Strong electron correlations have been a central issue in condensed matter physics and been the cause of various electronic phenomena, such as the Mott transition, unconventional superconductivity, charge/spin ordering, magnetic phase transition, and heavy fermion behavior. In such systems, complex phenomena are arising from coupled lattice, orbital, charge and spin degrees of freedom. To understand the mechanism of phase transitions and to control the properties, it is necessary to tackle the problems with complementary experimental techniques studying both atomic and electronic structures. In my talk, I will mainly present the recent experimental discoveries in intermetallic EuTGe₃ compounds.

Intermetallic EuTGe₃ (T: transition metal) forms a non-centrosymmetric BaNiSn₃-type structure and has been attracting considerable attention due to complex magnetic structures [1-3]. All the series of compounds possesses magnetic Eu²⁺ (4f⁷, J=7/2) ions and exhibit antiferromagnetic ordering in low temperature [1, 2, 4]. The magnetic structure varies depending on a choice of the transition metal.  In EuRhGe₃, the moments align antiferromagnetically in ab-plane at T_N=11.3 K, while along c-axis in EuCoGe₃ and EuIrGe₃ at 15.4 K and 12.3 K, respectively [1]. Below T_N, successive magnetic phase transitions are reported at T_N= 13.4 K in EuCoGe₃, and T_N= 7.5 K and T_N= 5.0 K in EuIrGe₃ [1, 3]. Although Eu²⁺ electronic state is more stable than Eu³⁺ (4f⁶, J=0), the energy difference between them is not very large and can be tuned by applying pressure and/or chemical substitution. I will present the experimental studies of electronic and crystal structures of EuTGe₃ (T= Co, Rh, Ir) under pressure by using x-ray spectroscopy and diffraction [5, 6]. Recent progress in an installation of diamond anvil cell for electrical resistivity measurement and preliminary result of EuTGe₃ will be also presented.

. 

[1] O. Bednarchuk et al., J. Alloys Comp. 622, 432-439 (2015)

[2] A. Maurya et al., J. Phys.: Condens. Matter 26, 216001 (2014); J. Magn. Magn. Mat. 401, 823 (2016); J. Phys.: Condens. Matter 27, 366001 (2015).

[3] T. Matsumura et al., J. Phys. Soc. Jpn. 91, 073703 (2022).

[4] Y. Utsumi et al., Phys. Rev. B 97, 115155 (2018).

[5] Y. Utsumi et al., Electron. Struct. 3, 034002 (2021).

[6] N. S. Dhami et al., Phys. Rev. B 107, 155119 (2023).