I am working on the magnetism. Even 3000 years of scientist’s dedication, the magnetism is central issue of physics. We have a lot of mysterious and unsolved problem. I have studied for almost 7 years from undergraduate student to postdoc. And I will have studied the magnetism throughout my carrier.
The magnetism is study of how and why spins align in the material. The smallest unit of magnetism is spin which is caused by rotation of electron (for simplicity here). Spin is quantum, so there are only two states up or down. So, only two states exist. Let’s consider two spin on each 2 sites. The interaction between two spin is parallel, spins align up and up (or down and down) which that material have possibility to be a ferromagnet. (Fig.1 above) However, the interaction between two spin is anti-parallel when spins align up and down (or down and up) which that material have possibility to be anti-ferromagnet. (Fig.1 below) In these cases, it is not so difficult to find the lowest energy of system.
Let’s move on to the next. Physicist likes symmetry. (Do you agree?) So, let’s introduce third site and spin, and put on perfect triangular lattice (which means the strength of interactions are same) with antiparallel interaction. This state is not stable. We don’t know which direction third one should align. Because 1st one you can put “up”, 2nd spin should be “down”. How about the spin on third site? Should it be “up” or “down”? That is question. We call this magnetic frustration. This problem is still fascinating.
Actually, in this case, the system compromises and forms 120 structures. These spins align with 120 degree. (Fig.3 ) This is lowest energy state, however this system is so unstable, so that dynamical or interesting phenomena in this system has been observed. Physicists have revealed a lot of things but still fascinating.
To study the magnetism, I use neutron scattering. Neutron has a spin. So there is interaction between neutron spin and spins in the material. Throughout interaction we will see dynamics of spin and structure of spin in the material.
