Note4 earses space after deleting files automatically?

Hi:
I have deleted an important file in the internal storage of my Samsung Galaxy Note4 16GB. I try to recover the file but failed. Actually I found that Note4 will earse the space automatically after deleting the file. I found that when I deleted the file, I can see the space is all 0x00 if I run dd if=/dev/block/mmcblk0p27 of=/storage/extSdCard/p27.img (of course I have root ) and checkout p27.img by winhex.

So, I wonder, if there is any mechanism on Note4 to earse free space autoly?

Thanks!