Using first-principles calculations to screen for fragile magnetism: Case study of ${\mathrm{LaCrGe}}_3$ and ${\mathrm{LaCrSb}}_3$

In this paper, we present a coupled experimental/theoretical investigation of pressure effect on the ferromagnetism of ${\mathrm{LaCrGe}}_3$ and ${\mathrm{LaCrSb}}_3$ compounds. The magnetic, electronic, elastic, and mechanical properties of ${\mathrm{LaCrGe}}_3$ and ${\mathrm{LaCrSb}}_3$ at ambient condition are studied by first-principles density-functional theory calculations. The pressure dependences of the magnetic properties of ${\mathrm{LaCrGe}}_3$ and ${\mathrm{LaCrSb}}_3$ are also investigated. The ferromagnetism in ${\mathrm{LaCrGe}}_3$ is rather fragile, with a ferro- to paramagnetic transition at a relatively small pressure (around 7 GPa from our calculations, and 2 GPa in experiments). The key parameter controlling the magnetic properties of ${\mathrm{LaCrGe}}_3$ is found to be the proximity of the peak of Cr density of states to the Fermi level, a proximity that is strongly correlated with the distance between Cr atoms along the $c$ axis, suggesting that there would be a simple way to suppress magnetism in systems with one-dimensional arrangement of magnetic atoms. By contrast, the ferromagnetism in ${\mathrm{LaCrSb}}_3$ is not fragile. Our theoretical results are consistent with our experimental results and demonstrate the feasibility of using first-principles calculations to aid experimental explorations in screening for materials with fragile magnetism.

Figure 1

Atomic structure of (a) ${\mathrm{LaCrGe}}_3$ and (b) ${\mathrm{LaCrSb}}_3$. Some atoms in both structures and unit cells of ${\mathrm{LaCrSb}}_3$ are repeated to show the one- and two-dimensional features of Cr in ${\mathrm{LaCrGe}}_3$ and ${\mathrm{LaCrSb}}_3$, respectively.

Figure 2

Band structures of (left) minority- and (right) majority spin and (middle) DOS of Cr $d$ orbitals of ${\mathrm{LaCrGe}}_3$.

Figure 3

Band structures of (left) minority- and (right) majority spin and (middle) DOS of Cr $d$ orbitals of ${\mathrm{LaCrSb}}_3$.

Figure 4

Formation enthalpy differences between FM and NM phases and magnetic moment of Cr atom as functions of pressure for ${\mathrm{LaCrGe}}_3$ and ${\mathrm{LaCrSb}}_3$. The inset shows the experimental results for the dependence of ${\mathrm{LaCrGe}}_3$ and ${\mathrm{LaCrSb}}_3{T}_{\mathrm{c}}$ on pressure [3, 5].

Figure 5

Magnetic moment of Cr as function of distance between Cr atom along the $c$ axis of ${\mathrm{LaCrGe}}_3$ under hydrostatic pressure and pressing along the $c$ axis. Diamond-marked point is for systems at ambient condition.

Figure 6

PDOS of Cr in ${\mathrm{LaCrGe}}_3$ under hydrostatic pressure and (in the inset) uniaxial pressure. PDOS of NM ${\mathrm{LaCrGe}}_3$ at 7 GPa and $c/c_0=0.97$ are plotted as half positive and half negative for better comparison.

Figure 7

Magnetic moment of Cr as functions (a) NN and (b) NNN distance of Cr-Cr NN in ${\mathrm{LaCrSb}}_3$ under hydrostatic pressure and pressing along the $c$ axis. Diamond-marked points are for system at ambient condition.