IOS application - define protocol in separate file

I have defined a protocol in a separate file (myProtocol.h). Here is the code for it:

#import <Foundation/Foundation.h>

@protocol myProtocol <NSObject>
    -(void) loadDataComplete;
@end

Now I want to call this method so I have done the following code:

firstViewController.h:

#import "myProtocol.h"

@interface firstViewController : UIViewController{
    id <myProtocol> delegate;
}
@property (retain) id delegate;
-(void) mymethod;

firstViewController.m

@implementation firstViewController
@synthesize delegate;

- (void)viewDidLoad {
    [self mymethod];
}

-(void) mymethod {
    //some code here...
    [delegate loadDataComplete];
}

I have another file where the protocol is also utilized:

secondViewController.h:

#import "myProtocol.h"
@interface secondViewController : UIViewController<myProtocol>{
}

secondViewController.m:

-(void) loadDataComplete{
    NSLog(@"loadDataComplete called");
}

but my secondViewController is not calling the protocol methad. Why is it so? Any suggestion will be appreciated.