Provided is a magnetic memory device and a method of forming the same. A first magnetic conductive layer is disposed on a substrate. A first tunnel barrier layer including a first metallic element and a first non-metallic element is disposed on the first magnetic conductive layer. A second magnetic conductive layer is disposed on the first tunnel barrier layer. A content of an isotope of the first metallic element having a non-zero nuclear spin quantum number is lower than a natural state.