Magnetism Lectures 1&2 (2024-2025) PDF

magnetism Lectures 1&2 Applications of magnetic materials Applications of magnetic materials. Magnetic elements present on a hard disk helps to represent computer data which is later ‘read’ by the computer to extract information. Magnets are used inside TVs, Sound speakers and radios. Th...

magnetism Lectures 1&2 Applications of magnetic materials Applications of magnetic materials. Magnetic elements present on a hard disk helps to represent computer data which is later ‘read’ by the computer to extract information. Magnets are used inside TVs, Sound speakers and radios. The small coil of wire and a magnet inside a speaker transforms the electronic signal to sound vibrations. Magnets are used inside a generator to transform mechanical energy to electrical energy where there are other kinds of motors which use magnets to change electrical energy to mechanical energy. Electrically charged magnets can help cranes to move large metal pieces. Magnets are used in filtering machines which separates metallic ores from crushed rocks. It is also used in food processing industries for separating small metallic pieces from grains etc.  Magnets are used in MRI machines which are used to create an image of the bone structure, organs, and tissues. Nanomagnetic materials are used as contrast agents in MRI imaging to are used for drug delivery and to cure cancer using hyperthermia. At home, you use magnets when you stick a paper on the refrigerator in order to remember something. Attaching a magnetic bottle opener to the fridge can come in handy. We often use pocket a compass to find out directions when we are on a trek. The pocket compass uses a magnetic needle to point north. The dark strip on the back of debit and credit cards is of magnetic nature and are used to store data just like computers’ hard drives. Magnets can help collect all the nails which are scattered on the ground after a repair job. Medical applications of magnetic materials  Magnetic materials can exist in 1) Bulk state 2) On the nanoscale What happens on the nanoscale reduced size Broken symmetry Magnetic systems of nanoscopic or mesoscopic scales (a) dimensions comparable to characteristic lengths, such as the limiting size of magnetic domains (b) broken translation symmetry, which results in sites with reduced coordination number, with broken exchange bonds and frustration. Also, nanoscopic or mesoscopic objects exhibit a higher proportion of surface (or interface) atoms. Close contact with other physical systems Another factor that modifies the magnetic properties of the nano- objects is that they are in general in close contact with other physical systems, for example: With a substrate or a capping layer, in the case of most thin films and multilayers. In the case of nanoparticles, these objects may be immersed in solid matrices or compacted in a container. In both cases, each particle may feel a strong interaction with its immediate neighborhood. Defects and imperfections Also, in general, as systems such as ensembles of nanoparticles are prepared with smaller dimensions, the importance of imperfections and defects becomes more relevant. making obtaining identical sets of nano-object smore difficult Magnetic materials We knew that magnetic field can be induced by the free charges that flow in a current-carrying wire loop and the direction of the induced magnetic field is described by the right-hand rule. On the atomic scale, all materials contain spinning electrons that circulate in orbits, and these electrons can also produce magnetic fields if each of theirs magnetic moments is properly oriented. Thus, a resultant magnetic moment in a macroscopic substance can be observed and such a substance is then said to be magnetised and this type of substance is called magnetic material.  A magnetic material is said to be linear, isotropic, or homogenous if it magnetic properties (i.e. r and m) is linear over a specified range of field, independent of the direction of field, or does not vary through out the whole medium of the material, respectively. Magnetic materials also classified as soft and hard materials. Soft materials are normally used as the magnetic core materials for inductors, transformers, and actuators in which the magnetic fields vary frequently. Hard materials or sometime called as permanent magnets are used to generate static magnetic fields in electric motors. Origin of magnetisation in materials The magnetisation in a material substance is associated with atomic current loops generated by two principal mechanisms: (1) orbital motions of the electrons around the nucleus and similar motions of the protons around each other in the nucleus and (2) Spinning motions of the electrons around its own axis. The magnetic moment of an electron is due to ❑ the combination of its orbital motion around the nucleus and spinning motions around its own axis. ❑ similarly, the magnetic moment of the nucleus also consist of the orbital and spin magnetic moments, which are much smaller than that of the electron. This is because the mass of the nucleus is larger than the mass of electron. Thus, the total magnetic moment of an atom is usually assumed to be calculated by the vector sum of the magnetic dipole moments of its electrons. The magnetic moment per atom The average magnetic dipole moment per atom 𝜇ҧ If N is the number of atoms per unit volume, the magnetization per unit volume, M is defined as 𝑀=𝑁 𝜇ҧ ഥ 𝐴. 𝑚2 𝜇: 𝑎𝑡𝑜𝑚 𝑁: 𝑚3 𝑀: 𝐴/𝑚 ( the same as the units of (H)) Energy difference in case of complete misalignment to complete alignment Into the atom Vector model of the atom Orbital angular momentum Example (electron in d subshell)  When H is reduced down to zero, the curve will move from point “a” to point: b”. At this point , it can be seen that some magnetic flux remains in the material even though the magnetizing force is zero. This is referred to as the point of retentivity on the graph and indicates the remanence or level of residual magnetism in the material. (some of the magnetic domains remain aligned but some lost their alignment.) As the magnetizing force is reversed, the curve moves to point “c”, where the flux has been reduced to zero. This is called the point of coercivity on the curve. ( the reversed magnetizing force has flipped enough of the domains so that the net flux within the material is zero.) The force required to remove the residual magnetism from the material, is called the coercive force ( field) or the coercivity of the material.