Magnetization and thermoremanent magnetization of Tb2Mo2O7 and Y2Mo2O7 spin glasses

Ali, Naushad; Hill, Peggy; Zhang, X; Willis, Frank

doi:10.1016/0925-8388(92)90323-2

Cited by 11 publications

(8 citation statements)

References 10 publications

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“…4,7 Bulk measurements showed several key signatures of a spinglass transition, such as a shift from the origin of a magnetic hysteresis loop, a disappearance of the thermoremanent magnetization at the glass temperature, and a logarithmic decay of the remanent magnetization. 5 A frequency shift of the sus-ceptibility peak, also typical for a spin glass, will be shown in Sec. III A of this paper.…”

Section: Introductionmentioning

confidence: 90%

“…Tb 2 Mo 2 O 7 was one of the first magnets in which the impact of geometrical frustration on the low-temperature magnetic properties of a system was realized. [1][2][3][4][5][6][7] Such frustration is the consequence of a geometric arrangement of the magnetic moments in the lattice in a way that prevents the system from minimizing the energy of all near-neighbor bonds at the same time. [8][9][10][11] As a result, many nearly degenerate groundstate configurations typically exist in frustrated magnets, making them particularly susceptible to fluctuations.…”

Section: Introductionmentioning

confidence: 99%

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High-resolution neutron scattering study ofTb2Mo2O7: A geometrically frustrated spin glass

et al. 2010

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The low-temperature magnetic properties of Tb 2 Mo 2 O 7 have been studied with bulk susceptibility measurements and with elastic and high-resolution inelastic neutron scattering. This system is a spin glass with a freezing temperature T g ϳ 25 K. A reverse Monte Carlo simulation of the neutron diffraction data shows weak ferromagnetic near-neighbor spatial correlations that do not extend beyond Շ10 Å. Neutron measurements of the spin dynamics reveal a slowing down with decreasing temperature without an anomaly at the glass transition. A low-lying Q-independent mode is seen at ប 0 ϳ 0.28 meV. This dispersionless crystal electric field transition is measurable up to 60 K.

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Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

High-resolution neutron scattering study ofTb2Mo2O7: A geometrically frustrated spin glass

et al. 2010

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“…The conventional nature of the spin-glass transition (freezing temperature T f = 22 K [12]) has been shown by exhaustive thermodynamic measurements, including non-linear susceptibility [12,13], specific heat [14,15], a.c. susceptibility [16], and thermo-remanent magnetization [17][18][19]. Inelastic neutron scattering [20], muon-spin rotation (µSR) [21], and neutron spin-echo studies [22,23] reveal a reduction in the spin-relaxation rate as T f is traversed.…”

mentioning

confidence: 99%

Orbital Dimer Model for the Spin-Glass State inY2Mo2O7
Thygesen
¹
,
Paddison
²
,
Zhang
³

et al. 2017
Phys. Rev. Lett.
41
1
51
0
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The formation of a spin glass usually requires both structural disorder and frustrated magnetic interactions. Consequently, the origin of spin-glass behaviour in Y2Mo2O7-in which magnetic Mo 4+ ions occupy a frustrated pyrochlore lattice with minimal compositional disorder-has been a longstanding question. Here, we use neutron and X-ray pair-distribution function (PDF) analysis to develop a disorder model that resolves apparent incompatibilities between previously-reported PDF, EXAFS and NMR studies and provides a new and physical mechanism for spin-glass formation. We show that Mo 4+ ions displace according to a local "2-in/2-out" rule on each Mo4 tetrahedron, driven by orbital dimerisation of Jahn-Teller active Mo 4+ ions. Long-range orbital order is prevented by the macroscopic degeneracy of dimer coverings permitted by the pyrochlore lattice. Cooperative O 2− displacements yield a distribution of Mo-O-Mo angles, which in turn introduces disorder into magnetic interactions. Our study demonstrates experimentally how frustration of atomic displacements can assume the role of compositional disorder in driving a spin-glass transition. PACS numbers: 75.50.Lk,61.05.fm,75.10.Nr,75.25.Dk In a spin-glass transition, spins freeze into a metastable arrangement without long-range order [1]. It is generally accepted that two conditions must be satisfied for a spin-glass transition to occur: interactions between spins must be disordered and these interactions must also be frustrated [2,3]. In canonical spin glasses-e.g., dilute magnetic alloys such as Cu 1−x Mn x [4] and site-disordered crystals such as Fe 2 TiO 5 [5]-the nature of structural disorder and its coupling to magnetism is well understood. However, spin-glass behaviour is also observed in well-ordered crystals where the geometry of the magnetic lattice alone can generate frustration (see, e.g., [6][7][8]). Here, the mechanism of spin-glass formation poses an important challenge for theory [9,10]. The prototypical material that shows this anomalous behaviour is Y 2 Mo 2 O 7 -a system with apparently unremarkable levels of structural disorder, but with thermodynamic properties indistinguishable from canonical spin glasses (for a review, see [11]).The structure and dynamics of Y 2 Mo 2 O 7 have been extensively studied. The conventional nature of the spin-glass transition (freezing temperature T f = 22 K [12]) has been shown by exhaustive thermodynamic measurements, including non-linear susceptibility [12,13], specific heat [14,15], a.c. susceptibility [16], and thermo-remanent magnetization [17][18][19]. Inelastic neutron scattering [20], muon-spin rotation (µSR) [21], and neutron spin-echo studies [22,23] reveal a reduction in the spin-relaxation rate as T f is traversed. Neutron diffraction measurements show that the average structure is well-described by the ordered pyrochlore model (space group F d3m) both below and above T f [24,25]. In this structure, the average positions of magnetic Mo 4+ ions describe a network of corner-sharing tetrahedra [ Fig. 1 coo...

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“…Materials with R = Nd and Sm are metallic, R = Tb, Dy, Ho, Er, and Y are insulating, and R=Gd is on the verge of the insulator-metal transition 33,34 (IMT). The highest ferromagnetic T c is ∼ 100K, in Nd, while the spin glass transition temperature, T SG is typically [35][36][37] ∼ 20K. The unusual features in transport include very large residual resistivity, ∼ 10 mΩcm close to the metal-insulator transition 34 , prominent anomalous Hall effect in metallic samples [38][39][40][41][42] , e.g, Nd 2 Mo 2 O 7 , and magnetic field driven metallisation in the weakly insulating samples 43 e.g, Gd 2 Mo 2 O 7 .…”

Section: Introductionmentioning

confidence: 99%

Ground State of the Two Orbital Hubbard Model on the Pyrochlore Lattice with Competing Double Exchange and Superexchange Interactions

Swain¹,

Majumdar²

2016

Preprint

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The two orbital Hubbard model, with the electrons additionally coupled to a complex magnetic background, arises in the pyrochlore molybdates. The background involves local moments Hund's coupled to the electrons, driving double exchange ferromagnetism, and antiferromagnetic tendency arising from competing superexchange. The key scales include the Hubbard repulsion and the superexchange, both of which can be tuned in these materials, controlling phase transitions from a ferromagnetic metal to a spin glass metal and then a spin glass (Mott) insulator. We provide a comprehensive description of the ground state of this model using an unrestricted Hartree-Fock scheme implemented via a simulated annealing procedure. We establish the metal-insulator transition line for varying Hubbard interaction and superexchange. The orbital disorder already present in the ferromagnetic case is further enhanced by antiferromagnetic coupling and the resulting magnetic disorder. This suppresses the kinetic energy and shifts the metal-insulator transition to lower Hubbard interaction. We characterise the changing nature of the metal-insulator transition by tracking the magnetic and orbital correlations, the density of states, and the optical conductivity. The metal-insulator transition shows increasing 'Anderson' character as the antiferromagnetic coupling is increased. This paper is focused on the ground state, a companion paper will discuss the finite temperature physics involving magnetic and orbital thermal fluctuations.

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Magnetization and thermoremanent magnetization of Tb2Mo2O7 and Y2Mo2O7 spin glasses

Cited by 11 publications

References 10 publications

High-resolution neutron scattering study ofTb2Mo2O7: A geometrically frustrated spin glass

High-resolution neutron scattering study ofTb2Mo2O7: A geometrically frustrated spin glass

Orbital Dimer Model for the Spin-Glass State inY2Mo2O7
Thygesen
¹
,
Paddison
²
,
Zhang
³

et al. 2017
Phys. Rev. Lett.
41
1
51
0
View full text Add to dashboard Cite

Ground State of the Two Orbital Hubbard Model on the Pyrochlore Lattice with Competing Double Exchange and Superexchange Interactions

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Magnetization and thermoremanent magnetization of Tb2Mo2O7 and Y2Mo2O7 spin glasses

Cited by 11 publications

References 10 publications

High-resolution neutron scattering study ofTb2Mo2O7: A geometrically frustrated spin glass

High-resolution neutron scattering study ofTb2Mo2O7: A geometrically frustrated spin glass

Orbital Dimer Model for the Spin-Glass State inY2Mo2O7Thygesen1, Paddison2, Zhang3 et al. 2017Phys. Rev. Lett.411510View full textAdd to dashboardCite

Ground State of the Two Orbital Hubbard Model on the Pyrochlore Lattice with Competing Double Exchange and Superexchange Interactions

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Product

Resources

About

Orbital Dimer Model for the Spin-Glass State inY2Mo2O7
Thygesen
¹
,
Paddison
²
,
Zhang
³

et al. 2017
Phys. Rev. Lett.
41
1
51
0
View full text Add to dashboard Cite