Partnership and power of atterney

I want to know whether any partner can appoint and give power of atterney to any third party..??

There are four partners Mr. A, Mr. B, Mr. C  and Mr. D. in the firm ABCD. They have prepared partnership deed too.

Now Mr. D without any reason want to appoint Mr. X as the power atternry holder on his behalf and wants to create disturbances in the firm's business through Mr. X. 

Now question is whether Mr. D alone has any right to appoint and give power of atterney to Mr. X....or else in doing so there must be a consent of all other partners and with the authority of other partners Mr. D can do so ...???? 

Please note that other parnters do not wish to have any disturbance from outsiders in the business....then what is the solution for this...? Can other partner seeks and put a legal stay on such action of Mr. D....? 

Please enlight the query as eary as possible