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

TL;DR

This study investigates the magnetic properties of M(VO)2(PO4)2 (M=Ca, Sr), revealing strong magnetic frustration due to competing ferro- and antiferromagnetic interactions, with complex magnetic behavior and long-range order at low temperatures.

Contribution

It provides a detailed experimental and theoretical analysis of magnetic frustration in three-dimensional vanadium phosphates with competing magnetic interactions.

Findings

Presence of ferro- and antiferromagnetic interactions with near-zero Curie-Weiss temperature

Weak exchange couplings with energy scale J_c = 10-15 K

Long-range antiferromagnetic order at low temperatures (1.5 K and 1.9 K)

Abstract

We present a detailed investigation of the magnetic properties of complex vanadium phosphates M(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 \theta_{CW} < 1 K that contrasts with the maximum of magnetic susceptibility at 3 K. Specific heat and NMR measurements also reveal weak exchange couplings with the thermodynamic energy scale J_c = 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 T_N = 1.5 K and 1.9 K, respectively. The spin model reveals an unusual example of controllable frustration in three-dimensional magnetic systems.