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Heat treatment is the central step for defining the magnetic properties by setting the structure, mechanical relaxation or adjusting the state of order in the material. Various forms of hysteresis loops can be tailored by annealing in a magnetic field. If the field stands parallel to the wound ribbon a rectangular ("Z") loop will arise. A magnetic field perpendicular to the ribbon results in a flat ("F") hysteresis loop. Annealing without any field typically results in a round ("R") shaped loop.

To avoid harmful oxidation processes heat treatment usually is performed in pure hydrogen gas. Temperature and time are the essential parameters for setting the structure or loop shape. For example, by a variation of the temperature during perpendicular field annealing, the F loop can be raised and the permeability can be adjusted specifically. Using VITROPERM® permeabilitiy can be changed in a wide range between 20,000 and 200,000, whereby the loop remains extremely linear. An important prerequisite is zero magnetostriction. Among others this must be reached during heat treatment. Together with permeability other application - specific variables such as coercivity or magnetization losses are defined simultaneously.

Permeability levels of VITROPERM after various heat treatment. RCCB specific measures at 50 Hz

µ(Hdc) curves of various materials as they are typically measured for applications in telecommunications.

Last update: 03.12.2012


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