Hysteresis is the lagging of magnetization (B) behind the applied magnetic field (H). The document defines hysteresis and explains it using a B-H loop. It also discusses hysteresis in terms of domain theory and defines key terms like retentivity, coercivity, and energy product. Additionally, it summarizes the differences between soft and hard magnets, types of superconductors, shape memory alloys, and metallic glasses.

1. Hysteresis:
Definition : Hysteresis means “Lagging”. The lagging of intensity of
magnetization (B) behind the intensity of magnetic field (H).
Explanation : A graph is drawn
between the intensity of Magnetization (B)
and intensity of magnetic field (H).
i) When the intensity of magnetic field H is
increased from zero, the intensity of
magnetism is also increased.
ii) Further increasing the value of H, the B value is also increased and finally
reaches the saturation point A in figure. ie., B is constant.
iii) Then decreasing the value of H, the B value is also decreased, But at the
point H = 0, But B = 0. Now the material retains some amount of magnetism is
known as Retentivity (or) Resudial magnetism. (point B in fig.)
iv) Further decreasing the value of H in negative side, the B value is also
decreased at point C the material is fully demagnetized. The force is required
for remove the resudial magnetism is called as Coercive force. (point C in fig.)
v) the cycle is continue in opposite direction as shown in fig. D is saturation
point, E is retentivity and F is the coercive force in negative direction. The
cycle is completed, it make the hysteresis loop.
Hysteresis Explained by Domain theory:
OA – Reversible domain
AB – Irreversible domain
BC – Domain Rotation
Br – Retentivity
Hc - Coercivity
ENERGY PRODUCT : Br x Hc

2. Soft magnet and Hard magnet
S.No Soft Magnet Hard Magnet
1
Easily magnetized and
demagnetized
Cannot easily magnetized and
demagnetized
2
It can be produced by heating
and slow cooling
It can be produced by heating and
sudden cooling
3 Hysteresis loop area is small Hysteresis loop area is high
4 Retentivity is small Retentivity is high
5 Coercivity is small Coercivity is high
6 Energy product value is small Energy product value is high
7 Eddy current loss is small Eddy current loss is high
8 It’s temporary magnet It’s permanent magnet
9
Ex. Iron – silicon alloy, Ferrous
nickel alloy, Ferrites Garnets
Ex. Alinico, chromium steel, tungsten
steel, carbon steel
10
Uses : Electromagnet, Computer
data storage, Transformer core
Uses : DC magnets
11

3. Type I and Type II super conductor
No Type I Type II
1 Exhibits complete Messiner’s effect
Does not exhibits complete Messiner’s
effect
2 Perfect Dia magnetism They are not perfect Dia magnetism
3 Only one critical point Two critical point
4 No mixed state Mixed state available
5 Critical magnetic field is 0.1 tesla Critical magnetic field is 30 tesla
6 Soft super conductor Hard super conductor
7
Small magnetic field is applied for
destroy the superconductivity
Large magnetic field is applied for
destroy the superconductivity
8
Changes normal to superconductor
is abruptly
Changes normal to superconductor is
gradually
9 Tin, Lead, Mercury Nb-Zr, Nb-Ti, Nb-Sn
10

4. SHAPE MEMORY ALLOYS
Definition: The ability of the metallic alloys to retain to their original shape when
heating or cooling is called as Shape Memory Alloys (SMA).
Types :
1. One way shape memory – It returns to its memory only when heating.
2. Two way shape memory - It returns to its memory on both cooling and heating.
Classification:
1. Piezo electricshape memory alloy materials 3. Electrostrictive SMA.
2. Magnetostrictive SMA 4. Thermo elastic SMA.
Example
Ni – Ti, Cu Zn Al, Cu Al Ni, Au – Cd, Ni - Mn – Ga and fe based alloys.
Working Principle:
The shape memory effect occurs between two temperature states known as
Martensite and Austenite.
The Martensite structure is a low
temperature phase and is relatively soft. It has
platelet structure,
The Austenite is a high temperature
phase and is hard, it has needle like structure.
In Austenite phase, the material is
cooling it changes to twinned Martensite and
the load is applied it changed to easily
deformed Martinsite because of it is relatively
soft. During the deformation, the resistivity,
thermal conductivity, Young’s modulus and yield strength are decreased by more than
40%.
Further heat is applied to the deformed Martinsite it return to the original
Austenite phase.
Characteristicsof Shape Memory Alloy:
1. Hysteresis
When the temperature is decreased in a metallicmaterial, the
phase transformation takes place from austenite to martensite.
This transformation takes place not only at a single temperature,
but over a range of temperatures. The hysteresis curve for a

5. shape memory alloy is shown below.
2. Pseudo elasticity
When a metallicmaterial is cooled from a temperature T to a lower temperature T it
deforms and changes its shape. On reheating the material to the temperature T the
shape change is received so that the material returns to its original state. This effect is
known as pseudo elasticity or thermo elastic property.
3. Super elasticity
When a material is deformed at a temperature slightly greater than its
transformationtemperature super elasticity property appears (Rubber like property).
Properties of Nickel – Titanium alloy (Ni-Ti):
 It has greater shape memory strain.
 It has more thermal stability and excellent corrosion resistance.
 It has higher ductility and more stable transformation temperatures.
 It has better bio-compatibility and it can be electrically heated.
Advantages:
1. Shape Memory alloy is simple, compact and safe.
2. It has good biocompatibility.
3. It is strong and has high corrosion resistance.
4. They have high power to weight ratio.
Disadvantages:
1. Shape Memory alloys has poor fatigue.
2. They are expensive.
3. It has low energy efficiency.
4. It has complex control.
5. They have limited bandwidth.
Applications of Shape Memory Alloys:
1. Eye glass frames:
2. Toys: toys such as butterflies, snakes etc., which are movable and flexible.
3. Helicopter blades: The life time of helicopter blades depends on vibrations and
their return to its original shape. Hence shape memory alloys are used in
helicopter blades.
4. Coffee Valves: Used to release the hot milk and the ingredients at a certain
temperature.
5. Medical Applications of Shape Memory Alloys:
 It is used as Micro – Surgical instruments.
 It is used as dental arch wires.

6.  It is used as flow control devices.
 It is used as ortho – dentil implants.
 It is used for repairing of bones.
 They are used to correct the irregularities in teeth.
6. Engineering Applications of Shape Memory Alloys:
 It is used as a thermostat valve in cooling system.
 It is used as a sealing plug for high pressure.
 It is used as a fire safety valve.
 It is used as blood clot filter and for fracture
pulling.
 It is used to make antenna wires in cell phones.
 It can be used as circuit edge connector.
METALLIC GLASSES
Definition:
Metallic glass are the amorphous metallic solids.
Which have high strength, good metallic properties, better corrosion resistance
and will possess both the properties of metallic and glasses.
Ex: Alloys of Fe, Ni, Al, Mn, Cu.
Glass Transition Temperature:
It is defined as a temperature at which the liquid like atomic structure is
obtained into a solid. This value of glass transition temperature for metallic alloys is
about 200C to 300C.
Methods of Production of Metallic Glasses:
Metallic glasses are manufactured by the following methods. They are,
1. Twin roller technique
2. Melt extraction technique
3. Melt spinning technique
Melt Spinning Technique
Principle:

7. “Quenching” is a technique used to form metallic glasses. Quenching means
rabid Cooling. Due to rabid cooling, atoms are arranged irregularly and from metallic
glasses.
Construction:
It consists of a refractory tube with fine nozzle at the bottom. The refractory
tube is placed over the rotating roller. The roller is rotated at a higher speed to
generate a velocity of more than 50 ms-1. An induction heater is wounded over the
refractory tube to heat the alloy to very high temperature.
Working:
The alloy is put into the refractory tube and induction heater is switched on.
This heats the alloy to very high temperature, hence the super heated molten alloy
ejected through the nozzle on the rotating roller and is suddenly made to cool. The
ejection rate may be increased by increasing the inert helium gas pressure inside the
refractory tube. Thus due to rapid quenching a glassy alloy ribbon called metallicglass
is formed over the rotating roller.
Types of Metallic Glasses:
1. Metal – Metalloid Glasses
The first class of metallic glasses is from transitionmetals (Fe,Co, Ni) Metalloid
(B, Si, C & P) so they are called metal-metalloid glasses.
2. Metal - Metal Glasses.
Nickal – Niobium (Ni - Nb)
Magnesium – Zinc (Mg - Zn)
Copper - Zirconium (Cu - Zr).
Properties of Metallic Glasses:
 It have very high strengthand stronger than metals because the absence of
grain boundaries and dislocations.
 It structure is Tetrahedral close Packing (TCP).
 It is having very high corrosion resistance.
 It has high workability and ductility.
 The electrical resistivity is very due to this eddy current loss is very small.

8.  It has both soft and hard magneticproperties.
 These are highly reactive and stable.
 It can also act as a catalyst.
Applications of Metallic Glasses:
 It is used as reinforcing element in concrete, Plastic and rubber.
 It is used to make pressure vessels and to construct larger fly wheels for energy
storage.
 It is used in magnetic resistance sensors and computer memories.
 It is used as core in motors.
 It is used to make razor blades and different kinds of springs.
 It is very useful to make medical surgical instruments.
 It is used in marine cables, chemical filters and inner surfaces of reactor vessels
etc.
 It is used to make containers for nuclear waste disposal and magnets for fusion
reactors.
 It is used in tape recorder heads, cores of high power transformers and
magnetic shields.
 It can be used as superconductor for producing high magnetic fields and
magnetic levitation effect.