Topological materials exhibiting giant magnetic responses have attracted a great deal of attention as a new material resource for magnetic sensors. By fabricating amorphous thin films of ferromagnetic Fe-Sn alloy that was inspired by a topological ferromagnet Fe3Sn2, the authors developed a Hall sensor based on large anomalous Hall effect of the Fe-Sn films. Furthermore, by combining the anisotropic and unidirectional magnetoresistance effects, three-dimensional magnetic-field sensing in a simple planar-type device configuration was demonstrated. This article overviews principles of thin-film magnetic sensors and introduces the synthesis of Fe-Sn amorphous films and the characteristics of the anomalous Hall effect-type Hall sensor and three-dimensional magnetic-field sensing device.