Why does a paramagnetic Sample display greater magnetisation (for the same magnetising field) when cooled?

cbse
waveoptics

#1

Answer the following questions:
(i) Why does a paramagnetic Sample display greater magnetisation (for the same magnetising field) when cooled?
(ii) If a toroid uses bismuth for its core, then will the field in the core be (slightly) greater or (slightly) less than when the core is empty?
(iii) Is the permeability of a ferromagnetic material independent of the magnetic field? If not, is it more for lower or higher fields?
(iv) Magnetic field lines are always nearly normal to the surface of a ferromagnet at every point. (This fact is analogous to the static electric field lines being normal to the surface of a conductor at every point.) Why?
(v) Would the maximum possible magnetisation
of a paramagnetic sample be of the same order of magnitude as the magnetisation of a ferromagnet?


#2

A paramagnetic sample displays greater magnetisation when cooled because at the lower temperatures, the tendency to disrupt the alignment of magnetic dipoles decreases due to the reduced random thermal motion of atoms or molecules.
(ii) Bismuth is a diamagnetic element, so the magnetic
field in the core will be slighdy less than when the core is empty, because the diamagnetic substances are feebly magnetised in the opposite direction of magnetic field.
(iii) No, the permeability of a ferromagnetic material is
not independent of the magnetic fields. By observing the hysteresis curve, the value of permeability is greater for lower fields.
(iv) The magnetic field lines are always nearly normal to
the surface of a ferromagnet at every point because the value of permeability for ferromagnetic substance is always greater than 1 (ยต>>1). It is based on the conditions of B and H at the interface of two media in the hysteresis curve.
(v) Yes, the maximum possible magnetisation of a
paramagnetic sample will be of the same order of magnitude as the magnetisation of a ferromagnet. Although, the condition of saturation for paramagnets, requires very high magnetising fields which cannot be achieved.