Should thank you notes after an interview be hand-written?
This is not necessary. Today, a 'thank you' send via email or Linkedin inMail is actually preferable and more environmentally conscience.
Thank you notes do not need to be hand-written. Sending an email is sufficient and most common.
While it is a "nice touch" and demonstrates that extra effort was taken, it is not necessary as email is a perfectly acceptable and expected form of business communication.
As much as I love a good note, the timeline to get the note in the hands of the right person is long. Go the efficient route and send an email! It will be equally appreciated and get your name in front of the recruiter one more time.