Anisotropic physical properties of the Taylor-phase ${\text{T}\text{-Al}}_{72.5}{\text{Mn}}_{21.5}{\text{Fe}}_{6.0}$ complex intermetallic

We have investigated anisotropic physical properties (the magnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient and the thermal conductivity) of the single-crystalline Taylor-phase ${\text{T}\text{-Al}}_{72.5}{\text{Mn}}_{21.5}{\text{Fe}}_{6.0}$ complex intermetallic that is an orthorhombic approximant to the $d\text{-Al-Mn-Pd}$ decagonal quasicrystal. The measurements were performed along the $a$, $b$, and $c$ directions of the orthorhombic unit cell, where $\left(a,c\right)$ atomic planes are stacked along the perpendicular $b$ direction. The ${\text{T}\text{-Al}}_{72.5}{\text{Mn}}_{21.5}{\text{Fe}}_{6.0}$ shows spin-glass behavior below the spin-freezing temperature $T_f\approx 29\text{K}$ with a small anisotropy in the magnetic susceptibility. The anisotropic electrical resistivities are rather large and show negative temperature coefficient. The resistivity is lowest along the stacking direction, which appears to be a common property of the decagonal-approximant phases with a stacked-layer structure. The temperature-dependent resistivity was theoretically reproduced by the quantum transport theory of slow charge carriers. The thermopower is positive for all three crystallographic directions, indicating that holes are the majority charge carriers, and no anisotropy can be claimed within the experimental precision. The same conclusion on the holes being the dominant charge carriers follows from the Hall-coefficient measurements, which is a sum of the (positive) normal Hall coefficient and the anomalous term, originating from the magnetization. The anisotropy of the thermal conductivity is practically negligible. The ${\text{T}\text{-Al}}_{72.5}{\text{Mn}}_{21.5}{\text{Fe}}_{6.0}$ Taylor phase can be considered as a “close-to-isotropic” complex intermetallic. The relation of the anisotropic physical properties of the Taylor phase to other families of decagonal-approximant phases with the stacked-layer structure is discussed.

Figure 1

(Color online) Anisotropic field-cooled (fc) and zero-field-cooled (zfc) magnetic susceptibilities of the single-crystalline ${\text{T}\text{-Al}}_{72.5}{\text{Mn}}_{21.5}{\text{Fe}}_{6.0}$ in the temperature range 2–50 K and magnetic field (a) 100 Oe and (b) 50 kOe, directed along the $a$, $b$, and $c$ crystallographic directions. The susceptibilities are calculated per mol of ${\text{Al}}_{0.725}{\text{Mn}}_{0.215}{\text{Fe}}_{0.06}$ “molecules” with the molar mass 34.724 g/mol.

Figure 2

(Color online) The $M\left(H\right)$ hysteresis loops at $T=2\text{K}$ for the field along the three crystallographic directions $a$, $b$, and $c$ in the sweep range $\pm 50\text{kOe}$. The three loops are practically indistinguishable on the graph.

Figure 3

(Color online) Anisotropy of the memory effect in the single-crystalline ${\text{T}\text{-Al}}_{72.5}{\text{Mn}}_{21.5}{\text{Fe}}_{6.0}$, by showing the difference $\Delta M=M_{\text{zfc}}\left(t_w=0\right)-M_{\text{zfc}}\left(t_w\right)$ between the reference (no-stop) zfc magnetization curve $M_{\text{zfc}}\left(t_w=0\right)$ and the zfc magnetization curves $M_{\text{zfc}}\left(t_w\right)$ with a stop at the aging temperature $T_1=14\text{K}$ for aging times $t_w$ between 1 min and 4 h. For more details on the memory effect see Ref. 15. In the panels (a), (b), and (c), the magnetic field was directed along the $a$, $b$, and $c$ crystallographic directions, respectively.

Figure 4

(Color online) (a) The anisotropic zfc and fc susceptibilities in the temperature range 2–300 K, measured in a magnetic field $H=1\text{kOe}$ along the three crystallographic directions $a$, $b$, and $c$. Solid curve is the Curie-Weiss fit with Eq. (1) in the high-temperature $T>60\text{K}$ paramagnetic regime and the fit parameters are given in the text. For $T>60\text{K}$, the three sets of experimental data and the fitting curve are indistinguishable, so that the same fit is valid for all three directions. (b) The $M\left(H\right)$ lines at $T=300\text{K}$ in the paramagnetic phase for the field along the three crystallographic directions. The three lines are indistinguishable on the graph.

Figure 5

(Color online) Temperature-dependent electrical resistivity of ${\text{T}\text{-Al}}_{72.5}{\text{Mn}}_{21.5}{\text{Fe}}_{6.0}$ along the three orthogonal crystallographic directions $a$, $b$, and $c$. Solid curves represent the fits with Eq. (3) using the quantum transport theory of slow charge carriers, and the fit parameters are collected in Table .

Figure 6

(Color online) Temperature-dependent anisotropic thermoelectric power (the Seebeck coefficient $S$) of ${\text{T}\text{-Al}}_{72.5}{\text{Mn}}_{21.5}{\text{Fe}}_{6.0}$ along the three orthogonal crystallographic directions $a$, $b$, and $c$.

Figure 7

(Color online) Anisotropic temperature-dependent Hall coefficient $R_H=E_y/j_x{B}_z$ of ${\text{T}\text{-Al}}_{72.5}{\text{Mn}}_{21.5}{\text{Fe}}_{6.0}$ for different combinations of directions of the current $j_x$ and magnetic field $B_z$ (given in the legend).

Figure 8

(Color online) (a) The anisotropic Hall coefficient $R_H^k$ of ${\text{T}\text{-Al}}_{72.5}{\text{Mn}}_{21.5}{\text{Fe}}_{6.0}$ as a function of the paramagnetic susceptibility ${\chi }_k$ from Fig. 4a for different combinations of directions of the current $j_x$ and magnetic field $B_z$ (given in the legend). (b) The Hall coefficient as a function of ${\chi }_k\left({\rho }_i{\rho }_j/{\rho }_{i0}{\rho }_{j0}\right)$, where $i$, $j$ denote the two orthogonal crystallographic directions perpendicular to the magnetic field direction $k$. ${\rho }_{i0}{\rho }_{j0}$ are arbitrary chosen RT $\left(T=295\text{K}\right)$ values of the electrical resistivity. The legend in the panel (b) is the same as in (a).

Figure 9

(Color online) The anisotropic thermal conductivities ${\kappa }_a$, ${\kappa }_b$, and ${\kappa }_c$ of ${\text{T}\text{-Al}}_{72.5}{\text{Mn}}_{21.5}{\text{Fe}}_{6.0}$ along the three crystallographic directions, normalized to their 300 K values.