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Tunable Ferromagnetism in a 2D Material at Room Temperature

Breakthroughs in next-generation spintronic logic and memory devices could hinge on our ability to control spin behavior in two-dimensional materials—stacks of ultrathin layers held together by relatively weak electrostatic (van der Waals) forces. The reduced dimensionality of these so-called “van der Waals materials” often leads to tunable electronic and magnetic properties, including intrinsic ferromagnetism. However, it remains a challenge to tune this ferromagnetism (e.g. spin orientation, magnetic domain phase, and magnetic long-range order) at ambient temperatures.

In this work, researchers performed a study of Fe3GeTe2, a van der Waals material that consists of Fe3Ge layers alternating with two Te layers. The material’s magnetic properties were characterized using a variety of techniques, including x-ray absorption spectroscopy (XAS) with x-ray magnetic circular dichroism (XMCD) contrast at Beamline 6.3.1 and photoemission electron microscopy (PEEM) at Beamline 11.0.1.1.

The results showed that, below 230 K (the Curie temperature), Fe3GeTe2 displays long-range magnetic order in the form of stripe domains with out-of-plane magnetizations. Above 230 K, this order disappears. The researchers then sought to tailor this phase by patterning the samples into diamond-shaped microstructures (sharp corners promote the reorientation of the magnetization vector). They found that the magnetic phase changed from an out-of-plane stripe phase below 230 K to an in-plane vortex phase above 230 K, which persisted to temperatures as high as 370 K, making it stable at room temperature.

These results open up exciting opportunities for the use of room-temperature van der Waals magnets in applications such as low-power spintronics, high-density magnetic storage, and flexible electronics.

PEEM images for unpatterned and patterned Fe3GeTe2 samples at 110 K and 300 K. The unpatterned samples formed stripe domains at 110 K, which disappeared at 300 K. The patterned samples formed out-of-plane stripe domains at 110 K and transitioned to in-plane vortex states at 300 K, demonstrating control over magnetism at room temperature and beyond.

Q. Li, M. Yang, C. Gong, R.V. Chopdekar, A.T. N’Diaye, J. Turner, G. Chen, A. Scholl, P. Shafer, E. Arenholz, A.K. Schmid, S. Wang, K. Liu , N. Gao, A.S. Admasu, S.-W. Cheong, C. Hwang, J. Li, F. Wang, X. Zhang, and Z.Q. Qiu, “Patterning-Induced Ferromagnetism of Fe3GeTe2 van der Waals Materials beyond Room Temperature,” Nano Lett. 18, 5974 (2018), doi:10.1021/acs.nanolett.8b02806.