Hard Magnetic Materials

For understanding the hard magnetic materials, we have to know certain terms. They are as follows:
  • Coercivity: The capability of a ferromagnetic material to hold up (resist) a peripheral magnetic field without getting demagnetized.
  • Retentivity (Br): It is the amount of magnetism that a ferromagnetic material can maintain even after the magnetic field is decreased to zero.
  • Permeability: It is used to determine how a material reacts to the applied magnetic field.
  • Magnetic materials are mainly classified (based on the magnitude of coercive force) into two sub domains - hard magnetic materials and soft magnetic materials,
Now, we can define hard magnetic materials. These materials are really hard in the basis that it is very difficult to get magnetised. The reason is that the domain walls are motionless owing to crystal defects and imperfections.

But if it gets magnetised, it will be permanently magnetised. That is why; it is also called as permanent magnetic material. They have coercive force greater than 10kA/m and have high retentivity. When we expose a hard magnet to an external magnetic field for the first time, the domain grows and rotates to align with the applied field at the saturation magnetization. After that, the field is removed. As a result, the magnetization is somewhat reverted but it does not track the magnetization curve any longer. A certain amount of energy (Br) is stored in the magnet and it becomes permanently magnetized.

Hysteresis Loop

The total area of the hysteresis loop = the energy which is dissipated when a material of unit volume is magnetized during a cycle of operation. The B-H curve or hysteresis loop of the hard magnetic materials will be always having large area because of large coercive force as shown in figure below. hard magnetic materials

BH Product

The product BH varies along the demagnetisation curve. The good permanent magnet will have maximum value of product BHmax. We have to know that the dimension of this BH implies energy density (Jm-3). So this is called the energy product. hard magnetic materials

Properties of Hard Magnetic Materials

  • Utmost retentivity and coercivity.
  • Value of energy product (BH) will be large.
  • The shape of BH loop is nearly rectangle.
  • High hysteresis loop.
  • Small initial permeability.
The properties of some important permanent magnetic material are shown in the table below.
Hard magnetic materialsCoercivity (Am-1)Retentivity (T)BHmax(Jm-1)
Alnico 5 (Alcomax)
(51Fe, 24 Co,14 Ni, 8Al, 3Cu)
Alnico 2
(55Fe, 12Co, 17Ni, 10Al, 6Cu)
Chrome steel
(98Fe, 0.9Cr, 0.6 C, 0.4Mn)
(57Fe, 28 O, 15Co)
Some important hard magnetic materials are the following:
The carbon steel have large hysteresis loop. Due to any shock or vibration, they lose their magnetic properties rapidly. But tungsten steel, chromium steel and cobalt steel have high energy product.
It is made up of aluminium, nickel and cobalt to boost to improve the magnetic properties. Alnico 5 is the most important material used to create permanent magnet. The BH product is 36000 Jm-3. It is used in high temperature operation.
Rare-Earth Alloys:
SmCo5, Sm2Co17, NdFeB etc.
Hard Ferrites or Ceramic magnets (like Barium Ferrites):
These materials can be powdered and used as a binder in plastics. The plastics made by this method are called plastic magnet.
Bonded Magnets:
It is used in DC motors, Stepper motors etc.
Nanocrystalline hard magnet (Nd-Fe-B Alloys):
The small size and weight of these material make it to use in medical devices, thin motors etc.

Applications of Hard Magnetic Materials

Hard magnetic materials have wide range of applications. They are as follows:
  • Automotive: motor drives for fans, wipers, injection pumps; starter motors; Control for seats, windows etc.
  • Telecommunication: Microphones, Loud Speakers, Telephone Ringers etc.
  • Data processing: Printers, Stepping Motors, Disc Drives and Actuators.
  • Consumer electronics: Home computers, Clocks, DC Motors for showers etc.
  • Electronic and instrumentation: Energy Meter Disc, Sensors, Dampers etc.
  • Industrial: Lifting apparatus, Robotics, Meters etc.
  • Astro and aerospace: Auto-compass, Couplings, Instrumentation etc.
  • Biosurgical: NMR/MRI body scanner, Wound Closures etc.


Closely Related Articles Magnetic FieldMagnetic FluxMagnetic PermeabilityHysteresis LoopMagnetic Field and Magnetic Circuit | Magnetic MaterialsMagnetic SaturationEnergy Stored in a Magnetic FieldStatic Electric Field | Electrostatic Induction A Current Carrying Conductor Within A Magnetic FieldMagnetic SusceptibilitySoft Magnetic MaterialsMagnetic Circuit with Air GapMore Related Articles Electric Current and Theory of Electricity | Heating and Magnetic EffectNature of ElectricityDrift Velocity Drift Current and Electron MobilityElectric Current and Voltage Division RuleRMS or Root Mean Square Value of AC SignalWorking Principle of a CapacitorQuality Factor of Inductor and CapacitorTransient Behavior of CapacitorCylindrical CapacitorSpherical CapacitorCapacitors in Series and ParallelHow to Test Capacitors?Electrical Conductance Conductivity of Metal Semiconductor and Insulator | Band TheoryWhat is Electrical Resistance?Resistivity and Laws of ResistanceProperties of Electric ConductorTemperature Coefficient of ResistanceResistance Variation with TemperatureSeries ResistanceActive and Passive Elements of Electrical CircuitElectrical DC Series and Parallel CircuitOhm's Law | Equation Formula and Limitation of Ohm's LawKirchhoff Current Law and Kirchhoff Voltage LawSingle and Multi Mesh AnalysisSuperposition TheoremThevenin Theorem and Thevenin Equivalent Voltage and ResistanceNorton Theorem | Norton Equivalent Current and ResistanceReciprocity TheoremNodal Analysis in Electric CircuitsMaximum Power Transfer TheoremDelta - Star transformation | Star - Delta TransformationElectric ChargeCoulombs Law | Explanation Statement Formulas Principle Limitation of Coulomb’s LawElectric Lines of ForceWhat is Electric Field?Electric Field Strength or Electric Field IntensityWhat is Flux? Types of Flux?Electric FluxElectric PotentialCapacitor and Capacitance | Types of CapacitorsEnergy Stored in CapacitorCharging a CapacitorDischarging a CapacitorFourier Series and Fourier TransformTrigonometric Fourier SeriesAnalysis of Exponential Fourier SeriesParity GeneratorElectric Circuit and Electrical Circuit ElementsSeries Parallel Battery CellsRL Series CircuitWhat is Inductor and Inductance | Theory of InductorRLC CircuitThree Phase Circuit | Star and Delta SystemRL Parallel CircuitRL Circuit Transfer Function Time Constant RL Circuit as FilterConstruction of AC Circuits and Working of AC CircuitsSeries RLC CircuitParallel RLC CircuitResistances in Series and Resistances in ParallelResonance in Series RLC CircuitPlanar and Non Planar Graphs of CircuitClipping CircuitMutual InductanceSelf InductanceSI System of UnitsElectrical International SymbolElectric Power Single and Three Phase Power Active Reactive ApparentVector Algebra | Vector DiagramRelationship of Line and Phase Voltages and Currents in a Star Connected SystemVector Diagram | Three Phase Vector DiagramTypes of Resistor Carbon Composition and Wire Wound ResistorVaristor Metal Oxide Varistor is Nonlinear ResistorCarbon Composition ResistorWire Wound ResistorVariable Resistors | Defination, Uses and Types of Variable ResistorsLight Dependent Resistor | LDR and Working Principle of LDRSource of Electrical EnergyVoltage SourceIdeal Dependent Independent Voltage Current SourceVoltage or Electric Potential DifferenceVoltage in SeriesVoltage in ParallelVoltage Drop CalculationVoltage DividerVoltage MultiplierVoltage DoublerVoltage RegulatorVoltage FollowerVoltage Regulator 7805Voltage to Current ConverterNew Articles Principle of Water Content Test of Insulating OilCollecting Oil Sample from Oil Immersed Electrical EquipmentCauses of Insulating Oil DeteriorationAcidity Test of Transformer Insulating OilMagnetic Flux