Heat capacities, third-law entropies and thermodynamic functions of the geometrically frustrated antiferromagnetic spinels GeCo2O4 and GeNi2O4 from T=(0 to 400) K

THz ESR Study of Peculiar Co Pyrochlore System GeCo2O4 Using Pulsed High Magnetic Field

“…The magnetic susceptibility at high temperature follows the Curie-Weiss behavior with a positive value of the Weiss temperature, θ = 81.0 K, which suggests the existence of stronger ferromagnetic (FM) interactions [14,15]. However, the system turns out to undergo the antiferromagnetic (AF) ordering at TN = 23.0 K from the DC susceptibility [15], the AC susceptibility [14], the specific heat [16,17], and the powder neutron diffraction [18] measurements. This antiferromagnetic ordering is accompanied by the cubic-to-tetragonal structural transition [17,19,20].…”

Epitaxial stabilization of thin films of the frustrated Ge-based spinels

“…More detailed recent studies show that this antiferromagnetic state is developed through two consecutive first-order phase transitions separated by ∼0.7 K (T N1 = 12.1 K and T N2 = 11.4 K) without any measurable structural distortion [7][8][9]20]. A subsequent muon-spin relaxation experiment suggested that these two transitions correspond to a distinct ordering of two magnetic subsystems [10].…”

“…These include the presence of substantial magnetic correlations in the paramagnetic state despite the low frustration factor ( f = CW /T N ∼ 0.7), the coexistence of gapped and gapless spin waves, and the missing of ∼40 % of the expected magnetic entropy [12]. Furthermore, unexpectedly the change in magnetic entropy is almost equal for both phase transitions [8,12], which clearly contradicts the picture of two separate orderings in the kagome and triangular planes (as a triangular lattice contains three times less Ni 2+ ions relative to the kagome lattice).…”

“…In this paper, we report on epitaxially stabilized thin films of two members of the "4-2" spinel family, GeNi 2 O 4 (GNO) * vasyukov@physics.msu.ru and GeCu 2 O 4 (GCO), which exhibit very different lowdimensional magnetic behavior. The bulk GNO undergoes a peculiar two-stage phase transition into a two-dimensional (2D) magnetic ground state [7][8][9][10][11][12], while the bulk GCO shows a multiferroic transition with interacting 1D S = 1/2 chains [13][14][15][16].…”