Cathode ray tube tension mask made of magnetostrictive material with compensation for terrestrial magnetism

A cathode ray tube comprising a tension mask made of a magnetostrictive material, wherein

• the magnetostrictive material has a positive magnetostrictive constant,
• the tension mask is stretched by a stretching force in a vertical direction so as to maintain the flatness of the tension mask with an angle defined by a direction of an easy axis of magnetization in-plane in the tension mask and a direction in which the stretching force is applied to the tension mask is being between 30° and 90°, and
• the combination of the direction and strength of the stretching force are set such that vertical magnetic permeability of the tension mask increases, due to a magnetoelastic effect caused by the stretching force in the magnetostrictive material of the tension mask,
• wherein the magnetostrictive material includes a plurality of polycrystalline grains, each having an axis oriented along the easy axis of magnetization.