Is it acceptable that a teacher assistant encourage students to read his authored materials too? During my leisure time, I used to prepare some pamphlets in the topic of courses I always wanted to teach. Each, full of examples and solved problems which I designed and solved myself, not photocopying from books and papers; that are so helpful to the engineering students.

If one day, I have the chance to teach in a TA class, is it ethical to ask the students to read my prepared materials too? Or the teaching assistant should only solve the problems of the reference book which is told by the professor of the course?
Your role as a teaching assistant is to further the educational goals of the course (as determined by the instructor and/or the department). 

If encouraging your students to read these materials furthers the educational goals of the course, then you should do so. If not, then you shouldn't.

Since the instructor and/or the department determines what the educational goals of the class are, you should check with them first, and use your extra material only with their approval. (Besides for the issue of making sure your material is consistent with the goals of the course, it also makes sense for them to be aware of what is going on.)