Soft ferrites like Mn-Zn and Ni-Zn ferrites are used as core materials in these applications in the frequencies ranging from a 100 kHz to 100 MHz. Typically these ferrites have high electrical resistance which results in very low eddy current losses. Most common radio magnets, including those used in loudspeakers, are ferrite magnets. Ferrite magnets have largely displaced Alnico magnets in these applications.
Ferrites are also used for power transformers which are used to transmit either over a single frequency or within a range such as in ultrasonic generators. For high frequency applications, upto about 5 MHz, Ni-Zn ferrites are useful while for frequencies upto 100 kHz, Mn-Zn ferrites are preferred due to their higher permeabilities.
Here, due to their high impedance to high frequency currents, ferrite components of Ni-Zn and Mn-Zn ferrites are able to prevent high frequency electrical noise due to electromagnetic interference from exiting or entering the equipment.
Data storage (e.g. magnetic recording tapes and hard disks)
In the magnetic tapes, elongated 0.2-.5 μm long hard magnetic oxide particles of γ - Fe2O4 are embedded in nonmagnetic binder. The particles have single domains magnetized along their major axes which are aligned in the plane of the tape. The coercive fields are typically between 50-100 kA.m-1. In magnetic hard-disks, core element is produced by forming several layers of materials (nonmagnetic underlayer, magnetic layer, overcoat, plus layer of lubricants on a nonmagnetic disk substrate). Here, the read/write head is not in direct contact with the hard disk (in contrast to floppy disk) due to an air bearing (≈ 50 nm); air flow is caused by the relative velocity between disk and head. These memories have high storage density of about 10 GB.in-2 and short access time.
Early computer memories stored data in the residual magnetic fields of hard ferrite cores, which were assembled into arrays of core memory. Ferrite powders are used in the coatings of magnetic recording tapes. One such type of material is iron (III) oxide.
Absorbing materials
In stealth aircrafts, ferrite particles are used as a component of radar-absorbing materials or coatings and in the absorption tile lining in the rooms used for electromagnetic compatibility measurements.
Microwave applications in the frequency ranges of 1-300 GHz
Materials like Mg-ferrites, Li-doped Ferrites and garnets are used for such applications such as phase shifters, circulators and isolators.
