Strong frustration due to competing ferro-antiferromagnetic interactions: magnetic properties of M(VO)2(PO4)2 (M=Ca and Sr)

R. NATH; A. A. TSIRLIN; E. E. KAUL; M. BAENITZ; N. BUETTGEN; H. ROSNER; C. GEIBEL

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Lugar: New York; Año: 2008 vol. 78 p. 2441801 - 2441813

0163-1829

We present a detailed investigation of the magnetic properties of complex vanadium phosphatesM(VO)2(PO4)2 (M = Ca, Sr) by means of magnetization, specific heat, 31P NMR measurements, and band structure calculations. Experimental data evidence the presence of ferro- and antiferromagnetic interactions in M(VO)2(PO4)2 resulting in a nearly vanishing Curie-Weiss temperature thetaCW<= 1K that contrasts with the maximum of magnetic susceptibility at 3 K. Specific heat and NMR measurements also reveal exchange couplings with the thermodynamic energy scale Jc = 10−15 K. Additionally, the reduced maximum of the magnetic specific heat indicates strong frustration of the spin system. Band structure calculations show that the spin systems of the M(VO)2(PO4)2 compounds are essentially three-dimensional with the frustration caused by competing ferro- and antiferromagnetic interactions. Both calcium and strontium compounds undergo antiferromagnetic long-range ordering at TN = 1.5 K and 1.9 K, respectively. The spin model of M(VO)2(PO4)2 reveals an unusual example of controllable frustration in three-dimensional magnetic systems.