What is the difference between MBA and Masters in a business subject, and which is better for a future researcher? What is the difference between MBA and Masters in a specific subject of Business studies like, master in Management? 

What will be a better option for one if he intends to be a researcher in future?
And does MBA degree specialize a specific subject of business studies?
An MBA is a professional degree designed for students who will go to work in industry and not pursue further graduate study or research.  Students in MBA programs typically all take the same courses in lock step with very few electives or options.  It generally isn't possible to specialize in a particular area in an MBA program.  In that sense, an MBA program is very much like medical school or law school and totally unlike graduate study in engineering and the arts and sciences.   Students in MBA programs usually have several years of full time experience working in low level corporate jobs after completing a bachelors degree.  Because they have had some exposure to the corporate/business world, the courses that they take draw on that experience.   

In comparison, the Master's in Management is a professionally oriented degree program aimed primarily at students who have just completed a bachelor's degree.  These programs tend to be more theoretical simply because students have less practical experience to draw on.  Many business schools also offer professionally oriented masters degrees in more specialized technical areas (e.g. a Master's degree in mathematical finance or operations research or analytics.)  

PhD programs in business schools are typically very separate from MBA programs and the students in the PhD program will typically take very few if any courses with the MBA students.  PhD students take more theoretical course work, take advanced courses in an area of specialization (e.g. accounting, finance, marketing, etc.) take course work in research methods, and then conduct research and write a dissertation.      

If you're just completing a bachelor's degree and want to get a masters and go to work in industry, than a Masters in Management is the typical path.  If you're just completing a bachelor's degree and want to become a business school professor then a PhD program would be appropriate.  If you've had several years of experience in business and want to move up in management, then an MBA would be the typical path for you.