W3Schools does not set the industry standards on HTML coding. They are simply a 3rd party reference site that is not affiliated with the W3C in anyway. W3Schools and other sites are often wrong when using cutting edge coding technologies such as Schema and Responsive design. When using fairly new code your one stop shop should be W3C as set the compliance standards, and maybe HTML5 Doctor if you need help understanding HTML5 through they are not official but highly respected.
Looking at your code it passes W3C validation without any issues with the link element contained within the <body> </body>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Untitled Document</title>
</head>
<body>
<div itemscope itemtype="http://schema.org/Book">
<span itemprop="name">The Catcher in the Rye</span>—
<link itemprop="url" href="http://en.wikipedia.org/wiki/The_Catcher_in_the_Rye" />
by <span itemprop="author">J.D. Salinger</span>
</div>
</body>
</html>
SHORT ANSWER: Yes, you can use <LINK> within <body> </body> but as Unor has mentioned in his answer must include itemprop.