Anomalous Metamagnetism in the Low Carrier Density Kondo Lattice ${\mathrm{YbRh}}_{3}{\mathrm{Si}}_{7}$

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Anomalous Metamagnetism in the Low Carrier Density Kondo Lattice ${YbRh}_{3} {Si}_{7}$

Binod K. Rai et al.

Phys. Rev. X 8, 041047 – Published 13 December 2018

Abstract

We report complex metamagnetic transitions in single crystals of the new low carrier Kondo antiferromagnet ${YbRh}_{3} {Si}_{7}$ . Electrical transport, magnetization, and specific heat measurements reveal antiferromagnetic order at $T_{N} = 7.5 K$ . Neutron diffraction measurements show that the magnetic ground state of ${YbRh}_{3} {Si}_{7}$ is a collinear antiferromagnet, where the moments are aligned in the $a b$ plane. With such an ordered state, no metamagnetic transitions are expected when a magnetic field is applied along the $c$ axis. It is therefore surprising that high-field magnetization, torque, and resistivity measurements with $H ∥ c$ reveal two metamagnetic transitions at $μ_{0} H_{1} = 6.7 T$ and $μ_{0} H_{2} = 21 T$ . When the field is tilted away from the $c$ axis, towards the $a b$ plane, both metamagnetic transitions are shifted to higher fields. The first metamagnetic transition leads to an abrupt increase in the electrical resistivity, while the second transition is accompanied by a dramatic reduction in the electrical resistivity. Thus, the magnetic and electronic degrees of freedom in ${YbRh}_{3} {Si}_{7}$ are strongly coupled. We discuss the origin of the anomalous metamagnetism and conclude that it is related to competition between crystal electric-field anisotropy and anisotropic exchange interactions.

Received 10 March 2018
Revised 26 September 2018

DOI:https://doi.org/10.1103/PhysRevX.8.041047

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Antiferromagnetism Electronic structure Hall effect Magnetotransport Metamagnetism Semimetals

Condensed Matter, Materials & Applied Physics

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Quantum-mechanical interactions in crystalline materials are responsible for an abundance of behaviors such as metamagnetic transitions—sudden increases in the magnetization of a material with small changes in an applied magnetic field. These behaviors are governed by competition between different energy scales, the exact nature of which remains unsolved. Understanding this competition could pave the way to predicting and controlling the physical properties and functionalities in crystalline systems. One tool to probe this complex energy landscape is an applied magnetic field to measure the relative changes in behaviors displayed by the magnetic moments and conduction electrons. In this work, we report the discovery of multiple metamagnetic transitions in the crystalline material ${YbRh}_{3} {Si}_{7}$ , when a magnetic field is applied perpendicularly to the orientation of its magnetic moment.

We grow single crystals of ${YbRh}_{3} {Si}_{7}$ and measure their electrical resistivity, magnetization, and heat capacity. Using neutron scattering, we find that the crystal’s magnetic ground state is a collinear antiferromagnet with magnetic moments aligned in the crystal plane. In this highly ordered state, no metamagnetic transitions are expected when a perpendicular magnetic field is applied. And yet we find two such transitions, which suggests the need for a more advanced explanation than typical theory can supply.

We suspect that it will be necessary to develop a theory that incorporates the crystal’s electric field and anisotropic interactions between the localized magnetic moments that cause long-range magnetic order. This description of anomalous metamagnetism in ${YbRh}_{3} {Si}_{7}$ could provide a unique opportunity to uncover new quantum phases in crystalline materials.

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Vol. 8, Iss. 4 — October - December 2018

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Figure 1
(a) Zero-field temperature-dependent electrical resistivity $ρ$ of ${YbRh}_{3} {Si}_{7}$ at different annealing times. The solid line is the data for ${LuRh}_{3} {Si}_{7}$ . (b) Low-temperature $ρ$ at $μ_{0} H = 0$ and 9 T applied parallel to the $c$ axis. (c) Hall coefficient $R_{H}$ measured at $μ_{0} H = 9 T$ between 300 and 10 K. (d) Inverse magnetic susceptibility $H / M$ vs $T$ for ${YbRh}_{3} {Si}_{7}$ with $μ_{0} H = 0.1 T$ parallel to $c$ (blue triangles) and $a b$ (red squares) together with a polycrystalline average (purple circles) and Curie-Weiss fits (solid lines). Inset: Low-temperature magnetic susceptibility $M / H$ . Note that $1 emu = 1 G {cm}^{3} = 10^{- 3} {Am}^{2}$ . (e) DOS projected onto the orbital angular-momentum components of the ${Yb}^{3 +}$ ion. (f) Powder neutron diffraction patterns at 1.5 K (data, crosses; Bragg peak positions, short vertical lines; difference between data and refined pattern, indigo curve), with the AFM structure of the system with collinear moments parallel to the $a$ axis (left inset) and an enhanced view of the (0 0 3) and (1 0 1) magnetic Bragg peaks at small angles (right inset). (g) Agreement of the single-crystal magnetic structure refinement at $T = 4.5 K$ . (h) Magnetic order parameter measured at the (0 2– $5)_{M}$ peak upon warming. Error bars represent 1 standard deviation.
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Figure 2
(a) $H = 0$ $C_{p} (T)$ for ${YbRh}_{3} {Si}_{7}$ (full circles) and its nonmagnetic analogue (line) ${LuRh}_{3} {Si}_{7}$ . Inset: Log-log plot of $(C_{p} - C_{n}) / T$ vs $T$ , where $C_{n}$ is the nuclear contribution to the specific heat. (b) Magnetic entropy $S_{mag} (T)$ . (c) Band structure of ${YbRh}_{3} {Si}_{7}$ with so-called “fat bands” highlighting the contribution from Yb $f$ orbitals and (d) Rh and Si atoms. Thicker sections of the bands represent a larger partial contribution of the respective orbitals.
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Figure 3
(a) $C_{p}$ vs $T$ for ${YbRh}_{3} {Si}_{7}$ with magnetic fields ( $μ_{0} H \geq 6 T$ ) applied parallel to the $c$ axis. Inset: Low magnetic-field data ( $μ_{0} H \leq 6.15 T$ ). (b) $C_{p}$ vs $T$ with $H | | a b$ . (c) $M$ vs $H$ at $T = 1.8 K$ for $H | | a b$ (dashed line) and $H | | c$ (solid line) up to $μ_{0} H = 7 T$ . The $c$ -axis moment from neutron diffraction is given by the solid symbols. The inset shows the low-field data for $H | | a b$ . (d) $H | | c$ magnetoresistance isotherms. (e)–(g) Left axis: Magnetization at $T = 1.44 K$ , torque at $T = 2 K$ , and resistivity at $T = 1.47 K$ as a function of magnetic field $H | | c$ . Right axis: Derivative plots with respect to $H$ . Dashed lines indicate the metamagnetic transitions at $μ_{0} H_{1}$ and $μ_{0} H_{2}$ .
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Figure 4
$T - H$ phase diagram of ${YbRh}_{3} {Si}_{7}$ together with three distinct magnetic spin configurations in different magnetic-field regions. A picture of the crystal is shown in the inset.
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Physical Review X

Anomalous Metamagnetism in the Low Carrier Density Kondo Lattice YbRh3Si7

Binod K. Rai et al.

Phys. Rev. X 8, 041047 – Published 13 December 2018

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Anomalous Metamagnetism in the Low Carrier Density Kondo Lattice ${YbRh}_{3} {Si}_{7}$