class 12th magnetic-properties-of-materials.pptx

class 12th magnetic-properties-of-materials.pptx

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  Magnetism and Matter Title Themost common term which are related to magnetic property Types of Magnetic Material Magnetic properties of Materials. Hysterisis loop (Hysterisis curve) Hard and soft magnetic materials Application of Hysterisis loop Examples Application Of Magnetic property By - Rewandas Borkar (Physics Teacher)
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  The most commonterm which are related to magnetic property . Magnetic moment μm : A vector quantity associated with the magnetic properties of electric current loops or, more generally, magnets. It is equal to the amount of current flowing through the loop multiplied by the area encompassed by the loop, and its direction is established by the right hand rule for rotations μm = IA I= Circulating current ; A= Area coverage by loop
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  Magnetic field orIntensity A field of force associated with changing electric fields, as when electric charges are in motion. Magnetic fields exert deflective forces on moving electric charges. Most magnets have magnetic fields as a result of the spinning motion of the electrons orbiting the atoms of which they are composed; electromagnets create such fields from electric current moving through coils total magnetic field B in the material is given by B = μ0(H + M) H=B/ μ0
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  Magnetization Vector M TheAverage Dipole moment per unit volume is called Magnetization vector M ,
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  Magnetic Permeability (μ): Magneticpermeability is a measure of a material’s ability to conduct or allow the passage of magnetic field lines through it. It quantifies the extent to which a material can support the formation of a magnetic field within itself. Formula: B = μ H, where: B is the magnetic flux density, H is the applied magnetic field, μ is the magnetic permeability of the material. Units: Measured in henries per meter (H/m) or newtons per ampere squared (N/A²).
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  Magnetic susceptibility χm Inelectromagnetism, the Magnetic Susceptibility (χ): Magnetic susceptibility is a dimensionless quantity that measures how much a material becomes magnetized in response to an applied magnetic field. It indicates the extent to which a material can be magnetized. The Relation Between χm and μr , μr = 1+ χm In summary: Magnetic susceptibility tells us how easily a material can be magnetized. Magnetic permeability tells us how easily a magnetic field can pass through a material.
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  What is Magneticproperties of Materials ? It is common characteristics of Materials . Magnetic properties of material involve concept based on the magnetic dipole moment. Some of the material has the ability to create internal Dipole moment . For this reason this kinds of material present special type of properties. Some common characteristics of this material is … 1. attracting other magnetic material. 2. Inducing pole in this material . 3. The polarity of two pole are opposite .
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  Types of MagneticMaterial The magnetic behavior of materials can be classified into the following major groups: 1. Diamagnetism 2. Paramagnetism 3. Ferromagnetism
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  Diamagnetism In the presenceof an external magnetic field, some electrons are speeded up and some are slowed down. The electrons whose moments were anti-parallel are speeded up according to Lenz’s law and this produces an induced magnetic moment in a direction opposite to the field. The induced moment disappears as soon as the external field is removed. • When placed in a non-uniform magnetic field, the interaction between induced magnetic moment and the external field creates a force which tends to move the material from stronger part to weaker part of the external field. It means that diamagnetic material is repelled by the field. • This action is called diamagnetic action and such materials are known as diamagnetic materials. Examples: Bismuth, Copper and Water, air, hydrogen, lead, sodium Chloride, silicon etc.
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  Diamagnetism Diamagnetism is afundamental property of all matter, although it is usually very weak. Diamagnetic substances are composed of atoms which have no net magnetic moments (ie., all the orbital shells are filled and there are no unpaired electrons). The properties of diamagnetic materials are i. Magnetic susceptibility is negative. ii. Relative permeability is slightly less than unity. iii.The magnetic field lines are repelled or expelled by diamagnetic materials when placed in a magnetic field. iv. Susceptibility is nearly temperature independent.
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  plot M vsH
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  Paramagnetism This class ofmaterials, some of the atoms or ions in the material have a net magnetic moment due to unpaired electrons in partially filled orbitals. One of the most important atoms with unpaired electrons is iron. In the presence of an external magnetic field, the torque acting on the atomic dipoles will align them in the field direction. As a result, there is net magnetic dipole moment induced in the direction of the applied field. The induced dipole moment is present as long as the external field exists. resulting in a net positive magnetization and positive susceptibility. Materials which exhibit weak magnetism in the direction of the applied field are known as paramagnetic materials. Examples: Aluminium, Platinum, chromium, manganese, calcium, lithium, oxygen, copper chloride, niobium etc. The properties of paramagnetic materials are: i. Magnetic susceptibility is positive and small. ii. Relative permeability is greater than unity. iii.The magnetic field lines are attracted into the paramagnetic materials when placed in a magnetic field. iv. Susceptibility is inversely proportional to temperature.
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  Paramagnetis m Curie’s law The magnetizationof a paramagnetic material is directly proportional to the external magnetic field and inversely proportional to the absolute temperature of the material. Mz α Bext / T Mz = C Bext / T Bext = μ0​H Mz = C (μ0​H / T) Mz = ᵡ H ᵡ = Cμ0​/ T
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  When temperature isincreased, thermal vibration will upset the alignment of magnetic dipole moments. Therefore, the magnetic susceptibility decreases with increase in temperature. In many cases, the susceptibility of the materials is
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  Ferromagnetism An atom ora molecule in a ferromagnetic material possesses net magnetic dipole moment as in a paramagnetic material. A ferromagnetic material is made up of smaller regions, called ferromagnetic domain (Figure 3.27). (Domain Size = 1mm) A Domain is a region inside of material where the group of magnetic moments naturally align in the same direction. Within each domain, the magnetic moments are spontaneously aligned in a direction. This alignment is caused by strong interaction arising from electron spin which depends on the inter-atomic distance. Each domain has net magnetisation in a direction. However the direction of magnetisation varies from domain to domain and thus net magnetisation of the specimen is zero.
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  Ferromagnetism In the presenceof external magnetic field, two processes take place 1.the domains boundaries displacement 2.the domains rotation (rotated so that they are aligned with the field.) As a result of these mechanisms, there is a strong net magnetisation of the material in the direction of the applied field (Figure). Materials which exhibit strong magnetism in the direction of applied field are called ferromagnetic materials. Examples: Iron, Nickel, gadolinium (Gd), Dysprosium (Dy) and Cobalt etc.
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  Ferromagnetism The properties offerromagnetic materials are: i. Magnetic susceptibility is positive and large. ii. Relative permeability is large. iii. The magnetic field lines are strongly attracted into the ferromagnetic materials when placed in a magnetic field. iv. Susceptibility is inversely proportional to temperature.
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  Curie-Weiss law As temperatureincreases, the ferromagnetism decreases due to the increased thermal agitation of the atomic dipoles. At a particular temperature, ferromagnetic material becomes paramagnetic. This temperature is known as Curie temperature TC . The susceptibility of the material above the Curie temperature is given by This relation is called Curie-Weiss law. The constant C is called Curie constant and temperature T is in kelvin. A plot of magnetic susceptibility with temperature is as shown in Figure.
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  Hysteresis (or hysteresisloop) It is a graphical representation of the relationship between the magnetizing field (H) and the resulting magnetization (B or M) in a ferromagnetic material. It shows how a material’s magnetization changes when subjected to an increasing and then decreasing external magnetic field. In addition to the Curie temperature and saturation magnetization, ferromagnetism can retain a memory of an applied field once it is removed. This behavior is called hysteresis and a plot of the variation of Magnetization with magnetic field or (Magnetic Intensity H) is called a hysteresis loop. When a ferromagnetic material is kept in a magnetising field, the material gets magnetised by induction. An important characteristic of ferromagnetic material is that the variation of magnetic induction with magnetising field is not linear. It means that the ratio B/H = µ is not a constant.
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  Hysteresis 1.Closed curve ACDEFGKCis called hysteresis loop and it represents a cycle of magnetisation. 2.The residual magnetism AD present in the specimen is called remanence or retentivity. It is defined as the ability of the materials to retain the magnetism in them even magnetising field vanishes. 3.The magnitude of the reverse magnetising field for which the residual magnetism of the material vanishes is called its coercivity. The magnetising field AE in the reverse direction is required to bring residual magnetism to zero 4.In the entire cycle, the magnetic induction B lags behind the magnetising field H. This phenomenon of lagging of magnetic induction behind the magnetising field is called hysteresis. Hysteresis means ‘lagging behind’.
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  Significance of theHysteresis Curve: 1. Energy Loss: The area inside the hysteresis loop represents energy lost as heat due to the internal friction of the magnetic domains being aligned and realigned During the magnetisation of the specimen through a cycle, there is loss of energy in the form of heat. This loss is attributed to the rotation and orientation of molecular magnets in various directions. It is found that the energy lost (or dissipated) per unit volume of the material when it is carried through one cycle of magnetisation is equal to the area of the hysteresis loop. The loss in energy is measured in joules.
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  2. Soft vs.Hard Magnetic Materials: Soft magnetic materials (e.g., iron) have narrow hysteresis loops, meaning they require less energy to magnetize and demagnetize. They are used in applications where materials are continuously cycled through magnetization, like in transformer cores. Hard magnetic materials (e.g., permanent magnets) have wide hysteresis loops, indicating that they retain their magnetization well, even when the external field is removed. Based on the shape and size of the hysteresis loop, ferromagnetic materials are classified as soft magnetic materials with smaller area and hard magnetic materials with larger area. The comparison of the hysteresis loops for two magnetic materials is shown in Figure 3.31. Properties of soft and hard magnetic materials are compared in Table 3.2.
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  Hard and softmagnetic materials
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  Applications of hysteresisloop The significance of hysteresis loop is that it provides information such as retentivity, coercivity, permeability, susceptibility and energy loss during one cycle of magnetisation for each ferromagnetic material. Therefore, the study of hysteresis loop will help us in selecting proper and suitable material for a given purpose. Some examples: i) Permanent magnets: The materials with high retentivity, high coercivity and high permeability are suitable for making permanent magnets. Examples: Steel and Alnico ii) Electromagnets: The materials with high initial permeability, low retentivity, low coercivity and thin hysteresis loop with smaller area are preferred to make electromagnets. Examples: Soft iron and Mumetal (Nickel Iron alloy). iii) Core of the transformer: The materials with high initial permeability, large magnetic induction and thin hysteresis loop with smaller area are needed to design transformer cores. Examples: Soft iron
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  EXAMPLE The following figureshows the variation of intensity of magnetisation with the applied magnetic field intensity for three magnetic materials X, Y and Z. Identify the materials X,Y and Z.
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  Solution The slope ofM-H graph measures the magnetic susceptibility, which is χm = M / H Material X: Slope is positive and larger value. So, it is a ferromagnetic material. Material Y: Slope is positive and lesser value than X. So, it could be a paramagnetic material. Material Z: Slope is negative and hence, it is a diamagnetic material.
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  magnetic shielding The useof a shell or box of magnetic material of high permeability to protect sensitive instruments from stray magnetic fields is called magnetic shielding. The permeability of the material being many order of magnitudes greater than air, the magnetic field lines pass through the shell. The saturation v induction B of the material must be greater than the external field to be shielded. from below figure shows the cross section of a cylindrical or spherical shield in which the central region is the field-free region.
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  [Note : Themost widely used alloy for magnetic shielding purposes is the patented MuMetal®. Its composition of 80% nickel, 4.5% molybdenum and balance iron gives it high permeability.]
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  Application Of Magneticproperty In real world there many operation of magnetic property . This property is use as two form as Electromagnetic field and magnetic field . 1. Electronic Motor and Generator 2. Magnetic storage 3. Magnetic bearing 4. Magnetic separator and Holding Device 5. A magnetic resonance angiogram (MRA) 6. Burglar alarm etc.
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  Magnetic storage Magnetic storageand magnetic recording are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads.
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  Magnetic bearing A magneticbearing is a bearing which supports a load using magnetic levitation. Magnetic bearings support moving machinery without physical contact, for example, they can levitate a rotating shaft and permit relative motion with very low friction and no mechanical wear.
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  Magnetic separator andHolding Device Magnetic separator for particle size less than 3mm magnetite, pyrrhotite, ilmenite and other materials, wet magnetic separation, but also for coal, non- metallic minerals, building materials and other materials in addition to iron work.Available downstream, semi-reflux, reflux-type and other forms of magnetic separator, cylinder surface magnetic field strength can be produced according to the actual use of the special.
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  Magnetic Resonance Angiogram(MRA) A magnetic resonance angiogram (MRA) is a type of magnetic resonance imaging (MRI) scan that uses a magnetic field and pulses of radio wave energy to provide pictures of blood vessels inside the body. In many cases MRA can provide information that can't be obtained from an X-ray, ultrasound, or computed tomography (CT) scan.
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  Burglar alarm Passive magneticfield detection This buried security system is based on the Magnetic Anomaly Detection principle of operation. The system uses an electromagnetic field generator powered by two wires running in parallel. Both wires run along the perimeter and are usually installed about 5 inches apart on top of a wall or about 12"/30 cm below ground. The wires are connected to a signal processor which analyzes any change in the magnetic field.