I second Mr. Sudhir; Head HR is the highest position as the HEAD itself represents the power and high position in the department. Secondly, an HR Manager can be called the department head if there is no higher authority defined or designated, such as the General Manager, who is of higher rank than the Manager, as we all know. However, it also depends on the authority and power provided to an HR personnel.
For example, if an HR department has a Manager (HR Manager) with higher authority and all other personnel working under him, he automatically becomes the Head of the Department. But if you want to define or designate the positions and power for two personnel, the HR Manager must come under the Head of the Department as "Head Corporate and HR."
Hierarchy:
Head HR → Manager-HR → other executives/personnel
Could you please let us know more about what you are planning to do and what you need? Please define the purpose so that we can understand your query better and provide you with more appropriate answers.