Single-crystal Fe16N2 films have been grown epitaxially on Fe(001)/InGaAs(001) and InGaAs(001) substrates by molecular beam epitaxy (MBE). Saturation flux density Bs of Fe16N2 films has been demonstrated to be 2.8–3.0 T at room temperature, which is very close to the value obtained by Kim and Takahashi using polycrystalline evaporated Fe–N films. Temperature dependence of Bs has been measured. Bs changed with temperature reversibly up to 400 °C, while beyond 400 °C, Bs decreased irreversibly. X-ray diffraction showed that Fe16N2 crystal is stable up to 400 °C, while beyond 400 °C, Fe16N2 dissolves into Fe and Fe4N, and also some chemical reactions between Fe16N2 and the substrate occurs. This caused the temperature dependence of Bs mentioned above. From the temperature dependence of Bs up to 400 °C, the Curie temperature of Fe16N2 is estimated to be around 540 °C by using the Langevin function. The above mentioned Bs of 2.9 T at room temperature and 3.2 T at −268 °C corresponded to an average magnetic moment of 3.2μB per Fe atom and 3.5μB, respectively. These values of the magnetic moment of Fe atoms are literally giant, far beyond the Slater–Pauling curves. The origin of the giant magnetic moment has been discussed based on the calculation carried out by Sakuma. However, there was a significant disagreement between experimental values and calculated ones, so the origin remained to be clarified. Also, magneto-crystalline anisotropy of Fe16N2 films has been investigated.

Exchange couplings between antiferromagnetic Mn–Ir and ferromagnetic Ni–Fe layers have been investigated while varying the Mn–Ir composition. These exchange couplings appeared at room temperature at Ir compositions between 20 and 46 at.%. The maximum exchange coupling field of 3.2 kA/m was obtained for Mn–20 at.%Ir(59 nm)/Ni–Fe(20 nm)/Zr(10 nm). Dependence of the exchange coupling fields on each layer thickness was also investigated. The Mn–Ir/Ni–Fe bilayers maintained high exchange coupling fields at Mn–Ir layer thicknesses above 10 nm.

We studied an antiferromagnetic CrMnPt x ͓͑Cr:MnӍ1:1͒ in atomic percent͔ film for an exchange-biased layer, focusing especially on the relationships between the exchange coupling properties of the CrMnPt x ͑top͒/Ni 81 Fe 19 ͑bottom͒ films and the character of its CrMnPt x film. The best Pt content to obtain a large exchange coupling of the CrMnPt x film was 5.0-8.0 at. %. Typically, the exchange coupled 50 nm CrMnPt 5Ϫ8 /40 nm Ni 81 Fe 19 films exhibited a relatively large exchange coupling field of ϳ22 Oe and a high blocking temperature of ϳ380°C. Besides, the CrMnPt 5Ϫ8 film deposited on the Ni 81 Fe 19 film had a considerably high resistivity of ϳ300-350 ⍀ cm. These large exchange coupling and high resistivity values were obtained only when the ␣-phase with a disordered bcc structure was stabilized in the CrMnPt x film by the underlying fcc Ni 81 Fe 19 film. The Pt within the CrMnPt x film might localize the Mn magnetic moment. As to why the CrMnPt x film having the Pt content of 5.0-8.0 at. % could give the Ni 81 Fe 19 film a large exchange coupling, this was attributed to the nearest neighbor Mn-Mn atomic distance within the CrMnPt 5Ϫ8 film being the same as the distance at which the Mn-Mn exchange interaction showed the maximum negative value. Furthermore, the decrease in size of the exchange coupling field and lowered blocking temperature for t CrMnPt Ͻ30 nm ͑t CrMnPt : CrMnPt x film thickness͒ were thought to originate from a decrease of antiferromagnetic CrMnPt x anisotropy with decreasing t CrMnPt .

Among metal additives M(M:Pt, Pd, Rh, Ir, and Cu) of antiferromagnetic CrMnMx films, Pd was the most suitable M for obtaining large exchange coupling. For the 50 nm CrMnPd5/40 nm Ni81Fe19 films, the exchange coupling field of ∼28 Oe and the blocking temperature of ∼380 °C could be obtained. The CrMn(Pt, Pd, or Rh)x films having the optimum content of ∼8, ∼5, or ∼11 at.% exhibited the same high blocking temperature. The high blocking temperature of the CrMnPt8, CrMnPd5, and CrMnRh11 films was attributed to the nearest neighbor Mn–Mn within the respective films being at the same distance as that at which the Mn–Mn exchange integral showed the maximum negative value.

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