Pub Date : 2023-12-10DOI: 10.1134/s1063776123100060
M. A. Morozova, O. V. Matveev, D. V. Romanenko, S. A. Nikitov
Abstract
The influence of double (electrical and magnetic) nonlinearity on the Bragg resonances of the hybrid electromagnetic-spin waves in a multiferroic crystal has been theoretically and experimentally revealed. The multiferroic crystal consists of an yttrium iron garnet layer with a periodic system of grooves on the surface and a ferroelectric strontium–barium titanate layer. A dispersion relation for the hybrid waves is obtained, and the mechanism of formation of main and hybrid band gaps, namely, suppression bands, is revealed. It is shown that taking into account the magnetic nonlinearity leads to frequency rearrangement of both band gaps and taking into account the electrical nonlinearity leads to frequency rearrangement of only the hybrid band gap. In the general case, the effects of the electrical and magnetic nonlinearities on the hybrid band gap can be compensated.
{"title":"Bragg Resonances in a Multiferroic Double-Nonlinearity Crystal","authors":"M. A. Morozova, O. V. Matveev, D. V. Romanenko, S. A. Nikitov","doi":"10.1134/s1063776123100060","DOIUrl":"https://doi.org/10.1134/s1063776123100060","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The influence of double (electrical and magnetic) nonlinearity on the Bragg resonances of the hybrid electromagnetic-spin waves in a multiferroic crystal has been theoretically and experimentally revealed. The multiferroic crystal consists of an yttrium iron garnet layer with a periodic system of grooves on the surface and a ferroelectric strontium–barium titanate layer. A dispersion relation for the hybrid waves is obtained, and the mechanism of formation of main and hybrid band gaps, namely, suppression bands, is revealed. It is shown that taking into account the magnetic nonlinearity leads to frequency rearrangement of both band gaps and taking into account the electrical nonlinearity leads to frequency rearrangement of only the hybrid band gap. In the general case, the effects of the electrical and magnetic nonlinearities on the hybrid band gap can be compensated.</p>","PeriodicalId":629,"journal":{"name":"Journal of Experimental and Theoretical Physics","volume":"28 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138562143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-10DOI: 10.1134/s1063776123100138
V. V. Val’kov
Abstract
The effective the two-band Hamiltonian is obtained for iridium oxides with account for strong electron correlations (SEC) and the spin–orbit interaction. The intraatomic electron correlations in iridium ions induce the formation of Hubbard fermions (HF) filling the states in the valence band. Another consequence of SEC is associated with the emergence of the antiferromagnetic (AFM) exchange interaction between HF in accordance with the Anderson mechanism. As a result, a long-range antiferromagnetic order is established in the system, and in the conditions of band overlapping, the intersite Coulomb interaction induces a phase transition to the excitonic insulator (EI) state with a long-range AFM order. The system of integral self-consistent equations, the solution to which determines the excitonic order parameter components Δi,j(k), sublattice magnetization M, Hubbard fermion concentration nd, and chemical potential μ, is obtained using the atomic representation, the method of two-time temperature Green’s functions, and the Zwanzig–Mori projection technique. The symmetry classification of AFM EI phases is performed, and it is shown that in the nearest neighbor approximation, state Δi,j(k) with the s-type symmetry corresponds to the ground state, while the phases with the d- and p-symmetries are metastable.
摘要 在考虑强电子关联（SEC）和自旋轨道相互作用的情况下，得到了铱氧化物的有效两带哈密顿。铱离子中的原子内电子相关诱导形成了填充价带状态的哈伯德费米子（HF）。根据安德森机制，SEC 的另一个结果与 HF 之间出现的反铁磁（AFM）交换相互作用有关。因此，在系统中建立了长程反铁磁阶，在能带重叠的条件下，场内库仑相互作用诱导了向具有长程 AFM 阶的激子绝缘体（EI）态的相变。利用原子表示法、双时间温度格林函数法和 Zwanzig-Mori 投影技术，得到了积分自洽方程组，该方程组的解决定了激子阶参数分量 Δi、j(k)、亚晶格磁化 M、哈伯德费米子浓度 nd 和化学势 μ。对 AFM EI 相进行了对称性分类，结果表明，在近邻近似中，具有 s 型对称性的态Δi, j(k)对应于基态，而具有 d 型和 p 型对称性的相则是可转移的。
{"title":"Antiferromagnetic Excitonic Insulator","authors":"V. V. Val’kov","doi":"10.1134/s1063776123100138","DOIUrl":"https://doi.org/10.1134/s1063776123100138","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The effective the two-band Hamiltonian is obtained for iridium oxides with account for strong electron correlations (SEC) and the spin–orbit interaction. The intraatomic electron correlations in iridium ions induce the formation of Hubbard fermions (HF) filling the states in the valence band. Another consequence of SEC is associated with the emergence of the antiferromagnetic (AFM) exchange interaction between HF in accordance with the Anderson mechanism. As a result, a long-range antiferromagnetic order is established in the system, and in the conditions of band overlapping, the intersite Coulomb interaction induces a phase transition to the excitonic insulator (EI) state with a long-range AFM order. The system of integral self-consistent equations, the solution to which determines the excitonic order parameter components Δ<sub><i>i</i>,</sub> <sub><i>j</i></sub>(<i>k</i>), sublattice magnetization <i>M</i>, Hubbard fermion concentration <i>n</i><sub><i>d</i></sub>, and chemical potential μ, is obtained using the atomic representation, the method of two-time temperature Green’s functions, and the Zwanzig–Mori projection technique. The symmetry classification of AFM EI phases is performed, and it is shown that in the nearest neighbor approximation, state Δ<sub><i>i</i>,</sub> <sub><i>j</i></sub>(<i>k</i>) with the <i>s</i>-type symmetry corresponds to the ground state, while the phases with the <i>d</i>- and <i>p</i>-symmetries are metastable.</p>","PeriodicalId":629,"journal":{"name":"Journal of Experimental and Theoretical Physics","volume":"208 1 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138569798","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-10DOI: 10.1134/s1063776123100011
K. N. Boldyrev, M. Diab, I. A. Gudim, M. N. Popova
Abstract
The high-resolution optical absorption spectra of NdFe3(BO3)4 single crystals have been recorded at temperatures from 4 to 40 K in the IR range of f–f transitions in a Nd3+ ion. Light linearly polarized at different angles to the C2 axes in the basal plane has been passed along the trigonal C3 axis. Below the temperature of magnetic moment ordering into a collinear antiferromagnetic structure (TN ≈ 30 K), dichroism, that is, the absorption versus polarization dependence, arises. The temperature and angular dependences of dichroism indicate that the magnetic moments of iron are directed along the C2 axes up to about 17 K, the number of domains with variously directed C2 axes being different. The mechanism of linear dichroism has been discussed. Below 17 K, a smooth transition to the helicoidal magnetic phase has been observed, with the collinear phase coexisting with the helicoidal one. Data presented in this article contradict the earlier concept of magnetic moments fluctuating in the low-temperature phase near the C2 axis within the ±10° interval.
{"title":"Optical Linear Dichroism in the ab-Plane of NdFe3(BO3)4 Ferroborate","authors":"K. N. Boldyrev, M. Diab, I. A. Gudim, M. N. Popova","doi":"10.1134/s1063776123100011","DOIUrl":"https://doi.org/10.1134/s1063776123100011","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The high-resolution optical absorption spectra of NdFe<sub>3</sub>(BO<sub>3</sub>)<sub>4</sub> single crystals have been recorded at temperatures from 4 to 40 K in the IR range of <i>f</i>–<i>f</i> transitions in a Nd<sup>3+</sup> ion. Light linearly polarized at different angles to the <i>C</i><sub>2</sub> axes in the basal plane has been passed along the trigonal <i>C</i><sub>3</sub> axis. Below the temperature of magnetic moment ordering into a collinear antiferromagnetic structure (<i>T</i><sub>N</sub> ≈ 30 K), dichroism, that is, the absorption versus polarization dependence, arises. The temperature and angular dependences of dichroism indicate that the magnetic moments of iron are directed along the <i>C</i><sub>2</sub> axes up to about 17 K, the number of domains with variously directed <i>C</i><sub>2</sub> axes being different. The mechanism of linear dichroism has been discussed. Below 17 K, a smooth transition to the helicoidal magnetic phase has been observed, with the collinear phase coexisting with the helicoidal one. Data presented in this article contradict the earlier concept of magnetic moments fluctuating in the low-temperature phase near the <i>C</i><sub>2</sub> axis within the ±10° interval.</p>","PeriodicalId":629,"journal":{"name":"Journal of Experimental and Theoretical Physics","volume":"35 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138569413","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-10DOI: 10.1134/s1063776123100096
D. V. Popov, R. G. Batulin, M. A. Cherosov, I. V. Yatsyk, T. I. Chupakhina, Yu. A. Deeva, I. I. Fazlizhanov, R. M. Eremina, T. Maiti
Abstract
A double perovskite Sr2CrNbO6 powder compound was studied by using X-ray diffraction, AC and DC magnetization, and ESR measurements. Two transitions in antiferromagnetically ordered regimes were observed through magnetization measurements at T = 5 and 2 K and were confirmed by the linear dependence of the magnetization on the applied magnetic field at these temperatures, approximations of the temperature dependence of the ESR linewidth, and AC magnetization. The zero field cooling curve was approximated by Bonner–Fisher law for quasi one dimensional chain with the exchange integral J/kB = 1 K between chromium spins. An approximation of linear part of magnetic susceptibility temperature dependence was performed using Curie–Weiss law. To describe the obtained effective moment μeff = 3.577μB, the presence Cr3+ and Cr4+ ions is estimated at a respective ratio about 0.8 : 0.2.
{"title":"Magnetic Properties of the Double Perovskite Sr2CrNbO6","authors":"D. V. Popov, R. G. Batulin, M. A. Cherosov, I. V. Yatsyk, T. I. Chupakhina, Yu. A. Deeva, I. I. Fazlizhanov, R. M. Eremina, T. Maiti","doi":"10.1134/s1063776123100096","DOIUrl":"https://doi.org/10.1134/s1063776123100096","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>A double perovskite Sr<sub>2</sub>CrNbO<sub>6</sub> powder compound was studied by using X-ray diffraction, AC and DC magnetization, and ESR measurements. Two transitions in antiferromagnetically ordered regimes were observed through magnetization measurements at <i>T</i> = 5 and 2 K and were confirmed by the linear dependence of the magnetization on the applied magnetic field at these temperatures, approximations of the temperature dependence of the ESR linewidth, and AC magnetization. The zero field cooling curve was approximated by Bonner–Fisher law for quasi one dimensional chain with the exchange integral <i>J</i>/<i>k</i><sub>B</sub> = 1 K between chromium spins. An approximation of linear part of magnetic susceptibility temperature dependence was performed using Curie–Weiss law. To describe the obtained effective moment μ<sub>eff</sub> = 3.577μ<sub>B</sub>, the presence Cr<sup>3+</sup> and Cr<sup>4+</sup> ions is estimated at a respective ratio about 0.8 : 0.2.</p>","PeriodicalId":629,"journal":{"name":"Journal of Experimental and Theoretical Physics","volume":"85 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138569540","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-10DOI: 10.1134/s1063776123100199
{"title":"95th Anniversary of the Birthday of Ludmila Prozorova","authors":"","doi":"10.1134/s1063776123100199","DOIUrl":"https://doi.org/10.1134/s1063776123100199","url":null,"abstract":"","PeriodicalId":629,"journal":{"name":"Journal of Experimental and Theoretical Physics","volume":"69 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138569344","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-10DOI: 10.1134/s1063776123100175
Yu. S. Gokhfeld, N. V. Kazak, N. A. Bel’skaya, M. S. Molokeev, I. A. Gudim, O. A. Kondratiev, E. V. Eremin, Yu. V. Knyazev, D. A. Velikanov, S. G. Ovchinnikov
Abstract
Cu2FeBO5 ludwigite single crystals have been grown from a solution–melt by spontaneous crystallization. Using the X-ray diffraction method, the crystal structure has been resolved in detail. Cations in sites M2, M3, and M4 have turned out to be structurally disordered. It has been found that oxygen atoms are disordered in one of five nonequivalent sites (O4). As can be seen from Mössbauer spectroscopy data, Fe3+ ions occupy four nonequivalent sites with different distortions of coordination octahedra. In the temperature range 40 K ≤ T ≤ 300 K, the spectra represent a superposition of quadrupole doublets. Static susceptibility measurements have revealed two magnetic features at T1 = 35 K and T2 = 20 K and spin-glass effects. Specific heat measurements in the interval 4–300 K have not discovered magnetic-transition-related anomalies.
摘要 通过自发结晶，从溶液熔体中生长出了 Cu2FeBO5 绿泥石单晶。利用 X 射线衍射方法详细解析了晶体结构。结果表明，位于 M2、M3 和 M4 位点的阳离子在结构上是无序的。研究还发现，氧原子在五个非等价位点（O4）中的一个位点处于无序状态。从莫斯鲍尔光谱数据可以看出，Fe3+ 离子占据了四个非等价位点，配位八面体的畸变程度各不相同。在 40 K ≤ T ≤ 300 K 的温度范围内，光谱代表了四极双重的叠加。静态磁感应强度测量显示了在 T1 = 35 K 和 T2 = 20 K 时的两个磁性特征以及自旋玻璃效应。4-300 K区间的比热测量没有发现与磁转变有关的异常现象。
{"title":"Structural Disorder, Specific Heat, and Magnetic Transitions in Cu2FeBO5","authors":"Yu. S. Gokhfeld, N. V. Kazak, N. A. Bel’skaya, M. S. Molokeev, I. A. Gudim, O. A. Kondratiev, E. V. Eremin, Yu. V. Knyazev, D. A. Velikanov, S. G. Ovchinnikov","doi":"10.1134/s1063776123100175","DOIUrl":"https://doi.org/10.1134/s1063776123100175","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>Cu<sub>2</sub>FeBO<sub>5</sub> ludwigite single crystals have been grown from a solution–melt by spontaneous crystallization. Using the X-ray diffraction method, the crystal structure has been resolved in detail. Cations in sites M2, M3, and M4 have turned out to be structurally disordered. It has been found that oxygen atoms are disordered in one of five nonequivalent sites (O4). As can be seen from Mössbauer spectroscopy data, Fe<sup>3+</sup> ions occupy four nonequivalent sites with different distortions of coordination octahedra. In the temperature range 40 K ≤ <i>T</i> ≤ 300 K, the spectra represent a superposition of quadrupole doublets. Static susceptibility measurements have revealed two magnetic features at <i>T</i><sub>1</sub> = 35 K and <i>T</i><sub>2</sub> = 20 K and spin-glass effects. Specific heat measurements in the interval 4–300 K have not discovered magnetic-transition-related anomalies.</p>","PeriodicalId":629,"journal":{"name":"Journal of Experimental and Theoretical Physics","volume":"27 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138569539","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-10DOI: 10.1134/s1063776123100163
V. N. Glazkov, Yu. V. Krasnikova, I. K. Rodygina, M. Hemmida, M. Hirrle, H.-A. Krug von Nidda, T. Masuda
Abstract
We report results of a multi-frequency (0.8–60 GHz) electron spin resonance study of the spin dynamics in the quasi-2D square lattice antiferromagnet Ba2MnGe2O7 both in antiferromagnetically ordered and paramagnetic phases. We directly observe two zero-field gaps in the excitation spectrum of the ordered phase, the larger one being due to easy-plane anisotropy, and the smaller one indicates the presence of fourth-order in-plane anisotropy probably related to the multiferroic properties of this compound. We observe effects of hyperfine interaction on the electron spin resonance spectra in the antiferromagnetically ordered state, which turns out to be comparable with in-plane anisotropy. The hyperfine field strength is found from the observed low-temperature electron spin resonance data. The spin dynamics of the paramagnetic phase is characterized by strong broadening of the ESR absorption line, which can be ascribed to the vortex dynamics of a 2D magnet.
{"title":"Magnetic Resonance in the Quasi-2D Square Lattice Easy-Plane Antiferromagnet Ba2MnGe2O7","authors":"V. N. Glazkov, Yu. V. Krasnikova, I. K. Rodygina, M. Hemmida, M. Hirrle, H.-A. Krug von Nidda, T. Masuda","doi":"10.1134/s1063776123100163","DOIUrl":"https://doi.org/10.1134/s1063776123100163","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>We report results of a multi-frequency (0.8–60 GHz) electron spin resonance study of the spin dynamics in the quasi-2D square lattice antiferromagnet Ba<sub>2</sub>MnGe<sub>2</sub>O<sub>7</sub> both in antiferromagnetically ordered and paramagnetic phases. We directly observe two zero-field gaps in the excitation spectrum of the ordered phase, the larger one being due to easy-plane anisotropy, and the smaller one indicates the presence of fourth-order in-plane anisotropy probably related to the multiferroic properties of this compound. We observe effects of hyperfine interaction on the electron spin resonance spectra in the antiferromagnetically ordered state, which turns out to be comparable with in-plane anisotropy. The hyperfine field strength is found from the observed low-temperature electron spin resonance data. The spin dynamics of the paramagnetic phase is characterized by strong broadening of the ESR absorption line, which can be ascribed to the vortex dynamics of a 2D magnet.</p>","PeriodicalId":629,"journal":{"name":"Journal of Experimental and Theoretical Physics","volume":"37 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138569541","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-10DOI: 10.1134/s1063776123100084
V. A. Polyakov, N. B. Perkins
Abstract
We consider the effect of vacancies on the low-energy excitation spectrum of a quantum spin liquid realized in the exactly solvable Yao–Lee model [H. Yao and D.-H. Lee, Phys. Rev. Lett. 107, 087205 (2011)]. Physically, vacancies can appear for different reasons (e.g., because of zero magnetic moments on the lattice, or the presence of nonmagnetic impurities, or a random reduction of local bonds of magnetic moments with the remaining lattice). It is shown numerically that the finite density of random vacancies in this model leads to the accumulation of states near zero energy, which can be detected from the change of the behavior of heat capacity at low temperatures. Moreover, it is shown that the low-energy modes are localized more strongly than remaining eigenmodes. This effect is illustrated using the inverse participation ratio (IPR). In the case of time reversal symmetry breaking (e.g., due to the presence of a magnetic field), a gap is opened in the fermion spectrum of the model, and vacancy-induced localized states appear. The energies of these states depend on the structure of the interactions responsible for the time inversion symmetry breaking.
摘要 我们考虑了空位对量子自旋液体低能激发光谱的影响，该量子自旋液体是在可精确求解的姚李模型中实现的 [H. Yao and D.-H. Lee, Phys. Rev. Lett.物理上，空位的出现可能有不同的原因（例如，由于晶格上的磁矩为零、或存在非磁性杂质、或磁矩与剩余晶格的局部结合随机减少）。数值结果表明，该模型中随机空位的有限密度会导致零能量附近状态的积累，这可以从低温下热容量行为的变化中检测到。此外，研究还表明低能模式的局部化比其余特征模式更强。这种效应用反参与比（IPR）来说明。在时间反转对称性破缺的情况下（例如，由于磁场的存在），模型的费米子谱中会出现一个缺口，并出现空位诱导的局域态。这些态的能量取决于导致时间反转对称性破缺的相互作用的结构。
{"title":"Role of Vacancies in the Yao–Lee Model","authors":"V. A. Polyakov, N. B. Perkins","doi":"10.1134/s1063776123100084","DOIUrl":"https://doi.org/10.1134/s1063776123100084","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>We consider the effect of vacancies on the low-energy excitation spectrum of a quantum spin liquid realized in the exactly solvable Yao–Lee model [H. Yao and D.-H. Lee, Phys. Rev. Lett. <b>107</b>, 087205 (2011)]. Physically, vacancies can appear for different reasons (e.g., because of zero magnetic moments on the lattice, or the presence of nonmagnetic impurities, or a random reduction of local bonds of magnetic moments with the remaining lattice). It is shown numerically that the finite density of random vacancies in this model leads to the accumulation of states near zero energy, which can be detected from the change of the behavior of heat capacity at low temperatures. Moreover, it is shown that the low-energy modes are localized more strongly than remaining eigenmodes. This effect is illustrated using the inverse participation ratio (IPR). In the case of time reversal symmetry breaking (e.g., due to the presence of a magnetic field), a gap is opened in the fermion spectrum of the model, and vacancy-induced localized states appear. The energies of these states depend on the structure of the interactions responsible for the time inversion symmetry breaking.</p>","PeriodicalId":629,"journal":{"name":"Journal of Experimental and Theoretical Physics","volume":"107 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138569634","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Spin-Flop Transition in Spiral Magnets","authors":"S. K. Gotovko, V. I. Marchenko","doi":"10.1134/s1063776123100047","DOIUrl":"https://doi.org/10.1134/s1063776123100047","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>It has been shown that at spin-flop transition in spiral magnets LiCuVO<sub>4</sub>, LiCu<sub>2</sub>O<sub>2</sub>, and CuCrO<sub>2</sub>, Goldstone mode looses its stability.</p>","PeriodicalId":629,"journal":{"name":"Journal of Experimental and Theoretical Physics","volume":"7 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138569351","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-10DOI: 10.1134/s1063776123100059
S. V. Grigoriev, L. A. Azarova, K. A. Pshenichnyi, O. I. Utesov
Abstract
Dispersion of spin waves in the amorphous ferromagnetic alloy Fe48Ni34P18 can be described within the model of a ferromagnet with random anisotropy: (epsilon )(q) = Aq2 + gμBH + δω(q), where δω(q) is an additional term linear in |q|. The method of small-angle scattering of polarized neutrons is used to prove the importance of the additional term δω(q) in dispersion. The measurements are carried out for different values of the external magnetic field H and neutron wavelength λ. The scattering map of neutrons represents a circle centered at the point q = 0. The stiffness A of spin waves is derived directly from the λ-dependence of the radius of this circle. The spin-wave stiffness A of the amorphous alloy weakly decreases from 140 to 110 meV Å2 as temperature increases from 50 to 300 K. The field dependence of the radius demonstrates the presence of an additional term δω(q) in the form of an energy gap that is almost independent of field and temperature. The value of the additional term is Δ = 0.015 ± 0.002 meV.
AbstractDispersion of spin waves in the amorphous ferromagnetic alloy Fe48Ni34P18 can be described within the model of a ferromagnet with random anisotropy：(epsilon )(q) = Aq2 + gμBH + δω(q)，其中 δω(q)是与|q|线性的附加项。利用极化中子的小角散射方法证明了附加项 δω(q) 在色散中的重要性。测量对外部磁场 H 和中子波长 λ 的不同值进行。中子散射图表示一个以 q = 0 点为中心的圆。随着温度从 50 K 上升到 300 K，非晶合金的自旋波刚度 A 从 140 meV Å2 微弱下降到 110 meV Å2。半径的磁场依赖性证明了能隙形式的附加项 δω(q)的存在，它几乎与磁场和温度无关。附加项的值Δ = 0.015 ± 0.002 meV。
{"title":"Dispersion Relation in Amorphous Ferromagnets","authors":"S. V. Grigoriev, L. A. Azarova, K. A. Pshenichnyi, O. I. Utesov","doi":"10.1134/s1063776123100059","DOIUrl":"https://doi.org/10.1134/s1063776123100059","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>Dispersion of spin waves in the amorphous ferromagnetic alloy Fe<sub>48</sub>Ni<sub>34</sub>P<sub>18</sub> can be described within the model of a ferromagnet with random anisotropy: <span>(epsilon )</span>(<i>q</i>) = <i>Aq</i><sup>2</sup> + <i>g</i>μ<sub>B</sub><i>H</i> + δω(<i>q</i>), where δω(<i>q</i>) is an additional term linear in |<i>q</i>|. The method of small-angle scattering of polarized neutrons is used to prove the importance of the additional term δω(<i>q</i>) in dispersion. The measurements are carried out for different values of the external magnetic field <i>H</i> and neutron wavelength λ. The scattering map of neutrons represents a circle centered at the point <i>q</i> = 0. The stiffness <i>A</i> of spin waves is derived directly from the λ-dependence of the radius of this circle. The spin-wave stiffness <i>A</i> of the amorphous alloy weakly decreases from 140 to 110 meV Å<sup>2</sup> as temperature increases from 50 to 300 K. The field dependence of the radius demonstrates the presence of an additional term δω(<i>q</i>) in the form of an energy gap that is almost independent of field and temperature. The value of the additional term is Δ = 0.015 ± 0.002 meV.</p>","PeriodicalId":629,"journal":{"name":"Journal of Experimental and Theoretical Physics","volume":"53 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2023-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138569475","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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