YbCrO₃纳米粉末的制备及其结构和磁性的研究

The Preparation of YbCrO₃ Nanometer Powder and the Study of Its Structure and Magnetism

摘要: 为探究粉末尺寸对稀土铬氧化物的结构、磁性的影响机制，我们用溶胶凝胶法成功制备出不同尺寸的YbCrO₃粉末样品。结构和磁性的研究表明晶胞体积随着粉末尺寸的增大而减小，同时Cr-O键长基本不变，而Cr-O-Cr键角逐渐减小，且制备的粉末尺寸随着烧结温度的升高而逐渐增大。Cr-O-Cr键角对YbCrO₃粉末的磁性影响反应在随着粉末尺寸的增大，热磁曲线上T_comp、T_max、M_max明显增大及奈尔温度T_N微弱增大。一方面，Cr-O-Cr键角的减小削弱Cr³⁺离子之间的反铁磁耦合强度；另一方面，其长程有序度逐渐提高增强Cr³⁺离子之间的反铁磁耦合强度。二者的竞争关系使得T_N随着粉末尺寸的增大而轻微增大。同时M-T曲线的拟合结果也表明，在T_N以下，Cr-O-Cr键角的减小和长程序的提高增强了Cr³⁺-O²⁻-Cr³⁺超交换作用，提高了Cr³⁺的净磁矩M_Cr及Cr³⁺对Yb³⁺作用的内场H_I。低温下的磁滞回线表明粉末样品的正向交换偏置场随着Cr-O-Cr键角减小而增大。

Abstract: In order to explore the influence of structure and magnetism of rare earth chromium oxide from powder size, YbCrO₃ powder samples with different sizes were successfully fabricated by sol-gel method. The studies of structure indicate that the size of powder increases with the increase of sintering temperature, and cell volume and Cr-O-Cr bond angle decrease with the increase of powder size, while the Cr-O bond length is nearly unchanged. The effection of Cr-O-Cr bond angle on the magnetic properties of YbCrO₃ powder was reflected on the obvious increase of T_comp, T_max and M_max and weak increase of Neil temperature T_N in thermomagnetic curves with the increase of powder size. On the one hand, the decrease of the Cr-O-Cr bond angle weakened the an-ti-ferromagnetic coupling strength between Cr³⁺ ion; on the other hand, the gradually increase of long range order enhanced the anti-ferromagnetic coupling strength between Cr³⁺ ion. The com-petition made the T_N slightly increase with the increase of the powder size. The M-T curve fitting results also showed that, under T_N, the decrease of the Cr-O-Cr bond angle and the increase of long range order enhanced the Cr³⁺-O²⁻-Cr³⁺ superexchange effect, improved the net magnetic moment of Cr³⁺ (M_Cr) and the infield of Yb³⁺ from Cr³⁺ (H_I). The low temperature hysteresis loop showed that positive exchange bias field increased with the decreases of Cr-O-Cr bond angle.