Unit 04
Magnetic materials
Q1) Categorize the magnetic materials in brief?
A1) Magnetic materials can be categorized basically three types. Based on the bahavourial of magnetic materials. These are diamagnetic, ferromagnetic and paramagnetic materials that are described below.
Diamagnetism materials
In diamagnetism materials are the orbital motion electrons are around nucleus develops a magnetic field perpendicular to plane orbit. So, different electron orbit has the finite orbital magnetic dipole moment. Orbital planes are oriented in the random way, the sum of the vector magnetic moments are zero and so there is no resultant of the megnatic moment for the each atoms. This process is named diamagnetic action and these materials are called as the diamegnatic materials. Materials are bismuth, water and copper etc. properties of the diamagntism materials are-
Negative magnetic susceptibility
Relative permeability is less than unity.
Magnetic field line is expelled through diamagnetic materials while take placed in the magnetic field.
Susceptibility is temperature independent.
Paramegnatic materials
Some of the magnetic materails are, every moleculas or atom contains net magnetic dipople moment that is the vector sum of the orbital and the spin magnetic momnets of the electrons. Besides of the random orinetaion of the magnetism moments, the complete magnetic momnet of materails is zero. Exmaple of the paramegntaic materials are alumium, chromium and platinum etc. propeties of the paramegnatic materails are –
Susceptibilty of the magntic is positive and small.
Relative permebaility is greater than the unity
Magnetic field line is attretcd into paramagnatic materials while take place in the magnatic field.
Susceptibilty, invresly proportional to the tempertaure.
Curies law
Due to the increament of the temperature thermal vibration will be upset alignment of the magnetic dipole moments. So, the magnetic susceptibility is decreases with the incrasease in the temperature. In the many other cases matearials susceptibility is
This relation named curies law.
Ferromagnetism materials
Molecule or an atom in the ferromagnetic material procedures net magnetic dipole moment as in the paramagnetic materials. A ferromagnetic material is developed from the smaller regions, named ferromagnetic domain in the figure. Within the each domain, magnetic moments are spontaneously aligned the directions. This alignment is reasoned through the powerful interactions arising from the electron spin that relies on inter atomic distance. Every domains have net magnetization in the direction. But direction of the magnetsation differ from the domain to domain and so net magnetization of the specimen is zero.
Two processes are take place in the presence of the external magnatic field.
Ferri-magnetism
Ferri-magnetism materials are type of the permanent magnetism which happens in the solids in that magnetic fields related with the individual atoms impulsively align themselves, some of the parallel or in the similar direction and another normally antiparallel or paired off in the different direction, like in the antiferromagnetism. Single crystals magnetic behavior of the ferromagnetic materials may be assigned to parallel alignment, atoms diluting effect in antiparallel arrangements contains magnetic strength of these materials normally less than which of purely ferromagnetic solids like iron matel. Ferrimagnetism take place mainly in the magnetic oxides which are known as the ferrites. The original magnetism exhibited through the lodestones and recorded as early in the 6th century BC, is which of the ferrite mineral magnetite, this compound has negative oxygen ions O2 and +ve iron ions in the two states, iron(II) ions, Fe2+, and iron (III) ions, Fe3+. Oxygen ions are not magnetic and but both iron ions are.
Q2) Explain the applications of the Ferro magnetic materials ?
A2) Ferromagnetic materials applications are comprehensive. Hysteresis curve is plays a big role and it has great importance.
It has its applications in the transformers, magnetic tape recording and electromagnetic.
Nano wires, power generation, distribution and shape memory alloys, electronics and carbon nano tubes, for sudden cooling, in nuclear reactors neutron absorber, easy polarization and high magnetic susceptibility, and magnetic tape emulsion.
Q3) Define parameters of the magnetic materials?
A3) Parameters of magnetic materials
Magnetic permeability
In the electromagnetism, permeability is the measurement of the resistance of the material against formation of the magnetic field, also known as distributed inductance in the transmission line. Magnetic permeability is crucially represented by Greek letter μ. Magnetic permeability is relatively increase or decrease, in resultant magnetic field inside a substance compared with magnetizing field in that provided materials is placed, or the material property which is equal to magnetic flux density B developed within material through magnetizing field partitioned through magnetic field strength H of magnetic field. Magnetic permeability μ is the defined as the μ=B/H. Flux density B is measured by the actual magnetic field within the materials which is considered magnetic field lines concentration or the flux is per unit cross sectional area. H is the magnetic field strength is measure of magnetizing field which is developed through the electric current flow in the wire coil.
Magnetic susceptibility
In magnetic field, the magnetic susceptibility is the measurement of material will become magnetized in applied magnetic field. This is the dimensionless proportionality constant which indicates magnetization degree of the material in the response to applied magnetic field. It is due to interactions of the electrons and nuclei with externally applied magnetic filed. We can define magnetic susceptibility mathematically is ratio of the magnetizing to applied magnetizing field intensity. X=M/H
Where X= magnetic susceptibility
M=magnetization
H=field intensity
Magnetization
The process of magnetization of the given sample material M can be described as net magnetic moment for which material per unit volume.
Q4) Explain the ferro-magnetic behavior below the critical temperature?
A4) Materials are when ferromagnetic below critical temperatures. In the absence of the applied magnetic field materials are called ferromagnetic. In the absence of the magnetic field material has been spontaneous magnetization that is a outcome of ordered magnetic moments. Which is for the ferromagnetism, atoms are aligned and symmetrical in the similar direction of creating a permanent magnetic field. Through exchange interactions magnetic interactions are held together, or thermal disorder would overcome weak magnetic interactions moments. Exchange interaction has been a 0 parallel probability electrons engaging similar point in time, indirect a preferred a parallel alignment in material. The Boltzmann factor gives heavily as this prefers interacting particle to be aligned in similar direction. This reasons ferromagnets to have been strong magnetic field and high critical temperature of around 1000K (730 degree C). Below the critical temperature atoms are parallel and aligned, this is cause of spontaneous magnetism and the material is ferromagnetic. Above the critical temperature material is paramagnetic, in this atoms are lose their order magnetic moments while materials undergoes in a phase transition.
Q5) Seeing below diagram find out the axial field of a finite solenoid and hence demonstrate and it is similar to the bar magnet.
A5) According to the above diagram this consist of n turn per unit length. Radius is a and length is 2l. axial field is evaluated at the point P, at a distance from the r centre, solenoid is . Let we consider the circular thickness element dx of solenoid at the distance x from its centre point. It consists of ndx turns. Let solenoid current is . And magnetic field magnitude on the axis of the circular current loop at the point p for the circular element is provided by
Total field magnitude is given by integrating from x= -/ to x=+/ so, we have
For far axial solenoid field, 4.e.,r>>a and r>>l. Then, dominator is approximated given by
Since field of the magnetic bar magnitude. It is the proof that a bar magnet and solenoid develop a similar magnetic fields. So the bar magnet magnetic moment, is equal to magnetic moment of equivalent solenoid which develops the similar magnetic field.
Q6) Describe the applications of the ferro magnetic materials?
A6) Ferromagnetic materials applications are comprehensive. Hysteresis curve is plays a big role and it has great importance.
It has its applications in the transformers, magnetic tape recording and electromagnetic.
Nano wires, power generation, distribution and shape memory alloys, electronics and carbon nano tubes, for sudden cooling, in nuclear reactors neutron absorber,
Q7) What are the major technical/industrial uses of the magnetic materials?
A7) When iron makes a good magnet, it has the limitations like loss of magnetism, heating by the eddy currents and low magnetic force. So the industrial magnets are made from the materials which resist de-magnetism, this consists high resistivity. Magnets are used in the industry.
Ferrite magnets
Ferrite magnets are also known as ceramic magnets and is a chemical compound of an iron oxide and different metals. Soft ferrites are containing the nickel, zinc or manganese compounds, consist low coercivity and these are commonly utilized in the high-frequency of the transformers and inductors. Hard ferrites are utilizing strontium, cobalt and barium, keep their magnetism and utilized in the loudspeakers, radios, relays, microwaves, permanent magnet motors and disc drives. Magnetic tapes utilizes iron oxides to save the information. Present generation of the magnetic tape can be store 330 TB of the data.
Alnico magnets
These magnets were developed on the year 1930s and speedily become famous. These provide good magnetic strength and the withstand temperatures up to the 245 degree C. these are made from the nickel, cobalt, and aluminum these are expensive. They should be cast and magnetic field is placed during the heat treatment. These magnets are utilized in the electric motors, couplings, ABS systems guitar pick ups, military, magnetic bearings and aerospace applications.
Neodymium magnets
These magnets are too strong and replacing earlier magnets types. These are most powerful permanent magnets which are presently available, permitting too small magnets to be utilized. This characteristics suits their utilization in the small sensors, hard drives and audio equipment. Other applications are include in the medical imaging, cordless tools, loudspeakers and as the magnetic bearings.
Electromagnets
While there is a require to handle magnetic force, electromagnets are utilized. Utilizing low coercivity materials are electromagnets utilized electric coils to quickly switch magnetic field. This makes the power transformer powerful and feasible superconducting magnets utilized in the magnetic levitation, MRI imaging and levitating trains. AC motors are a kind of electromagnets as the rotating magnetic fields force rotors to the spin. Another applications are including lifting the magnets, relays and solenoids.
Q8) What the reason of magnetic property in the materials?
A8) Magnetic property is the force which is exerted by the magnets while they attract each other. Magnetism is caused by electric motion charge. Each substance is developed by the tiny units named atoms. Every atoms have the electrons, which carry electric charges. Spinning such as tops electrons circle nucleus or the core of the atom. Electrons movements are creates an electric current and causes every electrons to act such as microscopic magnet. Most of the substances, equal electrons spin in the opposite directions, that cancels out their magnetism. So the materials like paper are said to be weak magnet. In the many substance like iron, nickel and cobalt most electrons are spinning in the similar directions. This all are making the atoms in these substance strongly magnetic however they are not magnets. To become the material magnetized other strongly magnetic substance should enter magnetic field of an existing magnets. Magnetic field is area around the magnet which has magnetic force.
Q9) Due to the hysteresis effect in the magnetic materials estimate the energy amount.
A9) When a ferromagnetic materials is magnetized is in the one directions, if applied magnetizing field is removed it will not relaxed back to 0 magnetization. A field in the opposite direction requires to push it down to 0. If an alternating magnetic field is applied to the object, a loop called a hysteresis loop can be traced for its magnetization. The lack of the magnetization curve retractability is the property called hysteresis, which is related to the presence of the magnetic domains in the materials. Upon reorientation of the magnetic domains it takes some of the energy to transform them around. This property is useful as the magnetic “memory” of the ferromagnetic materials. Some of the ferromagnetic materials compositions can maintain an induced magnetization forever and are useful as “permanent magnets”, the magnetic memory properties of the iron and chromium oxides make them useful for the recording audio tape and fro data storage on the computer discs.
Q10) Describe briefly the effect of temperatures (above and below curie temperatures ) on using Weiss theory ferromagnetic materials.
A10) Curie-Weiss theory that explains the ferromagnetism’s qualitative interpretation. Also call it theory of the molecular fields. In this principle the ferromagnetic materials are shown as a special case of paramagnetic content. In this, due to applied external field, there is also an internal field. The total field which the ferromagnetic materials experiences is given as.
OverrightarrowBTotal=overrightarrowBoperatornameint+overrightarrowBext,app
Where
OverrightarrowBTotal= net field
OverrightarrowBoperatornameint= = internal magnetic field (or) Weiss field
OverrightarrowBext,app= externally applied field.
OverrightarrowBoperatornameintpropto Magnetization (M)
OverrightarrowBoperatornameint=lambdamu0M
Mu0- magnetic permeability of free space
Lambda- constant
M – magnetization
Equation 1+ equation 2
OverrightarrowBTot=lambdamu0M+overrightarrowBext
As we know, magnetic susceptibility (χ) is given by
Chi=fracmu0MBTotal … (3)
Chi=fracmu0MBapp+lambdamu0M … (4)
Assuming temperature dependence of magnetic susceptibility (χ) is given by curie law
Chi=fracCT … (5)
Where C – is constant
T – is Temperature
This equation is known as curie law for paramagnetism.
Compared equation 4 and 5
FracCT=fracmu0MBapp+lambdamu0M Cleft(Bapp+lambdamu0Mright)=mu0MT C,Bapp=left(T−Clambdaright)mu0M fracCT−Clambda=fracmuoMBapp fracCT−Clambda=chi
Where Clambda=theta fracCT−theta=chi … (6)
θ – characteristic temperature (or) curie temperature we call this above equation (6) as curie – Weiss law.
Case 1 T> θ
For ferromagnetic materials, this curie-Weiss law holds well for ferromagnetic materials is positive. There is no ferromagnetic activity above the certain characteristics of the temperature-it is known as the materials critical temperature or curious temperature. It works as it of paramagnetic nature.
When T> θ
The inner field of the magnetic substance disappears. Now the magnetic atomic moment isn’t matched with each other.
Case 2 T> θ
Temperature below the curie temperature characteristics that the magnetic substance functions as a ferromagnetic materials. That means the magnetization is random.
There is a powerful internal field which even in the absence of the external applied field aligns the atomic magnetic moments.
