Gilbert Damping Ratio in Ferromagnets

[sokrates]

Does anyone know the highest alpha (Gilbert damping ratio) you could get on ferromagnets?

People for various reasons aim for the lowest alpha and it is around 0.008 these days (dimensionless). But I need to know whether higher values are possible or not.

A brief reminder on what alpha is: It is the phenomenological damping parameter that enters the Landau-Lifgarbagez-Gilbert equation which is usually used to model magnetization dynamics of a magnet in the 'macrospin' approximation; where all the individual spins (that are locked into the magnet) are assumed to rotate in unison (hence the name, macrospin)

How large can alpha be? Can it be as high as 0.5 for instance?

 

[BigJDubs]

It is possible to have an alpha as high as 0.5 in ferromagnets, however, this is not typical. The highest alpha values typically seen in ferromagnets are around 0.2. High alpha values tend to lead to higher energy dissipation and increased coercivity, which is why they are not often used.

 

[charng]

I can provide some information on the Gilbert damping ratio in ferromagnets. The Gilbert damping ratio, also known as the phenomenological damping parameter, is a measure of how quickly a magnetic system loses energy during its dynamic motion. It is an important parameter in understanding the behavior of ferromagnetic materials.

To answer the question of the highest alpha that can be achieved in ferromagnets, it is important to note that the value of alpha is dependent on various factors such as material properties, temperature, and external magnetic field. In general, the lowest alpha values are desirable as they indicate minimal energy loss and better stability of the magnetic system.

Currently, the lowest alpha values achieved in ferromagnets are around 0.008, as mentioned in the content. However, it is possible to achieve higher values of alpha, up to 0.5, in certain materials and conditions. For instance, some studies have reported alpha values as high as 0.4 in iron-nickel alloys at low temperatures and in the presence of strong magnetic fields.

It is worth noting that higher values of alpha are usually associated with materials that have a high degree of disorder or defects, such as amorphous ferromagnets or nanoparticles. In these materials, the damping is dominated by spin scattering at the interfaces between different grains or phases, resulting in higher alpha values.

In summary, the highest alpha that can be achieved in ferromagnets depends on various factors and can reach values as high as 0.5 in certain materials and conditions. However, the current trend is to aim for lower alpha values for better stability and energy efficiency in magnetic systems.