Theory-guided investigation on magnetic evolution of MnPt5−x_{5-x}Pdx_xP and discovery of anti-CeCoIn5_5-type ferromagnetic MnPd5_5P

We report the magnetic changes from canted antiferromagnetic to ferromagnetic orderings in anti-115-type MnPt$_{5-x}$Pd$_x$P ($x$ = 1, 2, 2.5, 3, 4, and 5) and the discovery of a new rare-earth-free ferromagnet, MnPd$_5$P by both theoretical prediction and experimental investigation. The family compounds were synthesized using high temperature solid state method and characterized to crystalize in the anti-CeCoIn$_5$ type with the space group P4/mmm exhibiting a two-dimensional layered structural feature. The magnetic property measurements indicate that the compounds ordered from canted A-type antiferromagnet in MnPt$_5$P to ferromagnet above the room temperature with varying degrees of coercivity and magnetic moments in MnPd$_5$P by reducing the spin orbital coupling. The results of the MnPt$_{5-x}$Pd$_x$P have been analyzed in comparison to the other candidates of the 151 family of Mn(Pt/Pd)$_5$(P/As) to understand the complex structure-magnetism relationships

High Temperature Ferromagnetism in Cr1+x_{1+x}Pt5−x_{5-x}P

We present the growth and basic magnetic and transport properties of Cr$_{1+x}$Pt$_{5-x}$P. We show that single crystals can readily be grown from a high-temperature solution created by adding dilute quantities of Cr to Pt-P based melts. Like other 1-5-1 compounds, Cr$_{1+x}$Pt$_{5-x}$P adopts a tetragonal P4/mmm structure composed face-sharing CrPt$_3$ like slabs that are broken up along the c-axis by sheets of P atoms. EDS and X-ray diffraction measurements both suggest Cr$_{1+x}$Pt$_{5-x}$P has mixed occupancy between Cr and Pt atoms, similar to what is found in the closely related compound CrPt$_3$, giving real compositions of Cr$_{1.5}$Pt$_{4.5}$P (x = 0.5). We report that Cr$_{1.5}$Pt$_{4.5}$P orders ferromagnetically at T$_C$ = 464.5 K with a saturated moment of $\approx$ 2.1 $\mu_{\textit{B}}$/Cr at 1.8 K. Likely owing to the strong spin-orbit coupling associated with the large quantity of high Z Pt atoms, Cr$_{1.5}$Pt$_{4.5}$P has exceptionally strong planar anisotropy with estimated anisotropy fields of 345 kOe and 220 kOe at 1.8 K and 300 K respectively. The resistance of Cr$_{1.5}$Pt$_{4.5}$P has a metallic temperature dependence with relatively weak magnetoresistance. Electronic band structure calculations show that CrPt$_5$P has a large peak in the density of states near the Fermi level which is split into spin majority and minority bands in the ferromagnetic state. Furthermore, the calculations suggest substantial hybridization between Cr-3d and Pt-5d states near the Fermi level, in agreement with the experimentally measured anisotropy

Continuous spin excitations in the three-dimensional frustrated magnet K2Ni2(SO4)3

Continuous spin excitations are widely recognized as one of the hallmarks of novel spin states in quantum magnets, such as quantum spin liquids (QSLs). Here, we report the observation of such kind of excitations in K2Ni2(SO4)3, which consists of two sets of intersected spin-1 Ni2+ trillium lattices. Our inelastic neutron scattering measurement on single crystals clearly shows a dominant excitation continuum, which exhibits a distinct temperature-dependent behavior from that of spin waves, and is rooted in strong quantum spin fluctuations. Further using the self-consistent-gaussian-approximation method, we determined the fourth- and fifth-nearest neighbor exchange interactions are dominant. These two bonds together form a unique three-dimensional network of corner-sharing tetrahedra, which we name as ''hyper-trillium'' lattice. Our results provide direct evidence for the existence of QSL features in K2Ni2(SO4)3 and highlight the potential for the hyper-trillium lattice to host frustrated quantum magnetism.Comment: 6 pages and 5 figures, plus several pages of supplemental material, comments are welcom

Mn(Pt1−x_{1-x}Pdx_{x})5_5P: Isovalent Tuning of Mn Sublattice Magnetic Order

We report the growth and characterization of MnPd$_5$P, a ferromagnet with T$_C$ $\approx$ 295 K, and conduct a substitutional study with its antiferromagnetic analogue MnPt$_5$P. We grow single crystals of MnPd$_5$P and Mn(Pt$_{1-x}$Pd$_x$)$_5$P by adding Mn into (Pt$_{1-x}$Pd$_{x}$)-P based melts. All compounds in the family adopt the layered anti-CeCoIn$_5$ structure with space group P4/mmm, and EDS and XRD results indicate that MnPt$_5$P and MnPd$_5$P form a solid solution. Based on magnetization and resistance data, we construct a T-x phase diagram for Mn(Pt$_{1-x}$Pd$_x$)$_5$P and demonstrate the antiferromagnetic order found in MnPt$_5$P is extraordinarily sensitive to Pd substitution. At low Pd fractions (x $<$ 0.010), the single antiferromagnetic transition in pure MnPt$_5$P splits into a higher temperature ferromagnetic transition followed on cooling by a lower temperature ferromagnetic to antiferromagnetic transition and then by a re-entrant antiferromagnetic to ferromagnetic transition at lower temperatures. The antiferromagnetic region makes up a bubble that persists to x $\approx$ 0.009 for T $\approx$ 150 K, with all samples x $<$ 0.009 recovering their initial ferromagnetic state with further cooling to base temperature. Over the same low x range we find a non-monotonic change in the room temperature unit cell volume, further suggesting that pure MnPt$_5$P is close to an instability. Once x $>$ 0.010, Mn(Pt$_{1-x}$Pd$_x$)$_5$P undergoes a single ferromagnetic transition. The Curie temperature increases rapidly with x, rising from T$_C$ $\approx$ 197 K at x = 0.013 to a maximum of T$_C$ $\approx$ 312 K for x $\approx$ 0.62, and then falls back to T$_C$ $\approx$ 295 K for pure MnPd$_5$P (x = 1). Given that Pt and Pd are isoelectronic, this work raises questions as to the origin of the extreme sensitivity of the magnetic ground state in MnPt$_5$P upon introducing Pd

Theoretical investigations of hydrogen absorption in the A15 intermetallics Ti3Sb and Ti3Ir

Ti3Sb and Ti3Ir adopt the A15 (Cr3Si type) structure and are reported to incorporate hydrogen atoms to an extent, respectively, of Ti3SbH∼3 and Ti3IrH3.8. First-principles electronic structure calculations were performed to identify factors contributing to the difference in maximum hydrogen composition for these two intermetallic compounds. Relative energies and changes in energy densities of states and crystal orbital Hamilton populations upon H insertion in the intermetallic compounds were examined. In both compounds, hydrogen atoms are attracted to [Ti4] tetrahedral interstitial sites over any others. The natures of metal-hydrogen and metalloid-hydrogen bonding and the effects of hydrogen insertion on metal-metal and metal-metalloid bonding have an influence on the maximum hydrogen contents for Ti3Sb and Ti3Ir.This article is published as Miller, Gordon J., Ranuri S. Dissanayaka Mudiyanselage, and Weiwei Xie. "Theoretical investigations of hydrogen absorption in the A15 intermetallics Ti3Sb and Ti3Ir." Zeitschrift für Naturforschung B 76, no. 10-12 (2021): 819-826. DOI: 10.1515/znb-2021-0137 Copyright 2021 Gordon J. Miller et al. Attribution 4.0 International (CC BY 4.0) Posted with permission

New Tetragonal ReGa5(M) (M = Sn, Pb, Bi) Single Crystals Grown from Delicate Electrons Changing

Single crystals of the new Ga-rich phases ReGa~5(Sn), ReGa~5(Pb) and ReGa~5(Bi) were successfully obtained from the flux method. The new tetragonal phases crystallize in the space group P4/mnc (No. 128) with vertex-sharing capped Re2@Ga14 oblong chains. Vacancies were discovered on the Ga4 and Ga5 sites, which can be understood as the direct inclusion of elemental Sn, Pb and Bi into the structure. Heat capacity measurements were performed on all three compounds resulting in a small anomaly which resembles the superconductivity transition temperature from the impurity ReGa5 phase. The three compounds were not superconducting above 1.85 K. Subsequently, electronic structure calculations revealed a high density of states around the Fermi level, as well as non-bonding interactions that likely indicate the stability of these new phases

LiYbSe2: Frustrated Magnetism in a New Pyrochlore Lattice

Three-dimensionally (3D) frustrated magnets generally exist in the magnetic diamond and pyrochlore lattices, in which quantum fluctuations suppress magnetic orders and generate highly entangled ground states (GS). LiYbSe2 in a previously unreported pyrochlore lattice was discovered from LiCl flux growth. Distinct from the quantum spin liquid (QSL) candidate NaYbSe2 hosting a perfect triangular lattice of Yb3+, LiYbSe2 crystallizes in the cubic pyrochlore structure with space group Fd-3m (No. 227). The Yb3+ ions in LiYbSe2 are arranged on a network of corner-sharing tetrahedra, which is particularly susceptible to geometrical frustration. According to our temperature-dependent magnetic susceptibility measurements, the dominant antiferromagnetic interaction in LiYbSe2 is expected to appear around 8 K. However, no long-range magnetic order is detected in thermomagnetic measurements above 70 mK. Specific heat measurements also show magnetic correlations shifting with applied magnetic field with a degree of missing entropy that may be related to the slight mixture of Yb3+ on the Li site. Such magnetic frustration of Yb3+ is rare in pyrochlore structures. Thus, LiYbSe2 shows promises in intrinsically realizing disordered quantum states like QSL in pyrochlore structures

High Temperature Ferromagnetism in Cr1+xPt5−xP

We present the growth and basic magnetic and transport properties of Cr1+xPt5−xP. We show that single crystals can readily be grown from a high-temperature solution created by adding dilute quantities of Cr to Pt-P based melts. Like other 1-5-1 compounds, Cr1+xPt5−xP adopts a tetragonal P4/mmm structure composed face-sharing CrPt3 like slabs that are broken up along the c-axis by sheets of P atoms. EDS and X-ray diffraction measurements both suggest Cr1+xPt5−xP has mixed occupancy between Cr and Pt atoms, similar to what is found in the closely related compound CrPt3, giving real compositions of Cr1.5Pt4.5P (x = 0.5). We report that Cr1.5Pt4.5P orders ferromagnetically at TC = 464.5 K with a saturated moment of ≈ 2.1 μB/Cr at 1.8 K. Likely owing to the strong spin-orbit coupling associated with the large quantity of high Z Pt atoms, Cr1.5Pt4.5P has exceptionally strong planar anisotropy with estimated anisotropy fields of 345 kOe and 220 kOe at 1.8 K and 300 K respectively. The resistance of Cr1.5Pt4.5P has a metallic temperature dependence with relatively weak magnetoresistance. Electronic band structure calculations show that CrPt5P has a large peak in the density of states near the Fermi level which is split into spin majority and minority bands in the ferromagnetic state. Furthermore, the calculations suggest substantial hybridization between Cr-3d and Pt-5d states near the Fermi level, in agreement with the experimentally measured anisotropy.This article is published as Slade, Tyler J., Nao Furukawa, Tanner R. Smith, Juan Schmidt, Ranuri S. Dissanayaka Mudiyanselage, Lin-Lin Wang, Weiwei Xie, Sergey L. Bud'ko, and Paul C. Canfield. "High-temperature ferromagnetism in Cr 1+ x Pt 5− x P." Physical Review Materials 7, no. 2 (2023): 024410. DOI: 10.1103/PhysRevMaterials.7.024410. Copyright 2023 American Physical Society. Posted with permission. DOE Contract Number(s): AC02-07CH11358; NSF-DMR-205328

Mn(Pt1−xPdx)5P: Isovalent Tuning of Mn Sublattice Magnetic Order

We report the growth and characterization of MnPd5P, a rare-earth-free ferromagnet, with TC approximate to 295 K and planar anisotropy, and conduct a substitutional study with its antiferromagnetic analog MnPt5P. All compounds in the family adopt the layered anti-CeCoIn5-type structure with the space group P4/mmm, and EDS and x-ray diffraction results indicate that MnPt5P and MnPd5P form a complete solid solution. Based on measurements of the temperature-and field-dependent magnetization and resistance, we construct a temperature -composition (T -x) phase diagram for Mn(Pt1-xPdx )5P and demonstrate that the essentially antiferromagnetic order found in MnPt5P is extraordinarily sensitive to Pd substitution. At low Pd fractions (x 0.010, Mn(Pt1-xPdx )5P undergoes a only single transition into the ferromagnetic phase. The Curie temperature initially increases rapidly with x, rising from TC approximate to 197 K at x = 0.013 to a maximum of TC approximate to 312 K for x approximate to 0.62, and then falling back to TC approximate to 295 K for pure MnPd5P (x = 1.00). Given that Pt and Pd are isoelectronic, this work raises questions as to the origin of the extreme sensitivity of the magnetic ground state and the nature of the re-entrant ferromagnetism at dilute Pd levels.This article is published as Slade, Tyler J., Ranuri S. Dissanayaka Mudiyanselage, Nao Furukawa, Tanner R. Smith, Juan Schmidt, Lin-Lin Wang, Chang-Jong Kang et al. "Mn (Pt 1− x Pd x) 5 P: Isovalent tuning of Mn-sublattice magnetic order." Physical Review B 107, no. 13 (2023): 134429. DOI: 10.1103/PhysRevB.107.134429. Copyright 2023 American Physical Society. Posted with permission. DOE Contract Number(s): AC02-07CH11358; FOA-0001276; NSF-DMR-2053287; DMR-1644779; 2022R1C1C1008200