Memory dumps are a copy of what contain in the RAM during SQL or system crash or even a manual dump. Memory dumps are useful when working with any SQL server troubleshooting because it helps to identify exactly what was running on a system when the problem occurred. A Memory dump is basically the contents of Memory written out to a file.
Below query returns one row for each memory dump file generated by the SQL Server Database Engine.
SELECT [filename], creation_time, size_in_bytes/1048576.0 AS [Size (MB)]
FROM sys.dm_server_memory_dumps WITH (NOLOCK)
ORDER BY creation_time