Manganese is not ferromagnetic because its magnetic moments do not align in the same direction spontaneously. While it is true that manganese has more unpaired electrons compared to iron, the arrangement and interactions of these electrons play a crucial role in determining the magnetic properties of a material.
In ferromagnetic materials like iron, the unpaired electrons align their spins in the same direction, creating a strong overall magnetic field. This alignment occurs naturally at the atomic level, resulting in a macroscopic magnetic effect.
On the other hand, manganese has a more complex electron configuration and crystal structure that prevents the spontaneous alignment of its magnetic moments. Even though it has more unpaired electrons, the interactions between these electrons are not favorable for spontaneous alignment, leading to a lack of macroscopic ferromagnetism.
Explaining the exact electronic and magnetic properties of materials can be quite technical, involving quantum mechanics and complex interactions between electrons. However, the fundamental reason why manganese is not ferromagnetic despite having more unpaired electrons than iron is that the arrangement and interactions of those unpaired electrons do not promote spontaneous alignment and the creation of a strong overall magnetic field.