Electrical, optical, and magnetic properties of amorphous yttrium iron oxide thin films and consequences for non-local resistance measurements
Electrical, optical, and magnetic properties of amorphous yttrium iron oxide thin films and consequences for non-local resistance measurements
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DOI：
10.1063/5.0144371
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发表时间：
2023-06
影响因子：
3.2
通讯作者：
M. Roos;S. Bleser;L. Hernandez;G. Diederich;M. Siemens;M. Wu;B. Kirby;B. Zink
中科院分区：
文献类型：
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作者：
M. Roos;S. Bleser;L. Hernandez;G. Diederich;M. Siemens;M. Wu;B. Kirby;B. Zink
我们介绍了非晶态氧化钇(a-Y-Fe-O)薄膜的磁特性、电荷电阻率和光致发光测量，并与非晶态锗(a-Ge)薄膜进行了比较。我们用SQUID磁强计和偏振中子反射仪测量了它们的磁性质。这些结果不仅证实了a-Y-Fe-O是一种以反铁磁交换为主的强相互作用和高度受挫的无序磁性材料，而且最好的电学理解是无序半导体。与无定形锗一样，a-Y-Fe-O在很宽的温度范围内都能在局域电子态中实现可变范围的跳跃。我们还阐明了通过这种半导体介质的电荷传输对于非局部电压测量的结果，该测量旨在探测名义上绝缘的磁性材料中的自旋传输。我们进一步比较了用“准直流”自动电流反转进行的非局部电阻测量和用锁定放大器进行的交流测量。这些结果表明，“准直流”测量具有频率高达约22赫兹的有效交流电流激励，并且这种有效交流激励可能会导致这些测量中的伪影，包括非局部电阻的错误符号。这项对a-Y-Fe-O非局域电阻测量的全面研究表明，在微米尺度上没有自旋输运的证据，这与我们最初的工作相反，并与其他小组最近的研究一致。
We present magnetic characterization, charge resistivity, and optical photoluminescence measurements on amorphous yttrium iron oxide thin films (a-Y–Fe–O), with supporting comparisons to amorphous germanium (a-Ge) films. We measured magnetic properties with both SQUID magnetometry and polarized neutron reflectometry. These results not only confirm that a-Y–Fe–O is a disordered magnetic material with strong predominantly antiferromagnetic exchange interactions and a high degree of frustration, but also that it is best understood electrically as a disordered semiconductor. As with amorphous germanium, a-Y–Fe–O obeys expectations for variable-range hopping through localized electron states over a wide range of temperature. We also clarify the consequences of charge transport through such a semiconducting medium for non-local voltage measurements intended to probe spin transport in nominally insulating magnetic materials. We further compare non-local resistance measurements made with “quasi-dc” automated current reversal to ac measurements made with a lock-in amplifier. These show that the “quasi-dc” measurement has an effective ac current excitation with frequency up to approximately 22 Hz, and that this effective ac excitation can cause artifacts in these measurements including incorrect sign of the non-local resistance. This comprehensive investigation of non-local resistance measurements in a-Y–Fe–O shows no evidence of spin transport on micrometer length scales, which is contrary to our original work, and in line with more recent investigations by other groups.