Effect Of Annealing Process On High-Frequency Magnetic Properties Of NiCuZn Ferrite

The annealing process has an important influence on the high frequency magnetic properties of ferrite.In this paper,the high-frequency magnetic properties of LSF50NiCuZn ferrite under different annealing conditions were studied,which could provide technical support for the optimization of annealing process.The complex permeability curves of LSF50 NiCuZn ferrite were measured.According to its characteristics,the complex permeability curves were partitioned into three parts:low-frequency zone?1¹00 kHz?,intermediate-frequency zone?100kHz¹0 MHz?and high-frequency zone?10¹00 MHz?.In low-frequency zone,the test results were volatile and were not suitable for the characterization of ferrite magnetic properties.The test results of intermediate-frequency and high-frequency zone were accurate and were suitable to evaluate the magnetic properties of ferrite.The effect of annealing process on magnetic properties was small.In order to reduce the influence of initial deviation,the concept of change rate was introduced in this paper.In intermediate-frequency zone,?'_chg?the change rates of?'?and?”_chg?the change rates of?”?were introduced.In high-frequency zone,f_c?chg??the change rates of cutoff frequency?and?”_max?chg?(the change rates of?”_max)were introduced.The change of annealing temperature and annealing time affected the high-frequency magnetic properties of ferrite materials.And the reasons of these effects were the grain size and the stress state of ferrite.When the annealing process leaded to the increase of grain size,?'and?”would increase,while f_c decreased.If the annealing process decreased the compressive stress in ferrite materials,?'and?”_max in the compressive stress direction would be reduced.The?'_chg and?”_max?chg?of LSF50 NiCuZn ferrite was influenced by the grain size and internal stress.According to the sensitivity to the grain size and internal stress,annealing process could be divided into different temperature ranges.Different annealing temperatures could be divided into two parts,which are the stress-dominant area and the grain-size-dominant area,and their boundary was between 400⁶00°C.Different annealing time could be divided into two parts,which are the stress-dominant zone and the grain-size-dominant zone,and the boundary was near the recrystallization temperature of ferrite materials.According to the frequency,the effect of annealing process on the magnetic properties of ferrite could be different.When the frequency was 100 k Hz¹0 MHz,annealing at 200°C for 0.5h could get the best magnetic property.When the frequency was 25 MHz,annealing at 900°C for 2h could get the best magnetic property.