms.

Figure 19

(Color online) The DOS of (a) ${\text{YFe}}_2{\text{Zn}}_{20}$, (b) ${\text{YRu}}_2{\text{Zn}}_{20}$, and (c) ${\text{YCo}}_2{\text{Zn}}_{20}$ near $E_F$ (in St/eV cell) (solid line) and PDOS of Fe, Ru, and Co atoms (blue dashed line) (in St/eV cell). $E_F$ is shown by vertical lines. 518 and 522 corresponds to the number of valence electrons in the unit cell calculated in the rigid band approximation from the DOS of ${\text{YFe}}_2{\text{Zn}}_{20}$.

Figure 20

(Color online) The red solid line corresponds to the DOS of (a) FM-ordered ${\text{GdFe}}_2{\text{Zn}}_{20}$, (b) FM-ordered ${\text{GdRu}}_2{\text{Zn}}_{20}$, and (c) AFM ${\text{GdCo}}_2{\text{Zn}}_{20}$ near $E_F$ (in St/eV cell) and partial DOS of Fe, Ru, and Co atoms (blue dashed line) (in St/eV cell). $E_F$ is shown by vertical lines. 518 and 522 corresponds to the number of valence electrons in the unit cell calculated in the rigid band approximation from the DOS.

Figure 21

(Color online) Lattice constants of the series of $\text{Gd}{\left({\text{Fe}}_x{\text{Co}}_{1-x}\right)}_2{\text{Zn}}_{20}$ (open circle) and $\text{Y}{\left({\text{Fe}}_x{\text{Co}}_{1-x}\right)}_2{\text{Zn}}_{20}$ (solid triangle). Fe concentration of $\text{Gd}{\left({\text{Fe}}_x{\text{Co}}_{1-x}\right)}_2{\text{Zn}}_{20}$ series inferred from EDS measurements (solid square).

Figure 22

(Color online) Zero field cooled $M/H$ $\left(H=1000\text{Oe}\right)$ of $\text{Gd}{\left({\text{Fe}}_x{\text{Co}}_{1-x}\right)}_2{\text{Zn}}_{20}$ series versus temperature for $x=1.00$, 0.88, 0.75, 0.50, 0.25, and 0 from right to left. Note that the data from two samples of $x=0.88$ are shown. Inset: Magnetic phase transition temperatures, obtained from the resistivity data, for $\text{Gd}{\left({\text{Fe}}_x{\text{Co}}_{1-x}\right)}_2{\text{Zn}}_{20}$.

Figure 23

(Color online) Low-temperature $\left(T=1.85\text{K}\right)$ magnetization versus applied field for the $\text{Gd}{\left({\text{Fe}}_x{\text{Co}}_{1-x}\right)}_2{\text{Zn}}_{20}$ series. Inset: Saturated moments as a function of $x$.

Figure 24

(a) $H/M$ $\left(H=1000\text{kOe}\right)$ of ${\text{GdFe}}_2{\text{Zn}}_{20}$ as a function of temperature. The dash line represents the Curie–Weiss fit above 250 K. (b) Temperature varied ${\theta }_C$. (c) Temperature varied ${\mu }_{\text{eff}}$. (See text.)

Figure 25

(Color online) (a) $H/M$ $\left(H=1000\text{kOe}\right)$ of $\text{Gd}{\left({\text{Fe}}_x{\text{Co}}_{1-x}\right)}_2{\text{Zn}}_{20}$ as a function of temperature. (b) Temperature varied ${\theta }_C$. (See text.)