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In the last two decades, novel material classes, such as topological materials and
more recently, quasi-2D magnets, have been experimentally realized. The presence
of electron correlations in a system with topological and magnetic order can lead to
exotic ground states. Magnetic van der Waals (vdW) compounds have become in the
past few years increasingly attractive for fundamental investigations since they provide
an immense possibility to study quantum magnetic phenomena in low dimensions.
First, we will focus on a single crystal of LaAgSb2 which has a square net crystal
structure, exhibiting multiple charge density wave transitions (CDW) as the
temperature is lowered. We find large planar Hall (PHE) signals in the CDW phase,
which are still finite in the high temperature phase though they change sign. Optimising
the structure within first-principles calculations, one finds an unusual chiral metallic
phase with broken inversion symmetry. The consequences of such structure on the
transport behaviour due to these CDW transitions will be discussed.
In the second part, I will discuss the transport and electron spin resonance (ESR)
measurements in a van der Waal Ferromagnet, Fe4GeTe2. The magnetization data
exhibit a Ferromagnetic transition at ~270K with unusual temperature dependence
compared to the conventional Ferromagnet. At ~100K, there is a spin reorientation
transition (SRT) where the easy axis changes from in-plane to out of plane. Our
transport data indicates that the Hall coefficient changes sign and the
magnetoresistance, anomalous Hall magnitude become maximum near the SRT,
providing the important role of SRT on the electron transport. The ESR data reveals
the unusual evolution of the magnetic anisotropy field with temperature. Combination
of these measurements indicate interplay between magnetism and band topology, and
the emergence of nontrivial phases at low temperature.
References:
1. Disentangling the unusual magnetic anisotropy of the near-room-temperature
ferromagnet Fe4GeTe2, Riju Pal et al., Advanced Functional Materials (in press).
2. Spin-reorientation driven emergent phases and unconventional magnetotransport
in quasi-2D vdW ferromagnet Fe4GeTe2, Riju Pal et al., npj 2D Mater Appl 8, 30
(2024).
3. Detection of nontrivial topology driven by charge density wave in a semi-Dirac
metal, Rafiqul Alam et al., Advanced Functional Materials, 33 (44), 2306751
(2023). |