Unusual magnetic transition near metal-insulator transition and paramagnetic anomaly in VO2

• Published in: Applied physics letters Vol. 110; no. 17
• Main Authors: Yin, Chongyang, Zhang, Run, Qian, Guoyu, Fu, Qingshan, Li, Canglong, Wang, Mingchao, Zhu, Changming, Wang, Liguang, Yuan, Songliu, Zhao, Xiujian, Tao, Haizheng
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 24-04-2017
• Subjects: Applied physics; Curie temperature; Dimers; Insulators; Magnetic permeability; Magnetic transitions; Metal-insulator transition; Paramagnetism; Temperature dependence; Vanadium dioxide
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4982589

Experiments for vanadium dioxide show a magnetic transition characterized by a sharp variation in susceptibility associated with the metal-insulator transition at the temperature T
c. The sample is shown to be of Pauli paramagnetism above T
c but of anomalous paramagnetism below T
c. Considering co-contributions of Pauli paramagnetism of residual V4+ ions and Curie-like paramagnetism of V-V dimers, we propose a phenomenological expression for the temperature-dependent susceptibility below T
c, which yields an excellent agreement with the experimental data. The unusual temperature dependence of Curie-like susceptibility below T
c is explained to be due to the fact that every dimer is formed by spin paring at an angle θ close to 180° and hence has an effective spin expressed as
S
e
f
f
=
cos
(
θ
/
2
)
which decreases with lowering temperature. The observed metal-insulator and magnetic transitions are argued to be due to a transition from the high-temperature Pauli paramagnetic state of V4+ ions to the low-temperature dimerized state.