Purification and shape control of iron nitride with giant magnetization

(1)将α-Fe细粉在130℃下低温氮化100小时，得到晶粒尺寸为100nm的Fe__<16> n_2，结晶良好，纯度高。室温饱和磁化强度为225emu/g。该数值比α-Fe起始粉大16%。其穆斯堡尔谱中有三种铁磁成分。平均磁矩为2.52μB。假设19%的超顺磁性杂质变为铁磁性，可以计算出270emu/g的巨磁化强度。(2)溅射沉积的α-Fe薄膜在220℃以下进行氮化处理后，未检测到氮化铁。膜沉积60min，膜厚360nm。α-Fe薄膜越薄，沉积时间越短，Fe_3N等氮化铁的形成温度越低。Α-Fe薄膜越薄，晶格越膨胀，晶粒尺寸越小。扫描探针显微镜观察到α-Fe薄膜是由较小的α-Fe颗粒连接而成。这三个因素都可能影响在较低温度下氮化膜较薄的实验结果。(3)在75Fe-25Ni复合材料或合金靶材上溅射沉积了以A1N为绝缘层的自旋隧道结铁磁薄膜。在前一层膜中分别观察到含有30 ~ 40at%Ni的Α-(Fe, Ni)和含有40 ~ 55at%Ni的γ-(Fe, Ni)。前者表现出较大的饱和磁化强度，约为200emu/g。在100W射频功率（55Oe）和250W射频功率（30Oe）下沉积的膜的矫顽力有足够的差异。

(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).