Nuclear Magnetic Resonance and X-ray Reflectometry of Co/Cu Superlattices

Abstract

The state of interfaces in Co/Cu superlattices with various thicknesses of non-magnetic Cu layers (t_cu) has been studied by the methods of nuclear magnetic resonance (NMR) and X-ray reflectometry. The samples glass/Fe(5 nm)/[Co(1.5 nm)/Cu(t_cu)]₁₀/Cr(3 nm) were fabricated by the method of magnetron sputtering on glass substrates under constant current in the ULVAC MPS-4000-C6 device. The ⁵⁹Co NMR spectra were taken in a local magnetic field in the frequency range of 90–240 MHz at 4.2 K in the pulsed NMR spectrometer. The spin echo signal was formed by a sequence of two coherent radio-frequency pulses (τ_p)_x − t_del − (τ_p)_y − t_del – echo forming an alternate magnetic field with the round component amplitude H₁ of about 10 Oe in a resonance coil. It has been shown both by NMR and X-ray reflectometry that the structure of interfaces deteriorates with an increase of the Cu layers thickness, and similar dependences of the parameters characterizing structural imperfection of interfaces were obtained by these two methods.