Nuclear Forward Scattering of Synchrotron Radiation in Pulsed High Magnetic Fields

We report the demonstration of nuclear forward scattering of synchrotron radiation from ${}^{57}\mathrm{Fe}$ in ferromagnetic $\alpha$ iron in pulsed high magnetic fields up to 30 T. The observed magnetic hyperfine field follows the calculated high field bulk magnetization within 1%, establishing the technique as a precise tool for the study of magnetic solids in very high magnetic fields. To perform these experiments in pulsed fields, we have developed a detection scheme for fully time resolved nuclear forward scattering applicable to other pump probe experiments.

Figure 1

(a) Nuclear level scheme for the for the 14.413 keV Mössbauer transition of ${}^{57}\mathrm{Fe}$ in $\alpha$ Fe. (b) Magnetic field pulse. (c) Experiment.

Figure 2

NFS in pulsed high magnetic fields from a $10\mu \mathrm{m}$ thick, polycrystalline foil of ferromagnetic $\alpha$ Fe. (a) Simulation of the NFS intensity as a function of delay and the field at the nucleus for a Lamb-Mössbauer factor of 0.82. (b) Experimentally observed events as a function of delay and the applied field. Note the different vertical scales and ranges.

Figure 3

Selected time spectra. Nuclear forward scattering intensity as a function of time with respect to the last prompt pulse. The spectra were extracted from Fig. 2 through binning in time (0.8 ns) and field (2 T). Points, data with statistical error; line, fit to the data.

Figure 4

(a) Field at the ${}^{57}\mathrm{Fe}$ nuclei and energy difference $\Delta E$ as a function of the applied magnetic field. The points were obtained by fitting the time spectra in Fig. 3. Line: Calculated internal field. Inset: Sample geometry. (b) Points, left label: Measured field at the ${}^{57}\mathrm{Fe}$ nuclei minus the applied field. Error bars: Fitting error. Line, right label: Calculation of the magnetic hyperfine field minus the demagnetizing field.