分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2017-11-27
摘要: The critical behavior of the single crystal helimagnet MnSi is investigated by means of bulk dc-magnetization at the boundary between the conical state and paramagnetic phase. We obtain the critical exponents (¯ = 0:242 § 0:006, ° = 0:915 § 0:003, and ± = 4:734 § 0:006), where the self-consistency and reliability are veri¯ed by the Widom scaling law and the scaling equation. The critical exponents of MnSi belong to the universality class of tricritical mean-¯eld theory, which unambiguously indicates a tricritical phenomenon at the boundary between the ¯rst-order phase transition and the second-order one induced by the external magnetic ¯eld. The tricritical point (TCP) is determined as HTCP ¼ 3200 Oe at the critical temperature, consistent with the previous report [Phys. Rev. Lett. 110, 177207 (2013)]. The critical behavior suggests a long-range magnetic coupling with the exchange distance decaying as J(r) ¼ r¡4:3 in MnSi.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2017-11-27
摘要: The pyrochlore iridate Gd2Ir2O7 has been investigated by means of the electron paramagnetic resonance (EPR) spectroscopy. A magnetic transition at T¤ » 20 K is found in addition to the transition at TC » 130 K, which has not been reported previously. The phase transition at TC, which corresponds to a resistivity transition, is resulted from the long-range spin ordering of Ir4+ ions in all-in/all out state. However, the magnetic transition at T¤, which is regardless of resistivity transition, is not caused by Ir4+ but Gd3+ ions. Both of the magnetic transitions are irrelevant to the lattice distortion. We suggest that the competition between the enhanced paramagnetism of Gd3+ ions and the f ¡ d interaction should be responsible for the magnetic transition at T¤.