The present disclosure discloses a device with a protective layer, including a substrate, a seed layer formed on the substrate, and a diamond-like carbon layer formed on the seed layer, where the seed layer is a silicon nitride layer, and a content of nitrogen in the silicon nitride layer is 9%-17%. The present disclosure further discloses a microwave-assisted magnetic recording (MAMR) head slider, a head gimbal assembly, and a disk drive unit. The device has good thermal stability, oxidation resistance and corrosion resistance, thereby improving reliability and prolonging service life of an MAMR head.