So where do magnetic properties come from?
In the case of magnetites (all iron and oxygen) and ferrites (mix of iron and other 2+ metal ions and oxygen) it is because of their electrons and orientation.
These particles are made of Mn(II), Zn (II), and Fe (III) and are in the ratio: A(II)B2(III)O4.
So there are twice as many irons as manganese or zinc.
The fill a lattice known as a spinel. Spinels have 2 different types of coordination sites - how many oxygens are bound to the metal ion.
8 sites are tetrahedral (Td), the metal is bound to 4 oxygens.
16 sites are octahedral (Oc), the metal is bound to 6 oxygens.
Usually, the 2+ metal ions fill the Td spots and the 3+ ions fill the Oc spots.
But, this ferrite is a mixed spinel, so the Td and Oc sites are filled with both the 2+ and 3+ ions.
Zn(II) prefers the Td spots. This is important.
All of this lead up is to say that the orientation of metal ion is different between Td and Oc sites and that affects the magnetic moments.
Td and Oc sites will have opposite magnetic moments.
The short version of magnetic moments, is that the more unpaired d electrons has, the greater it's magnetism.
Fe(III) and Mn(II) both have 5 unpaired d electrons, the maximum.
Since there are 8 Td, and 16 Oc sites, you would think that the 8 Td will cancel 8 of the Oc magnetic moments.
But! Zn(II) has no unpaired electrons. It has no magnetic moment.
And! Since it prefers the Td spots, there are now fewer metal ions in the Td sites to counter the Oc spots.
And this! Makes the ferrite very magnetic!
#everydayscience #chemistry #nanoparticles #research #PhD #magnets #magnetism #metals #spinels #crystallattice