Q about diff. between ferro and paramagnetism under a strong mag field

[parsa418]

Hi
From what I understand ferromagnetic materials have domains that contain magnetic dipoles that are almost all parallel to each other. However these domains have random directions.
Under a magnetic field the domains in the ferromagnetic material that are magnetized in the field direction grow and the domains that aren't shrink.
However, in a paramagnetic material there are no domains. Under a magnetic field a lot of the dipole moments of a paramagnetic material become parallel with the field.
My first question is what makes having domains in a material better for magnetization?
My second question is under a strong magnetic field shouldn't both paramagnetic materials and ferromagnetic materials become equally magnetized because eventually all the dipole moments of both materials become parallel with the magnetic field? (is saturation magnetization related to this?)
Any help will be much appreciated
Thank you
Parsa

 

[tiny-tim]

Hi Parsa!

My second question is under a strong magnetic field shouldn't both paramagnetic materials and ferromagnetic materials become equally magnetized because eventually all the dipole moments of both materials become parallel with the magnetic field? (is saturation magnetization related to this?)

I think it's only a question of degree …

both para and ferro depend on the exchange interaction (see http://en.wikipedia.org/wiki/Exchange_interaction), and if it's strong enough you get ferro, see http://en.wikipedia.org/wiki/Paramagnetism#Relation_to_electron_spins …

"If there is sufficient energy exchange between neighbouring dipoles they will interact, and may spontaneously align or anti-align and form magnetic domains, resulting in ferromagnetism (permanent magnets) or antiferromagnetism, respectively."​

My first question is what makes having domains in a material better for magnetization?

No, domains make it worse …

to produce a strong ferromagnet, we need to eliminate the domains!

 

[parsa418]

Thank you tiny-tim. Sorry for the late reply. I was travelling.