Sorry, but I think it is rather absurd that one should say "thank you" to his subordinates (that is, those who are inferior to him in position or age).
When we accept something (goods or deed) that is unlikely to be naturally given, we feel it grateful. On the other hand, it is a matter of course that subordinates should do something for their superiors.
Do you often appreciate breathing in the air? Likewise, we never need to say "thank you" to the people of lower-rank.