Valence change and magnetic order in YbMn6Ge(6-x)Sn(x)

Anomalous Hall effect and magnetic transition in the kagome material YbMn6Sn6

We investigate the magnetic and transport properties of a kagome magnet YbMn6Sn6. We have grown YbMn6Sn6single crystals having a HfFe6Ge6type structure with ordered Yb and Sn atoms, which is different from the distorted structure previously reported. The single crystal undergoes a ferromagnetic phase transition around 300 K and a ferrimagnetic transition at approximately 30 K, and the magnetic transition at low temperature may be correlated to the ordered Yb sublattice. Negative magnetoresistance has been observed at high temperatures, while the positive magnetoresistance appears at 5 K when the current is oriented out of kagome plane. We observe a large anisotropic anomalous Hall effect with the intrinsic Hall contribution of 141 Ω-1cm-1forσzxintand 32 Ω-1cm-1forσxyint, respectively. These values are similar to those in YMn6Sn6with the same anisotropy. The magnetic transition and anomalous Hall behavior in YbMn6Sn6highlights the influence of the ordered Yb atoms and rare earth elements on its magnetic and transport properties.

Crystal Growth and Physical Properties of Hybrid CoSn-YCo6Ge6 Structure Type LnxCo3(Ge1-ySny)3 (Ln = Y, Gd)

There is an ongoing interest in kagome materials because they offer tunable platforms at the intersection of magnetism and electron correlation. Herein, we examine single crystals of new kagome materials, LnxCo3(Ge1-ySny)3 (Ln = Y, Gd; y = 0.11, 0.133), which were produced using the Sn flux-growth method. Unlike many of the related chemical analogues with the LnM6X6 formula (M = transition metal and X = Ge, Sn), the Y and Gd analogues crystallize in a hybrid YCo6Ge6/CoSn structure, with Sn substitution. While the Y analogue displays temperature-independent paramagnetism, magnetic measurements of the Gd analogue reveal a magnetic moment of 8.48 μB, indicating a contribution from both Gd and Co. Through anisotropic magnetic measurements, the direction of Co-magnetism can be inferred to be in plane with the kagome net, as the Co contribution is only along H//a. Crystal growth and structure determination of YxCo3(Ge,Sn)3 and GdxCo3(Ge,Sn)3, two new hybrid kagome materials of the CoSn and YCo6Ge6 structure types. Magnetic properties, heat capacity, and resistivity on single crystals are reported.

Nonpareil Yb behavior in YbMn6Ge(6-x)Sn(x)

We investigate the temperature dependence of the Yb valence in YbMn6Ge1.8Sn4.2 and YbMn6Ge1.6Sn4.4 using resonant inelastic x-ray scattering experiments. Yb is found to be in an intermediate valent state in the whole investigated temperature range (10-450 K). We thus prove that the unusually high magnetic ordering temperature of Yb (∼60 and 90 K for x=4.2 and 4.4, respectively) involves an intermediate valent Yb, an unprecedentedly observed phenomenon. Further, an anomalous increase in the Yb valence is observed upon cooling. A scenario is proposed to explain this unusual behavior. It is based on the presence of magnetically ordered Mn moments and on an Anderson Hamiltonian with a Zeeman term modeling the magnetic interactions.