how specify a directory to file when downloading it

I use this code to download a file from remote server to mine and the file is created and saved but in the home directory and i want it in the plugin directory

$url ='*.dat';
// Use wp_remote_get to fetch the data
$response = wp_remote_get($url);

// Save the body part to a variable
$fileContent = $response['body'];

// Create the name of the file and the declare the directory and path

$file ='*.dat';

// Now use the standard PHP file functions
$fp = fopen($file, "w");
fwrite($fp, $fileContent);
fclose($fp);