How can we recover data from formated memorycard?

Deleting or formatting won't make the data in memory card erased permanently.

Those deleted data is still stored on the memory card, it's just invisible or inaccessible. Only the FAT or NFTS table is erased (the information about where those data were saved), but the real data are still intact there in sectors of the hard drive.

So as long as those data are not overwritten by new data, it's highly possible to recover them. And the MOST Effective way is to rely on some format recovery programs.

Note: before the data is recovered, never attempt to put more files to the disk. As saving more files may cause original data overwritten. Once overwritten, it's impossible to recover the lost items.