The $R{M}_6{X}_6$ family of materials ($R$ = rare-earth, $M$ = transition metal, $X=\mathrm{Ga}$, Si, Ge, Sn) produces an array of emergent phenomena, such as charge density waves, intrinsic Hall effects, and complex magnetic order, due to its kagome net of transition metal atoms, its local-moment magnetic anisotropies, and its extensive chemical tunability. Here, we report ${\mathrm{UNb}}_6{\mathrm{Sn}}_6$, a new “166” material containing both an actinide and a $4d$ transition metal, along with its nonmagnetic analog ${\mathrm{ThNb}}_6{\mathrm{Sn}}_6$, to investigate the properties of a $5f\text{−}4d$ electron 166 system. ${\mathrm{UNb}}_6{\mathrm{Sn}}_6$ crystallizes in the hexagonal $P6/mmm$ space group with a small degree of disorder due to shifts in the size of the CoSn-like cages along the $c$ axis. Upon cooling at zero magnetic field, the material undergoes two magnetic phase transitions at $T_2=46\mathrm{K}$ and $T_{\mathrm{N}}=43\mathrm{K}$. The low-temperature, zero-field phase is an antiferromagnet with ordered uranium moments and a k = (0,0,1/2) propagation vector determined by neutron diffraction. Remarkably, with a magnetic field applied along the $c$ axis, five additional magnetic transitions occur, evidenced by magnetization and resistivity data, before the moment saturates at 2.62 ${\mu }_{\mathrm{B}}/\mathrm{U}$ at 2 K and $\ge 13.6\mathrm{T}$. In two magnetic phase regions, the Hall resistivity of ${\mathrm{UNb}}_6{\mathrm{Sn}}_6$ significantly deviates from the magnetization, suggesting that the phases have a large Berry curvature or a change in the Fermi surface. The unknown magnetic ordering of the field-dependent phases of ${\mathrm{UNb}}_6{\mathrm{Sn}}_6$ demonstrates the complexity of the $5f\text{−}4d$ 166 system and encourages further study of its properties.

Close

PrevNext

View figure in article

• Electronic structure
• Flat bands
• Hall effect
• Magnetic phase transitions
• Kagome metal
• Strongly correlated systems