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Conventional adhesive bonding caused reductions of 50 percent or more in the 100 gauss magnetic permeabilities (at frequencies of 60 to 5 × 105Hz) of laminated 4-79 molybdenum Permalloy cores. Oxidizing the laminations prior to adhesive bonding decreased these reductions as much as 50 percent. A method of stress-free joining was developed using simultaneous annealing and diffusion bonding of laminations which had been either pre-oxidized or coated with magnesium methoxide. Cores fabricated in this manner exhibited permeabilities similar to unbonded cores at low frequencies, and permeabilities higher than conventional adhesively bonded cores at high frequencies.