Stability of ferromagnetic state of epitaxially grown ordered FeRh thin films

We report on the magnetic properties of $B2$ -type ordered FeRh epitaxial thin films deposited on MgO(001) substarates as a function of film thickness. All the films show a clear magnetic phase transition from the antiferromagnetic state to the ferromagnetic state with increasing temperature while the transition temperature of a $10\text{-}\mathrm{nm}$ -thick film decreases down to $300\mathrm{K}$ . The $10\text{-}\mathrm{nm}$ -thick film also shows a large magnetization even in the antiferromagnetic state compared with other thicker films. These magnetization data indicate that the ferromagnetic state is becoming more stable than the antiferromagnetic state with decreasing film thickness. Such thickness dependent magnetic properties are qualitatively compatible with a theoretical prediction for FeRh(001) thin layers.