Magnetic domain structure, magnetocrystalline anisotropy and domain wall energy in the polycrystalline intermetallic LaMn2Ge2 compounds

Applying the powder pattern method, the domain structures of polycrystalline intermetallic LaMn2Ge2 compound were studied on the grain surfaces parallel and perpendicular to the easy direction of magnetisation (c axis). The domain structures observed are typical for the un axial materials. On the grain surfaces that are parallel to the c axis domains with 180o Bloch walls are apparent. At the grain boundaries closure domains occur in the from of daggers and subdaggers. On the grain surfaces that are perpendicular to the c axis a labyrinth-like structure is observed. Domain walls become crinkled to reduce the magnetostatic energy of the surface and dagger-like closure domains are also visible as small circles. The domain wall energy density γ was determined from dependence of the domain width D on the crystal thickness L in the magnetically preferred direction, applying different models of the domain structure. A good agreement was obtained between thr values of the domain wall energy determined from the Kittel's model (γ = 6.2 mJ/m2) and Hubert's model (γ 6.4 mJ/m2). However, using Bodenberger and Hubert method of domain wall energy determination from the grains surface perpendicular to the easy direction of magnetisation, lower value of domain wall energy was obtained (γ = 2.0 mJ/m2). Moreover, the magnetocrystalline anisotropy constants K1 and K2 were determined from the torque curves applying: Fourier analysis (K1 = 22.8 kJ/m3 and K2= 15.2 kJ/m3), torque curves maxima (K1 = 23.8 kJ/m3) and slope of the torque curves (K1 = 17.4 kJ/m3). (author)