Ising-like antiferromagnetism on the octahedral sublattice of a cobalt-containing garnet and the potential for quantum criticality

Abstract

In this contribution, we report that ${\mathrm{CaY}}_{2}{\mathrm{Co}}_{2}{\mathrm{Ge}}_{3}{\mathrm{O}}_{12}$ exhibits an unusual anisotropic and chainlike antiferromagnetic arrangement of spins despite crystallizing in the highly symmetric garnet structure. Using low-temperature powder neutron diffraction and symmetry analysis, we identify a magnetic structure consisting of chainlike motifs oriented along the body diagonals of the cubic unit cell with moments pointing parallel to the chain direction due to the strong Ising character of the Co ions. Antiferromagnetic order sets in below 6 K and exhibits both temperature- and field-induced magnetic transitions at high fields. Combining the results, we present a magnetic phase diagram that suggests ${\mathrm{CaY}}_{2}{\mathrm{Co}}_{2}{\mathrm{Ge}}_{3}{\mathrm{O}}_{12}$ undergoes a quantum phase transition at low temperatures and moderate fields.