In Realuk_Login_IndexController::loginAction() you're setting response body but response itself is never send to the client, instead you're redirecting to the home page. You can either send the response by using:

$this->getResonse()->sendResponse();

or pass json data to the home page:

$jsonData = array( 'json' => Mage::helper('core')->urlEncode( Mage::helper('core')->jsonEncode($result) )); $this->_redirect('home', $jsonData);

In Realuk_Login_IndexController::loginAction() you're setting response body but response itself is never send to the client, instead you're redirecting to the home page. You can either send the response by using:

$this->getResonse()->sendResponse();

or pass json data to the home page:

$jsonData = array(
    'json' => Mage::helper('core')->urlEncode(
        Mage::helper('core')->jsonEncode($result)
));
$this->_redirect('home', $jsonData);