Micromagnetics of Closed-Edge Laminations

According to previous work, lamination of the film core in a recording head eliminates noisy closure domains - but introduces potentially noisy curling- edge walls. In quest of a possible means of avoiding the edge walls, we minimize the energy of an infinite strip composed of two laminations connected along their edges. Under the conditions that the spacer thickness is ≥ 0.2 x (magnetic-sublayer thickness) and that the energy is less than that of the closure-domain state, we predict: 1) Fully stray-field-free flux closure with no walls occurs if the sum of anisotropy and exchange - stiffness energies within the magnetic connections is negative. 2) If this energy sum is positive, then a part of the flux leaks through the spacer, forming edge walls whose angle is < 90°. Polarization switching of these walls contributes to hysteresis. 3) If a pair of would-be edge walls are so thick as to impinge on each other then the actual ground state is one of saturation along the hard axis. An advantage of closed edges is the need for thicker and therefore fewer sublayers. A disadvantage of thicker sublayers is greater eddy currents. © 1990 IEEE