Temperature- and field-induced transformation of the magnetic state in Co2.5Ge0.5BO5

A tetravalent-substituted cobalt ludwigite Co2.5Ge0.5BO5 has been synthesized using the flux method. The compound undergoes two magnetic transitions: a long-range antiferromagnetic transition at TN1 = 84 K and a metamagnetic one at TN2 = 36 K. The sample-oriented magnetization measurements revealed a fully compensated magnetic moment along the a- and c-axes and an uncompensated one along the b-axis leading to high uniaxial anisotropy. A field-induced enhancement of the ferromagnetic correlations at TN2 is observed in specific heat measurements. The DFT+GGA calculation predicts the spin configuration of (↑↓↓↑) as a ground state with a magnetic moment of 1.37 μB/f.u. The strong hybridization of Ge(4s, 4p) with O (2p) orbitals resulting from the high electronegativity of Ge4+ is assumed to cause an increase in the interlayer interaction, contributing to the long-range magnetic order. The effect of two super–superexchange pathways Co2+-O-B-O-Co2+ and Co2+-O-M4-O-Co2+ on the magnetic state is discussed.This work has been financed by the Russian Foundation for Basic Research (project no. 20-02-00559). The authors acknowledge financial support from the Spanish Agencia Estatal de Investigación, through projects MAT2017-83468-R (AEI/FEDER, UE) and PID2020-115159GB-I00/AEI/10.13039/501100011033, the Aragonese project RASMIA E12_20R (co-funded by Fondo Social Europeo), and of the European Union FEDER (ES).Peer reviewe

Magnon mode in α‐MnS Raman spectrum

Представлены спектры комбинационного рассеяния моносульфида марганца (α‐MnS) со структурой NaCl в температурном интервале 5–300 К. При низких темпепературах обнаружен новый пик 22 cm–1. Температурная зависимость этого пика позволяет отнести его к магнонной моде при k = 0. Это хорошо согласуется с волновым числом магнона, рассчитанного с использованием программного пакета Munich SPRKKR

Electronic and magnetic states of Fe ions in Co2FeBO5

The ludwigite Co2FeBO5 has been studied experimentally using 57Fe Mössbauer spectroscopy and theoretically using DFT + GGA calculations. The room-temperature Mössbauer spectra are composed of four quadrupole doublets corresponding to the high-spin Fe3+ ions in octahedral oxygen coordination. All components undergo splitting below 117 K due to the magnetic hyperfine fields. The DFT + GGA calculations performed for three models of Fe ion distributions have revealed that the ground state corresponds to the “Fe4(HS)” model with the high-spin Fe3+ ions located at the M4 site and the high-spin Co2+ ions located at the M1, M2, and M3 sites. A ferrimagnetic ground state, with the Co and Fe magnetic moments being nearly parallel to the b-axis and a total magnetic moment of circa 1.1μB f.u.−1, was found. The other Fe distributions cause an increase in the local octahedral distortions and transformation of the spin state. The calculated quadrupole splitting values are in good agreement with the experimental values obtained by Mössbauer spectroscopy.This research is funded by the Russian Foundation for Basic Research (project no. 20-02-00559 and 21-52-12033), the Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science (project no. 19-42-240016) and the President Council on Grants (project no. MK-2339.2020.2). The authors acknowledge financial support from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO Grant No. MAT2017-83468-R and from the regional Government of Aragón (E12-20R RASMIA project).Peer reviewe