Magnetic structure of the ${\mathrm{Eu}}^{2+}$ moments in superconducting ${\mathrm{EuFe}}_2{\left({\mathrm{As}}_{1-x}{\mathrm{P}}_x\right)}_2$ with $x=0.19$

The magnetic structure of the ${\mathrm{Eu}}^{2+}$ moments in the superconducting ${\mathrm{EuFe}}_2{\left({\mathrm{As}}_{1-x}{\mathrm{P}}_x\right)}_2$ sample with $x=0.19$ has been determined using neutron scattering. We conclude that the ${\mathrm{Eu}}^{2+}$ moments are aligned along the c direction below $T_{\mathrm{C}}=19.0\left(1\right)$ K with an ordered moment of 6.6(2) ${\mu }_B$ in the superconducting state. An impurity phase similar to the underdoped phase exists within the bulk sample which orders antiferromagnetically below $T_{\mathrm{N}}=17.0\left(2\right)$ K. We found no indication of iron magnetic order, nor any incommensurate magnetic order of the ${\mathrm{Eu}}^{2+}$ moments in the sample.

Figure 1

Temperature dependence of the magnetic susceptibility measured on heating of the zero-field cooled (ZFC) and field cooled (FC) sample along the a-b plane at an applied magnetic field of 25 Oe. $T{}_{\mathrm{SC}}$ and $T{}_{\mathrm{C}}$ denote superconducting and ferromagnetic transition temperatures, respectively. The transition temperatures were determined from the minima/maxima of the derivative curve of the ZFC data.

Figure 2

(a) Temperature dependence of the integrated intensity for the (2 2 0) reflection. (b) Temperature dependence of the full width at half maximum (FWHM) for the same reflection. (c) Rocking scans at the expected position of the Fe magnetic order at ($\frac{1}{2}$ $\frac{1}{2}$ 3) at 25 K and at the background position of ($\frac{1}{2}$ $\frac{1}{2}$ 2.7).

Figure 3

Scans along the [0 0 1] direction at $T$ = 2 and 25 K, respectively. For the (0 0 1) reflection, measurement has been performed only at 2 K due to the technical difficulties. The break in measurement data between $L$ = 1.1 and 1.75 is due to the same difficulties. The temperature-independent peak near $L$ = 5.04 is due to aluminum (Al). The peak positions near the (0 0 $L$) with $L$ = odd were determined after fitting the peaks using Gaussian profiles.

Figure 4

(a),(b) Two-dimensional contour maps in the ($H$ $H$ $L$) and in the ($H$ 0 $L$) planes at $T$ = 2 K. Insets show both figures with different intensity scales to visualize the weakest peaks, if any. No data were collected in the white rectangular region of (a). (1 1 0) and (1 0 1) are allowed nuclear peak positions. The weak peak at (1 0 0) indicates antiferromagnetic order of the ${\mathrm{Eu}}^{2+}$ moments with propagation vector $\tau$ = (0 0 1) associated with the minor phase.

Figure 5

Rocking scans for the (a)–(c) (0 0 2), (0 0 4), and (0 0 6) reflections, (d)–(f) (1 1 0), (1 0 1), and (1 1 2) reflections, and (g)–(i) (0 0 2.95), (0 0 4.95), and (1 0 0) reflections at 2 and 25 K, respectively. Note the intensity scales for the (0 0 $L$) reflections with $L$ = odd and $L$ = even.

Figure 6

Temperature dependence of the integrated intensity for the (1 1 0) reflection measured during heating and cooling and for the (1 0 1) reflection measured during heating. (b) For comparison, we also show the temperature dependencies of the (0 0 2.95) and (1 0 0) reflections corresponding to the minor phase. The solid lines are fit to the data as described in the text.

Figure 7

Comparison between the observed ratio ($R_{\mathrm{obs}}$), fitted ratio ($R_{\mathrm{fit}}$), and calculated ratio ($R_{\mathrm{cal}}$) for the measured reflections. Details have been outlined in the text.