Magnetic hard-axis ordering near ferromagnetic quantum criticality

Abstract

We investigate the interplay of quantum fluctuations and magnetic anisotropies in metallic ferromagnets. Our central result is that fluctuations close to a quantum critical point can drive the moments to point along a magnetic hard axis. As a proof of concept, we show this behavior explicitly for a generic two-band model with local Coulomb and Hund's interactions, and a spin-orbit-induced easy plane anisotropy. The phase diagram is calculated within the fermionic quantum order-by-disorder approach, which is based on a self-consistent free energy expansion around a magnetically ordered state with unspecified orientation. Quantum fluctuations render the transition of the easy-plane ferromagnet first-order below a tricritical point. At even lower temperatures, directionally dependent transverse fluctuations dominate the magnetic anisotropy and the moments flip to lie along the magnetic hard axis. We discuss our findings in the context of recent experiments that show this unusual ordering along the magnetic hard direction.

5 pages, 3 figures

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• Anomalous metamagnetism in the low carrier density Kondo lattice YbRh3Si7
• Evolution from Ferromagnetism to Antiferromagnetism in Yb(Rh1-xCox)2Si2
• Ferromagnetic ordering along the hard axis in the Kondo lattice YbIr3Ge7
• Magnetic field-induced softening of spin waves and hard-axis order in Kondo-lattice ferromagnet CeAgSb${}_2$
• Ferromagnetic quantum critical point in a locally noncentrosymmetric and nonsymmorphic Kondo metal
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• Hidden Charge Order of Interacting Dirac Fermions on the Honeycomb Lattice
• Magnetic fluctuations in the itinerant ferromagnet LaCrGe3 studied by 139La NMR
• Importance of anisotropic interactions for hard-axis/plane ordering of Ce-based ferromagnets
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