Title: Itinerant ferromagnetism in van der Waals ${\mathrm{Fe}}_{5–x}{\mathrm{Ge}\mathrm{Te}}_2$ crystals above room temperature

Abstract

Two-dimensional (2D) van der Waals (vdW) magnets have recently attracted increasing attention, as they provide a novel system for exploring 2D magnetism. However, intrinsic ferromagnetism in 2D systems has almost exclusively been observed at low temperatures, limiting their technological relevance. ${\mathrm{Fe}}_{\mathrm{N}}{\mathrm{Ge}\mathrm{Te}}_2$ ( $N=3$, 4, and 5) systems are currently becoming the most attractive 2D vdW materials due to their relatively high Curie temperatures and large saturation magnetization. However, the nature of their complex yet intriguing magnetic behaviors is still unclear, in part due to the multiple inequivalent iron sites and iron vacancies. In this study, we show evolution of magnetic ordering transitions in ${\mathrm{Fe}}_{5–x}{\mathrm{Ge}\mathrm{Te}}_2$ with high Curie temperature and a strong saturation magnetization using photoemission electron microscopy and transport measurements. At 275 K, the ferromagnet transitions to a ferrimagnet, and below 110 K transitions to a state with glassy clusters. These are evidenced from temperature-dependent magnetic stripe domain evolution and anisotropic magnetoresistance measurements. Our findings show a clear magnetic ground state of ${\mathrm{Fe}}_{5–x}{\mathrm{Ge}\mathrm{Te}}_2$ at room temperature which signals that ${\mathrm{Fe}}_{5–x}{\mathrm{Ge}\mathrm{Te}}_2$ system is a very promising candidate for spintronic devices and provides a material design pathway to further increase the Curie temperature and saturation moments in vdW ferromagnets.

Authors:

Zhang, Hongrui ^[1]; Chen, Rui ^[1]; Zhai, Kun ^[2]; Chen, Xiang ^[1]; Caretta, Lucas  ^[1];

• Search DOE PAGES for author "Caretta, Lucas"
• Search DOE PAGES for ORCID "0000-0001-7229-7980"

Huang, Xiaoxi ^[1]; Chopdekar, Rajesh V.  ^[3];

• Search DOE PAGES for author "Chopdekar, Rajesh V."
• Search DOE PAGES for ORCID "0000-0001-6727-6501"

Cao, Jinhua ^[1]; Sun, Jirong  ^[4];

• Search DOE PAGES for author "Sun, Jirong"
• Search DOE PAGES for ORCID "0000-0003-4531-4794"

Yao, Jie ^[5]; Birgeneau, Robert ^[1]; Ramesh, Ramamoorthy ^[1]

---

+ Show Author Affiliations

1. Univ. of California, Berkeley, CA (United States)
2. Yanshan University (China)
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS) & Materials Sciences Division
4. Chinese Academy of Sciences (CAS), Beijing (China). Inst. of Physics
5. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division

Publication Date:

Wed Aug 19 00:00:00 EDT 2020

Research Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division

OSTI Identifier:

1775404

Grant/Contract Number:  

AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review B

Additional Journal Information:

Journal Volume: 102; Journal Issue: 6; Journal ID: ISSN 2469-9950

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; magnetic phase transitions; magnetotransport; spintronics; Van der Waals systems