Question

Which of the following substances is antiferromagnetic?
(a).$MnO$
(b).$Cr{{O}_{2}}$
(c).$F{{e}_{3}}{{O}_{4}}$
(d).$NaCl$

Answer 1

Hint: In materials that display antiferromagnetism, atom or molecular magnetic moments, typically associated with electron spins, align in a normal pattern with adjacent spins (on different sublattices) pointing in opposite directions.

Complete answer:
One component of the combined electromagnetic force is magnetism. It refers to physical effects induced by the force of magnets, objects creating fields that attract or repel other objects.
A magnetic domain is a region within a magnetic material where a uniform direction of magnetization is in. This implies the individual atomic magnetic moments are associated with each other and point in the same direction.
These are the products which are ferromagnetic, ferrimagnetic, and antiferromagnetic. There are no magnetic domains in paramagnetic and diamagnetic materials, in which the dipoles align in response to an external field but do not align spontaneously.
 The$MnO$ has antiferromagnetism..
Anti-Ferromagnetism is a form of solid magnetism in which adjacent ions act as a tiny magnet. At low temperature, some ions align themselves.

Adjacent ions that serve as small magnets (in this case manganese ions, $M{{n}^{2+}}$) bind themselves spontaneously to the opposite or antiparallel at relatively low temperatures.
$NaCl$ has a diamagnetic character. Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates in them in the opposite direction an induced magnetic field which causes repulsive force.
$Cr{{O}_{2}}$ has ferromagnetic properties. Ferromagnetism is the fundamental process by which certain materials shape, or are attracted to, permanent magnets.
$F{{e}_{3}}{{O}_{4}}$is ferrimagnetic at room temperature. Ferrimagnetic material is one that has populations of atoms with opposing magnetic moments, as in antiferromagnetism; however, the opposing moments are different in ferrimagnetic materials and there is a spontaneous magnetization.

Note:
-The root of magnetism lies in the electrons' orbital and spin motions, and how they interact with each other.
-Some may find that shocking, but all the matter is magnetic. It is just because some materials are much more magnetic than others. The principal difference is that there is no mutual interaction of atomic magnetic moments in some materials, while there is a very strong interaction between atomic moments in other materials.