how to add chance of adding temporarty stats when receiving damage?

[Heartfelt]

  - Id: 19266
    AegisName: Survive_Circlet_
    Name: Survivor's Circlet
    Type: Armor
    Weight: 500
    Defense: 10
    Slots: 1
    Locations:
      Head_Top: true
    EquipLevelMin: 1
    Refineable: true
    View: 1220
    Script: |

how can i add 15% chance of gaining 20% of magic attack  for 3 seconds every time the wearer receive any damage?
please help
thanks

[Emistry]

try

autobonus2 "{ bonus bMatkRate,20; }",150,3000;