Transverse and Lateral Structure of the Spin-Flop Phase in $\mathrm{F}\mathrm{e}/\mathrm{C}\mathrm{r}$ Antiferromagnetic Superlattices

Direct evidence of the nonuniformly canted state of the spin-flop phase induced by a magnetic field applied to $\mathrm{F}\mathrm{e}/\mathrm{C}\mathrm{r}(100)$ superlattices is obtained by polarized neutron reflectometry. It is unambiguously demonstrated that the magnetization of the alternating Fe layers is twisted through the multilayer stack proving a stable noncollinear configuration. The maximal tilt at the end layers progressively reduces towards the center of the multilayer. The set of tilt angles is deduced from a model-free data evaluation employing the supermatrix routine. Spin-flip off-specular scattering is determined by the in-plane magnetization fluctuations and is fitted by a theoretical model of domains.

Figure 1

(a) Experimental two-dimensional (2D) map of the intensity scattered from the $\mathrm{F}\mathrm{e}/\mathrm{C}\mathrm{r}$ ML as a function of $(p_i-p_f)$ and $(p_i+p_f)$, with $p_i$ and $p_f$ the perpendicular to the sample surface components of the incoming and the outgoing wave vector, respectively (see inset). The logarithmic intensity color scale is shown on the side. The incoming neutrons are in the $-$ state. (b) 2D model fit to the experimental data in (a). (c) Experimental 2D intensity map as in (a) with the analyzed region (“$--$” state) between the dashed lines.

Figure 2

(a) Measured reflected intensity (solid line) multiplied by $\sin ({\alpha }_i)$ along the specular line together with the fit (dashed line) extracted as a vertical cut from Figs. 1a, 1b, respectively. (b) Measured off-specular intensity (solid line) along the $1/2$-order Bragg sheet together with the fit (dashed line) extracted as a horizontal cut from Figs. 1a, 1b.

Figure 3

(a) Configuration of the magnetization ${\mathbf{M}}_n$ in the $\mathrm{F}\mathrm{e}/\mathrm{C}\mathrm{r}$ ML in the external field $\mathbf{H}$ applied in plane along one of the easy axes; dashed lines mark the hard axes. Only Fe layers are shown. The only possible two types of domains (left and right) are depicted. Brackets A and B indicate the two transverse antiphase parts of one lateral domain. The canting angles ${\phi }_n$ between ${\mathbf{M}}_n$ and $\mathbf{H}$ are shown on the right-hand side. (b) Magnetic parts of the neutron scattering length density $N{b}_m^{\parallel }$ (left) and $N{b}_m^{\perp }$ (right) proportional to $M_n^{\parallel }$ and $M_n^{\perp }$. The dashed line indicates $M^{\parallel }$.