arXiv subjects

Michael O Ogunbunmi

Publications and source records attributed to Michael O Ogunbunmi.

3 recordsLinked to original sources

arXiv2019

Crystal structure and thermodynamic properties of the non-centrosymmetric PrRu$_4$Sn$_6$ caged compound

PrRu$_4$Sn$_6$ is a tetragonal, non-centrosymmetric structure compound. It is isostructural to the extensively studied Kondo insulator CeRu$_4$Sn$_6$ which crystallizes in the YRu$_4$Sn$_6$-type structure with space group $I$\={4}2$m$. In this structure, the Pr atom fills the void formed by the octahedral Ru$_4$Sn$_6$ units which results in a tetragonal body-centred arrangement. Here we present reports on the physical and magnetic properties of PrRu$_4$Sn$_6$. The temperature dependences of specific heat, $C_p(T)$, electrical resistivity, $ρ(T)$, and magnetic susceptibility, $χ(T)$, reveal the absence of a long-range magnetic ordering down to 2 K. $χ(T)$ follows a Curie-Weiss behaviour above 100 K with an effective magnetic moment, $μ_\mathrm{eff}$ = 3.34 $μ_B$/Pr and paramagnetic Weiss temperature, $θ_p$ = $-$19.47 K indicating a dominant antiferromagnetic interaction. The magnetization at 2 K is quasi-linear in nature and attains a value of 0.86 $μ_B$/Pr at 7 T which is well reduced compared to the calculated value of 3.32 $μ_B$/Pr expected for a free Pr$^{3+}$ ion. This is attributed to possible magneto-crystalline anisotropy in the system. $C_p(T)$ indicates the presence of a optical-phonon mode which is supported by a glass-like thermal conductivity above $\sim$45 K. This observation is associated with caged structured compounds where the low-frequency optical-phonon mode of the guest atom interacts with the host lattice, resulting in the scattering of heat-carrying quasiparticles.

cond-mat.str-el↗

arXiv2019

Magnetic and physical properties of new hexagonal compounds PrPt$_4X$ ($X$ = Ag, Au)

We have synthesized PrPt$_4$Ag and PrPt$_4$Au compounds for the first time and report their crystal structure, as well as magnetic and physical properties in the temperature range of 1.9~K to 300~K. Both compounds are derived from the substitution of Pt with Ag and Au, respectively in the parent compound PrPt$_5$ which crystallizes in the hexagonal CaCu$_5$-type structure. Here we observed the preservation of the hexagonal CaCu$_5$-type structure under such substitutions, which is in contrast to the observations in PrCu$_4$Ag and PrCu$_4$Au adopting the cubic MgCu$_4$Sn-type structure upon substitution on parent hexagonal PrCu$_5$. The temperature dependences of specific heat $C_p(T)$, and electrical resistivity $ρ(T)$ of PrPt$_4$Ag show an anomaly at 7.6~K. This is absent in the magnetic susceptibility $χ(T)$, thus suggesting a possible multipolar ordering of the Pr$^{3+}$ moment. PrPt$_4$Au on the other hand does not show any anomaly but an upturn in $C_p(T)/T$ below about 10~K and attains 1.23~J/(mol K$^2$) at 1.9~K. In addition, $ρ(T)$ $\sim T$ for nearly a decade in temperature. These observations for PrPt$_4$Au are the hallmark of a non-Fermi liquid (nFL) behavior and is characteristic of a system near a quantum critical point. The analyses of the low-temperature $C_p(T)$ for PrPt$_4$Ag and PrPt$_4$Au give values of the Sommerfeld coefficient, $γ= 728.5~$mJ/(mol K$^2$) and 509.1~mJ/(mol K$^2$), respectively, indicating a significant enhancement of the quasiparticle mass in the two compounds.

cond-mat.str-el↗

arXiv2019

Investigation of the magnetic ground state of PrRu$_2$Ga$_8$ compound

We have investigated the ground state properties of the orthorhombic structure compound PrRu$_2$Ga$_8$ through electronic and magnetic properties studies. The compound crystallizes in the CaCo$_2$Al$_8$-type structure, belonging to space group $Pbam$ (No. 55). The temperature dependence specific heat shows a $λ$-type anomaly at $T_N$ = 3.3 K, indicating a bulk phase transition probably of antiferromagnetic origin. At the Néel temperature $T_N$, the entropy approaches the value of 4.66~J/mol.K which is about 0.8Rln(2), where R is the universal gas constant. The analysis of the low temperature specific heat gives $γ$ = 46 mJ/mol.K$^2$. The temperature dependence DC magnetic susceptibility $χ(T)$ confirms the anomaly at 3.3 K and follows the Curie-Weiss law for temperatures above 50~K, with the calculated effective magnetic moment, $μ_\mathrm{eff}$ = 3.47(2)~$μ_B$/Pr and Weiss temperature $θ_p$ = --7.80(1)~K. This effective magnetic moment value is in good agreement with the Hund$^\prime$s rule theoretical free-ion value of 3.58~$μ_B$ for Pr$^{3+}$. The electrical resistivity data also shows an anomaly at $T_N$ and a broad curvature at intermediate temperatures probably due to crystalline electric field (CEF) effects. The Pr$^{3+}$ in this structure type has a site symmetry of $C_s$ which predicts a CEF splitting of the $J$ = 4 multiplet into 9 singlets and thus rule out in principle the occurrence of spontaneous magnetic order. In this article we discuss the magnetic order in PrRu$_2$Ga$_8$ in line with an induced type of magnetism resulting from the admixture of the lowest CEF level with the first excited state.

cond-mat.str-el↗