How to slow down a gameobject that has rigidbody

I have Player with a rigidbody player script that stops abruptly when i take my off the joystick. However i want it drift forward before stopping

[RequireComponent (typeof (Rigidbody))] public class PlayerController : MonoBehaviour {

 public    LayerMask groundLayers; 
 public CapsuleCollider CapCol;
 private Vector3 JumpMovement;

 private    Rigidbody myRigidbody;
 public Vector3 velocity;
 [SerializeField] float jumpForce;
 private AudioManager audioManager;
 // variable to hold shaking acceleration value
 Vector3 accelerationDir;

 [SerializeField]private GameObject overheadtextSphere;
 // Use this for initialization
 void Start () 
 {
     myRigidbody = GetComponent<Rigidbody> ();

     CapCol = GetComponent<CapsuleCollider> ();

     audioManager = FindObjectOfType<AudioManager> ();


 }

 void Update()
 {
     // Read new acceleration Input from mobile device
     accelerationDir = Input.acceleration;

     /* If you shake the mobile device hard enough
     (accelerations Square Magnitude greater then 5 for example)
     if (accelerationDir.sqrMagnitude >= 4f) 
     {
         Jump ();
     } */

     /*if(Input.touchCount > 0)
     {
         Touch touch = Input.GetTouch (0);
     }*/

 }
  void FixedUpdate() 
 {

    myRigidbody.MovePosition (myRigidbody.position + velocity * Time.fixedDeltaTime);

 /*    if (Input.GetKeyDown (KeyCode.Space) && IsGrounded() )
     {
         
     }*/
         
 }

public void Jump() { jumpForce = 10; if(IsGrounded()) { myRigidbody.AddForce (Vector3.up * jumpForce, ForceMode.Impulse); audioManager.Play ("Jump"); }

 } 
 public bool IsGrounded()
 {
     //.9 is 90% the sphere, jump only if touch the ground
     return Physics.CheckCapsule (CapCol.bounds.center, new Vector3 (CapCol.bounds.center.x, CapCol.bounds.min.y,
         CapCol.bounds.center.z), CapCol.radius * .1f, groundLayers);

 }

 public Vector3 GetPosition()
 {
     return transform.position;
 }
 public void Move(Vector3 _velocity) {

     velocity = _velocity;

 }
 public void LookAt(Vector3 lookPoint) {

     Vector3 heightCorrectedPoint = new Vector3 (lookPoint.x, transform.position.y, lookPoint.z);

     transform.LookAt (heightCorrectedPoint);

 }

}

[RequireComponent (typeof (PlayerController))] public class Player : LivingEntity {

 public float moveSpeed = 5f;
 PlayerController controller;
 Camera viewCamera;
 [SerializeField] VirtualJoystick joystick;
 [SerializeField] GameObject JoyStickbase;

 // Use this for initialization

protected override void Start () { base.Start (); controller = GetComponent (); viewCamera = Camera.main;

     if(Manager.Instance.sceneIndex == 5)
     {
         first_rank_label = KOmode.Instance.rank_text;
         last_rank_label = KOmode.Instance.Lastrank_text;
         playertag = this.gameObject.tag;
         melee_bool = true;

     }
 }
 void Update () 
 {
     Vector3 moveInput = new Vector3 (SimpleInput.GetAxis ("Horizontal"), 0, SimpleInput.GetAxis ("Vertical"));  //controls looking with mouse
 //    Vector3 moveInput = new Vector3(joystick.Horizontal(),0,joystick.Vertical());
     Vector3 moveVelocity = moveInput * moveSpeed;
     controller.Move (moveVelocity);

 /*    if (Time.timeScale < 1)   // To move fast during slowmotion
     {
         controller.Move (moveVelocity*  5); // time gets slowed by 20,so we multiply by 20
     }*/

     Ray ray = viewCamera.ScreenPointToRay (Input.mousePosition);
     Plane groundPlane = new Plane (Vector3.up, Vector3.zero);
     float rayDistance;

     if (groundPlane.Raycast(ray,out rayDistance)) {

         Vector3 point = ray.GetPoint(rayDistance); // point of interception

         controller.LookAt(point);
     }
     if(Input.touchCount > 0)
     {
         Touch touch = Input.GetTouch (0);
         //Vector3 touchPosition = Camera.main.WorldToScreenPoint (touch.position);
         JoyStickbase.transform.position = touch.position;
     }

     Vector3 namePos = Camera.main.WorldToScreenPoint (this.transform.position);

     if(melee_bool)
     {
         if(playertag == KOmode.Instance._firstRankplayer)
         {
             //first_rank_label = KOmode.Instance.rank_text;
             first_rank_label.transform.position = namePos;
         }

         if(playertag == KOmode.Instance._lastRankPlayer)
         {
             //last_rank_label = KOmode.Instance.Lastrank_text;
             last_rank_label.transform.position = namePos;
         }
     }
 
 }
     

}