Which of the following statements are correct?
A. Ferrimagnetic substances lose ferrimagnetism on heating and become paramagnetic.

B. Ferrimagnetic substances do not lose ferrimagnetism on heating and remain ferrimagnetic.

C. Antiferromagnetic substances have domain structures similar to ferromagnetic substances and their magnetic moments are not cancelled by each other.

D. In ferromagnetic substances all the domains get oriented in the direction of magnetic field and remain as such even after removing magnetic field.

Ferrimagnetic substances are materials that have domains of atoms of opposing magnetic moments which are unequal in number, therefore causing spontaneous magnetization, that is, they show behaviour just like ferromagnets below the Curie Temperature and show no magnetic order above the Curie Temperature, as in, they become paramagnetic. So, option (i) is a correct statement.

Option (ii) is incorrect as ferrimagnetic substances do become paramagnetic on heating.

Antiferromagnetic substances are materials with equal populations of atoms of opposing magnetic moments, and their magnetic moments are cancelled by each other. Option (iii) is incorrect.

Ferromagnetic substances, in unmagnetized state have little to no net magnetic field. They become aligned on application of an external magnetic field, and remain aligned even on the removal of the field, creating a magnetic field of their own extending into space around the material, thus creating a "permanent" magnet. Option (iv) is correct.

Thus, (i) and (iv) are the correct option.