The remote control of the electrical conductance through nanosized junctions at room temperature will play an important role in future nano-electromechanical systems and electronic devices. This can be achieved by exploiting the magnetostriction effects of ferromagnetic materials. Here we report on the electrical conductance of magnetic nanocontacts obtained from wires of the giant magnetostrictive compound Tb0.3Dy0.7Fe1.95 as an active element in a mechanically controlled break-junction device. The nanocontacts are reproducibly switched at room temperature between “open” (zero conductance) and “closed” (nonzero conductance) states by variation of a magnetic field applied perpendicularly to the long wire axis. Conductance measurements in a magnetic field oriented parallel to the long wire axis exhibit a different behaviour where the conductance switches between both states only in a limited field range close to the coercive field. Investigating the conductance in the regime of electron tunneling by mechanical or magnetostrictive control of the electrode separation enables an estimation of the magnetostriction. The present results pave the way to utilize the material in devices based on nano-electromechanical systems operating at room temperature.

BackgroundThe prevalence of root caries is increasing with greater life expectancy and number of retained teeth. Therefore, new preventive strategies should be developed to reduce the prevalence of root caries. The aim of this study was to investigate the effects of fluoridated milk on the remineralization of root dentin and to compare these effects to those of sodium fluoride (NaF) application without milk.MethodsThirty extracted human molars were divided into 6 groups, and the root cementum was removed from each tooth. The dentin surface was demineralized and then incubated with one of the following six solutions: Sodium chloride NaCl, artificial saliva, milk, milk+2.5 ppm fluoride, milk+10 ppm fluoride and artificial saliva+10 ppm fluoride. Serial sections were cut through the lesions and investigated with polarized light microscopy and quantitative morphometry, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The data were statistically evaluated using a one-way ANOVA for multiple comparisons.ResultsThe depth of the lesion decreased with increasing fluoride concentration and was the smallest after incubation with artificial saliva+10 ppm fluoride. SEM analysis revealed a clearly demarcated superficial remineralized zone after incubation with milk+2.5 ppm fluoride, milk+10 ppm fluoride and artificial saliva+10 ppm fluoride. Ca content in this zone increased with increasing fluoride content and was highest after artificial saliva+10 ppm fluoride incubation. In the artificial saliva+10 ppm fluoride group, an additional crystalline layer was present on top of the lesion that contained elevated levels of F and Ca.ConclusionIncubation of root dentin with fluoridated milk showed a clear effect on root dentin remineralization, and incubation with NaF dissolved in artificial saliva demonstrated a stronger effect.

We report a chemical substitution-induced ferromagnetic quantum critical point in polycrystalline Ni1−xRhx alloys. Through magnetization and muon spin relaxation measurements, we show that the ferromagnetic ordering temperature is suppressed continuously to zero at xcrit = 0.375 while the magnetic volume fraction remains 100% up to xcrit, pointing to a second order transition. Non-Fermi liquid behavior is observed close to xcrit, where the electronic specific heat C el /T diverges logarithmically, while immediately above xcrit the volume thermal expansion coefficient αV /T and the Grüneisen ratio Γ = αV /C el both diverge logarithmically in the low temperature limit, further indication of a ferromagnetic quantum critical point in Ni1−xRhx.

The heavy-fermion compound CeCu_{6-x}Au_{x} has become a model system for unconventional magnetic quantum criticality. For small Au concentrations 0≤x<0.16, the compound undergoes a structural transition from orthorhombic to monoclinic crystal symmetry at a temperature T_{s} with T_{s}→0 for x≈0.15. Antiferromagnetic order sets in close to x≈0.1. To shed light on the interplay between quantum-critical magnetic and structural fluctuations we performed neutron-scattering and thermodynamic measurements on samples with 0≤x≤0.3. The resulting phase diagram shows that the antiferromagnetic and monoclinic phase coexist in a tiny Au concentration range between x≈0.1 and 0.15. The application of hydrostatic and chemical pressure allows us to clearly separate the transitions from each other and to explore a possible effect of the structural transition on the magnetic quantum-critical behavior. Our measurements demonstrate that at low temperatures the unconventional quantum criticality exclusively arises from magnetic fluctuations and is not affected by the monoclinic distortion.

Cerium is a fascinating element exhibiting, with its different phases, long-range magnetic order and superconductivity in bulk form. The coupling of the 4f electron to sd conduction electrons and to the lattice is responsible for unique structural and electronic properties like the isostructural first-order solid-solid transition from the cubic γ phase to the cubic α phase, which is accompanied by a huge volume collapse of 14 %. While the γ − α phase transition has been investigated for decades, experiments aiming at disentangling the 4f contribution to the electric conductance of the different phases have not been performed. Here we report on the strongly enhanced conductance of single-atom Ce contacts. By controlling the content of α-Ce employing different rates of cooling, we find a strong correlation between the fraction of α-Ce and the magnitude of the last conductance plateau before the contact breaks. We attribute the enhanced conductance of α-Ce to the additional contribution of the 4f level.1 Cerium is perhaps the elemental material that exhibits the most pronounced configurational changes. Under ambient pressure, Ce is in the fcc phase (γ-Ce) in the configuration [Xe](6s5d) 3 4f 1 , with the 4f electron strongly localized, and exhibits Curie-Weiss-type paramagnetism [1,2]. However, below ∼ 200 K the ground state of α-Ce is [Xe](6s5d) 4 4f 0 and the 4f electron is delocalized [3]. α-Ce has the same fcc structure as γ-Ce, but the lattice constant a changes from 5.15 to 4.85Å. Noteworthy, α ′ -Ce, a high pressure variant of the α phase, is even superconducting with T c = 1.7 K [4,5]. Cerium is thus a paradigm of the interplay of magnetism and superconductivity.The early proposal describing the γ → α phase transition by the promotion of the f electron to the sd conduction band [1,6] was found to be in disagreement with subsequent experiments [7,8,9,10] and, furthermore, not confirmed by band-structure calculations [11]. Instead, a delocalization of the 4f electron into a 4f band in α-Ce was suggested pointing towards an orbitally selective Mott transition (MT) [7,12].The nature of the γ − α transition, which can be tuned at ambient temperature by hydrostatic pressure, is still under debate [13,14,15]. The issue is complicated by the existence of an intervening (320 ≥ T ≥ 170 K) dhcp phase (β-Ce). The β phase has similar electronic properties as the γ phase, with localized 4f moments that order antiferromagnetically below 12.5 K [16,17]. This has been confirmed by density functional theory (DFT) in the local density approximation taking the onsite Hubbard interaction into account (LDA + U) [18]. The γ − α transition proceeds much faster than the γ − β transition. Since the transitions between these phases are of first order, it is very difficult to obtain single-phase Ce modifications [16,19].Although the structural and electronic properties of α-, β-, and γ-Ce have been studied experimentally and theoretically for decades, the different contributions of s, d, and f electrons to the total conductance have no...