How to get data from json in amchart

I have Created pie chart using javascript amchart plugin. So I need to get data from json object. These data
stored in database.I am working in codeignitor framework. It is a php framework.

I have written code to get data from database.

function getCountJSON($first_tbl, $first_tbl_field, $second_tbl, $second_tbl_field) {
        $result = $this->gm->getQueryCount($first_tbl, $first_tbl_field, $second_tbl, $second_tbl_field);
        $result_array = array();

        foreach ($result as $r) {
            $result_array[] = array('country' => $r['country_name'], 'count' => $r['query_count']);
        }
        echo json_encode($result_array);
    }

Now I need to get my JSON Object by using ajax request. I used following code snippet to get data from ajax request.

AmCharts.loadJSON = function (url) {

                // create the request
                if (window.XMLHttpRequest) {
                    // IE7+, Firefox, Chrome, Opera, Safari
                    var request = new XMLHttpRequest();
                } else {
                    // code for IE6, IE5
                    var request = new ActiveXObject('Microsoft.XMLHTTP');
                }

                // load it
                // the last "false" parameter ensures that our code will wait before the
                // data is loaded
                request.open('POST', url, false);
                request.send();

                // parse and return the output
                return eval(request.responseText);
 />            };

I have taken the JSON object to javascript variable.

var chartData1 = AmCharts.loadJSON("ajax/getCountJSON/countries/country_name/customers/country_id");

I Got following Result in amchart.

Thank you !