Singlet Ground State Magnet Research Articles

High temperature singlet-based magnetism from Hund\u2019s rule correlations

Uranium compounds can manifest a wide range of fascinating many-body phenomena, and are often thought to be poised at a crossover between localized and itinerant regimes for 5f electrons. The antiferromagnetic dipnictide USb2 has been of recent interest due to the discovery of rich proximate phase diagrams and unusual quantum coherence phenomena. Here, linear-dichroic X-ray absorption and elastic neutron scattering are used to characterize electronic symmetries on uranium in USb2 and isostructural UBi2. Of these two materials, only USb2 is found to enable strong Hund’s rule alignment of local magnetic degrees of freedom, and to undergo distinctive changes in local atomic multiplet symmetry across the magnetic phase transition. Theoretical analysis reveals that these and other anomalous properties of the material may be understood by attributing it as the first known high temperature realization of a singlet ground state magnet, in which magnetism occurs through a process that resembles exciton condensation.

Fragile singlet ground-state magnetism in the pyrochlore osmatesR2Os2O7(R=Yand Ho)

The singlet ground state magnetism in pyrochlore osmates Y$_2$Os$_2$O$_7$ and Ho$_2$Os$_2$O$_7$ is studied by DC and AC susceptibility, specific heat, and neutron powder diffraction measurements. Despite the expected non-magnetic singlet in the strong spin-orbit coupling (SOC) limit for Os$^{4+}$ ($5d^4$), Y$_2$Os$_2$O$_7$ exhibits a spin-glass (SG) ground state below 4 K with weak magnetism, suggesting possible proximity to a quantum phase transition between the non-magnetic state in the strong SOC limit and the magnetic state in the strong superexchange limit. Ho$_2$Os$_2$O$_7$ has the same structural distortion as occurs in Y$_2$Os$_2$O$_7$. However, the Os sublattice in Ho$_2$Os$_2$O$_7$ shows long-range magnetic ordering below 36\,K. The sharp difference of the magnetic ground state between Y$_2$Os$_2$O$_7$ and Ho$_2$Os$_2$O$_7$ signals the singlet ground state magnetism in $R_2$Os$_2$O$_7$ is fragile and can be disturbed by the weak $4f-5d$ interactions.

Neutron diffraction study of the field-induced order in singlet-ground state magnet CsFeCl 3

The neutron diffraction experiments have been successfully performed in the whole field region of the field-induced ordered phase in the singlet-ground state magnet CsFeCl 3 for the first time. The field dependence of neutron magnetic reflection have clearly demonstrated that the field induced order is described by the order parameter 〈 S x 〉. The magnetic ordering is discussed in the context of a Bose–Einstein condensation of magnetic excitations.

Nuclear magnetic relaxation of the singlet ground state magnet PrPtAl

27Al NMR measurements of an intermetallic compound PrPtAl were performed to study the unusual properties above T C (5.8 K). A distinct enhancement of relaxation rate below 50 K was observed. This suggests that ferromagnetic ordering in this singlet ground state magnet is mainly driven by the development of the so-called central peak rather than softening effect of the magnetic excitations.

μSR on an induced-moment spin glass system: Hg 1-x Fe x Se

Zero and longitudinal field μSR have been used to examine the singlet ground state magnetism of the diluted magnetic semiconductor Hg1-xFexSe. For x\geq 0.05\ μSR experiments indicate spin glass behaviour which is limited to sample regions with locally enhanced Fe2+ content. Longitudinal field spectra in the glassy state reveal a static local field \sim 50 mT due to induced moments of Fe2+. These are proposed to originate from a distribution of bound magnetic polaron energies.

Theory of excitations in the 1d singlet ground state magnet CsFeCl 3

CsFeCl 3 is a quasi one-dimensional planar magnet. Compared with the similar CsNiF 3 there is, however, a significant coupling between the chains which leads to an interesting soft mode behaviour. Using the correlation theory the temperature dependence and damping of the excitons are calculated and it is predicted that a central peak should appear at the soft mode wave vector. This mode absorbs all the spectral weight at the transition to long range order, whereas the soft mode tends to a finite frequency with decreasing weight.

Singlet ground state magnetism: II. magnetic excitons in paramagnetic TbP

The magneticΓ 1 –Γ 4 exciton of the singlet ground state system TbP has been studied by inelastic neutron scattering above the antiferromagnetic ordering temperature. Considerable dispersion and a pronounced splitting was found in the [100] and [110] directions. Both the band width and the splitting increased rapidly as the transition temperature was approached in accordance with the predictions of the RPA-theory. The dispersion is analysed in terms of a phenomenological model using interactions up to the fourth nearest neighbour.

Singlet-groundstate magnetism in TbP

Elastic neutron scattering and magnetic susceptibility data are reported for temperatures around the Neel-point,TN=7.3 K, and for zero magnetic field. AboveTN, the temperature dependence of the magnetic central peak intensity can adequately be described within the RPA assuming isotropic exchange between nearest and next-nearest neighbours as the only parameters. This two-parameter model is quantitatively confirmed by the susceptibility data. AtTN, magnetic Bragg-intensities arise almost discontinuously (reaching 70% of the saturation within 0.1 K) accompanied by thermal hysteresis. For all temperatures belowTN the sublattice magnetic moment is explained by solutions of meanfield equations, if an effective quadrupole-quadrupole interaction is included. The quadrupolar coupling parameter is fully consistent with a value determined recently from the softening of thec44-mode. These results show, that earlier suggestions of renormalization group results upon the origin of the first order phase transition in TbP are not needed.