Magnetic Materials PDF

Magnetic materials Dr. Shereef Ahmed Fareed  Magnetic materials Contents 1. Introduction to Magnetism 2. Magnetic Properties of Materials 3. Classification of Magnetic Materials 4. Magnetic Domains and Hysteresis 5. Magnetic Models and Theories 6. Magnetic...

Magnetic materials Dr. Shereef Ahmed Fareed  Magnetic materials Contents 1. Introduction to Magnetism 2. Magnetic Properties of Materials 3. Classification of Magnetic Materials 4. Magnetic Domains and Hysteresis 5. Magnetic Models and Theories 6. Magnetic Measurements and related Techniques 7. Magnetic nanomaterials and spintronics 8. Fundamentals of magnetocaloric effect 9. Understanding giant magnetoresistance (GMR) 10. Applications of Magnetic Materials  Magnetic materials 1. Introduction to Magnetism Electron Spin Intrinsic Spin: Electrons possess an intrinsic property called "spin," which gives rise to a magnetic moment. Each electron acts like a tiny magnet due to its spin. Spin Alignment: In a magnetic material, the alignment of these spins can lead to various magnetic behaviors. In most materials, electron spins are randomly oriented, canceling out any net magnetic moment. Orbital Motion Electron Orbits: The movement of electrons around the nucleus creates a current loop, generating a magnetic field. The orbital motion contributes to the magnetic moment of an atom. Combination of Spins and Orbits: The total magnetic moment of an atom is a result of both the intrinsic spin of electrons and their orbital motion.  Magnetic materials 2. Magnetic Properties of Materials Magnetic Field Strength (H): Measures the intensity of the magnetic field generated by currents or magnetic materials. It is measured in amperes per meter (A/m). Magnetic Flux Density (B): Represents the amount of magnetic field passing through a unit area. It is measured in teslas (T) and relates to H through the permeability of the material. 1 tesla is equal to 1 weber per square meter (Wb/m²). B = H  Magnetic materials 2. Magnetic Properties of Materials Permeability (μ): Indicates how easily a material can be magnetized or how well it can support the formation of a magnetic field. It is expressed in H/m. Absolute Permeability (μ): The permeability of a material in a vacuum. Relative Permeability (μr): The ratio of a material's permeability to that of free space (vacuum).  Magnetic materials 2. Magnetic Properties of Materials Magnetic Susceptibility (χ): A dimensionless quantity that indicates how much a material will become magnetized in an applied magnetic field. It is the ratio of the magnetization (M) to the magnetic field strength (H). Magnetization (M): The degree to which a material is magnetized in response to an external magnetic field. It is measured in amperes per meter (A/m).  Magnetic materials 2. Magnetic Properties of Materials Coercivity (Hc): The measure of a material's resistance to becoming demagnetized. It indicates the strength of the external magnetic field required to reduce the magnetization to zero. Or we can say, magnetic coercivity refers to the intensity of the external magnetic field required to reduce the magnetization of a material to zero after it has been magnetized to saturation. Remanence (Br): The magnetization left in a material after an external magnetic field is removed. It reflects how much magnetic field the material retains. Saturation Magnetization (Ms): The maximum magnetization a material can achieve in an external magnetic field, beyond which increases in the field do not lead to an increase in magnetization.  Magnetic materials 2. Magnetic Properties of Materials Curie Temperature (Tc): The temperature above which a ferromagnetic material loses its permanent magnetic properties and becomes paramagnetic. The Néel temperature: it describes a temperature limit at which an antiferromagnetic substance becomes a paramagnet Hysteresis Loop: A graph that shows the relationship between magnetic flux density (B) and magnetic field strength (H) as a material is magnetized and demagnetized, illustrating the concepts of coercivity and remanence. Eddy Current Losses: Losses due to induced currents in conductors exposed to changing magnetic fields, affecting efficiency in electrical systems.  Magnetic materials 2. Magnetic Properties of Materials Magnetic Domain: Regions within ferromagnetic materials where the magnetic moments of atoms are aligned in the same direction.  Magnetic materials 3. Classification of Magnetic Materials 4. Magnetic Domains and Hysteresis Diamagnetic Materials: Description: These materials exhibit a weak, negative response to an external magnetic field, meaning they are slightly repelled. Example: Bismuth, copper, and most non-metals.  Magnetic materials 3. Classification of Magnetic Materials 4. Magnetic Domains and Hysteresis Paramagnetic Materials: Description: These materials have a small, positive susceptibility to magnetic fields, becoming weakly magnetized in the direction of the field. The magnetization disappears when the field is removed. Example: Aluminum, platinum, and certain metal ions.  Magnetic materials 3. Classification of Magnetic Materials 4. Magnetic Domains and Hysteresis Ferromagnetic Materials: Description: These materials can be permanently magnetized. They have a high susceptibility and exhibit strong magnetization, forming magnetic domains that align in the presence of a magnetic field. Example: Iron, nickel, and cobalt.  Magnetic materials 3. Classification of Magnetic Materials 4. Magnetic Domains and Hysteresis Ferrimagnetic Materials: Description: Similar to ferromagnetic materials, but they consist of two or more different types of ions that have opposite magnetic moments, leading to a net magnetization. Example: Magnetite (Fe₃O₄) and certain ceramic materials.  Magnetic materials 3. Classification of Magnetic Materials 4. Magnetic Domains and Hysteresis Antiferromagnetic Materials: Description: These materials have neighboring magnetic moments that align in opposite directions, canceling each other out. They exhibit no net magnetization at absolute zero. Example: Manganese oxide (MnO) and iron oxide (FeO).  Magnetic materials 3. Classification of Magnetic Materials 4. Magnetic Domains and Hysteresis Superparamagnetic Materials: Description: These are typically very small ferromagnetic or ferrimagnetic nanoparticles that exhibit a single magnetic domain. They can be magnetized by an external magnetic field but do not retain magnetization once the field is removed. Example: Iron oxide nanoparticles used in biomedical applications. Magnetic materials Magnetic materials a) Paramagnetic b) Ferromagnetic c) Antiferromagnetic d) Ferrimagnetic  Magnetic materials Curie-Weiss law “Curie law” where C is Curie constant and can be calculated by: Where μeff is the effective magnetic moment, N is defined as the number density of magnetic moments and kB is Boltzmann constant.  Magnetic materials Curie-Weiss law Due to an additional exchange interaction, we can obtain the Curie-Weiss paramagnetism as appeared in the high-temperature paramagnetic phase of a ferromagnetic material. Curie-Weiss law is described as: ) Where θ is the Curie-Weiss temperature, in ferromagnetic interaction θ is greater than zero (θ > 0) for a parallel alignment of the magnetic moments and less than zero (θ < 0) for antiferromagnetic interaction  Magnetic materials Magnetic Susceptibility (Faraday method) The magnetic susceptibility is calculated by: Xg = ∆m g / m H (dH/dz) Xm = Xg (m.wt) where: m.wt is the molecular weight of the sample ∆m is the measured pull H is the coersive field Magnetic materials Magnetic materials Magnetic materials  Magnetic materials µeff = 2.83 √1/slope Magnetic materials  Magnetic materials 1. What is the difference between diamagnetic, paramagnetic, and ferromagnetic susceptibility?  Magnetic materials 2. What is the significance of the hysteresis loop?  Magnetic materials 3. What does the area within a hysteresis loop represent?  Magnetic materials 4. What is remanence (Br) in the context of the hysteresis loop? And What is coercivity (Hc)?  Magnetic materials 5. What is the difference between hard and soft magnetic materials in terms of the hysteresis loop?  Magnetic materials 6. What is the relationship between magnetization and magnetic field strength in a linear magnetic material?  Magnetic materials 7. How does temperature affect magnetization according to Curie's law?  Magnetic materials 8. What are some practical applications of the Curie-Weiss law?  Magnetic materials 9. What is the physical interpretation of the negative susceptibility observed in some materials?  Magnetic materials 10. What types of materials does the Curie-Weiss law apply to?