Magnetic field induced enhancement of spin-order peak intensity in ${\text{La}}_{1.875}{\text{Ba}}_{0.125}{\text{CuO}}_4$

We report on neutron-scattering results on the impact of a magnetic field on stripe order in the cuprate ${\text{La}}_{1.875}{\text{Ba}}_{0.125}{\text{CuO}}_4$. It is found that a 7 T magnetic field applied along the $c$ axis causes a small but finite enhancement of the spin-order peak intensity and has no observable effect on the peak width. Inelastic neutron-scattering measurements indicate that the low-energy magnetic excitations are not affected by the field, within experimental error. In particular, the small energy gap that was recently reported is still present at low temperature in the applied field. In addition, we find that the spin-correlation length along the antiferromagnetic stripes is greater than that perpendicular to them.

Figure 1

(Color online) Spin-order peak (0.615,0.5,0) intensity and width. (a) Background subtracted peak intensity in zero field (circles) and 7 T field (diamonds). (b) Peak intensity difference between 7 and 0 T measurements (triangles) and relative intensity difference $S$ defined as $\left(I_{7\text{T}}-I_{0\text{T}}\right)/I_{0\text{T}}$ (squares). (c) Resolution-corrected peak width along $\left(0.615+h,0.5,0\right)$ and $\left(0.615,0.5+k,0\right)$ in zero field (circles) and 7 T field (diamonds). Insets in (c) show scan profiles along $H$ and $K$ directions. Lines through the data are guides for the eyes. Vertical lines denote the onset temperatures, as discussed in the text. Two horizontal lines in the insets show the instrumental resolutions (FWHM). Error bars represent $1\pm \sigma$ uncertainties determined assuming Poisson statistics, and those smaller than the symbols are absent.

Figure 2

(Color online) Selected elastic scans along $\mathbf{Q}=\left(H,0.5,0\right)$ in zero field (open circles) and 7 T field (diamonds) at 5 and 45 K. Solid lines are guides for the eyes. The triangles show 55 K data as the background, as indicated by the dashed lines. The horizontal line in (a) shows the instrumental resolution (FWHM). Error bars represent the square root of the counts, and those smaller than the symbols are absent.

Figure 3

(Color online) Contour map of the spin-order peak (0.615,0.5,0) intensity as a function of temperature and magnetic field. Circles indicate the fields and temperatures at which the measurements were performed.

Figure 4

(Color online) ${\chi }^{″}\left({\mathbf{Q}}_0,\omega \right)$ with ${\mathbf{Q}}_0=\left(0.615,0.5,0\right)$ in zero field (circles) and 7 T field (diamonds) at 30, 45, and 60 K converted from the peak intensity, as discussed in the text. Error bars represent $1\pm \sigma$ uncertainties determined assuming Poisson statistics and those smaller than the symbols are absent.

Figure 5

(Color online) Scan profiles along $\mathbf{Q}=\left(H,0.5,0\right)$ at 30 K, with energies of $\hslash \omega =0.5$ and 1.5 meV, in zero field (circles) and 7 T field (diamonds). Lines through the data are guides for the eyes. Error bars represent the square root of the counts.