Impurity effects in highly frustrated diamond-lattice antiferromagnets

Savary, Lucile; Gull, Emanuel; Alicea, Jason; Bergman, Doron L.

doi:10.1103/physrevb.84.064438

Cited by 42 publications

(50 citation statements)

References 24 publications

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“…Interestingly, Monte Carlo calculations on the FCC system (20) reveal that domain walls have a significant effect and inhibit the apparent magnitude of the ordered sublattice magnetization. Alternatively, the recent work of Savary et al (48) suggests that the ground-state properties of certain diamond-lattice antiferromagnets are strongly affected by relatively small amounts of disorder, perhaps enhancing the propensity of CoAl 2 O 4 to form an actual spin glass and leading to strong sample dependence. We also note certain similarities between the current results and the two length scales observed in the scattering of order-by-disorder candidate Er 2 Ti 2 O 7 (24), although the latter exhibits a continuous phase transition and resolution-limited Bragg peaks at low temperatures.…”

Section: Resultsmentioning

confidence: 99%

Kinetically inhibited order in a diamond-lattice antiferromagnet

MacDougall

Gout

Zarestky

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Frustrated magnetic systems exhibit highly degenerate ground states and strong fluctuations, often leading to new physics. An intriguing example of current interest is the antiferromagnet on a diamond lattice, realized physically in A-site spinel materials. This is a prototypical system in three dimensions where frustration arises from competing interactions rather than purely geometric constraints, and theory suggests the possibility of unusual magnetic order at low temperature. Here, we present a comprehensive single-crystal neutron scattering study of CoAl 2 O 4 , a highly frustrated A-site spinel. We observe strong diffuse scattering that peaks at wavevectors associated with Néel ordering. Below the temperature T Ã ¼ 6.5 K, there is a dramatic change in the elastic scattering lineshape accompanied by the emergence of well-defined spin-wave excitations. T Ã had previously been associated with the onset of glassy behavior. Our new results suggest instead that T Ã signifies a first-order phase transition, but with true long-range order inhibited by the kinetic freezing of domain walls. This scenario might be expected to occur widely in frustrated systems containing firstorder phase transitions and is a natural explanation for existing reports of anomalous glassy behavior in other materials. F rustration occurs in spin systems when constraints prevent the formation of a ground state satisfying all of the pairwise interactions. The defining characteristics of frustration are massive ground-state degeneracy and concomitant strong fluctuations. The latter suppress magnetic order and lead to spin-liquid regimes extending to low temperature. There has been great interest in such spin liquids because of the plethora of emergent phenomena (1-3) resulting from an extreme sensitivity to small, often neglected degeneracy-breaking effects. Noteworthy examples include unusual short-range correlations (4, 5), apparent spinglass behavior in the absence of disorder (6-8), collective ring excitations in pyrochlore spinels (9-11), spontaneously reduced dimensionality in rare-earth titanates (12), and topological excitations like magnetic monopoles in spin-ice materials (13-15).The degeneracy-breaking effects can be small terms in the interaction Hamiltonian that enter the problem in a nonperturbative way. Examples include dipolar interactions in the pyrochlores (16) or spin-lattice interactions in multiferroics (17). Interestingly, degeneracy can also be broken in the complete absence of such interaction terms, through a mechanism known as "order-by-disorder" (18). Order-by-disorder refers to the scenario where the entropy associated with thermal or quantum fluctuations lowers the free energy of one ordered state compared to others of equal energy, thereby stabilizing order. Order-by-disorder was first predicted in studies of the diluted Ising model on a rectangular lattice (18). It has since emerged as a central feature in theories of various frustrated antiferromagnets, including the face-centered cubic (FCC) (19,20) as well a...

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Section: Resultsmentioning

confidence: 99%

Kinetically inhibited order in a diamond-lattice antiferromagnet

MacDougall

Gout

Zarestky

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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“…The effect of site inverson on the spin liquid state of Asite spinels have been treated theoretically wherein the effect of weak disorder is found to act as a degeneracy breaking mechanism to select a preferred ground state out of the manifold of available states. [30] The proposed "swiss cheese model" which takes in to account the disorder effects shows that the presence of finite amount of disorder does not diminish the frustration effects in an antiferromagnetic diamond lattice. The samples of FeAl 2 O 4 studied here contain low amounts of disorder, but even in the presence of it, frustration effects assume importance.…”

Section: +mentioning

confidence: 99%

Approaching the true ground state of frustratedA-site spinels: A combined magnetization and polarized neutron scattering study

Nair

Voigt

et al. 2014

Phys. Rev. B

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We re-investigate the magnetically frustrated, diamond-lattice-antiferromagnet spinels FeAl2O4 and MnAl2O4 using magnetization measurements and diffuse scattering of polarized neutrons. In FeAl2O4, macroscopic measurements evidence a "cusp" in zero field-cooled susceptibility around 13 K. Dynamic magnetic susceptibility and memory effect experiments provide results that do not conform with a canonical spin-glass scenario in this material. Through polarized neutron scattering studies, absence of long-range magnetic order down to 4 K is confirmed in FeAl2O4. By modeling the powder averaged differential magnetic neutron scattering cross-section, we estimate that the spinspin correlations in this compound extend up to the third nearest-neighbour shell. The estimated value of the Landé g factor points towards orbital contributions from Fe 2+ . This is also supported by a Curie-Weiss analysis of the magnetic susceptibility. MnAl2O4, on the contrary, undergoes a magnetic phase transition into a long-range ordered state below ≈ 40 K, which is confirmed by macroscopic measurements and polarized neutron diffraction. However, the polarized neutron studies reveal the existence of prominent spin-fluctuations co-existing with long-range antiferromagnetic order. The magnetic diffuse intensity suggests a similar short range order as in FeAl2O4. Results of the present work supports the importance of spin-spin correlations in understanding magnetic response of frustrated magnets like A-site spinels which have predominant short-range spin correlations reminiscent of the "spin liquid" state.

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“…The magnetic ground state changes to an AF state at J 2 /J 1 <1/8. Savary et al have considered theoretically the effects of the inversion in frustrated A-site magnetic spinels [4]. CoAl 2 O 4 is a partially inverted spinel with cobalt ions predominantly in the tetrahedral A site.…”

Section: Introductionmentioning

confidence: 99%

Multistage ordering and critical singularities inCo1−xZnxAl2
Naka
¹
,
Sato²,
Matsushita³
et al. 2015
Phys. Rev. B
9
7
28
1
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We report comprehensive studies of the crystallographic, magnetic, and thermal properties of a spinel-type magnetically frustrated compound, CoAl 2 O 4 , and a magnetically diluted system, Co 1 -x Zn x Al 2 O 4 . These studies revealed the effects of dilution and disorder when the tetrahedral magnetic Co ion was replaced by the nonmagnetic Zn ion. Low-temperature anomalies were observed in magnetic susceptibility at x < 0.6. A multicritical point was apparent at T = 3.4 K and x = 0.12, where the antiferromagnetic, spin-glass-like, and paramagnetic phases met. At that point, the quenched ferromagnetic component induced by a magnetic field during cooling was sharply enhanced and was observable below x = 0.6. At x ∼ 0.6, magnetic susceptibility and specific heat were described by temperature power laws, χ ∼ C/T ∼ T −δ , in accord with the site percolation threshold of the diamond lattice. This behavior is reminiscent of a quantum critical singularity. We propose an x-temperature phase diagram in the range 0 x 1 for Co 1 -x Zn x Al 2 O 4 . The transition temperature of CoAl 2 O 4 determined from magnetic susceptibility measured under hydrostatic pressure increased with increasing pressure.

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Impurity effects in highly frustrated diamond-lattice antiferromagnets

Cited by 42 publications

References 24 publications

Kinetically inhibited order in a diamond-lattice antiferromagnet

Kinetically inhibited order in a diamond-lattice antiferromagnet

Approaching the true ground state of frustratedA-site spinels: A combined magnetization and polarized neutron scattering study

Multistage ordering and critical singularities inCo1−xZnxAl2
Naka
¹
,
Sato²,
Matsushita³
et al. 2015
Phys. Rev. B
9
7
28
1
View full text Add to dashboard Cite

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Impurity effects in highly frustrated diamond-lattice antiferromagnets

Cited by 42 publications

References 24 publications

Kinetically inhibited order in a diamond-lattice antiferromagnet

Kinetically inhibited order in a diamond-lattice antiferromagnet

Approaching the true ground state of frustratedA-site spinels: A combined magnetization and polarized neutron scattering study

Multistage ordering and critical singularities inCo1−xZnxAl2Naka1, Sato2, Matsushita3 et al. 2015Phys. Rev. B97281View full textAdd to dashboardCite

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Multistage ordering and critical singularities inCo1−xZnxAl2
Naka
¹
,
Sato²,
Matsushita³
et al. 2015
Phys. Rev. B
9
7
28
1
View full text Add to dashboard Cite