Purification and shape control of iron nitride with giant magnetization

(1)对α-Fe微粉进行100 nm的低温氮化，在130℃下氮化100小时，可得到结晶良好的高纯Fe_(16)；N_2。产物的室温饱和磁化强度为225emu/g。这一数值比α-Fe起始粉高出16%。它的穆斯堡尔谱中有三种铁磁成分。它们的平均磁矩为2.52emu B。假定19%的超顺磁性杂质将转变为铁磁性，可计算出270emu/g的巨磁化强度。(2)溅射沉积的α-Fe薄膜在220 emu以下氮化后没有检测到氮化铁。薄膜沉积时间为60min，薄膜厚度为360 nm。沉积时间越短，沉积的α-Fe薄膜越薄，形成Fe3N等氮化铁的温度越低。薄膜越薄，Α-Fe晶格越大，晶体尺寸越小。扫描探针显微镜显示，α-Fe薄膜由较小的α-Fe颗粒组成。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)以AlN为绝缘层的自旋隧道结铁磁薄膜是在75Fe-25Ni复合材料或合金靶材上溅射制备的。前一层膜中含有30~40at%Ni的Α-(Fe，Ni)，后一层膜中分别含有40~55at%Ni的γ-(Fe，Ni)。前者显示出较大的饱和磁化强度，约为200emu/g。在100W射频功率(55Oe)和250W(30Oe)射频功率下沉积的薄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).