Ferromagnetic and Structural Properties of Nearly Perfect Thin Nickel Platelets

Abstract

Nearly perfect, single-crystal thin platelets of nickel and nickel alloy are readily grown non-epitaxially by the reduction of the halide. Thicknesses range from about 500 Å to over 105 Å; areas extend to over 1 mm2. Etching in HCl reveals dislocation densities generally either of zero or of 103–104 cm−2. Ferromagnetic domain studies with the platelets have yielded the following results: (1) 180 ° walls with mixed NéelBloch character may coexist with Bloch walls in both nickel and NiCo platelets at least 7000 Å thick. The presence of a geometrically required crosstie spot establishes the partially Néel-wall character. (2) one may precisely determine the applied field required to drive out a nucleus of reverse magnetization from the corner of a platelet by noting the form of the returning domain structure. (3) the 180 ° wall in a rectangular Ni-Co platelet with a simple closure pattern forms the arc of a circle in an applied field; i.e., there is a uniform effective pressure acting along its length. (4) Topological restraints are largely responsible for hysteresis in nickel platelets several thousand angstroms thick. In small driving fields Ni-Co rectangular platelets may have virtually no hysteresis or coercive force (Hc<0.01 Oe). In large fields there is hysteresis from irreversible topological changes, but there may still be no coercive force. (5) Near the transitional thickness for crosstie walls the platelets show both coercive forces of several tenths of an oersted and an after-effect. The ferromagnetic resonance experiments of Rodbell with nickel platelets are also briefly mentioned.