Magnetic Stripe cards

Coercivity is the term used to designate how strong a magnetic field must be to affect data encoded on the stripe, and therefore, how immune the data is to damage.

Measured in Oersteds (Oe), the coercivity of a common credit card is about 300 Oe, considered low coercivity. Consequently magnetic money clips, refrigerator magnets, etc., play havoc with the data on your credit card’s stripe. High coercivity (HiCo) magnetic stripe technology relies on particles -- generally barium ferrite (low coercivity uses iron oxide) -- with coercivity values ranging from 2500 to 4000 Oe.

The encoding technique is the same as for LoCo technology, except that it requires a stronger electrical current in the write head. Virtually immune to domestic-type magnets, HiCo substantially decreases the chances of accidental data erasure. Despite this superiority, HiCo hasn’t yet replaced LoCo technology, due to the widely established base of LoCo encoders and the increased cost of HiCo encoders. Standard magnetic stripe readers, however, can read either HiCo or LoCo stripes.

High-coercivity cards are currently used in applications where the need for performance, for example in critical test equipment, outweighs price. A single magnetic stripe can hold several tracks of recorded data, which can be rewritten and updated. The ISOIEC 7810, 11, 12, and 13 series of standards specify a three-track format, encoding scheme, and bit density for all financial card applications.