A permanent magnet motor is a D.C. motor with a permanent magnet field.
PMDC motor and Brushed motor are the type of a DC motor. In PMDC type we can not vary the field flux but in brushed DC motor we can vary it. PMDC motor we use permanent magnet thus it has high ppermeability . In brusehed motor we use electromagnet. Obviously permeability of that will be lower than that of permanent magnet .
PMDC motor is bulky in weight and the wear and tear will be much higher than brushed DC unless it is an BLDC motor.
The magnets in permanent-magnet motors are Rare-earth (those 30 metals found in the periodic table’s oft-omitted long center two rows); they’re used in many modern applications. Magnets made of rare-earth metals are particularly powerful alloys with crystalline structures that have high magnetic anistropy — which means they readily align in one direction, and resist it in others.
Discovered in the 1940s and identified in 1966, Rare-earth magnets are 33.3% to 200% more powerful than traditional ferrous magnets (generating fields up to 1.4 Teslas, in some cases). Their magnets are used in MRI machines, portable electronic devices, hysteresis clutches, accelerometers and, last but not least, permanent-magnet rotary and linear motors.
