[Paper Review] Growth and characterization of the magnetic topological insulator candidate Mn$_2$Sb$_2$Te$_5$

Ankush Saxena, V. P. S. Awana|arXiv (Cornell University)|Oct 16, 2023

Topological Materials and PhenomenaPhysics and Astronomy3 citations

TL;DR

This study reports the successful growth and comprehensive characterization of Mn₂Sb₂Te₅, a new magnetic topological insulator (MTI) candidate derived from the MnSb₂Te₄ family. The material exhibits metallic transport behavior with a resistivity upturn below ~20 K, negative magnetoresistance at low temperatures, and antiferromagnetic-like transitions at ~20 K and ~10 K, confirming its potential as a magnetic topological insulator with intrinsic magnetic order and topological surface states.

ABSTRACT

We report a new member of topological insulator (TI) family i.e., Mn$_2$Sb$_2$Te$_5$, which belongs to MnSb$_2$Te$_4$ family and is a sister compound of Mn$_2$Bi$_2$Te$_5$. An antiferromagnetic layer of (MnTe)$_2$ has been inserted between quintuple layers of Sb$_2$Te$_3$. The crystal structure and chemical composition of as grown Mn$_2$Sb$_2$Te$_5$ crystal is experimentally visualized by single crystal XRD (SCXRD) and field emission scanning electron microscopy (FESEM). The valence states of individual constituents i.e., Mn, Sb and Te are ascertained through X ray photo electron spectroscopy (XPS). Different vibrational modes of Mn$_2$Sb$_2$Te$_5$ are elucidated through Raman spectroscopy. Temperature-dependent resistivity of Mn$_2$Sb$_2$Te$_5$ resulted in metallic behaviour of the same with an up-turn at below around 20K. Further, the magneto-transport R(T) vs H of the same exhibited negative magneto-resistance (MR) at low temperatures below 20K and small positive at higher temperatures. The low Temperature -ve MR starts decreasing at higher fields. The magnetic moment as a function of temperature at 100Oe and 1kOe showed AFM like down turn cusps at around 20K and 10K. The isothermal magnetization (MH) showed AFM like loops with some embedded FM/PM domains at 5K and purely paramagnetic (PM) like at 100K. The studied Mn$_2$Sb$_2$Te$_5$ clearly exhibited the characteristics of a magnetic TI (MTI).

Motivation & Objective

• To synthesize and characterize a new member of the topological insulator family, Mn₂Sb₂Te₅, as a candidate for magnetic topological insulators (MTIs).
• To investigate the crystal structure, chemical composition, and electronic states of Mn₂Sb₂Te₅ using advanced characterization techniques.
• To determine the magnetic and transport properties of Mn₂Sb₂Te₅ to assess its potential for hosting topologically protected surface states.
• To explore the interplay between magnetism and topology in Mn₂Sb₂Te₅ by analyzing temperature-dependent resistivity, magneto-transport, and magnetization behavior.

Proposed method

• Single crystal X-ray diffraction (SCXRD) was used to determine the crystal structure and unit cell parameters of Mn₂Sb₂Te₅.
• Field emission scanning electron microscopy (FESEM) was employed to analyze the surface morphology and crystal quality.
• X-ray photoelectron spectroscopy (XPS) was applied to confirm the valence states of Mn, Sb, and Te in the compound.
• Raman spectroscopy was used to identify and assign vibrational modes in the Mn₂Sb₂Te₅ lattice.
• Temperature-dependent resistivity and magneto-resistivity measurements were performed to analyze electronic transport behavior.
• Magnetization measurements as a function of temperature and magnetic field were conducted to assess magnetic ordering and phase transitions.

Experimental results

Research questions

• RQ1 Does Mn₂Sb₂Te₅ exhibit the structural and electronic characteristics of a topological insulator with intrinsic magnetic order?
• RQ2 What is the nature of the electronic transport behavior in Mn₂Sb₂Te₅, particularly at low temperatures?
• RQ3 Does Mn₂Sb₂Te₅ display magnetic ordering, and if so, what type (AFM, FM, or PM) and at what transition temperatures?
• RQ4 How does the magnetoresistance of Mn₂Sb₂Te₅ vary with temperature and magnetic field, and what does this imply about its electronic structure?
• RQ5 To what extent do the observed magnetic and transport features support Mn₂Sb₂Te₅ as a candidate for a magnetic topological insulator?

Key findings

• Mn₂Sb₂Te₅ exhibits metallic transport behavior with a resistivity upturn below approximately 20 K, indicating possible electron correlation or Kondo-like effects.
• Negative magnetoresistance (MR) is observed at low temperatures below 20 K, which decreases at higher magnetic fields, suggesting spin-dependent transport mechanisms.
• Antiferromagnetic-like transitions are observed at ~20 K and ~10 K in temperature-dependent magnetization measurements at 100 Oe and 1 kOe, respectively.
• Isothermal magnetization (M-H) loops at 5 K show features consistent with antiferromagnetic ordering with embedded ferromagnetic or paramagnetic domains.
• At 100 K, the magnetization exhibits purely paramagnetic-like behavior, confirming the absence of long-range magnetic order at high temperatures.
• The combined structural, electronic, and magnetic characterization confirms Mn₂Sb₂Te₅ as a promising candidate for a magnetic topological insulator with intrinsic magnetic order and potential topological surface states.