I'm wondering whether domain walls hinder, increase or decrease magnetization?
Dear Rodziah Nazlan , i am satisfied by your answer, but i need more details..
magnetization corresponds to the velocity of magnetic domains growth(speed of domain wall motion). since the obstacles within the ferrite reduce the speed of domain walls, they reduce the magnetization.
If domain wall increases the magnetization will be decreases the size wall is affect to demagnetization of ferrites.
Domain wall motion means it's rotation under applied magnetic field, you can try to measure hysteresis loop and analyze using a single domain model of Stoner equation.
If the magnetic hysteresis mechanism is caused by irreversible rotation of spontaneous magnetization vector, the hysteresis loop of ferrite is measured to be rectangular (ratio of squareness Br/Bs is close to unity).
In the most general case, the answer depends on many factors. A more detailed answer is possible, if we know the nature (structure), the type of material. As already mentioned, the perfection of the material also plays a role. In addition, it is important to know is your ferrite single crystal, polycrystalline or in the form of nanoparticles (particles of the nanocomposite). In the latter two cases, the size of the grains (crystallites) has the value. Whether your ferrite sample is soft or hard magnetic material, in bulk or film form? Is the method of magnetization quasi-static or reversal in alternating fields (harmonic or pulsed fields), up to saturation or partial?
When the domain wall moves, the rotation of the magnetic moments also occurs but inside the walls, where this process is facilitated in comparison with a coherent rotation of the magnetization in the entire volume of the object. Thus, the mechanism of displacement of domain walls usually promotes magnetization. This is especially the case of large magnetic anisotropy and/or shape anisotropy of the sample. But if the coercivity of the walls is large, then the materials with low anisotropy is sometimes easier magnetized due to the coherent rotation of the magnetic moments (magnetization). Thus, the transition from single-domain state to a multi-domain state can increase the coercivity of the fine particles.
Generally, obstacles delay the movement, reducing the rate of magnetization, and in case insufficient magnetic fields the coercive force can interfere with even the achievement of such values of the magnetization, which could be obtained in advanced materials of the same composition and structure.
When the magnetization reversal of polycrystalline ferrite is done in alternating fields, the grain size (and length of domain walls) affects the resonant frequency of oscillations of the domain walls and, as a consequence, the speed and the intensity of magnetization.
If You want to study effect of domain wall motion on magnetization You may do several measurements like recoil curve measurements in magnetization and demagnetization direction (VSM), watch domain structure in different remanent states of the sample. But You must know that, all these measurements are not sufficient in order to determine proper solutions and should be supported by structure nd phase composition studies.
Usually if You have large grains (of sizes higher than exchange length) magnet will be magnetizing by nucleation of domain walls and domain wall motion in multidomain grains. If grains are fine they have coupled magnetic moments and are magnetizing as exchange spring magnets.
Imperfections of structure, borders between grains - depending on their distribution and inclusions of other phases will create pining sites wich will slow down reversal magnetization - but all of these are written to pinning /unpinning of domain walls - different type of reversal magnetization.
Problem is complex and You should first try to read generally about reversal magnetization and recoil curves, that will help You.
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