Abstract: A metal alloy is provided which includes by weight percentage of the metal alloy, 28 to 55 percent copper, 45 to 63 percent nickel, and 4 to 10 percent iron. The metal alloy may be weight percentage 28 percent copper, 62 percent nickel, and 10 percent iron. The metal alloy may be formed into a foil which may have a thickness of 100 ?m or less or 50 ?m or less. A magnetic field instrument may include a magnetometer core body formed from one or more layers of the foil. The magnetometer core body may be a ring core or a racetrack core. The magnetic field instrument may further include a sense winding and may further include a drive winding. The magnetic field instrument may be a fluxgate magnetometer.

Abstract: A direct-coupled fluxgate current sensor which is driven to hard saturation to achieve a sudden change in magnetic properties of the sensor, has: (a) a first closed loop core of ferromagnetic material encased in a sleeve wound with a first toroidal drive winding, the winding for the first core extending around the circumference of the first core; (b) a second closed loop core of ferromagnetic material encased in a sleeve wound with a second toroidal drive winding independent of the first winding, the winding for the second core extending around the circumference of the second core; and, (c) a closed loop core casing which is adapted to cooperate with the first core and the second core, the closed loop core casing and the first and second core being wound as a unit with a toroidal sense winding independent of the first and second toroidal drive windings, the winding for the closed loop core casing extending around the circumference of the closed loop core casing.