Magnetic properties and growth texture of high-coercive Nd–Fe–B thin films

We have investigated the growth texture and magnetic properties of sputtered Nd–Fe–B thin films with thicknesses from 5 to 350 nm. Films deposited directly onto a quartz substrate grow with a pronounced $c$ -axis texture perpendicular to the film plane and have a coercivity of about 160 kA/m. If the films thickness is reduced below 150 nm, a significant part of the Nd is oxidized by substrate oxygen and the coercivity decreases to values below 20 kA/m. The deposition of a 80 nm Cr buffer layer between substrate and Nd–Fe–B film prevents oxidation of the film and decreases the growth texture of the films. This enables us to fabricate Nd–Fe–B films as thin as 20 nm with good hard magnetic properties ${\mathrm{[H}}_{\mathrm{cj}}\text{=800\hspace{0.17em}}\mathrm{kA/m},$ $J_r\text{=1.1\hspace{0.17em}}\mathrm{T},$ and a maximum energy product ${\mathrm{(BH)}}_{\max }\text{=190\hspace{0.17em}}{\mathrm{kJ/m}}^{\mathrm{3}}$ perpendicular to film plane]. An inverse relationship between growth texture and coercivity is found which can be understood in terms of domain wall motion. The deposition of a Cr buffer leads to an island type of growth and a high surface roughness, while films without Cr buffer are very smooth. By depositing a protective Cr layer on top of the film, the corrosion resistance can be enhanced.