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Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties

Critical phenomenon of the noncentrosymmetric Cr11Ge19, which exhibits an itinerant ferromagnetic ground state, is investigated by scaling of the magnetic entropy change [ΔSM(T;H)]. It is found that parameters #14;FWHM (the full width at half maximum), ?ΔSmax M (the maximum of the magnetic entropy change), and RCP (the relative cooling power) of ΔSM(T) are governed by the power law of critical exponents. With the critical exponents, ΔSM(T;H) curves are scaled into a universal curve independent of temperature and field, which suggests that the magnetic transition is of a second order type. The universal collapse of ΔSM(T;H) indicates that the critical behavior of Cr11Ge19 can be well described by the scaling laws for the critical phenomenon. Moreover, the ΔSM follows the power law of Hn with n(T;H) = dlnjΔSMj=dln(H). The temperature dependence of n values reach minimum at #24; 71.5 K. Based on the magnetic specific change ΔCp(T;H), the actual magnetic transition temperature is strictly determined as TC = 71:3 #6; 0:2 K for the single crystal Cr11Ge19. |

submitted time
2017-11-27
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Anisotropic magnetic coupling with a two-dimensional characteristic in noncentrosymmetric Cr11Ge19

张蕾Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties

In this work, we successfully synthesize the single crystal Cr11Ge19. The magnetism of the noncentrosymmetric Cr11Ge19 with itinerant ferromagnetic ground state is thoroughly investigated on the single crystal. Based on the variation measurements including the angular rotation, temperature, and magnetic field dependence of magnetization, we find that this material exhibits strong magnetic anisotropy along the c-axis. To clearly reveal the magnetic interactions, the critical behavior is studied using the modified Arrott plot, the Kouvel-Fisher method, and the critical isotherm technique. Combining these different methods, three main critical exponents (β, γ, and δ) are obtained. The critical exponent β is close to the theoretical prediction of a three-dimensional XY model with spin-dimensionality n = 2, indicating two-dimensional magnetic coupling. Meanwhile, the critical exponent γ suggests that the magnetic interaction is of long-range type with magnetic exchange distance decaying as J(r) #25; r?4:61. We propose that the ferromagnetic ground state of Cr11Ge19 is formed by the polarized magnetic moments along the c-axis, while the long-range magnetic coupling is established within the ab plane. |

Critical phenomenon of the single crystal helimagnet MnSi

张蕾Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties

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 ? 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) ? r?4:3 in MnSi. |

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