Purification and shape control of iron nitride with giant magnetization

(1)将<16>晶粒尺寸为100 nm的α-Fe微粉在130℃低温氮化100 h，可得到结晶良好的高纯Fe_N_2。产物在室温下的饱和磁化强度为225 emu/g。该值比α-Fe起始粉末的值大16%。穆斯堡尔谱中有三种铁磁成分。它们的平均磁矩为2.52μB。假设19%的超顺磁性杂质转变为铁磁性，可以计算出270 emu/g的巨磁化强度。(2)溅射沉积的α-Fe薄膜在220℃以下氮化后没有检测到铁氮化物。薄膜沉积时间为60 min，薄膜厚度为360 nm。沉积时间越短，α-Fe薄膜越薄，Fe_3N等铁氮化物的形成温度越低。薄膜越薄，Α-Fe晶格越膨胀，晶粒尺寸越小.扫描探针显微镜观察表明，α-Fe薄膜由一系列细小的α-Fe颗粒连接而成。这三个因素可能会影响较薄的薄膜在较低温度下氮化的实验结果。(3)用75 Fe-25 Ni复合靶或合金靶溅射沉积了以AlN为绝缘层的自旋隧道结铁磁薄膜。在前一种膜中观察到含30 ~ 40at%Ni的Α-（Fe，Ni），在后一种膜中观察到含40 ~ 55at%Ni的γ-（Fe，Ni）。前者表现出约200 emu/g的大饱和磁化强度。在100 W（55 Oe）和250 W（30 Oe）的射频功率下沉积的薄膜的磁性有足够的差异。

(1) Well crystallized Fe__<16>N__2 was obtained in high purity by low temperature nitridation of α-Fe fine powder in 100nm crystallite size at 130℃ for 100hour. The product had a saturation magnetization of 225emu/g at room temperature. The value was 16% larger than that for α-Fe starting powder. There were three kinds of ferromagnetic components in its Mossbauer spectrum. Their average magnetic moment was 2.52μB. Giant magnetization of 270emu/g can be calculated by assuming that 19% of superparamagnetic impurity will turn to be ferromagnetic.(2) No iron nitride was detected after a nitridation below 220℃ of the sputter deposited α-Fe thin film. The film was deposited for 60mintute and its film thickness was 360nm. Formation temperature of iron nitrides such as Fe_3N became lower in the thinner α-Fe films deposited in shorter duration. Α-Fe crystal lattice expanded and its crystallite size became smaller in the thinner films. Scanning probe microscope showed that the α-Fe thinner film was composed with a linkage of smaller α-Fe particles. These three factors may affect the experimental result that the thinner films were nitrided in lower temperature.(3) Ferromagnetic thin films for spin tunnel junction using A1N as an insulating layer were sputter deposited from either 75Fe-25Ni composite or alloy targets. Α-(Fe, Ni) with 30〜40at%Ni was observed in the former film and γ-(Fe, Ni) with 40〜55at%Ni was in the latter film, respectively. The former showed a large saturation magnetization of around 200emu/g. There was an enough difference in magnetic coercivity between the films deposited at 100W of rf-power(55Oe) and at 250W(30Oe).