Differences between Hard and Soft Magnetic MaterialsIntroduction: Magnetism, the phenomenon by which materials assert an attractive or repulsive force or influence on other materials, has been known for thousands of years. However, the underlying principles and mechanisms that explain the magnetic phenomenon are complex and subtle, and their understanding has eluded scientists until relatively recent times. Many of our modern technological devices rely on magnetism and magnetic materials; these include electrical power generators and transformers, electric motors, radio, television, telephones, computers, and components of sound and video reproduction systems.Iron, some steels, and the naturally occurring mineral lodestone are well-known examples of materials that exhibit magnetic properties.The wide variety of magnetic materials can be rather sharply divided into two groups, the magnetically soft (easy to magnetize and demagnetize) and the magnetically hard (hard to magnetize and demagnetize). The distinguishing characteristic of the first group is high permeability, and it is chiefly this flux-multiplying power of the magnetically soft materials that fits them for their job in machines and devices. Magnetically hard materials, on the other hand, are made into permanent magnets; here a high coercivity is a primary requirement because a permanent magnet, once magnetized, must be able to resist the demagnetizing action of stray fields, including its own. The materials used for analog and digital magnetic recording can be regarded as a special category of permanent magnet materials, sometime called semi-hard magnets. Some other special magnetic materials and magnetic structures are used in other parts of digital computers.Examples of Hard Magnetic Materials:Magnet Steels , Lode stone, High Carbon Steel , ALNICO, Barium and Strontium Ferrites, Rare Earth Magnets, Exchange Spring Magnets , Nitride Magnets, Cobalt Platinum Magnets.Exapmles of Soft Magnetic Materials:Low carbon steel, non-oriented silicon steel , grain-oriented silicon steel , Low Carbon Steel, 6% Si Steel, Fe-Ni Alloys , Fe-Co Alloys, Amorphous or Non-crystalline Alloys (Metallic Glasses)

Comparison between Soft and Hard Magnetic Materials:

S.No.Hard Magnetic MaterialsSoft Magnetic Materials

1Materials which retain their magnetism and are difficult to demagnetize are called hard magnetic materials.These materials retain their magnetism even after the removal of the applied magnetic field. Hence these materials are used for making permanent magnets. In permanent magnets the movement of the domain wall is prevented. They are prepared by heating the magnetic materials to the required temperature and then quenching them. Impurities increase the strength of hard magnetic materials.Soft magnetic materials are easy to magnetize and demagnetize. These materials are used for making temporary magnets. The domain wall movement is easy. Hence they are easy to magnetize. By annealing the cold worked material, the dislocation density is reduced and the domain wall movement is made easier. Soft magnetic materials should not possess any void and its structure should be homogeneous so that the materials are not affected by impurities.

2They have large hysteresis loss due to large hysteresis loop area.They have low hysteresis loss due to small hysteresis area.

3 Susceptibility and permeability are low.Susceptibility and permeability are high.

4Coercivity and retentivity values are large. Coercivity and retentivity values are less.

5Magnetic energy stored is high.Since they have low retentivity and coercivity, they are not used for making permanent magnets.

6They possess high value of BH product.Magnetic energy stored is less.

7The eddy current loss is high.The eddy current loss is less because of high resistivity.

Uses of Soft Magnetic Materials:The uses of soft magnetic materials may be categorized as follows:1. Heavy-duty Flux Multipliers. These are the cores of transformers, generators, and motors. These machines are often large and heavy. A material with high working flux density is needed to keep the size and weight down, and low cost per pound is essential. Therefore iron is the magnetic material of choice. The industrial name is electrical steel; it is a very low-carbon steel either with no alloying additions or with up to about 3% of silicon, which primarily acts to increase the electrical resistivity. It is used in the form of sheets in the thickness range 0.11 mm (0.0040.04 inch). These materials are used almost exclusively at power frequencies (50 or 60 Hz).2. Light-duty Flux Multipliers. These are the cores of small, special-purpose transformers, inductors, etc., used mainly in electronic equipment. Here the cost of magnetic material is usually secondary to some particular magnetic requirement. Frequencies may range up to the megahertz region. Nickeliron alloys and soft ferrites fall in this class, with metallic alloys used at lower frequencies. Alloy sheet thicknesses may be as small as 6 mm (0.00025 inch).3. Microwave System Components. These comprise soft ferrites and garnets.Uses of Hard Magnetic Materials: Loud Speaker Permanent Magnetic motors Head Positioner (Computer Hard Disks) Force Applications (Attraction) Magnetic LevitationReference: INTRODUCTION TO MAGNETIC MATERIALS, B. D. CULLITY (University of Notre Dame) C. D. GRAHAM (University of Pennsylvania) Copyright # 2009 by the Institute of Electrical and Electronics Engineers, Inc. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. All rights reserved. Published simultaneously in Canada1