Sarkar Tathagata, Biswas Soumya, Kakkar Sonali, Raghu Appu Vengattor, Kaushik Som Datta, Bera Chandan, Kamble Vinayak B
School of Physics, Indian Institute of Science Education Research Thiruvananthapuram, Maruthamala PO, Vithura, Trivandrum, Kerala, 695551, INDIA.
Institute of Nano Science and Technology, Institute of Nano Science and Technology, Sector-81, Knowledge City, Sahibzada Ajit Singh Nagar Mohali, Punjab, IN 140306, Mohali, Punjab, 140306, INDIA.
J Phys Condens Matter. 2024 Sep 3. doi: 10.1088/1361-648X/ad76f2.
This paper reports on the spin glass-like coexistence of competing magnetic orders in oxygen-deficient V2O5 nanoparticles with a broad size distribution. X-ray photoelectron spectroscopy yields the surface chemical stoichiometry of nearly V2O4.65 due to significant defect density. Temperature-dependent electrical conductivity and thermopower measurements demonstrate a polaronic conduction mechanism with a hopping energy of about 0.112 eV. The V2O5-δ sample exhibits strong field as well as temperature-dependent magnetic behaviour when measured with a SQUID magnetometer, showing positive magnetic susceptibility across the temperature range of 2-350 K. Field-cooled and zero-field-cooled data indicate hysteresis, suggesting glassy behaviour. The formation of small polarons due to oxygen vacancy defects, compensated by V4+ charge defects, results in Magneto-Electronic Phase Separation (MEPS) and various magnetic exchanges, as predicted by first-principle calculations. This is evidenced by the strong hybridisation of V orbitals in the vicinity of vacant oxygen site. An increase in V4+ defects shows an antiferromagnetic (AFM) component. The magnetic diversity in undoped V2O4.9 originates from defect density and their random distribution, leading to MEPS. This involves localised spins in polarons and ferromagnetic (FM) clusters on a paramagnetic (PM) background, while V4+ dimers induce AFM interactions. Electron paramagnetic resonance spectra measured at different temperatures indicate a dominant paramagnetic signal at a g-value of 1.97 due to oxygen defects, with a broad FM resonance-like hump. Both signals diminish with increasing temperature. Neutron diffraction data rules out long-range magnetic ordering, reflecting the composition as V2O4.886. Despite the FM hysteresis, no long-range order is observed in neutron diffraction data, consistent with the polaron cluster-like FM with MEPS nature. This detailed study shall advance the understanding of the diverse magnetic behaviour observed in undoped non-magnetic systems.
本文报道了具有广泛尺寸分布的缺氧V2O5纳米颗粒中竞争磁序的自旋玻璃状共存。由于显著的缺陷密度，X射线光电子能谱得出表面化学计量比接近V2O4.65。与温度相关的电导率和热功率测量表明存在极化子传导机制，跳跃能约为0.112 eV。当用超导量子干涉仪磁强计测量时，V2O5-δ样品表现出强场以及与温度相关的磁行为，在2 - 350 K的温度范围内显示出正磁化率。场冷和零场冷数据表明存在磁滞现象，暗示了玻璃态行为。如第一性原理计算所预测的，由氧空位缺陷形成的小极化子，由V4+电荷缺陷补偿，导致磁电相分离（MEPS）和各种磁交换。这通过空位氧位点附近V轨道的强杂化得到证明。V4+缺陷的增加显示出反铁磁（AFM）成分。未掺杂的V2O4.9中的磁多样性源于缺陷密度及其随机分布，导致MEPS。这涉及极化子中的局域自旋和顺磁（PM）背景上的铁磁（FM）簇，而V4+二聚体诱导AFM相互作用。在不同温度下测量的电子顺磁共振光谱表明，由于氧缺陷，在g值为1.97时存在占主导地位的顺磁信号，并伴有一个宽的类似FM共振的驼峰。随着温度升高，这两个信号都减弱。中子衍射数据排除了长程磁有序，反映出其组成为V2O4.886。尽管存在FM磁滞，但在中子衍射数据中未观察到长程有序，这与具有MEPS性质的极化子簇状FM一致。这项详细研究将推进对未掺杂非磁性系统中观察到的多样磁行为的理解。
