Antiferromagnetism in a ${\text{Fe}}_{50}{\text{Pt}}_{40}{\text{Rh}}_{10}$ thin film investigated using neutron diffraction

The temperature-dependent magnetic structure of a 200 nm thick single-crystalline film of ${\text{Fe}}_{50}{\text{Pt}}_{40}{\text{Rh}}_{10}$ was studied by unpolarized and polarized neutron diffractions. By applying structure factor calculations, a detailed model of the magnetic unit cell was developed. In contrast to former studies on bulk samples, our experimental results show that the film remains in an antiferromagnetic state throughout the temperature range of 10–450 K. Remarkably, it can be demonstrated that the antiferromagnetic structure undergoes a smooth transition from a dominant out-of-plane order with the magnetic moments orientated in-plane to an in-plane order with the magnetic moments orientated perpendicular to the film plane. Theoretically this can be explained by the existence of two competing anisotropy contributions with different temperature dependencies.

Figure 1

Out-of-plane x-ray diffraction spectrum of a 200 nm ${\text{Fe}}_{50}{\text{Pt}}_{40}{\text{Rh}}_{10}$ film grown on a MgO substrate. The insert shows the rocking scan at the structural (001) Bragg peak of the film.

Figure 2

Unit cell of ${\text{Fe}}_{50}{\text{Pt}}_{50-x}{\text{Rh}}_x$ alloys in the $L{1}_0$ structure.

Figure 3

Phi scans showing the ${\text{Fe}}_{50}{\text{Pt}}_{40}{\text{Rh}}_{10}$ (011) and MgO (220) reflections. The scans reveal a $45°$ offset between film and substrate.

Figure 4

Temperature dependence of the integrated neutron-diffraction intensity at three in-plane (200), (100), $\left(\frac{1}{2}00\right)$ (open circles) and three out-of-plane (002), (001), $\left(00\frac{1}{2}\right)$ reflections (solid squares). The intensity of the $\left(\frac{1}{2}00\right)$ reflection was multiplied by a factor of 5 in the lower panel. The line of the (100) AF peak is a guide for the eyes. The lines for the $\left(00\frac{1}{2}\right)$ (black line) and $\left(\frac{1}{2}00\right)$ (gray line) peaks are fits (for further details see text).

Figure 5

The variation in the lattice parameters $a$ and $c$ with temperature.

Figure 6

Polarized neutron-diffraction scans of the $\left(00\frac{1}{2}\right)$, $\left(\frac{1}{2}00\right)$, and (100) AF reflections at 150 and 300 K plotted against the individual reciprocal-lattice units (RLUs). The data sets of the $\left(00\frac{1}{2}\right)$ reflection have been multiplied by a factor of 1/3.

Figure 7

Geometry of the $L{1}_0$ structured ${\text{Fe}}_{50}{\text{Pt}}_{40}{\text{Rh}}_{10}$ film. In $c$ direction the film build a natural multilayer with alternating planes of Fe atoms (gray) and Pt/Rh atoms (black). The light gray rectangular block contains the atoms that contribute to the part of the extended unit cell which is denoted as the ground level in a two-dimensional view (see Fig. 9).

Figure 8

Models of the magnetic configuration at low temperatures $T<250\text{K}$ and $T>330\text{K}$ for the ground and first level of the extended unit cell (see Fig. 7). The gray circles represent Fe atoms and the black circles Pt/Rh atoms. The latter are located $\left(1/2\right)c$ shifted along the $c$ axis with respect to the Fe atoms. For $T<250\text{K}$, the magnetic moments are tilted with respect to the $a$ and $b$ axes as shown by the arrows. Note the slight twists of the moments about the $c$ axis. The dots and the crosses indicate that components of the magnetic moments are pointing up or down, respectively. The ground and first level are shifted in $c$ direction about the distance between two Fe-atoms in this direction.

Figure 9

Orientation of the magnetic moment in the ${\text{Fe}}_{50}{\text{Pt}}_{40}{\text{Rh}}_{10}$ film. Here $\alpha$ is the angle to the in-plane $a$ axis and $\beta$ is the angel to the out-of-plane $c$ axis.

Figure 10

Total magnetization due to the (a) AF ordering, (b) in-plane angle $\alpha$, and (c) out-of-plane angle $\beta$ as a function of temperature.

Figure 11

The relation between the angles $\alpha$ and $\phi$. The axes $a$ and $b$ describe the crystallographic orientations with respect to the {100} and {010} directions while $a_m$ and $b_m$ denote to the principal axes of the magnetization in the sample at low temperatures.