xml serialization - remove namespace

I am serializing an object using c#. I am getting result in this format given bellow

<?xml version="1.0"?>
<Users xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <Users>
        <User Id="11005477969327" CreateDate="06/03/2011" LastSendDate="1/1/0001" />
        <User Id="11034688201594" CreateDate="04/22/2012" LastSendDate="1/1/0001" />
    <Users 
</User>

    

But I want result in this format.

<?xml version="1.0"?>
<Users>
  <User Id="11005477969327" SendDate="1/1/0001" NextSendDate="2/7/2012 11:13:30 AM" />
  <User Id="11034688201594" SendDate="1/1/0001" NextSendDate="2/7/2012 11:13:30 AM" />
</Users>

Here's my code:

public class Users
{
    [XmlArray("Users")]
    public List<User> ListData { get; set; }

    public string GetXML()
    {
        System.IO.MemoryStream ms = new System.IO.MemoryStream();

        XmlSerializer sr = new XmlSerializer(typeof(Users));
        sr.Serialize(ms, this);

        ms.Position = 0;
        return System.Text.Encoding.UTF8.GetString(ms.ToArray());
    }
}

public class User
{
    [XmlAttribute("Id")]
    public Int64 UserId { get; set; }

    [XmlAttribute("CreateDate")]
    public string CreateDate { get; set; }

    [XmlAttribute("LastSendDate")]
    public string LastSendDate { get; set; }
}