We report on the magnetic properties of isostructural oxides R6AO12 (R = a rare-earth element, A = Mo or W) with high concentrations of rare-earth elements. We measured the magnetization and specific ...heat. Tm6MoO12 is a van Vleck paramagnet with a nonmagnetic singlet ground state (GS). Ho6WO12 exhibits an antiferromagnetic long-range order (AFM LRO) lower than TN=2.1 K and its GS is a magnetic quasi-doublet. Dy6WO12 shows an AFM LRO lesser than TN=2.7 K and its GS is a magnetic Kramers doublet. Er6MoO12 and Er6WO12 are Curie-Weiss paramagnets at temperatures above 2 K and both have a magnetic Kramers doublet GS. We evaluated the magnetic entropy change. The temperature of the maximum magnetic entropy change for a magnetic-field change of 5 T is high (15 K) in Tm6MoO12 in spite of an oxide containing only rare-earth ions as the magnetic ions.
Stimulated by strong demand for thermal expansion control from advanced modern industries, various giant negative thermal expansion (NTE) materials have been developed during the last decade. ...Nevertheless, most such materials exhibit anisotropic thermal expansion in the crystal lattice. Therefore, strains and cracks induced during repeated thermal cycling degrade their performance as thermal-expansion compensators. Here we achieved giant isotropic NTE with volume change exceeding 3%, up to 4.1%, via control of the electronic configuration in Sm atoms of SmS, (4 f)
or (4 f)
(5d)
, by partial replacement of Sm with Y. Contrary to NTE originating from cooperative phenomena such as magnetism, the present NTE attributable to the intra-atomic phenomenon avoids the size effect of NTE and therefore provides us with fine-grained thermal-expansion compensators, which are strongly desired to control thermal expansion of microregions such as underfill of a three-dimensional integrated circuit. Volume control of lanthanide monosulfides via tuning of the 4 f electronic configuration presents avenues for novel mechanical functions of a material, such as a volume-change driven actuator by an electrical field, which has a different drive principle from those of conventional strain-driven actuators such as piezostrictive or magnetostrictive materials.
Broadband tunability is a central theme in contemporary nanophotonics and metamaterials research. Combining metamaterials with phase change media offers a promising approach to achieve such ...tunability, which requires a comprehensive investigation of the electromagnetic responses of novel materials at subwavelength scales. In this work, we demonstrate an innovative way to tailor band-selective electromagnetic responses at the surface of a heavy fermion compound, samarium sulfide (SmS). By utilizing the intrinsic, pressure sensitive, and multi-band electron responses of SmS, we create a proof-of-principle heavy fermion metamaterial, which is fabricated and characterized using scanning near-field microscopes with <50 nm spatial resolution. The optical responses at the infrared and visible frequency ranges can be selectively and separately tuned via modifying the occupation of the 4f and 5d band electrons. The unique pressure, doping, and temperature tunability demonstrated represents a paradigm shift for nanoscale metamaterial and metasurface design.
We have performed dielectric measurements and neutron diffraction experiments on the delafossite AgFeO2. A ferroelectric polarization P is approximately equal to 300 μC/m2 was observed in a powder ...sample, below 9 K. The neutron diffraction experiment demonstrated successive magnetostructural phase transitions at T(N1)=15 K and T(N2)=9 K. The magnetic structure for 9 K≤T≤15 K is a spin-density wave with a temperature dependent incommensurate modulation k=(-1, q, 1/2), q is approximately equal to 0.384. Below 9 K, the magnetic structure turns into elliptical cycloid with the incommensurate propagation vector k=(-1/2,q,1/2), q is approximately equal to 0.2026 Based on the deduced magnetic point-group symmetry m1' of the low-temperature polar phase, we conclude that the ferroelectric polarization in AgFeO2 is perpendicular to the monoclinic b axis and is driven by the inverse Dzyaloshinskii-Moriya effect with two orthogonal components p1 is proportional to r(ij)×(S(i)×S(j)) and p2 is proportional to S(i)×S(j).
Influence of random substitution of nonmagnetic ions on magnetocaloric effect is studied on manganese zinc ferrites from the viewpoints of Griffiths effects and frustration effects. The obtained ...results show that these side effects are insignificant at the ferrimagnetic transition in the range of zinc content below 70%. Consequently, the ferrite can keep a large magnetocaloric effect even when the transition temperature is lowered to a half of the original. This finding indicates that the nonmagnetic substitution is useful in adjusting the working temperature, if we utilize popular magnets such as ferrites with high Curie temperatures for the refrigerant consisting ubiquitous and nontoxic elements.
We report ultrafast electronic relaxation dynamics of yttrium-doped samarium monosulfide, Sm0.83Y0.17S, which is one of valence fluctuating compounds, by pump-probe measurements. We observed a large ...increase of the Drude weight in the reflectivity spectrum by the photo-excitation and a double exponential decay of the relaxation time to a metastable state. This suggests that the photo-induced effect can be explained as the change of carrier density. The metastable state has a long lifetime ( > 1 ns) and the carrier density is slightly higher than that before the photo-excitation.
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