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Register a new userMagnetic properties of monoclinic lanthanide orthoborates, $Ln$BO$_3$, $Ln$ = Gd, Tb, Dy, Ho, Er, Yb
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The lanthanide orthoborates, $Ln$BO$_3$, $Ln$ = Gd, Tb, Dy, Ho, Er, Yb crystallise in a monoclinic structure with the magnetic $Ln^{3+}$ forming an edge-sharing triangular lattice. The triangles are scalene, however all deviations from the ideal equilateral geometry are less than 1.5%. The bulk magnetic properties are studied using magnetic susceptibility, specific heat and isothermal magnetisation measurements. Heat capacity measurements show ordering features at $T leq$ 2 K for $Ln$ = Gd, Tb, Dy, Er. No ordering is observed for YbBO$_3$ at $T geq$ 0.4 K and HoBO$_3$ is proposed to have a non-magnetic singlet state. Isothermal magnetisation measurements indicate isotropic Gd$^{3+}$ spins and strong single-ion anisotropy for the other $Ln^{3+}$. The change in magnetic entropy has been evaluated to determine the magnetocaloric effect in these materials. GdBO$_3$ and DyBO$_3$ are found to be competitive magnetocaloric materials in the liquid helium temperature regime.
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The bulk magnetic properties of the lanthanide metaborates, $Ln$(BO$_2$)$_3$, $Ln$ = Pr, Nd, Gd, Tb are studied using magnetic susceptibility, heat capacity and isothermal magnetisation measurements. They crystallise in a monoclinic structure containing chains of magnetic $Ln^{3+}$ and could therefore exhibit features of low-dimensional magnetism and frustration. Pr(BO$_2$)$_3$ is found to have a non-magnetic singlet ground state. No magnetic ordering is observed down to 0.4 K for Nd(BO$_2$)$_3$. Gd(BO$_2$)$_3$ exhibits a sharp magnetic transition at 1.1 K, corresponding to three-dimensional magnetic ordering. Tb(BO$_2$)$_3$ shows two magnetic ordering features at 1.05 K and 1.95 K. A magnetisation plateau at a third of the saturation magnetisation is seen at 2 K for both Nd(BO$_2$)$_3$ and Tb(BO$_2$)$_3$ which persists in an applied field of 14 T. This is proposed to be a signature of quasi one-dimensional behaviour in Nd(BO$_2$)$_3$ and Tb(BO$_2$)$_3$.
The layered perovskite compounds are interesting due to their intriguing physical properties. In this article we report the structural, magnetic and dielectric properties of LnBaCuFeO5 (Ln=Nd, Eu, Gd, Ho and Yb). The structural parameters decrease from Nd to Yb due to the decrease in the ionic radii of the rare earth ions. An antiferromagnetic transition is observed for EuBaCuFeO5 near 120 K along with the glassy dynamics of the electric dipoles below 100 K. The magnetic transition is absent in other compounds, which may be due to the dominance of the magnetic moment of the rare earth ions. The dielectric constant does not show any anomaly, except in the case of HoBaCuFeO5 where it shows a weak frequency dependence around 54 K. These compounds show a significant enhancement of dielectric constant at high temperatures which have been attributed to Maxwell-Wagner effect. However, no significant magneto-dielectric coupling has been observed in these layered perovskites.
A detailed study on the crystal structure and bulk magnetic properties of Cr substituted Ising type lanthanide gallium garnets $Ln_3text{CrGa}_4text{O}_{12}$ ($Ln$ = Tb, Dy, Ho) has been carried out using room temperature powder X-Ray and neutron diffraction, magnetic susceptibility, isothermal magnetisation and heat capacity measurements. The magnetocaloric effect (MCE) in $Ln_3text{CrGa}_4text{O}_{12}$ is compared to that of $Ln_3text{Ga}_5text{O}_{12}$. In lower magnetic fields attainable by a permanent magnet ($leq$ 2 T), Cr substitution greatly enhances the MCE by 20% for $Ln$ = Dy and 120% for $Ln$ = Ho compared to the unsubstituted $Ln_3text{Ga}_5text{O}_{12}$. This is likely due to changes in the magnetic ground state as Cr substitution also significantly reduces the frustration in the magnetic lattice for the Ising type $Ln_3text{Ga}_5text{O}_{12}$.
A systematic study of the structural and magnetic properties of three-dimensionally frustrated lanthanide garnets $Ln_3A_2X_3text{O}_{12}$, $Ln$ = Gd, Tb, Dy, Ho, $A$ = Ga, Sc, In, Te, $X$ = Ga, Al, Li is presented. Garnets with $Ln$ = Gd show magnetic behaviour consistent with isotropic Gd$^{3+}$ spins; no magnetic ordering is observed for T $geq$ 0.4 K. Magnetic ordering features are seen for garnets with $Ln$ = Tb, Dy, Ho in the temperature range 0.4 < T < 2.5 K, however the nature of the magnetic ordering varies for the different $Ln$ as well as for different combinations of $A$ and $X$. The changes in magnetic behaviour can be explained by tuning of the magnetic interactions and changes in the single-ion anisotropy. The change in magnetic entropy is evaluated from isothermal magnetisation measurements to characterise the magnetocaloric effect in these materials. Among the Gd garnets, the maximum change in magnetic entropy per mole (15.45 J K$^{-1}$ mol$_{text{Gd}}^{-1}$) is observed for Gd$_3$Sc$_2$Ga$_3$O$_{12}$ at 2 K, in a field of 9 T. The performance of Dy$_3$Ga$_5$O$_{12}$ as a magnetocaloric material surpasses the other garnets with $Ln$ = Tb, Dy, Ho.
The spin-1/2 kagome antiferromagnets are key prototype materials for studying frustrated magnetism. Three isostructural kagome antiferromagnets LnCu$_3$(OH)$_6$Cl$_3$ (Ln = Gd, Tb, Dy) have been successfully synthesized by the hydrothermal method. LnCu$_3$(OH)$_6$Cl$_3$ adopts space group $Poverline{3}m1$ and features the layered Cu-kagome lattice with lanthanide Ln$^{3+}$ cations sitting at the center of the hexagons. Although heavy lanthanides (Ln = Gd, Tb, Dy) in LnCu$_3$(OH)$_6$Cl$_3$ provide a large effective magnetic moment and ferromagnetic-like spin correlations compared to light-lanthanides (Nd, Sm, Eu) analogues, Cu-kagome holds an antiferromagnetically ordered state at around 17 K like YCu$_3$(OH)$_6$Cl$_3$.
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