Which type of secondary storage consists of rotating platters, which are coated with a magnetic material, and read/write heads, which can detect and change the patterns of varying magnetic flux on the platters?

Hard Disk Drives (HDDs)

Explanation:

To store and retrieve data, magnetic storage is used. This is possible through the availability of magnetic coated rotating platters. Due to their ability to retain data stored on them, they are considered non-volatile storage devices.

Even though facing extinction due to the emergence of SSDs (Solid State Drives), HDDs are still the most used because they are less expensive.

Just as stated in the question, HDDs can detect and change the patterns o varying magnetic flux on the pattern and they also possess read/write heads for storage and retrieval of data.