Sheffield United sign two defenders
Both have joined on loan deals until the end of the season.
Twenty-year-old West Bromwich player Mattock, who can also play in midfield, goes straight into contention for Saturday's Championship trip to Coventry City.
Mattock, who has represented England at all age group levels, made his debut for hometown club Leicester City as a 16-year-old in April 2007.
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Hide AdAdams said: "Joe's young and enthusiastic and certainly gives us competition for places.
"He had an injury at West Brom at the start of the season which limited his opportunities, but he's naturally left-footed and having him here will help us climb the table."
Lowry, 21, joins from West Ham and spent part of last season on loan at Leeds United.
For more on this story read Friday's Yorkshire Post.