Download presentation

Presentation is loading. Please wait.

Published byDorian Kirkpatrick Modified over 3 years ago

1
Level Splitting in Frustrated non-Kramers doublet systems Collin Broholm and Joost van Duijn Department of Physics and Astronomy Johns Hopkins University Spin Fluctuations in Metallic Pyrochlore Systems

2
9/13-17/04International Workshop on Frustrated Magnetism 2 Collaborators Ruthenium pyrochlores K. H. Kim Rutgers N. HurRutgers D. AdrojaISIS Q. HuangNIST S.-W. CheongRutgers T. G. PerringISIS Iridium pyrochlores Satoru NakatsujiKyoto Yo MachidaKyoto Yoshiteru Maeno Kyoto Toshiro Sakakibara ISSP Takashi TayamaISSP

3
9/13-17/04International Workshop on Frustrated Magnetism 3 Outline Introduction Bulk properties of 4d n and 5d n pyrochlores Spin correlations on TM sites Crystal field excitations on RE sites Level splitting in Pr x Bi 2-x Ru 2 O 7 Ground state doublet spin dynamics Model of inhomogeneous level splitting Discussion and Conclusions Possible relevance for other non-Kramers doublet systems

4
9/13-17/04International Workshop on Frustrated Magnetism 4 The pyrochlore structure A 2 B 2 O 7 A and B sites on vertices of corner- sharing tetrahedra A 3+ site is trivalent RE with 8-fold O 2- coordination B 4+ site is tetravalent TM with 6-fold O 2- coordination Can have both A 3+ and B 4+ magnetism

5
9/13-17/04International Workshop on Frustrated Magnetism 5 B=Ru site magnetism of Y 2 Ru 2 O 7 □ Neutron Diffraction reveals long range magnetic order □ ZFC/FC hysteresis suggests some form of disorder that produces glassy canted AFM Taira et al. (2000) Taira et al. (1999)

6
9/13-17/04International Workshop on Frustrated Magnetism 6 “Strong Coupling” Transition in Y 2 Ru 2 O 7 T=90 K T=1.5 K

7
9/13-17/04International Workshop on Frustrated Magnetism 7 PM and AFM Spin Fluctuations □ Phase Transition pushes significant spectral weight into “resonance” □ The Q-dependence of scattering reflects the form factor for AFM cluster degrees of freedom 1.5 K 90 K 1.5 K 90 K

8
9/13-17/04International Workshop on Frustrated Magnetism 8 2 Magnetic Ions 2 Phase Transitions N. Taira et al. (2003) Er 2 Ru 2 O 7 M. Ito et al. (2001) Pr 3+ Yb 3+ R 2 Ru 2 O 7

9
9/13-17/04International Workshop on Frustrated Magnetism 9 Metal Insulator Transition Bi-doping increase bandwidth causing Mott Hubbard MIT Magnet order is found only in the insulating state Electronic DOS at E F is enhanced close to the MIT Yoshii and Sato (1999)

10
9/13-17/04International Workshop on Frustrated Magnetism 10 A Highly Entropic Metallic State K. H. Kim et al.

11
9/13-17/04International Workshop on Frustrated Magnetism 11 Praseodymium Crystal Field levels: 10 meV 50 meV 85 meV 105 meV 116 meV 0 200 K 5 K Pr 1.2 Bi 0.8 Ru 2 O 7 Five transitions from GS implies it is doublet:

12
9/13-17/04International Workshop on Frustrated Magnetism 12 Fluctuations in metallic Pr 1.2 Bi 0.8 Ru 2 O 7

13
9/13-17/04International Workshop on Frustrated Magnetism 13 Inhomogeneous Level Splitting Broad Spectrum unchanged Upon heating to Wave vector dependence Follows Pr form factor 2 Neutron Scattering measures the level splitting spectrum

14
9/13-17/04International Workshop on Frustrated Magnetism 14 Inhomogeneous two level system The level distribution function: Singlet-singlet susceptibility: Sample averaged susceptibility Fluctuation-dissipation theorem yields

15
9/13-17/04International Workshop on Frustrated Magnetism 15 Data Collapse Confirms “quenched broadening”

16
9/13-17/04International Workshop on Frustrated Magnetism 16 Specific heat of ()-split doublet C(T)/T (J/mole-f.u./K 2 )

17
9/13-17/04International Workshop on Frustrated Magnetism 17 Susceptibility of ()-split doublet For gapless spectrum low T limiting form is ~lnT For gapless spectrum low T limiting form is ~lnT

18
9/13-17/04International Workshop on Frustrated Magnetism 18 Clues to origins of level splitting T-independent distribution function ⇒ Static not dynamic phenomenon Continuous not discrete spectrum ⇒ Large rare defect or density wave producing distribution of environments Same distribution describes all x<1.2 ⇒ Distribution may not come from Bi doping Magnetic field enters in quadrature ⇒ Electrostatic not magnetostatic inhomogeneity

19
9/13-17/04International Workshop on Frustrated Magnetism 19 Where else might this occur? Elements that can have non-Kramers doublet ground states: Pr 3+, Pm 3+, Sm 2+, Eu 3+, Tb 3+, Ho 3+, Tm 3+, Yb 2+, and U 4+ Nominally cubic and stoichiometric systems may have clandestine level splitting disorder Doping effects may be controlled by the induced level splitting

20
9/13-17/04International Workshop on Frustrated Magnetism 20 Other Materials to Reconsider Tb 2 Ti 2 O 7 : A non ordering magnet with mysterious low energy mode Ho 2 Ti 2 O 7 : Long range ordered with unusual thermodynamics YbBiPt: Ultra heavy fermion system with mysterious low E mode (Robinson et al (1995). LiHo x Y 1-x F 4 quantum spin glass. Strain induced level splitting adds an effective transverse field Tb x Y 2-x Ti 2 O 7 : Dilution has added effect of neutralizing Tb through level splitting

21
9/13-17/04International Workshop on Frustrated Magnetism 21 Metal insulator transition in R 2 Ir 2 O 7 Yanagishima and Maeno (2001) Nakatsuji et al.

22
9/13-17/04International Workshop on Frustrated Magnetism 22 Conclusions Ir and Ru pyrochlores offer MIT transitions with frustrated magnetism Y 2 Ru 2 O 7 : “strong coupling” transition Spectral weight pushed to finite E resonance Q-dependence unaffected by ordering Pr x Bi 2-x Ru 2 O 7 : static inhomogeneous distribution of level splittings Neutrons: “T-independent” broad spectrum C(T)/T: broadened Schottky anomaly (T): possible logarithmic divergence at low T Watch out for level splitting in non-Kramers ions, which are “not really magnets”

Similar presentations

OK

Neutron Scattering of Frustrated Antiferromagnets Satisfaction without LRO Paramagnetic phase Low Temperature phase Spin glass phase Long range order Spin.

Neutron Scattering of Frustrated Antiferromagnets Satisfaction without LRO Paramagnetic phase Low Temperature phase Spin glass phase Long range order Spin.

© 2018 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google