Semiclassical magnetization dynamics in presence of magnetic fluctuations (including the quantum ones) is derived for a strongly correlated electronic system in the region of the linear magnetic ...response. Landau–Lifshitz (LL) and Gilbert (G) type equations are obtained with the effective parameters depending on the type of magnetic fluctuations and their magnitude and applied to evaluation of electron paramagnetic resonance (EPR) problem in Faraday geometry. It is shown that in the studied systems LL and G equations may not be equivalent except the case of weak relaxation, where consistent Landau–Lifshitz–Gilbert (CLLG) equation may be considered. Whereas G equation is affected by quantum fluctuations solely, the LL and CLLG equations may be renormalized by magnetic fluctuations of any nature. In contrast to G equation, the LL and CLLG magnetization dynamics may be characterized by the anisotropic relaxation term caused by anisotropic magnetic fluctuations. A consequence of anisotropic relaxation is the unusual polarization effect consisting in strong dependence of the EPR line magnitude on orientation of vector
h
of the oscillating magnetic field with respect to the crystal structure, so that EPR may be suppressed for some directions of
h
. In the case of dominating quantum fluctuations, the LL and CLLG equations may lead to a universal relation between fluctuation induced contributions to the EPR line width Δ
W
and g-factor Δ
g
in the form
Δ
W
/
Δ
g
=
a
0
k
B
T
/
μ
B
, where
a
0
is a numerical coefficient of the order of unity and independent of the quantum fluctuation magnitude. The applicability of the proposed semiclassical magnetization dynamics models to the EPR in spin nematic phases and detection by EPR method of a new group of magnetic phenomena – spin fluctuation transitions is discussed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Modern technique of electron spin resonance (ESR) measurements and data analysis in strongly correlated metals, which allows finding the full set of spectroscopic parameters including oscillating ...magnetization, relaxation parameter (line width), and hyromagnetic ratio (
g
-factor), is described. Application of the considered method is illustrated by such examples as metallic systems CeB
6
, Mn
1−
x
Fe
x
Si, GdB
6
, Ho
x
Lu
1−
x
B
12
, and metallic surface of topological Kondo insulator SmB
6
. It is shown that ESR in strongly correlated metals provides a unique tool for studying short-range correlations at the nanoscale of a spin polaron type, electron nematic effects, and spin fluctuation transitions. Application of ESR technique opens new opportunities for observation of quantum critical points, including hidden ones. In many cases, it is just ESR, which either indicates the necessity for clarification or deep revision of the prevailing paradigm, or constitutes the basis for a new concept of magnetic properties of various strongly correlated metals.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The experimental data on low-temperature (
T
< 40 K) neutron scattering and electron paramagnetic resonance for a helical magnet manganese monosilicide (MnSi) are analyzed. It is established that the ...smooth evolution of the parameters of spin fluctuations considered both in the conventional theory of magnetic phase transitions and in its generalization to the case of helical magnets is disturbed by the presence of spin-fluctuation transitions (SFTs) in which the amplitude of spin fluctuations and their correlation radius change sharply. In a zero magnetic field, the transition at the temperature
T
c
= 29 K, which is usually interpreted as the transition to a helical magnetically ordered phase, is preceded by two spin-fluctuation transitions with
T
1
= 32 K and
T
2
= 30.5 K. In a magnetic field of
B
~ 2 T at a temperature of 29 K coinciding with
T
c
, another spin-fluctuation transition with the parameters characteristic for the SFT inside the magnetically ordered phase is discovered. It is shown that, as the temperature decreases, MnSi at
T
=
T
1
undergoes the SFT with the appearance of helical fluctuations, while the appearance of a helical phase (
B
= 0) or a spin-polarized phase (
B
= 2 T) occurs at
T
=
T
2
and is accompanied by a spin-fluctuation transition.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The Landau–Lifshitz equation modified by quantum fluctuations of the magnetic moment is proposed, on the basis of which several new effects in electron paramagnetic resonance in strongly correlated ...electronic systems are predicted, including an increase in the integral intensity and the appearance of universal relations connecting the contribution to the linewidth, the shift of the resonance field, and the integrated intensity. It is expected that the magnitude of the quantum corrections will depend on a single dimensionless parameter
, where Δ
M
z
and
M
0
are the amplitude of fluctuations and the average value of the magnetic moment per magnetic ion, respectively.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•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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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Randomness and frustration are believed to be two crucial criteria for the formation of spin glass state. However, the spin freezing occurs in some well-ordered crystals below the related ...temperature
T
f
due to the instability of each spin state, which induces the variation of either magnetic moment value or exchange energy. Here we explore the new mechanism of the in-site originated disorder in antiferromagnets Gd
0.73
La
0.27
B
6
and GdB
6
, which is caused by the random mutual shifts of Gd
3+
spins from the centrally symmetrical positions in the regular cubic lattice. The universal scaling of ESR linewidth temperature dependencies to the power law
ΔH
(
T
) ~ ((
T
−
T
D
)
/T
D
)
α
with
α
= − 1.1 ± 0.05 in the paramagnetic phase of both compounds demonstrates the identity of the origin of magnetic randomness. In Gd
0.73
La
0.27
B
6
the resulting random spin configurations freeze at
T
f
≈ 10.5 K where the maximum of magnetization is observed. Below
T
f
the splitting of ZFC and FC magnetization curves takes place as well as the magnetic state depends on the antecedent sample history. In the case of GdB
6
the coherent displacement of Gd ions compete with these random shifts forming an antiferromagnetic (AFM) phase at
T
N
= 15.5 K, which prevails over the spin freezing at
T
f
≈ 13 K, expected from the ESR data. The observation of the hysteresis of the ESR spectrum in the AFM phase suggests that its properties may be determined by the competition of two types of AFM orders, which results in formation of stable magnetic domains with nonequivalent positions of AFM Gd pairs at
T
< 10 K.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A manganese monosilicide (MnSi) single crystal has been studied by the high-frequency (60 GHz) electron paramagnetic resonance method. The most currently detailed temperature dependences of the ...linewidth and
g
-factor have been obtained in the temperature range of 2–40 K. They indicate that a spin fluctuation transition occurs in the spin-polarized phase of МnSi, formed by magnetic polarons in a magnetic field of
B
~ 2 T at
K. This transition corresponds to change in the regime of magnetic fluctuations at a temperature much lower than the transition temperature
T
c
~ 30 K from the paramagnetic phase existing at
T
>
T
c
to the magnetically ordered phase occurring at
T
<
T
c
. This result extends the region of applicability of the concept of spin fluctuation transitions, which were previously considered only for magnetic states without long-range magnetic order. A model for the description of the electron paramagnetic resonance parameters in the system of magnetic polarons has been discussed.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Accurate low temperature charge transport measurements in combination with high-precision x-ray diffraction experiments have allowed detection of the symmetry lowering in the single domain ...Tm0.19Yb0.81B12 crystals that belong to the family of dodecaborides with metal-insulator transition. Based on the fine structure analysis we discover the formation of dynamic charge stripes within the semiconducting matrix of Tm0.19Yb0.81B12. The charge dynamics in these conducting nano-size channels is characterized by broad-band optical spectroscopy that allowed estimating the frequency (~2.4 × 1011 Hz) of quantum motion of the charge carriers. It is suggested that cooperative Jahn-Teller effect in the boron sublattice is a cause of the large-amplitude rattling modes of the Tm and Yb ions responsible for the 'modulation' of the conduction band along one of the directions through the variation of 5d-2p hybridization of electron states.
A simple semi-classical model of magnetization dynamics based on Landau-Lifshits equation of motion with anisotropic effective g-tensor and anisotropic spin relaxation is proposed and applied to the ...case of electron paramagnetic resonance (EPR). In the Faraday geometry, the model predicts polarization effect consisting in strong dependence of the EPR line shape and magnitude on orientation of vector
h
of oscillating magnetization with respect to the crystal structure, so that EPR may be suppressed for some directions of
h
. The EPR with anisotropic parameters possesses specific magnetic oscillations, which are different from standard circular rotation of the magnetization vector around the direction of external magnetic field. In general case, the trajectory of the magnetization vector end is either elongated quasi-ellipse, the position of the main axis of which depends on the magnitude of the external magnetic field, or magnetic oscillations may acquire almost linear character. The model is successfully applied for the quantitative accounting of the polarization effect for EPR mode observed in CuGeO
3
doped with 2% of Co impurity, which remained unexplained for more than 15 years.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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