Form is not validated in AngularJS

I have this simple form:

<form name="assignCtrl.carrierForm">
     <md-input-container class="md-block">
            <label>Company Name</label>
            <input required name="carrierName" ng-model="assignCtrl.searchKeyword">
            <div ng-messages="assignCtrl.carrierForm.carrierName.$error">
                <div ng-message="required">This field is required.</div>
            </div>
     </md-input-container>

    <md-input-container class="md-block">
        <label>Company Email</label>
        <input type="email" name="carrierEmail" ng-model="assignCtrl.companyEmail" required
                               ng-pattern="/^.+@.+\..+$/" minlength="5" maxlength="100"/>
        <div ng-messages="assignCtrl.carrierForm.carrierEmail.$error">
             <div ng-message="required">Email is required.</div>
             <div ng-message-exp="['pattern', 'minlength', 'maxlength']">Please enter a valid email
                                address.
             </div>
        </div>
     </md-input-container>

    <md-button type="submit" ng-disabled="assignCtrl.carrierForm.$invalid" ng-click="assignCtrl.createAndAssign()">Create and Assign
    </md-button>

</form>

It is not being validated! ng-messages do not appear at all.

form.$error is also empty:

{{assignCtrl.carrierForm.$error | json }}

What could be the reason?