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Hi. Thanks for theses slides. Quick question: on the last slide when you were calculating the "d" from final XRD graph, how can we determine each peak is correspond to which planes? i.e. how did you find out it was (111) or (222)? Thanks
If you know the crystal structure, you can calculate the d-spacing for each planes of (hkl) indices. Since h, k, l are integers, the values for the d-spacing are discrete, which can be used to match the observations.
I have a question. when 1:40 Antiferromagnetic Alignment why the Mn spin flips rather than oxygen spin?? Wouldn't oxygen spin be easier than manganese spin to change? Because oxygen spin is one per orbital, but manganese has three.
In the top row (initial state), two spins (electrons) are sitting in one oxygen 2p orbital state. The two spins are anti-aligned due to the Pauli exclusion principle. In fact, all oxygen 2p orbital states are doubly occupied. In contrast, the Mn 3d states are all singly occupied. Since there are 5 3d states for Mn, when one electron jump from O 2p to Mn 3d, it goes to an empty 3d state and align the spin with the others according to the Hund's rule (third row), resulting in the antiferromagnetic alignment or super exchange interaction.
Can you explain why a cristalline powder (in which crystals are oriented randomly) still gives discrete theta values for the corresponding crystal planes? Why don’t these peaks average out?
The diffraction 2theta angle (the angle between incident and scattered x-ray) corresponds to the spacing between crystal planes, which does not depend on the orientation of the crystal.
The antiferromagnet will acquire a tiny dipole moment due to the magnetic field of the magnet nearby, a process called magnetization. Most materials will get magnetized in a magnetic field, although the effect is particularly small for antiferromagnets.
@@SandBox86 that's correct. very small, but non-zero. The antiferromagnetic materials consist of magnetic atoms (or ions), which do respond to the external magnetic field. But most responses are canceled due to the antiferromagnetic order.
@@ferrothinfilmslab3411 developing the idea, so a body made of a ferromagnetic compound would also accept a maximum field (like a critical field)? Depends on temperature? So it produces Eddy's current in presence on movements? This antiferromagnetic materials becomes a temporal magnet?
@@SandBox86 I suppose there are two questions here. Let me try to answer them one by one. (1) Yes, like ferromagnets, antiferromagnets become non-magnetic or paramagnetic above a certain temperatures. (2) It takes really really high magnetic field to make the magnetization of an antiferromagnet comparable to that of a ferromagnet. The required field is too high to have practical meanings.
For diamagnetic materials, like glass, we will have a linear behavior with a negative slope, but if we decrease the temperature to 5 kelvin for example will the response stay the same? or not? what do you think?
hello! i want to ask a question, So if I have cobalt nanoparticles (Antiferromagnetic below T Neel =K) it's impossible to characterize them alone since they will not interact with an external magnetic field. so I should coat them with a ferromagnetic cobalt layer in order to magnetize the AFM surface below the FM cobalt then I will have an M (magnetization emu) vs H (external magnetic field Oe) hysteresis presenting an exchange bias? So in general antiferromagnetic materials will have a null ( M vs H curve?) below the Neel temperature? Thank you
In general any material has a M vs H curves, including the antiferromagnetic material. It's just that effect of the field on the antiferromagnet is very small. If you have a ferromagnetic adjacent to an antiferromagnet, your measurement of M vs H will be dominated by the response from the ferromagnet.
Yes, PLD is a PVD technique, although speed is not its particular strength. When thin films of complex composition, i.e., with many different elements, are concerned, PLD is especially advantageous.
First of all, these AFM magnetic structures are based on cubic arrangement of magnetic atoms and collinear alignment between the magnetic moments. In A type, the magnetic moments are aligned within atomic layers but anti-aligned between (2) neighboring layers. In C type, the magnetic moments are aligned within atomic chains but anti-aligned between (4) neighboring chains. In G type, every magnetic moment is anti-aligned with (6) neigboring atoms.
Hysteresis is a term (jargon) that describes a physical properties lags behind the driving force. In this case, magnetic moment is changed by the magnetic field. But when the magnetic field is removed, the magnetic moment does not go back to the original value.
Oh ok, imagine a copper tube coated with a single layer of antiferromagnetic material, and a solid fill of it too. It would be a very good conduit for pulsed DC in one direction, no?
Hi, let's me guess when you say good conduit for pulsed DC, you mean the antiferromagnetic layer can screen the magnetic field generated by the pulsed DC? In that case, a diamagnetic material is a better choice.
@@ferrothinfilmslab3411 yes, screen in it a way which increases the response curve of the attack di/dt, as well as reverse flow tendancy; overcoming the tendency for an impulse signal to be muddied by outside or inside "material" interference. However, impulse current types including superconductivity might already be the 99.9% resistance factor, due to cooper pairs, for signal quality preservation. I engineer for the preservation of energy organization in the sense of gathering it in packets of time via high power pulses. Let me know your thoughts and maybe expand on the topic you proposed?
Looked up a diamegnetic video. Seems like nornal bare wire is already fully diamagnetic. It seems like diamagnetic materials naturally compress magnetic fields, seemingly to allow larger magnetic fields, so perhaps a solid fill wire with a anti ferro film could be a type of enamle wire for pulsed DC. Since pulsed DC is essentially high voltage AC with true intermittent signal, the electeon flow is mostly in the lesser skin effect range. The prefered material pathway of wire would not remain polarized in a unilateral direcrion naturally, and hence introduce a slight resistance to each next current impulse. That is, unless influenced by a pre-organizimg material which will return to a particular balance state of net nutreal, yet that influences the lingering time of a material with a more random polarization tendancy. In short it increases efficiency of power transfer in impulsed current waveforms, but only in one direction, so its ideal for DC.
The picture in the video is a real setup of a home-made MOKE system, but the video is more about theory. Maybe it is a good idea to have a video on the setup.
@@uzhavansanthai1223 Are talking about ferrofluids type of solutions? In that case, I am not aware of any. For ferrofluids, the magnetic particles are attracted by each other due to their non-zero magnetic moments. Antiferromagnets don't have non-zero magnetic moments. Therefore, they won't be attracted by each other. In fact, one of the common antiferromagnet is Fe2O3 (the red rust). You can images how they behave in a solution.
They do involve some kind of chemical reactions. For example, in ArF laser, Ar reacts with F2 to form ArF. But ArF is only metastable, which makes it not the same as typical chemical reactions.
@@ferrothinfilmslab3411 but why its detail is rare on web , text books etc ? Why there's any experimental demonstration on RU-vid ? Is it extremely difficult to make ?
There are at least two reasons. 1) The laser gas (F2, ArF, KrF) are all very toxic (fatal if inhaled). 2) The lasing requires high voltage (30 kV). Therefore, excimer laser needs to be handled with extra safety measure, which of course makes it expensive.
Am I correct in thinking that? antiferromagnetic have no net magnetic moment (no applied field) antiferromagnet have net magnetic moment (applied field)
You are right. An antiferromagnetic material has no net magnetic moment. When a field is applied, an antiferromagnetic material can have net moment. But when the field is remove, the net moment goes back to zero.