A pole layer incorporate a track width defining and a wide portion. A
material forming the pole layer is an alloy whose major elements are iron
and nickel. In the alloy, where the proportions of iron and nickel with
respect to the total of iron and nickel are indicated as (100-M) weight %
and M weight %, respectively, M is greater than 0 and smaller than or
equal to 10. The internal stress of the pole layer is a tensile stress.
The magnetostriction constant of the material forming the pole layer is
positive. Where the anisotropy field of the pole layer is Hk (A/m), the
magnetostriction constant of the material forming the pole layer is
.lamda.(.times.10.sup.-6), and the internal stress of the pole layer is
.sigma. (MPa), the value of Hk/(.lamda..times..sigma.) is greater than
0.01 and smaller than 0.2.