JEE Main & Advanced Physics Magnetism Hysteresis Curve

  For ferromagnetic materials, by removing external magnetic field i.e. \[H=0\]. The magnetic moment of some domains remain aligned in the applied direction of previous magnetising field which results into a residual magnetism. The lack of retracibility as shown in figure is called hysteresis and the curve is known as hysteresis loop. (1) Retentivity : When H is reduced, I reduces but is not zero when \[H=0\]. The remainder value OC of magnetisation when \[H=0\] is called the residual magnetism or retentivity. The property by virtue of which the magnetism (I) remains in a material even on the removal of magnetising field is called Retentivity or Residual magnetism. (2) Corecivity or corecive force : When magnetic field H is reversed, the magnetisation decreases and for a particular value of H, denoted by \[{{H}_{c}}\], it becomes zero i.e., \[{{H}_{c}}=OD\] when \[l=0\]. This value of H is called the corecivity. Magnetic hard substance (steel) \[\to \] High corecvity Magnetic soft substance (soft iron) \[\to \]Low corecivity (3) When field H is further increased in reverse direction, the intensity of magnetisation attains saturation value in reverse direction (i.e. point E) (4) When H is decreased to zero and changed direction in steps, we get the part EFGB. Thus complete cycle of magnetisation and demagnetisation is represented by BCDEFGB. This curve is known as hysteresis curve   Comparison between soft iron and steel

Soft iron	Steel
The area of hysteresis loop is less (low energy loss)	The area of hysteresis loop is large (high energy loss)
Less relativity and corecive force	More retentivity and corecive force
Magnetic permeability is high	Magnetic permeability is less
I and \[\chi \] both  are high	I and \[\chi \] both  are low
It magnetised and demagnetised easily	Magnetisation and demagnetisation is not easy
Used in dynamo, transformer, electromagnet tape recorder and tapes etc.	Used for making permanent magnet.

  Comparative study of magnetic materials

Property	Diamagnetic substances	Paramagnetic substances	Ferromagnetic substances
Cause of magnetism	Orbital motion of electrons	Spin motion of electrons	Formation of domains
Explanation of magnetism	On the basis of orbital motion of electrons	On the basis of spin and orbital motion of electrons	On the basis of domains formed
Behaviour In a non-uniform magnetic field	These are repelled in an external magnetic field i.e. have a tendency to move from high to low field region.	These are feebly attracted in an external magnetic field i.e., have a tendency to move from low to high field region	These are strongly attracted in an external magnetic field i.e. they easily move from low to high field region
State of magnetisation	These are weekly magnetised in a direction opposite to that of applied magnetic field	These get weekly magnetised in the direction of applied magnetic field	These get strongly magnetised in the direction of applied magnetic field
When the material in the form of liquid is filled in the U-tube and placed between pole pieces.	Liquid level in that limb gets depressed	Liquid level in that limb rises up	Liquid level in that limb rises up very much
On placing the gaseous materials between pole pieces	The gas expands at right angles to the magnetic field.	The gas expands in the direction of magnetic field.	The gas rapidly expands in the direction of magnetic field
The value of magnetic induction B	\[B<{{B}_{0}}\] (where \[{{B}_{0}}\] is the magnetic induction in vacuum)	\[B>{{B}_{0}}\]	\[B>>{{B}_{0}}\]
Magnetic susceptibility \[\chi \]	Low and negative \[|\chi |\approx 1\]	Low but positive c » 1	Positive and high \[\chi \approx {{10}^{2}}\]
Dependence of \[\chi \] on temperature	Does not depend on temperature (except Bi at low temperature)	On cooling, these get converted to ferromagnetic materials at Curie temperature	These get converted into paramagnetic materials at Curie temperature
Relative permeability \[({{\mu }_{r}})\]	\[{{\mu }_{r}}<1\]	\[{{\mu }_{r}}>1\]	\[{{\mu }_{r}}>>1\] \[{{\mu }_{r}}={{10}^{2}}\]
Intensity of magnetisation \[(l)\]	I is in a direction opposite to that of H and its value is very low	I is in the direction of H but value is low	I is in the direction of H and value is very high.
I-H curves
Magnetic moment (M)	Very low \[(\approx 0)\]	Very low	Very high
Examples	Cu, Ag, Au, Zn, Bi, Sb, NaCl, \[{{H}_{2}}O\] air and diamond etc.	Al, Mn, Pt, Na, \[CuC{{l}_{2}},\,\,{{O}_{2}}\] and crown glass	Fe, Co, Ni, Cd, \[F{{e}_{3}}{{O}_{4}}\] etc.