Question

What is the main parameter to distinguish two types of magnetic materials namely soft and hard?

Answer 1

The tendency of a ferromagnetic material to maintain net magnetic domain alignment after the effect of an external magnetising field is removed is referred to as remanence also known as remanent or residual magnetization. The remanence of soft materials is low, while the remanence of hard materials is high.

Complete answer:
Magnetic materials have essential physical quantities, such as magnetic saturation, that are dependent on hysterical curves $\left( {Ms} \right)$ In general, we distinguish between two types of magnetic materials: soft magnetic materials (diamagnetic, paramagnetic, and ferromagnetic materials) and hard magnetic materials (ferromagnetic materials). Permanent magnets are made out of hard magnetic materials.

In response to external fields, soft materials magnetise very quickly. They can generate ridiculously strong B-fields in response to minuscule H-fields, with some super-materials generating B-fields of nearly $2.4{\text{ }}T$ in response to an H-field that could control a pair of headphones. These materials often have very low hysteresis, which means that removing an external field leaves the material with little to no net magnetization and, as a result, no external magnetic (B) field.

With an external field, hard magnetic surfaces are more difficult to magnetise. They can't generate as strong a B-field as some of their softer relatives, and getting them to produce some kind of useful B-field can take a lot of powerful H-fields. Hard materials, on the other hand, appear to maintain their B-field once magnetised, which means that even in the absence of an external H-field, they still have an external magnetic field.

Note: Soft magnetic materials are used in two major types of applications: AC and DC. The material is magnetised during DC implementations to perform an operation and then demagnetized until the operation is completed. Only ferromagnetic materials result in a large internal magnetization and a concentrated magnetic field within the cube.