YMnO3 exhibits a ferroelectric transition at high temperature (-900 K) and magnetic ordering at TN ti 70 K, where the dielectric constant shows an anomaly indicative of the magneto-dielectric effect. ...Here we report powder neutron diffraction experiments in this compound that show that the magnetic moment at saturation is reduced by application of hydrostatic pressure. Our results yield further insight about the nature of the spinlattice interaction in ferroic materials.
We have used specific heat and neutron diffraction measurements on single crystals of URu2–xFexSi₂ for Fe concentrations x ≤ 0.7 to establish that chemical substitution of Ru with Fe acts as ...“chemical pressure” Pch as previously proposed by Kanchanavatee et al. Phys. Rev. B 84, 245122 (2011) based on bulk measurements on polycrystalline samples. Neutron diffraction reveals a sharp increase of the uranium magnetic moment at x = 0.1, reminiscent of the behavior at the “hidden order” to large moment antiferromagnetic (LMAFM) phase transition observed at a pressure Px ≈ 0.5-0.7 GPa in URu₂Si₂. Using the unit cell volume determined from our measurements and an isothermal compressibility κT = 5.2×10⁻³ GPa⁻¹ for URu₂Si₂, we determine the chemical pressure Pch in URu2-xFexSi₂ as a function of x. The resulting temperature T-chemical pressure Pch phase diagram for URu2-xFexSi₂ is in agreement with the established temperature T-external pressure P phase diagram of URu₂Si₂.
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The Belitz-Kirkpatrick-Vojta (BKV) theory shows in excellent agreement with experiment that ferromagnetic quantum phase transitions (QPTs) in clean metals are generally first order due to the ...coupling of the magnetization to electronic soft modes, in contrast to the classical analogue that is an archetypical second-order phase transition. For disordered metals the BKV theory predicts that the secondorder nature of the QPT is restored because the electronic soft modes change their nature from ballistic to diffusive. Lastly, our low-temperature magnetization study identifies the ferromagnetic QPT in the disordered metal UCo1$-$xFexGe as the first clear example that exhibits the associated critical exponents predicted by the BKV theory.
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Two aspects of the ambient pressure magnetic structure of heavy fermion material CeRhIn
have remained under some debate since its discovery: whether the structure is indeed an incommensurate helix or ...a spin density wave, and what is the precise magnitude of the ordered magnetic moment. By using a single crystal sample optimized for hot neutrons to minimize neutron absorption by Rh and In, here we report an ordered moment of Formula: see text. In addition, by using spherical neutron polarimetry measurements on a similar single crystal sample, we have confirmed the helical nature of the magnetic structure, and identified a single chiral domain.
Magnetization measurements for magnetic fields mu sub(0)H up to 60 T are reported for the noncentrosymmetric spin-chain metal Yb sub(2) Fe sub(12)P sub(7). These measurements reveal behavior that is ...consistent with Ising-like spin chain magnetism that produces pronounced spin degeneracy. In particular, we find that although a Brillouin field dependence is observed in M(H) for Hperpendicularc with a saturation moment that is close to the expected value for free ions of Yb super(3+), non-Brillouin-like behavior is seen for H|| c with an initial saturation moment that is nearly half the free ion value. In addition, hysteretic behavior that extends above the ordering temperature T sub(M) is seen for H|| c but not for Hperpendicularc, suggesting out-of-equilibrium physics. This point of view is strengthened by the observation of a spin reconfiguration in the ordered state for H|| c which is only seen for T< or =, slant T sub(M) and after polarizing the spins. Together with the heat capacity data, these results suggest that the anomalous low temperature phenomena that were previously reported (Baumbach 2010 et al Phys. Rev. Lett. 105 106403) are driven by spin degeneracy that is related to the Ising-like one dimensional chain-like configuration of the Yb ions.
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