Ferromagnetic or paramagnetic materials are typically metals or semiconductors but, rarely, they may be insulators. YIG is perhaps the canonical well known ferromagnetic insulator. Does anyone know about other common ferromagnetic or paramagnetic materials that are good insulators?
why go big? what about iron oxide? many insulators shows ferromagnetic order and there exist numerous theoretical study to understand the interface between topology insulator and ferromagnetic insulator. LaY2Fe5O12 is other excellent example.
Garnets are not really ferromagnets, they are ferrimagnets. they have antiferromagnetic orientation of spins but since one type of spin is higher than the other type one has a resultant spin. The situation is like Fe3O4 and other spinel ferrites.
EuO is a ferromagnet and is a semiconductor. well semiconductors are also insulators with smaller band gap.
K2Cr8O16 remains ferromagnetic despite undergoing a phase transition from metal to insulator.
It looks like paramagnetic dielectrics are even more exotic than ferromagnetic ones. Here is an example: Tb3Ga5O12.
Sergei: Do you mean to say that ferroomagnetic insulators (dielectric) turns metallic at the ferro-para transition or you mean to say they are paramagnetic at room temperature?
Tapan, manganites are quite trivial in this sense. I guess the latter is more rare. Can you give an example of a REALLy good paramagnetic dielectric?
How about pyrochlore compounds R2Ti2O7? They are insulators and they do not order magnetically and are paramagnets. Do you say dielectric meaning insulator or you have something else in mind?
Exactly, and they are also "weird" (in a good sense). It's either frustrated classical spin ice (Ho2Ti2O7, Dy2Ti2O7) or quantum spin ice (Yb2Ti2O7).
Combination of high electrical resistance with ferromagnetic properties is a feature of composite materials - ferromagnetic nanoparticles in a dielectric matrix (granular magnets). Ferromagnetic nanoparticles would be metallic but the ferromagnetic metal content should be below the percolation threshold.
True, the composites significantly increase a "zoo" of materials with unconventional magnetic properties. But, as understand, the topic starter is specifically concerned with COMMON materials.
R2Ti2O7 are all paramagnetic. They cannot order due to magnetic frustration but the rare earth atoms have magnetic moments and therefore paramagnetic.
Shiddaling, as Tapan correctly pointed out, pyrochlore compounds R2Ti2O7 are PM dielectrics. Paramagnetism (PM) is NOT an ordered phase. That is why these materials sometimes are referred to as "spin ice", which also has a disordered structure (like PM).
Rare earth moments are robust and large and you cannot destroy them. You can destroy the magnetic order however by introducing topological frustration. As Sergei pointed out before they become disordered spin ice.
Thanks a lot for all your answers! They are great and very helpful!
After looking all these, I'm wondering whether there is any compound with which by changing the temperature one can keep the insulating state but one can have a phase transition from a ferromagnet to a paramagnet at, let's say, 200 or 300 K. May it be a garnet like Tb3-xYxFe5O7?
Another question might be whether a magnetically doped (Cr or Fe) topological insulator can be also considered to belong to this group of materials
Any cuprates High t_c superconductors at finite temperature is a Paramagnet ic Mott Insulator in certain doping regimes.. So are organic superconductors. I can cite many for parmagnetic insulators.
EuO (europium oxide) is a ferromagnetic insulator with a relatively simple crystal structure.
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