An automated electromagnetic separator is installed above a conveyor belt in a milling facility to extract magnetic contaminants from processed grains. The contaminants typically consist of soft iron filings and hardened carbon-steel fragments.
Describe how to construct a basic electromagnet that could be used to generate the magnetic field for this separator.
When the system is powered down for maintenance, the electrical current is switched off. The operator observes that the soft iron filings immediately fall back onto the conveyor belt, but the hardened steel fragments remain firmly attached to the separator's core. Explain this observation, referencing the magnetic properties of both materials.