Various metal-in-gap heads have been developed for the high density recording system. We report on a metal-in-gap head composed of a Mn-Zn ferrite core and FeGaSiRuO metal film which is prepared by sputtering, and in which the metal film is shown to run parallel to the gap-forming layer. In this type of head, the boundary between the metal and the ferrite usually acts as a pseudo-gap, resulting in a ripple in the playback output spectrum. It was found through experiments that some metal elements and oxygen contained in both the magnetic metal alloy and the ferrite diffuse around the boundary during the heating process. Due to the diffusion of these elements, nonmagnetic and less magnetic layers grow at the boundary and form a pseudo-gap. We suppressed the formation of these undesired layers by using FeGaSiRuO alloy having high B_s, thus remarkably reducing the ripple of playback output spectrum.