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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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The in-plane ferromagnetic ordering in half-metallic CuCr2Se4?xBrx (x=0.25) single crystal

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

The transport property of chalcogenide spinel CuCr2Se4 with an itinerant ferromagnetic ground state can be modulated by doping of bromine, where the half-metallic state can be realized around x = 0.25 in CuCr2Se4?xBrx system. In this work, the single crystal CuCr2Se4?xBrx (x =0.25) with the cleave surface (111) plane has been investigated by the electron paramagnetic resonance (EPR) spectroscopy. The EPR results show that the in-plane magnetization is strong while the out-ofplane one is weak, which indicate that the spins are ferromagnetic ordered within the (111) plane. In addition, the isothermal EPR spectra in the ferromagnetic phase display that the spin coupling strength (λ) and crystal field (ΔCF ) depend on the rotation angle φ as relation λ/ΔCF / cos φ. Moreover, the peak-to-peak linewidth ΔHPP increases linearly with the decrease of temperature, which suggests that the spin-orbit coupling is enhanced linearly with temperature cooling. |

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. |

submitted time
2017-11-27
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