Magnetic frustration in the site ordered Mg3Fe4(VO4)6 vanadate

Abstract

The magnetic properties of the site ordered multicomponent vanadate Mg 3 Fe 4 ͑VO 4 ͒ 6 are studied using dc magnetization and electron paramagnetic resonance ͑EPR͒ measurements. The static susceptibility shows antiferromagnetic interactions between Fe 3+ spins with a Curie-Weiss temperature ⌰ = −111͑1͒ K, while a transition to a spin-glass-like state is observed at T Ϸ 8.5 K, indicating appreciable spin frustration. EPR measurements corroborate the presence of antiferromagnetically coupled Fe 3+ spins from high temperatures, while a distinct change in the temperature variation of the EPR parameters is observed at T Ͻ 80 K, complying with the mean-field energy scale provided by the Curie-Weiss temperature of the system. The resulting magnetic inhomogeneity that persists despite the absence of cation disorder between magnetic and diamagnetic metal ions is attributed to the presence of small amounts of oxygen deficiency that modifies the connectivity and superexchange coupling between Fe 3+ spins and leads to a disordered magnetic ground state.

High temperature EPR study of the M3Fe4V6O24 (M = Cu, Zn, Mg and Mn)

“…In the whole studied range of temperatures a symmetric and intense resonance line was observed for all four investigated compounds. The experimental spectra were successfully fitted with Lorentzian lineshape function, similar as it was previously done in the case of lower temperatures [5]. Fig.…”

“…Furthermore, detailed structural studies have been presented in earlier papers [3,5,7,13]. EPR measurement in the range of 293 K to 493 K were carried out on Radiopan SE/X 2544-M spectrometer equipped with a homemade high-temperature unit.…”

“…The M 3 Fe 4 V 6 O 24 (M = Cu, Zn, Mg, Mn and Co) compounds have been investigated for some time due to their interesting physical properties and ability to be used in different applications [1][2][3][4][5][6][7][8]. Some of them belong to the howardevansitegroup of minerals and recently two new minerals of this type were discovered in volcanic exhalations from the last eruptions of volcanoes in Kamchatka [9].…”

“…The M ion site may be occupied by magnetic or diamagnetic ions and in case of the former one a more complex magnetic system is achieved. Measurements of DC magnetic susceptibility χ as a function of * E-mail: gzolnierkiewicz@zut.edu.pl temperature showed that the Curie-Weiss behavior, χ = C/(T -θ), dominates at high temperatures with a negative Curie-Weiss temperature θ (the largest value of θ was found for the compound M = Mn and the smallest for M = Cu) [5,7,12,13]. It should be emphasized that introduction of a strong magnetic ion at M site significantly increases the value of θ, while weak magnetic ions, like copper, reduces it.…”

“…Thus it is evident that the relaxation processes significantly depend on the presence of magnetic ions (M = Cu and Mn) and it is seen that the higher the magnetic moment the more intense change of the EPR parameters of that compound. Despite the fact that their crystallographic structures are well known, one of the main problems lies in determination of the magnetic centres that are responsible for the formation of the observed EPR spectra [3,5,7,8,13]. In [16] it was suggested that there is a strong possibility of the occurrence of magnetic clusters in these compounds.…”