Nanocrystalline core, a soft magnetic core is a component used in electornic and electrical devices to channel and concentrate magnetic field. 
The choice of core material and design depends on the specific requirements of the application, such as frequency range, current capacity, and efficiency. Take 1K107A and 1K107B as comparing:
1K107A has higher magnetic permeability at low frequencies, such as 50Hz and below 1KHZ
1K107B has higher magnetic permeability at high frequencies, such as 10KHZ, 100KHZ, and 200KHZ
1K107A is mainly used for transformers and transformers

1K107B is mainly used for CMC, reactor, etc. in higher frequency applications

Typical Characteristic 1k107 & 1K107B

1K107A Material Core Loss:
50KHZ 100mT 4.2W/kg
50KHZ 200mT 16.7W/kg
50KHZ 500mT 110W/kg

100KHZ，200mT,48.9W/kg