property/global command for multiple atom types

Hi
In my simulation, I am using three types of atoms (say 1,2,3) I need to define the contact stiffness between each of them (E1,E2, E3)
For that I am using the following
fix m1 all property/global youngsModulus peratomtype ${E1} ${E2} ${E3}

As far as I can understand, this command has assigned a young modulus to each of the particles. How it takes care say when atom 1 and 3 come in contact. Is there a way to assign contact modulus like that? I tried peratomtypepair but it did not work.

Thanks
Shubham