Ferrite, Types of Ferrites and Ferrite Formula

Ferrite Formula and Types of Ferrites

Ferrite material

Ferrite is usually ceramic, standardized material and it has ferrimagnetic properties. We can say in other words that, Ferrite is a ceramic material made by reacting or relating metal oxides into a magnetic material. Ferrites are insulators and having ferrimagnetic property i.e. they can be easily magnetized.

More details on Ferrite you can find in my previous blog;

“Ferrite, Ferrite structure and Ferrite properties”.

Ferrite Formula

The ferrite formula is commonly stated as MeFe₂O₄.

Where “Me” signifies a divalent metal ion.

e.g.  Fe²⁺, Ni²⁺, Mn²⁺, Mg²⁺, Zn²⁺, Cu²⁺, Co²⁺, etc.

Types of Ferrites

On the basis of their resistance to being demagnetized, Ferrites can be divided into two types of ferrites; Soft and Hard Ferrites.

     1) Hard Ferrite Core

Hard Ferrite Cores have high coercivity i.e. it can withstand an external applied magnetic field without becoming demagnetized.

The coercivity for ferromagnetic material is the strength of the externally applied magnetic field needed to decrease the magnetization of that material to zero, once the magnetization of that material has been bring to saturation.

Hard Ferrite Applications: Hard Ferrite Cores are used to make permanent magnets which can be used in speakers and motors.

     2) Soft Ferrite Core

Soft Ferrite Cores have low coercivity i.e. it can’t withstand an external applied magnetic field and easily demagnetized.

They simply change their magnetization, and they act as conductors of magnetic fields.

Soft Ferrite Applications: Soft Ferrite Cores are used to make ferrite cores for high frequency applications like Inductors and Transformers.

Soft Ferrite Materials are characterised by Spinel or cubic crystal structure. Generally at high frequencies, soft ferrites have many advantages as compare to conventional metallic type materials.

Different core geometries optimized for specific applications can be achieved by shaping ferrites.

Inductors and Transformers using Soft Ferrite Cores

Advantages of soft ferrites are listed below;

• Resistivity is high.

• Wide range of operating frequencies can be supported.

• With high permeability low loss can be achieved.

• Different types of material according to applications can be selected.

• Flexibility in the choice of core shapes.

• Low cost can be achieved.

Disadvantages of soft ferrites are listed below;

• Saturation flux density is low.

• Thermal conductivity is poor.

• Tensile strength is low.

• Fragile material.

There are two types of soft ferrite materials;

Nickel-Zinc (NiZn) and Manganese-Zinc (MnZn).

Ferrite Powder

Let’s explain the difference between them;

Manganese-Zinc Ferrites

Ferrite Formula for Manganese-Zinc is;

 Mn_aZn_(1-a)Fe₂O₄

MnZn Ferrite Cores

• This is most common type of soft ferrite and is used in many applications as compare to nickel-zinc ferrites.

• In the MnZn type a big range of materials is possible. The selection of material is mostly a purpose of the application that needs to be achieved.

• Mostly the application gives the required material characteristics, which helps to define the chemical composition and properties of the ferrite material.

• For frequencies less than 2 MHz Manganese-zinc ferrite is mainly used.

• The MnZn ferrites are categorized by the permeabilities (µ) > 1000 and saturation flux density (Bsat) to 5300 Gauss.

• Power, shielding and linear inductive components are some of the usual applications of MnZn Ferrites.

• The MnZn ferrite materials are usually used up to frequencies < 10 MHz.

• The MnZn ferrite materials can be used for pulse applications into the nanosecond range.

• MnZn materials are usually supports temperature range more than 200 °C.

• These cores are easily available in both regular and customized geometry shape i.e. client suggested or application specific.

• Manganese-zinc cores (MnZn) are inductive up to frequencies of 20MHz to 30MHz.

• At higher frequencies i.e. more than 80MHz the core material has more losses and is no longer operative.

• MnZn materials have a high permeability as compare to NiZn ferrites which have a low permeability.

• In the applications where the operating frequency is less than 5 MHz, Manganese-zinc ferrites are used.

• The common mode inductors are the exclusion, where the impedance of MnZn material makes it the finest choice up to frequency 70 MHz.

Nickel-Zinc Ferrites

Ferrite Formula for Nickel-Zinc is;

 Ni_aZn_(1-a)Fe₂O₄

NiZn Ferrite Cores

• The NiZn based soft ferrites is considered by its high material resistivity. It’s very high as compare to MnZn ferrites.

• High resistivity NiZn ferrite makes it operational from 2 MHz to several hundred megahertz.

• An enormous number of nickel-zinc materials have been researched and developed to support such an extensive frequency range and different types of applications.

• The NiZn ferrite core material is considered by permeability’s (µ) up to 2500.

• Usual applications contains;

1. RF transformers (includes both: inductively coupled and transmission line broadband to support frequencies more than 1GHz).
2. Pulse power modules (here pulse shaping and fast switching up to < 10 nanoseconds is required).
3. For common inductive or interference suppression application in the range of MHz.

• These NiZn material cores are easily available in both regular and personalised geometry shape i.e. client suggested or application specific.

• Nickel-zinc material cores (NiZn) are inductive up to the frequency range of 60MHz. After which the core material act as a lossy for up to frequencies of 1GHz and above.

• Nickel-zinc ferrite cores have a higher resistivity as compare to Manganese-zinc ferrite cores and are used at frequencies from 2 MHz to more than hundred megahertz.

• NiZn ferrite cores are recommended for the application range from 70 MHz to several hundred GHz.

Basic Material Characteristics of MnZn and NiZn

Some of the basic material characteristics of both Manganese-zinc ferrites and Nickel-zinc ferrites are given below;

Material Characterisitics of Soft Ferrites
Sr. No.	Characteristics	MnZn	NiZn
1	Initial Permeability (µi)	450 to 15000	14 to 2000
2	Saturation Flux Density (Bms)	363mT to 530mT	275mT to 470mT
3	Curie Temperature (Tc)	100°C < 300°C	90°C < 300°C
4	Resistivity (ρ)	0.12Ωm to 10000Ωm	>10⁶Ωm
5	Density (d)	4.70g/cm³ to 5.00g/cm³	4.60g/cm³ to 5.10g/cm³

Conclusion

Both types of ferrites i.e. Soft Ferrite Cores and Hard Ferrite Cores have their own advantages and used according to the supporting applications. Nearly all applications include these ferrite cores.


Hard ferrite cores which can be magnetized quite strongly are mostly used in motors. On the other hand Soft ferrite cores are found in nearly every electronics applications for the purpose of interference suppression, switching transformer for high frequency applications and radio frequency applications.