I second Mr Sudhir, Head HR is the highest position as the HEAD itself represent the power and high position in the department.
Second, HR Manager can be called the department head if there is no higher power authority defined or designated such as the General Manager is more high rank the Manager that we all knows. However, it is also depends on the authority and power provided to an HR Personnel.
For example :
if an HR Department having a Manager (HR Manager) with the higher authority and rest all personnel are working under him, is the Head of the Department automatically, but if you wants to define or designate the two positions and power for two personnel, HR Manager must come under the Head of Department as "Head Corporate and HR"
Head HR- > Manager-HR -> other executives /personnel
Could you please let us know more on what actually you gonna do and want. Please define the purpose so that we all can understand your query well and give you the more appropriate answers