Matsayin Kirki Da Dukkake Tsakiya
Don samar da hard magnetic materials, yana da shawarar yadda ake nufin wasu kalmomi. Su ne su:
Coercivity: Yadda ake iya gudanar ferromagnetic material da kyau (resist) na tsakanin magnetic field ba ta lura.
Retentivity (Br): Shi ne mafi girman maginitoci da ferromagnetic material yana iya bincike kafin ake haka magnetic field ta zama zero.
Permeability: A taimakawa wajen nuna yadda mutanen aiki da applied magnetic field.
Magnetic materials suna kula (kamar hanyoyin coercive force) zuwa biyu masu sauran - hard magnetic materials da soft magnetic materials,
Daga nan, za a iya nufin hard magnetic materials. Wasu waɗannan materials suna da nasara mai yawa saboda ya fi yawan da ita da shiga magnetize. Sabubbin shine domain walls ba su iya yi ƙarin abinda saboda crystal defects da na'urar ƙasa.
Amma idan ta shiga magnetize, za ta zama permanent magnetized. Saboda haka; ana kiran shi da permanent magnetic material. Suna da coercive force da take da 10kA/m da kuma retentivity mai yawa. Idan ake bayar hard magnet da external magnetic field tare da rai, domain ya ƙara da yake ƙirƙira don a tabbatar da applied field a saturation magnetization. Baɗan nan, an koye field. Amma, magnetization ya ci ƙarin amma ba ta ci ƙarin da ake nufin magnetization curve. A kan ya fara energy (Br) a cikin magnet da ya zama permanent magnetized.
Hysteresis Loop
Jimlar hysteresis loop = energy da aka fara a cikin material da take da volume da ke magnetize a cikin cycle of operation. B-H curve ko hysteresis loop da hard magnetic materials yana da jimlar mai yawa saboda coercive force mai yawa kamar yadda ake nuna a figure.
BH Product
product BH yana ƙoƙari a cikin demagnetisation curve. Permanent magnet mai kyau yana da maximum value of product BHmax. Ana buƙata cewa dimension of this BH na nufin energy density (Jm-3). Saboda haka, ake kira shi energy product.
Properties of Hard Magnetic Materials
Utmost retentivity and coercivity.
Value of energy product (BH) will be large.
The shape of BH loop is nearly rectangle.
High hysteresis loop.
Small initial permeability.
Properties of some important permanent magnetic material are shown in the table below.
| Hard magnetic materials | Coercivity (Am-1) | Retentivity (T) | BHmax(Jm-1) |
| Alnico 5 (Alcomax)(51Fe, 24 Co,14 Ni, 8Al, 3Cu) | 44,000 | 1.25 | 36,000 |
| Alnico 2(55Fe, 12Co, 17Ni, 10Al, 6Cu) | 44,800 | 0.7 | 13,600 |
| Chrome steel(98Fe, 0.9Cr, 0.6 C, 0.4Mn) | 4,000 | 1.0 | 1,600 |
| Oxide(57Fe, 28 O, 15Co) | 72,000 | 0.2 | 4,800 |
Some important hard magnetic materials are the following:
Steel
The carbon steel have large hysteresis loop. Due to any shock or vibration, they lose their magnetic properties rapidly. But tungsten steel, chromium steel and cobalt steel have high energy product.
Alnico
It is made up of aluminium, nickel and cobalt to boost to improve the magnetic properties. Alnico 5 is the most important material used to create permanent magnet. The BH product is 36000 Jm-3. It is used in high temperature operation.
Rare-Earth Alloys:
SmCo5, Sm2Co17, NdFeB etc.
Hard Ferrites or Ceramic magnets (like Barium Ferrites):
These materials can be powdered and used as a binder in plastics. The plastics made by this method are called plastic magnet.
Bonded Magnets:
It is used in DC motors, Stepper motors etc.
Nanocrystalline hard magnet (Nd-Fe-B Alloys):
The small size and weight of these material make it to use in medical devices, thin motors etc.
Applications of Hard Magnetic Materials
Hard magnetic materials have wide range of applications. They are as follows:
Automotive: motor drives for fans, wipers, injection pumps; starter motors; Control for seats, windows etc.
Telecommunication: Microphones, Loud Speakers, Telephone Ringers etc.
Data processing: Printers, Stepping Motors, Disc Drives and Actuators.
