A refractive index nL and an attenuation rate kL of a magnetic layer are obtained by irradiating linearly polarized light at an irradiation angle of 70° from a lengthwise direction of the magnetic layer to the surface of the magnetic layer, and a vertical reflectance RL during vertical incidence of the linearly polarized light in the lengthwise direction is obtained based on nL and kL. A refractive index nT and an attenuation rate kT of the magnetic layer are obtained by irradiating linearly polarized light at an irradiation angle of 70° from a width direction of the magnetic layer to the surface of the magnetic layer, and a vertical reflectance RT during vertical incidence of the linearly polarized light in the width direction is obtained from nT and kT. If a variation rate A (%) of RL and RT is A=|RL/RT−1|×100, the relationship A≤10% is established.