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Register a new userX-ray diffraction by magnetic charges (monopoles)
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Magnetic charges, or magnetic monopoles, may form in the electronic structure of magnetic materials where ions are deprived of symmetry with respect to spatial inversion. Predicted in 2009, the strange magnetic, pseudoscalars have recently been found different from zero in simulations of electronic structures of some magnetically ordered, orthorhombic, lithium orthophosphates (LiMPO4). We prove that magnetic charges in lithium orthophosphates diffract x-rays tuned in energy to an atomic resonance, and to guide future experiments we calculate appropriate unit-cell structure factors for monoclinic LiCoPO4 and orthorhombic LiNiPO4.
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CeB6, a typical Gamma_8-quartet system, exhibits a mysterious antiferroquadrupolar ordered phase in magnetic fields, which is considered as originating from the T_{xyz}-type magnetic octupole moment induced by the field. By resonant x-ray diffraction in magnetic fields, we have verified that the T_{xyz}-type octupole is indeed induced in the 4f-orbital of Ce with a propagation vector (1/2, 1/2, 1/2), thereby supporting the theory. We observed an asymmetric field dependence of the intensity for an electric quadrupole (E2) resonance when the field was reversed, and extracted a field dependence of the octupole by utilizing the interference with an electric dipole (E1) resonance. The result is in good agreement with that of the NMR-line splitting, which reflects the transferred hyperfine field at the Boron nucleus from the anisotropic spin distribution of Ce with an O_{xy}-type quadrupole. The field-reversal method used in the present study opens up the possibility of being widely applied to other multipole ordering systems such as NpO2, Ce_{x}La_{1-x}B_{6}, SmRu_{4}P_{12}, and so on.
Multiferroic TbMnO3 is investigated using x-ray diffraction in high magnetic fields. Measurements on first and second harmonic structural reflections due to modulations induced by the Mn and Tb magnetic order are presented as function of temperature and field oriented along the a and b-directions of the crystal. The relation to changes in ordering of the rare earth moments in applied field is discussed. Observations below T_N(Tb) without and with applied magnetic field point to a strong interaction of the rare earth order, the Mn moments and the lattice. Also, the incommensurate to commensurate transition of the wave vector at the critical fields is discussed with respect to the Tb and Mn magnetic order and a phase diagram on basis of these observations for magnetic fields H||a and H||b is presented. The observations point to a complicated and delicate magneto-elastic interaction as function of temperature and field.
We investigate the thermal-driven charge density wave (CDW) transition of two cubic superconducting intermetallic systems Lu(Pt1-xPdx)2In and (Sr1-xCax)3Ir4Sn13 by means of x-ray diffraction technique. A detailed analysis of the CDW modulation superlattice peaks as function of temperature is performed for both systems as the CDW transition temperature T_CDW is suppressed to zero by an non-thermal control parameter. Our results indicate an interesting crossover of the classical thermal-driven CDW order parameter critical exponent from a three-dimensional universality class to a mean-field tendency, as T_CDW vanishes. Such behavior might be associated with presence of quantum fluctuations which influences the classical second-order phase transition, strongly suggesting the presence of a quantum critical point (QCP) at T_CDW = 0. This also provides experimental evidence that the effective dimensionality exceeds its upper critical dimension due to a quantum phase transition.
We report on the study of a magnetic dislocation in pure chromium. Coherent x-ray diffraction profiles obtained on the incommensurate Spin Density Wave (SDW) reflection are consistent with the presence of a dislocation of the magnetic order, embedded at a few micrometers from the surface of the sample. Beyond the specific case of magnetic dislocations in chromium, this work may open up a new method for the study of magnetic defects embedded in the bulk.
Rare earth (R) half-Heusler compounds, RBiPt, exhibit a wide spectrum of novel ground states. Recently, GdBiPt has been proposed as a potential antiferromagnetic topological insulator (AFTI). We have employed x-ray resonant magnetic scattering to elucidate the microscopic details of the magnetic structure in GdBiPt below T_N = 8.5 K. Experiments at the Gd L_2 absorption edge show that the Gd moments order in an antiferromagnetic stacking along the cubic diagonal [1 1 1] direction satisfying the requirement for an AFTI, where both time-reversal symmetry and lattice translational symmetry are broken, but their product is conserved.
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