Imprinting Magnetic Information in Manganites with X Rays

The effect of x rays on an orbital and charge ordered epitaxial film of a ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_3$ is presented. As the film is exposed to x rays, the antiferromagnetic response increases and concomitantly the conductivity of the film improve. These results are discussed in terms of a persistent x-ray induced doping, leading to a modification of the magnetic structure. This effect allows writing electronic and magnetic information in the film and represents a novel way of manipulating magnetism.

Figure 1

Pictorial view of the x-ray induced electron doping with canting of the manganese magnetic moments of ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$, $0.4\le x\le 0.5$, and corresponding changes in the magnetic structure.

Figure 2

X-ray exposure dependence of the ($1/4$ $1/4$ 0) reflection (left-hand side axis) and in situ collected electrical conductivity (right-hand side axis) of epitaxial ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_3$ thin film at $T=50\mathrm{K}$. The energy of the x-ray beam was tuned to the resonance of Mn $L_3$ edge (642.5 eV) with incoming $\pi$ polarization. Inset: sketch of the experimental procedure for recording the x-ray induced changes of both the diffracted intensity and the photoconductivity.

Figure 3

Reciprocal space ($h$ $-h$ 0) scan of the ($1/4$ $1/4$ 0) reflection at x-ray energy 642.5 eV using incident $\pi$ polarization, taken at $T=50\mathrm{K}$, at different x-ray exposure time. Inset: evolution of the correlation length with respect to x-ray exposure time obtained through a fit with a Lorentzian.

Figure 4

Bragg peak intensity map of the ($1/4$ $1/4$ 0) reflection of the ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_3$ thin film at $T=50\mathrm{K}$. Before (a) and after (b) exposure to the x rays in the two positions (indicated by the arrows) for approximately 60 minutes. All experiments are performed at 50 K with 643.25 eV with $\pi$ incident polarization. X-ray exposure effects were erased by warming up the sample above $T_{\mathrm{OO}}$ as shown in the pattern collected after cooling (c).

Figure 5

Bragg peak intensity map of the ($1/4$ $1/4$ 0) reflection of the ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_3$ film at $T=50\mathrm{K}$ before (a) and after (b) exposing with different x-ray conditions (see text) at four positions indicated by arrows, where in (c) the time dependence of the x-ray Bragg intensity at these positions is illustrated. The different curves are shifted to each other along the vertical axis for clarity. Writing the information in position (i), $3\times {10}^{12}\mathrm{photons}/\mathrm{s}$ were used with as beam size of $100\times 50\mu \mathrm{m}$ [21]. Position (ii) was exposed to $6\times {10}^{12}\mathrm{photons}/\mathrm{s}$ where for positions (iii) and (iv), we exposed with $1.2\times {10}^{13}$ and $2.14\times {10}^{13}\mathrm{photons}/\mathrm{s}$, respectively. The vertical spot size varied from 50 [position (i) and (ii)], to 100 [position (iii)], and $200\mu \mathrm{m}$ for position (iv).