Observation of Pure Nuclear Diffraction from a Fe/Cr Antiferromagnetic Multilayer

We report the observation of nuclear resonant diffraction of synchrotron radiation from a ${}^{57}$Fe/Cr multilayer. The multilayer consists of 25 ${}^{57}$Fe(17 Å)/Cr(10 Å) bilayers with the Cr layer thickness chosen so as to exhibit antiferromagnetic (AF) coupling of the ${}^{57}$Fe layers. Because of the AF alignment of the layers, the magnetic periodicity of the multilayer is twice the electronic periodicity, resulting in a pure nuclear Bragg reflection that appears during nuclear resonant diffraction. The pure nuclear Bragg reflection presents a means of filtering synchrotron radiation to the level of 1$0^{–8}$ eV at the nuclear resonance energy of 14.4 keV.