In contrast to magnetic order formed by electrons’ dipolar moments, ordering phenomena associated with higher-order multipoles (quadrupoles, octupoles, etc.) are more difficult to characterize ...because of the limited choice of experimental probes that can distinguish different multipolar moments. The heavy-fermion compoundCeB6and its La-diluted alloys are among the best-studied realizations of the long-range-ordered multipolar phases, often referred to as “hidden order.” Previously, the hidden order in phase II was identified as primary antiferroquadrupolar and field-induced octupolar order. Here, we present a combined experimental and theoretical investigation of collective excitations in phase II ofCeB6. Inelastic neutron scattering (INS) in fields up to 16.5 T reveals a new high-energy mode above 14 T in addition to the low-energy magnetic excitations. The experimental dependence of their energy on the magnitude and angle of the applied magnetic field is compared to the results of a multipolar interaction model. The magnetic excitation spectrum in a rotating field is calculated within a localized approach using the pseudospin representation for theΓ8states. We show that the rotating-field technique at fixed momentum can complement conventional INS measurements of the dispersion at a constant field and holds great promise for identifying the symmetry of multipolar order parameters and the details of intermultipolar interactions that stabilize hidden-order phases.
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Spatial anisotropy generated spontaneously in the translationally invariant metallic phase, i.e. electron nematic effect, addresses a great challenge for both experimentalists and theoreticians. An ...interesting option for the realization of the electron nematic phase is provided by the system with orbital ordering, as long as both orbitally ordered states and electron nematic phases possess broken spatial symmetry. Here we report the detailed study of the angular dependences of the magnetoresistance in the orbitally ordered antiferroquadrupole (AFQ) phase of CeB
. Our data allowed revealing the electron nematic effect, which develops when magnetic field exceeds a critical value of 0.3-0.5T. As a result, new transition inside the AFQ phase corresponding to the change of the symmetry of magnetic scattering on spin fluctuations in CeB
is discovered.
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A detailed investigation of contributions to the magnetization of nonmagnetic YB
6
, LaB
6
, and YbB
6
hexaboride single crystals has been performed, and a procedure for their separation has been ...proposed. It has been shown that a low value of electronic susceptibility χ
e
(
T
) in YB
6
and LaB
6
hexaborides seems to be associated with a small effective mass of band carriers,
m
* ~ 0.5
m
0
. As a result of this, the Pauli component and Landau diamagnetism cancel each other. It has been found that χ
e
(
T
) varies in the intervals
T
<
T
* (
T
* ~ 50 K) and
T
> 150 K, which are attributed to an order–disorder transition below
T
* and a carriers-related contribution due to the Jahn–Teller structural instability of the boron frame work.
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A three-dimensional (
H
, φ, θ,
T
= 2 K) magnetic phase diagram has been constructed for the first time for the antiferromagnetic metal Er
11
B
12
with an amplitude-modulated magnetic structure ...exhibiting an electronic instability (dynamic charge stripes). The boundaries determining the shape of the main magnetic phases in the
H
–φ–θ space are reconstructed from measurements of the magnetoresistance. The role of dynamic charge stripes, which suppress the indirect Ruderman–Kittel–Kasuya–Yoshida exchange between the magnetic moments of the nearest Er
3+
ions, and of the single-ion anisotropy in the formation of a complicated multicomponent phase diagram of Er
11
B
12
is discussed.
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By measuring room temperature infrared (40–35000 cm
–1
) reflectivity of metallic LuB12 single crystals with different isotopic compositions (
nat
B,
10
B,
11
B), we find that to model the spectrum ...we had to introduce, additionally to Drude free-carrier component, a broad excitation with unusually large dielectric contribution (Δε = 8000 ± 4000), which is characterized by a non-Lorentzian lineshape. It is suggested that the origin of the excitation is connected with cooperative dynamics of Jahn–Teller active B
12
molecules producing quasilocal vibrations (rattling modes) of caged lutetium ions. The coupling of the Lu
3+
rattling motions with the charge carriers of conduction band is proposed to be the reason of strongly damped character of the excitation.
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The broad-band reflection spectra of YB
6
and YbB
6
hexaborides with Jahn–Teller instability of the boron cage have been measured at room temperature. An optical conductivity analysis has revealed, ...along with the Drude electronic components, heavily overdamped collective modes, which are notable in YB
6
for high dielectric contributions, Δε = 2000–5700. The fraction of nonequilibrium charge carriers in YB
6
, which is at the boundary of structural instability in the hexaboride family, reaches 85–90%, whereas this fraction in doped YbB
6
semiconductor is not higher than 25%. It has been shown that unlike the predictions of the topological Kondo insulator model, the surface “metallization” in Yb
2+
B
6
crystals can be explained by additional doping of a surface layer with Yb
3+
ions.
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The galvanomagnetic characteristics of SmB
6
single crystals are studied within the temperature range of 1.9‒3.6 K at different orientations of the crystal faces. As a result, the electrical ...resistivities of the surfaces corresponding to the (100), (110), (111), and (211) crystallographic planes are determined. It is shown that the effective parameters of charge carriers, which determine the surface conductivity in SmB
6
, depend both on the orientation of the surface and on the method of its processing. It is found that the etching of polished polar surfaces formed by (100) planes leads at 1.9 K to a decrease in the density and to an increase in the mobility of surface
n
-type charge carriers from 113/
a
2
and 1.12 cm
2
/(V s) to 0.76/
a
2
and 18 cm
2
/(V s), respectively (lattice parameter
a
≈ 4.134 Å). For etched nonpolar surfaces corresponding to the (110) and (111) planes, the maximum density of surface charge carriers (per unit area of the surface Brillouin zone) is found to increase by factors of 2.3 and 3.9, respectively. It is proposed to use this parameter as a simple criterion to identify the features of electron transport due to the nontrivial topology of the band structure of SmB
6
.
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18.
Antiferromagnetic Resonance in GdB6 Semeno, A. V.; Gil’manov, M. I.; Sluchanko, N. E. ...
JETP letters,
08/2018, Volume:
108, Issue:
4
Journal Article
Peer reviewed
The electron spin resonance has been measured for the first time both in the paramagnetic phase of the metallic GdB
6
antiferromagnet (
T
N
= 15.5K) and in the antiferromagnetic state (
T
<
T
N
). In ...the paramagnetic phase below
T
* ~ 70 K, the material is found to exhibit a pronounced increase in the resonance linewidth and a shift in the g-factor, which is proportional to the linewidth Δ
g
(
T
) ~ Δ
H
(
T
). Such behavior is not characteristic of antiferromagnetic metals and seems to be due to the effects related to displacements of Gd
3+
ions from the centrosymmetric positions in the boron cage. The transition to the antiferromagnetic phase is accompanied by an abrupt change in the position of resonance (from μ
0
H
0
≈ 1.9 T to μ
0
H
0
≈ 3.9 T at ν = 60 GHz), after which a smooth evolution of the spectrum occurs, resulting eventually in the formation of the spectrum consisting of four resonance lines. The magnetic field dependence of the frequency of the resonant modes ω
0
(
H
0
) obtained in the range of 28–69 GHz is well interpreted within the model of ESR in an antiferromagnet with the easy anisotropy axis ω/γ = (
H
0
2
+2
H
A
H
E
)
1/2
, where
H
E
is the exchange field and
H
A
is the anisotropy field. This provides an estimate for the anisotropy field,
H
A
≈ 800 Oe. This value can result from the dipole−dipole interaction related to the mutual displacement of Gd
3+
ions, which occurs at the antiferromagnetic transition.
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•Magnetic H-T and H-φ phase diagrams of ErB12 include a number of different AF states.•Angular MR and magnetization dependences are highly anisotropic at T < TN.•Dynamic charge stripes in RB12 play a ...key role in the formation of MR anisotropy.•Strong anisotropy in ErB12 is due to the destruction of the RKKY exchange interaction.
The nature of charge transport and magnetization anisotropy was investigated in the ErB12 antiferromagnetic metal with both cooperative Jahn-Teller distortions of the fcc crystal structure and electronic instability (dynamic charge stripes). A butterfly pattern of the H-φ magnetic phase diagram in the (1 1 0) plane was reconstructed, including a large number of different magnetic phases separated from each other by radial and circular boundaries. It is argued that fluctuations of electron density are responsible for the suppression of the indirect Ruderman-Kittel-Kasuya-Yoshida (RKKY) exchange between the nearest neighbored Er3+ ions located along the 〈110〉 directions producing the magnetic phase diversity in ErB12.
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Abstract
Electron spin resonance (ESR) in strongly correlated metals is an exciting phenomenon, as strong spin fluctuations in this class of materials broaden extremely the absorption line below the ...detection limit. In this respect, ESR observation in CeB
6
provides a unique chance to inspect Ce
3+
magnetic state in the antiferroquadrupole (AFQ) phase. We apply the original high frequency (60 GHz) experimental technique to extract the temperature and angular dependences of
g
-factor, line width and oscillating magnetization. Experimental data show unambiguously that the modern ESR theory in the AFQ phase considering the Γ
8
ground state of Ce
3+
ion completely fails to predict both the
g
-factor magnitude and its angular dependence. Alignment of the external magnetic field along 100 axis induces a strong (more than twofold) broadening of ESR line width with respect to the other crystallographic directions and results also in the anomalous temperature dependences of the
g
-factor and oscillating magnetization. In this experimental geometry the latter parameter surprisingly exceeds total static magnetization by 20% at
T
* ~ 2.5 K. We argue that the unusual physical picture of ESR in CeB
6
may be strongly affected by spin fluctuations and dynamic collective effects predominantly pronounced in 100 direction.
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