If you don't have a backup of those important data, most likely they are gone. That's the risk of not having a backup, isn't it?
First make a clone of this disk on another disk; then try a few of the DIY programs mentioned in http://www.cnet.com/forums/discussions/lost-and-found-or-the-storage-forum-sticky-354911/ on the clone. But I'm afraid it won't work, since you erased the most important part of the disk.
Hello,
I wanted to format one partition on my computer which had to be cleaned but accidentally chose another partition (partition D) where all the important data is stored. The formatting was at slow speed (the check mark was removed from "Quick Format" option before the formatting started). After 9 percent of the partition had been formatted, I realized that I had chosen a wrong partition with all the important data on it. I instantly terminated the formatting process by switching off the computer to make sure that the process stops immediately. Now Windows system says that the partition is not accessible.
Does anyone know how to restore the data in the partition and regain access to it?

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