How to post a value to a controller function on button click using Ajax and also redirect to new page at the same time?

I have a button Next that changes the page -

<a class="disabled" href="step">
   <button class="btn btn-primary launch-btn disabled next">NEXT</button>
</a>

Also, when this button is clicked, I have an Ajax function that sends data to a controller function -

<script type="text/javascript">
$(function(){
    $('.next').click(function() {
    var a = $('#box').data('val');

    $.ajax({
       type: "POST",
       url: "<?php echo base_url(); ?>study/CreateData",
       data: a,
       success: function(data)
       {
          console.log(data); 
       },
       error: function()
       {
          console.log("fail");
       } 
     });
  });
});
</script>

And I'm using this to receive the value from Ajax -

public function CreateData() {
        $data = $this->input->post('data');
        return $data;
    }

When the Next button hits its controller where it changes to a new page, I'm trying to retrieve the value posted by Ajax to the CreateData() function -

public function step()
    {
        $data = $this->CreateData();
        if(!empty($data)){
            print_r($data); exit;
        }
        else {
            echo "blank"; exit;
        }
        $this->load->view('step2');
    }

However, this keeps echoing blank. This obviously means that the $data being returned is empty but I'm not sure why. The success function in my Ajax script is logging data, so it's posting the value to CreateData(). What am I doing wrong here?