Metallic quantum ferromagnets

Brando, M.; Belitz, D.; Grosche, F. M.; Kirkpatrick, T. R.

doi:10.1103/revmodphys.88.025006

Cited by 331 publications

(348 citation statements)

References 542 publications

(595 reference statements)

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“…The extreme chemical disorder in these alloys is an essential component of the physics, suppressing a first order ferromagnetic transition that invariably occurs in many other potential ferromagnetic quantum critical point (FQCP) systems. 9 In carefully prepared single crystals with electropolished surfaces and minimum mechanical damage, we find that the BKV theory 17,18 of metallic ferromagnetic QCPs provides an excellent description of all of our data. The approximate temperature-magnetic field phase diagram that describes the boundary between the quantum critical and the Fermi liquid regions is also determined for the NiCoCr 0.8 composition from magnetization data.…”

Section: Introductionmentioning

confidence: 92%

“…Studies of several low dimensional magnetic materials have greatly improved our understanding of QCP physics in insulating solids, [6][7][8] but our understanding of QCP phenomena in metallic systems is much less clear. 2,9,10 One hindrance is that few systems are microscopically homogeneous near the QCP, due to the need for small concentrations of dopants, and this can disrupt the feedback loop between theory and experiment.…”

Section: Introductionmentioning

confidence: 99%

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Quantum critical behavior in the asymptotic limit of high disorder in the medium entropy alloy NiCoCr0.8

et al. 2017

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The behavior of matter near a quantum critical point is one of the most exciting and challenging areas of physics research. Emergent phenomena such as high-temperature superconductivity are linked to the proximity to a quantum critical point. Although significant progress has been made in understanding quantum critical behavior in some low dimensional magnetic insulators, the situation in metallic systems is much less clear. Here, we demonstrate that NiCoCr x single crystal alloys are remarkable model systems for investigating quantum critical point physics in a metallic environment. For NiCoCr x alloys with x ≈ 0.8, the critical exponents associated with a ferromagnetic quantum critical point are experimentally determined from low temperature magnetization and heat capacity measurements. All of the five exponents (γ T ≈ 1/2, β T ≈ 1, δ ≈ 3/2, νz m ≈ 2, α T ≈ 0) are in remarkable agreement with predictions of Belitz-Kirkpatrick-Vojta theory in the asymptotic limit of high disorder. Using these critical exponents, excellent scaling of the magnetization data is demonstrated with no adjustable parameters. We also find a divergence of the magnetic Gruneisen parameter, consistent with a ferromagnetic quantum critical point. This work therefore demonstrates that entropy stabilized concentrated solid solutions represent a unique platform to study quantum critical behavior in a highly tunable class of materials.

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Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Quantum critical behavior in the asymptotic limit of high disorder in the medium entropy alloy NiCoCr0.8

et al. 2017

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“…24 The first, in which fluctuations contribute a negative term to the bosonic self-energy, leading to an SDW instability at finite wavevector |Q|, was already discussed in the previous section. The second is a fluctuation-induced first-order phase transition into the FM phase, the possibility of which can be inferred by the presence of a nonanalytic term in the order parameter in the free energy expansion.…”

Section: Free Energy Expansionmentioning

confidence: 99%

Incommensurate spin density wave at a ferromagnetic quantum critical point in a three-dimensional parabolic semimetal

Murray

Vafek

2015

Phys. Rev. B

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We explore the ferromagnetic quantum critical point in a three-dimensional semimetallic system with upward-and downward-dispersing bands touching at the Fermi level. Evaluating the static spin susceptibility to leading order in the coupling between the fermions and the fluctuating ferromagnetic order parameter, we find that the ferromagnetic quantum critical point is masked by an incommensurate, longitudinal spin density wave phase. We first analyze an idealized model which, despite having strong spin-orbit coupling, still possesses O(3) rotational symmetry generated by the total angular momentum operator. In this case, the direction of the incommensurate spin density wave propagation can point anywhere, while the magnetic moment is aligned along the direction of propagation. Including symmetry-allowed anisotropies in the fermion dispersion and the coupling to the order parameter field, however, the ordering wavevector instead breaks a discrete symmetry and aligns along either the [111] or [100] direction, depending on the signs and magnitudes of these two types of anisotropy. PACS numbers:For decades it has been understood that electron interactions may lead to interesting consequences at low energy scales in three-dimensional (3D) semimetallic systems, in which spin-orbit coupling combines with cubic crystalline symmetries, leading to a band degeneracy at the Fermi energy. 1-8 Such a band structure has long been known to occur in HgTe and α-Sn (gray tin), and has possibly been discovered more recently in the pyrochlore Pr 2 Ir 2 O 7 . 9-14 Since the low-energy effective theory for these systems was first developed by Luttinger 1 , it has been argued using various approaches that interactions could lead to an excitonic instability at low temperatures 2,6 , or that the system may be described by an exotic non-Fermi liquid phase, characterized by nontrivial power-law scaling of various physical quantities with temperature. [3][4][5] In more recent work, the properties of such a system near an Ising antiferromagnetic quantum critical point were explored, and the critical theory was found to be governed by unusual critical exponents and emergent spatial anisotropy of the fermion dispersion. 7 The theory describing the quantum phase transition into an insulating nematic phase has also been developed recently. 8In this work we explore the fate of a 3D semimetal in the vicinity of a ferromagnetic (FM) quantum critical point. Working at zero temperature and approaching the quantum critical point from the paramagnetic side, we find that it is unstable toward an incommensurate spin density wave (SDW) phase. In the most symmetric version of the theory, there is a combined O(3) rotational symmetry for spin and spatial degrees of freedom, which is spontaneously broken by the SDW wavevector. The O(3) symmetry is reduced to a discrete symmetry by either of two sources of anisotropy: the Yukawa coupling of the fermions to the fluctuating FM field, or the dispersion of the fermions themselves.(Throughout this work, by anisotro...

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“…PACS numbers: 71.10.Ay, 71.27.+a, 74.62.Bf Quantum phase transitions (QPTs) have been a topic of intense research efforts for several decades [1][2][3][4]. Here the earliest theory of a QPT was provided by Stoner in 1938 for itinerant ferromagnets [5].…”

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confidence: 99%

Quantum Critical Scaling in the Disordered Itinerant Ferromagnet UCo1−xFexGe

et al. 2016

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Belitz-Kirkpatrick-Vojta (BKV) theory shows in excellent agreement with experiment that ferromagnetic quantum phase transitions (QPTs) in clean metals are generally first-order due to the coupling of the magnetization to electronic soft modes, in contrast to the classical analogue that is an archetypical second-order phase transition. For disordered metals BKV theory predicts that the second order nature of the QPT is restored because the electronic soft modes change their nature from ballistic to diffusive. Our low-temperature magnetization study identifies the ferromagnetic QPT in the disordered metal UCo1−xFexGe as the first clear example that exhibits the associated critical exponents predicted by BKV theory.

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Metallic quantum ferromagnets

Cited by 331 publications

References 542 publications

Quantum critical behavior in the asymptotic limit of high disorder in the medium entropy alloy NiCoCr0.8

Quantum critical behavior in the asymptotic limit of high disorder in the medium entropy alloy NiCoCr0.8

Incommensurate spin density wave at a ferromagnetic quantum critical point in a three-dimensional parabolic semimetal

Quantum Critical Scaling in the Disordered Itinerant Ferromagnet UCo1−xFexGe

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