Coercivity and microstructure of Sm(Co0.87Cu0.13)7.8

Abstract

The magnetic hardness of Sm(Co_0.87Cu_0.13)_7.3 in bulk form is caused by pinning of the domain walls at precipitates which are of the Sm(Co,Cu)₅ type. The hard magnetic properties of both the 2 : 17 matrix and the 1 : 5 precipitate phase have been investigated in the temperature range between 77 and 800 K. The domain‐wall energies have been determined from the surface domain patterns observed by means of the magneto‐optical Kerr effect. It is shown that the coercivity mechanism in Sm(Co_0.87Cu_0.13)_7.8 cannot be explained by the difference of the magnetic crystal anisotropy constants K₁ of matrix and precipitate phase only. However, the coercivity may be described by the decrease in the domain‐wall energy γ at the precipitates. γ of the 2 : 17 matrix was found to be five times that of the 1 : 5 precipitate phase (38 and 7.5 erg cm⁻², respectively) resulting in an attractive interaction between the precipitates and the domain wall. The magnetic field necessary to overcome this attractive interaction has been estimated to be approximately 5 kOe, i.e., comparable to the experimentally obtained value of 4 kOe.