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    Experimental quantum thermodynamics with linear optics
    (2019) Zanin, Guilherme Luiz; Häffner, Thomas; Talarico, Marcello Antônio Alves; Duzzioni, Eduardo Inacio ; Ribeiro, Paulo Henrique Souto; Landi, Gabriel Teixeira; Céleri, Lucas Chibebe
    The study of non-equilibrium physics from the perspective of the quantum limits of thermodynamics and fluctuation relations can be experimentally addressed with linear optical systems. We discuss recent experimental investigations in this scenario and present new proposed schemes while discussing the potential advances they could bring to the field of quantum thermodynamics.
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    Enhancing the charging power of quantum batteries
    (2017) Campaioli, Francesco; Pollock, Felix A.; Binder, Felix C.; Céleri, Lucas Chibebe; Goold, John; Vinjanampathy, Sai; Modi, Kavan
    Can collective quantum effects make a difference in a meaningful thermodynamic operation? Focusing on energy storage and batteries, we demonstrate that quantum mechanics can lead to an enhancement in the amount of work deposited per unit time, i.e., the charging power, when N batteries are charged collectively. We first derive analytic upper bounds for the collective quantum advantage in charging power for two choices of constraints on the charging Hamiltonian. We then demonstrate that even in the absence of quantum entanglement this advantage can be extensive. For our main result, we provide an upper bound to the achievable quantum advantage when the interaction order is restricted; i.e., at most k batteries are interacting. This constitutes a fundamental limit on the advantage offered by quantum technologies over their classical counterparts.
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    Full thermalization of a photonic qubit
    (2020) Oliveira, André Gustavo de; Gomes, Rafael de Morais; Brasil, Vitor Cardoso Castro; Silva, Nara Rubiano da; Céleri, Lucas Chibebe; Ribeiro, Paulo Henrique Souto
    The generalized amplitude damping (GAD) quantum channel implements the interaction between a qubit and an environment with arbitrary temperature and arbitrary interaction time. Here, we implement a photonic version of the GAD for the case of infinite interaction time (full thermalization). We also show that this quantum channel works as a thermal bath with controlled temperature.
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    Remote preparation of single photon vortex thermal states
    (2020) Häffner, Thomas; Zanin, Guilherme Luiz; Gomes, Rafael de Morais; Céleri, Lucas Chibebe; Ribeiro, Paulo Henrique Souto
    Photon pairs produced in spontaneous parametric down-conversion are naturally entangled in their transverse spatial degrees of freedom including the orbital angular momentum. Pumping a nonlinear crystal with a zero-order Gaussian mode produces quantum correlated signal and idler photons with equal orbital angular momentum and opposite signs. Measurements performed on one of the photons prepares the state of the other remotely. We study the remote state preparation in this system from the perspective of its potential application to Quantum Thermodynamics.
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    Quantum Markov monogamy inequalities
    (2022) Capela, Matheus; Céleri, Lucas Chibebe; Araújo, Rafael Chaves Souto; Modi, Kavan
    Markovianity lies at the heart of communication problems. This in turn makes the information-theoretic characterization of Markov processes worthwhile. Data-processing inequalities are ubiquitous in this sense, assigning necessary conditions for all Markov processes. We address here the problem of the information-theoretic analysis of constraints on Markov processes in the quantum regime. We show the existence of a class of quantum data-processing inequalities called here quantum Markov monogamy inequalities. This class of necessary conditions on quantum Markov processes is inspired by its counterpart for classical Markov processes, thus providing a strong link between classical and quantum constraints on Markovianity. We go on to construct a family of multitime quantum Markov monogamy inequalities, based on the process tensor formalism and that exploits multitime correlations. We then show, by means of an explicit example, that the Markov monogamy inequalities can be stronger than the usual quantum data-processing inequalities.
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    Bounding generalized relative entropies: nonasymptotic quantum speed limits
    (2021) Pires, Diego Paiva; Modi, Kavan; Céleri, Lucas Chibebe
    Information theory has become an increasingly important research field to better understand quantum mechanics. Noteworthy, it covers both foundational and applied perspectives, also offering a common technical language to study a variety of research areas. Remarkably, one of the key information-theoretic quantities is given by the relative entropy, which quantifies how difficult is to tell apart two probability distributions, or even two quantum states. Such a quantity rests at the core of fields like metrology, quantum thermodynamics, quantum communication, and quantum information. Given this broadness of applications, it is desirable to understand how this quantity changes under a quantum process. By considering a general unitary channel, we establish a bound on the generalized relative entropies (Rényi and Tsallis) between the output and the input of the channel. As an application of our bounds, we derive a family of quantum speed limits based on relative entropies. Possible connections between this family with thermodynamics, quantum coherence, asymmetry, and single-shot information theory are briefly discussed.
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    Spin and localization of relativistic fermions and uncertainty relations
    (2016) Céleri, Lucas Chibebe; Kiosses, Vasilis; Terno, Daniel R.
    We discuss relations between several relativistic spin observables and derive a Lorentz-invariant characteristic of a reduced spin density matrix. A relativistic position operator that satisfies all the properties of its nonrelativistic analog does not exist. Instead we propose two causality-preserving positive operator-valued measures (POVMs) that are based on projections onto one-particle and antiparticle spaces, and on the normalized energy density. They predict identical expectation values for position. The variances differ by less than a quarter of the squared de Broglie wavelength and coincide in the nonrelativistic limit. Since the resulting statistical moment operators are not canonical conjugates of momentum, the Heisenberg uncertainty relations need not hold. Indeed, the energy density POVM leads to a lower uncertainty. We reformulate the standard equations of the spin dynamics by explicitly considering the charge-independent acceleration, allowing a consistent treatment of backreaction and inclusion of a weak gravitational field.
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    Work distribution in a photonic system
    (2016) Talarico, Marcello Antônio Alves; Monteiro, Paula Borges; Mattei, Eduardo Cerutti; Duzzioni, Eduardo Inacio; Ribeiro, Paulo Henrique Souto; Céleri, Lucas Chibebe
    We present a proposal of a setup to measure the work distribution of a process acting on a quantum system emulated by the transverse degrees of freedom of classical light. Hermite-Gaussian optical modes are used to represent the energy eigenstates of a quantum harmonic oscillator prepared in a thermal state. The Fourier transform of the work distribution, or the characteristic function, can be obtained by measuring the light intensity at the output of a properly designed interferometer. The usefulness of the approach is illustrated by calculating the work distribution for a unitary operation that displaces the linear momentum of the oscillator. Other types of processes and quantum systems can be implemented with the same scheme. We also show that the setup can be used to investigate the energy distribution for open dynamics described by completely positive maps. We discuss the feasibility of the experiment, which can be realized with simple linear optical components.
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    Kolmogorov-Sinai entropy and dissipation in driven classical Hamiltonian systems
    (2018) Capela, Matheus; Sanz, Mikel; Solano, Enrique; Céleri, Lucas Chibebe
    A central concept in the connection between physics and information theory is entropy, which represents the amount of information extracted from the system by the observer performing measurements in an experiment. Indeed, Jaynes' principle of maximum entropy allows to establish the connection between entropy in statistical mechanics and information entropy. In this sense, the dissipated energy in a classical Hamiltonian process, known as the thermodynamic entropy production, is connected to the relative entropy between the forward and backward probability densities. Recently, it was revealed that energetic inefficiency and model inefficiency, defined as the difference in mutual information that the system state shares with the future and past environmental variables, are equivalent concepts in Markovian processes. As a consequence, the question about a possible connection between model unpredictability and energetic inefficiency in the framework of classical physics emerges. Here, we address this question by connecting the concepts of random behavior of a classical Hamiltonian system, the Kolmogorov-Sinai entropy, with its energetic inefficiency, the dissipated work. This approach allows us to provide meaningful interpretations of information concepts in terms of thermodynamic quantities.
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    Spin-phase-space-entropy production
    (2018) Santos, Jader Pereira dos; Céleri, Lucas Chibebe; Brito, Frederico Borges de; Landi, Gabriel Teixeira; Paternostro, Mauro
    Quantifying the degree of irreversibility of an open system dynamics represents a problem of both fundamental and applied relevance. Even though a well-known framework exists for thermal baths, the results give diverging results in the limit of zero temperature and are also not readily extended to nonequilibrium reservoirs, such as dephasing baths. Aimed at filling this gap, in this paper we introduce a phase-space-entropy production framework for quantifying the irreversibility of spin systems undergoing Lindblad dynamics. The theory is based on the spin Husimi-Q function and its corresponding phase-space entropy, known as Wehrl entropy. Unlike the von Neumann entropy production rate, we show that in our framework, the Wehrl entropy production rate remains valid at any temperature and is also readily extended to arbitrary nonequilibrium baths. As an application, we discuss the irreversibility associated with the interaction of a two-level system with a single-photon pulse, a problem which cannot be treated using the conventional approach.
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    Quantum work for sudden quenches in Gaussian random Hamiltonians
    (2018) Cavalcante, Eric Gomes Arrais; Wisniacki, Diego A.; Céleri, Lucas Chibebe; Almeida, Norton Gomes de; Roncaglia, Augusto J.; Toscano, Fabricio
    In the context of nonequilibrium quantum thermodynamics, variables like work behave stochastically. A particular definition of the work probability density function (pdf) for coherent quantum processes allows the verification of the quantum version of the celebrated fluctuation theorems, due to Jarzynski and Crooks, that apply when the system is driven away from an initial equilibrium thermal state. Such a particular pdf depends basically on the details of the initial and final Hamiltonians, on the temperature of the initial thermal state, and on how some external parameter is changed during the coherent process. Using random matrix theory we derive a simple analytic expression that describes the general behavior of the work characteristic function G(u), associated with this particular work pdf for sudden quenches, valid for all the traditional Gaussian ensembles of Hamiltonians matrices. This formula well describes the general behavior of G(u) calculated from single draws of the initial and final Hamiltonians in all ranges of temperatures.
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    Experimental study of the generalized Jarzynski fluctuation relation using entangled photons
    (2020) Ribeiro, Paulo Henrique Souto; Häffner, Thomas; Zanin, Guilherme Luiz; Silva, Nara Rubiano da; Araújo, Renné Luiz Câmara Medeiros de; Silva, Willamys Cristiano Soares; Assis, R. J. de; Céleri, Lucas Chibebe; Forbes, Andrew
    Optical modes possessing orbital angular momentum constitute a very useful platform for experimental studies on the quantum limits of thermodynamics. Here, we present experimental results for entangled photon pairs subjected to thin turbulence simulated with spatial light modulators and interpret them in the context of the generalized Jarzynski's fluctuation relation. By holographic measurement of the orbital angular momentum, we obtain the work distribution produced by the turbulence for single- and double-sided turbulence channels. The use of Klyshko's advanced-wave picture allows us to interpret the experimental scheme as a two-way process in a fully quantum picture.
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    Two-point measurement of entropy production from the outcomes of a single experiment with correlated photon pairs
    (2022) Horacio Aguilar, Gabriel; Silva, Thais de Lima; Guimarães, Thiago Elbert; Piera, Rodrigo Sebastian; Céleri, Lucas Chibebe; Landi, Gabriel Teixeira
    Fluctuation theorems are one of the pillars of nonequilibrium thermodynamics. Broadly speaking, they concern the statistical distribution of quantities such as heat, work, or entropy production. Quantum experiments, however, usually can only assess these distributions indirectly, or reconstruct them a posteriori. In this Letter we report an experiment where the distribution of entropy production is obtained directly from the outcomes (clicks) of an optical experiment simulating the interaction between a two-level system and a thermal reservoir. The setup consists of entangled photon pairs, one of which is sent to an interferometer implementing a finite-temperature amplitude damping channel, and is designed so as to allow full access to the two-point measurement statistics of both system and reservoir. First, by measuring the entangled pair, we directly implement the two-point measurement scheme in the system, avoiding the destructive nature of photodetection. Second, each optical path of the interferometer is associated with a specific transition of the reservoir. Thus, by blocking all but one of the paths, we can measure the conditional entropy production, given a specific reservoir trajectory.
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    Experimental investigation of linear-optics-based quantum target detection
    (2019) Horacio Aguilar, Gabriel; Souza,  M. A. de; Gomes, Rafael de Morais; Thompson, Jayne; Gu, Mile; Céleri, Lucas Chibebe; Walborn, Stephen Patrick
    The development of new techniques to improve measurements is crucial for all sciences. By employing quantum systems as sensors to probe some physical property of interest allows the application of quantum resources, such as coherent superpositions and quantum correlations, to increase measurement precision. Here we experimentally investigate a scheme for quantum target detection based on linear optical measurement devices, when the object is immersed in unpolarized background light. By comparing the quantum (polarization-entangled photon pairs) and the classical (separable polarization states) strategies, we found that the quantum strategy provides us an improvement over the classical one in our experiment when the signal-to-noise ratio is greater than 1/40, or about 16 dB of noise. This is in constrast to quantum target detection considering nonlinear optical detection schemes, which have shown resilience to extreme amounts of noise. A theoretical model is developed which shows that, in this linear-optics context, the quantum strategy suffers from the contribution of multiple background photons. This effect does not appear in our classical scheme. By improving the two-photon detection electronics, it should be possible to achieve a polarization-based quantum advantage for a signal-to-noise ratio that is close to 1/400 for current technology.
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    Influence of spin glass-like magnetic relaxation on the zero-field-cooled exchange bias effect
    (2018) Bufaiçal, Leandro Felix de Sousa; Bittar, Eduardo Matzenbacher; Garcia, Flávio; Bufaiçal, Leandro Felix de Sousa
    The zero-field-cooled exchange bias (ZEB) effect is a remarkable phenomenon recently reported for some reentrant spin glass-like compounds. In this work, the time evolution of magnetization is thoroughly investigated for two ZEB materials in order to figure out the role played by the spin glass-like phase on such effect. La1.5Sr0.5CoMnO6 and La1.5Ca0.5CoMnO6 were chosen as representative samples of ZEB systems, since the former compound presents the largest ZEB reported so far, while the second has a much smaller effect, despite being structurally/chemically similar. Comprehensive magnetic measurements were carried on both samples, and the results are discussed in terms of the amount and time evolution of the spin glass-like phase under the influence of a varying field. We also propose a phenomenological model, based on the pinning of spin glass-like moments and on the dynamics of their magnetic relaxation, to explain the asymmetry observed in the hysteresis loops. The good agreement between the simulated and experimental results confirms our hypothesis that the spin glass-like phase is key to the ZEB effect.
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    Tuning the spontaneous exchange bias effect with Ba to Sr partial substitution in La1.5(Sr0.5−xBax)CoMnO
    (2020) Belluz, Marlon Boldrin; Silva, A. G.; Coutrim, Leandro Tolentino; Jesus, Jonathas Rafael de ; Oliveira, Calazans Barbosa Marques Macchiutti de; Bittar, Eduardo Matzenbacher; Bufaiçal, Leandro Felix de Sousa
    The spontaneous exchange bias (SEB) effect is a remarkable phenomenon recently observed in some reentrant spin-glass materials. Here, we investigate the SEB in La1.5(Sr0.5−xBax)CoMnO6 double-perovskites, a system with multifarious magnetic phases for which a notable increase in the exchange bias field is observed for intermediate Sr/Ba concentrations. The Ba to Sr substitution leads to the enhancement of the crystal lattice, which is accompanied by the increase in both the effective magnetic moment (μeff) and the antiferromagnetic (AFM) transition temperature that is observed below the ferromagnetic ordering. Such an increase is likely related to the increased fraction of Co3+ in the high spin configuration, leading to the enhancement of the Co3+–O–Mn4+ AFM phase and the reduction in the uncompensation of the AFM coupling between Co and Mn. The combined effect of the increased μeff and AFM phase plausibly explains the changes in the SEB effect.
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    Compensation temperatures and exchange bias in La1.5Ca0.5CoIrO6
    (2016) Coutrim, Leandro Tolentino; Bittar, Eduardo Matzenbacher; Stavale Junior, Fernando Loureiro; Garcia, Flávio; Saitovitch, Elisa Maria Baggio; Abbate, Miguel; Mossanek, Rodrigo José Ochekoski; Martins, H. P.; Tobia, D.; Pagliuso, Pascoal Jose Giglio; Bufaiçal, Leandro Felix de Sousa
    We report on the study of magnetic properties of the La1.5Ca0.5CoIrO6 double perovskite. Via ac magnetic susceptibility we have observed evidence of weak ferromagnetism and reentrant spin glass behavior on an antiferromagnetic matrix. Regarding the magnetic behavior as a function of temperature, we have found that the material displays up to three inversions of its magnetization, depending on the appropriate choice of the applied magnetic field. At low temperature, the material exhibits exchange bias effect when it is cooled in the presence of a magnetic field. Also, our results indicate that this effect may be observed even when the system is cooled at zero field. Supported by other measurements and also by electronic structure calculations, we discuss the magnetic reversals and spontaneous exchange bias effect in terms of magnetic phase separation and magnetic frustration of Ir4+ ions located between the antiferromagnetically coupled Co ions.
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    Physical properties of Sr2FeIrO6 and Sr1.2La0.8FeIrO6 double perovskites obtained by a new synthesis route
    (2016) Bufaiçal, Leandro Felix de Sousa; Coutrim, Leandro Tolentino; Santos, Tatiane Oliveira dos; Terashita, Hirotoshi; Jesus, Camilo Bruno Ramos de; Pagliuso, Pascoal Jose Giglio ; Bittar, Eduardo Matzenbacher
    Previous works on Sr2-xLaxFeIrO6 double perovskite (DP) series reported a possible ferromagnetic transition at T ~ 700 K for the x ¼ 0.8 concentration, for which was observed the presence of spurious Fe2O3 phase. In order to prevent the formation of this impurity phase and check if this high temperature magnetic transition is intrinsic of the material, different synthesis routes became necessary. In this work, polycrystalline samples of Sr2-xLaxFeIrO6 (x ¼ 0.0 and 0.8) have been synthesized by solid state reaction using a new heating treatment. The sample's properties were investigated by synchrotron x-ray powder diffraction (SXRD), transmission electron microscopy (TEM), magnetic susceptibility, specific heat and electrical resistivity, and compared with the previously reported results. The SXRD data revealed a structural transition induced by La to Sr substitution (I2/m4P21/n). Moreover, it was not detected the presence of Fe2O3 on the samples obtained by the new route, which might be related to the absence of high temperature magnetic ordering. The magnetometry results indicated the emergence of Ir4þ with La doping, being corroborated by specific heat measurements which suggest Fe3þ/Ir5þ and Fe3þ/Ir4þ configurations for x ¼ 0.0 and 0.8 compounds, respectively. Temperature dependent electrical resistivity measurements showed that Sr2þ to La3þ substitution leads to a decrease of electrical resistivity, possibly associated with the increase in the number of Ir valence electrons.
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    Effect of structural and magnetic disorder on the 3d−5d exchange interactions in La2−xCaxCoIrO6
    (2020) Bufaiçal, Leandro Felix de Sousa; Sadrollahi, Elaheh; Litterst, Fred Jochen; Silva, Danilo Rigitano Gomes; Granado, E.; Coutrim, Leandro Tolentino; Araújo, Eduardo B.; Fontes, M. B.; Saitovitch, Elisa Maria Baggio; Bittar, Eduardo Matzenbacher
    The delicate balance between spin-orbit coupling, Coulomb repulsion, and crystalline electric field interactions observed in Ir-based oxides is usually manifested as exotic magnetic behavior. Here we investigate the evolution of the exchange coupling between Co and Ir for partial La substitution by Ca in La2CoIrO6. A great advantage of the use of Ca2+ as a replacement for La3+ is the similarity of their ionic radii. Thus, the observed magnetic changes can more easily be associated with electronic variations. A thorough investigation of the structural, electronic, and magnetic properties of the La2−xCaxCoIrO6 system was carried out by means of synchrotron x-ray powder diffraction, muon spin rotation and relaxation (μSR), AC and DC magnetization, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism, Raman spectroscopy, electrical resistivity, and dielectric permittivity. Our XAS results show that up to 25% Ca substitution at the La site results in the emergence of Co3+, possibly in a high-spin state, while the introduction of a larger amount of Ca leads to an increase in the Ir valence. The competing magnetic interactions resulting from the mixed valences lead to the coexistence of a magnetically ordered and an emerging spin-glass (SG) state for the doped samples. Our μSR results indicate that for La2CoIrO6 a nearly constant fraction of a paramagnetic (PM) phase persists down to low temperatures, possibly related to the presence of a small amount of Ir3+ and to the antisite disorder at Co/Ir sites. For doped compounds the PM phase freezes below 30 K, but there is still some dynamics associated with the SG. The dielectric data obtained for the parent compound and the one with 25% Ca doping indicate a possible magnetodielectric effect, which is discussed in terms of the electron hopping between the transition-metal ions, the antisite disorder at Co/Ir sites, and the distorted crystalline structure.
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    Zero-field-cooled exchange bias effect in phase-segregated La2−xAxCoMnO6−δ (A=Ba,Ca,Sr;x=0,0.5)
    (2019) Coutrim, Leandro Tolentino; Silva, Danilo Rigitano Gomes; Oliveira, Calazans Barbosa Marques Macchiutti de; Mori, Thiago José de Almeida; Serrano, Raimundo Lora; Granado, E.; Sadrollahi, Elaheh; Litterst, Fred Jochen; Fontes, M. B.; Saitovitch, Elisa Maria Baggio; Bittar, Eduardo Matzenbacher; Bufaiçal, Leandro Felix de Sousa
    In the zero-field-cooled exchange bias (ZEB) effect, the unidirectional magnetic anisotropy is set at low temperatures even when the system is cooled in the absence of an external magnetic field. La1.5Sr0.5CoMnO6 stands out as presenting the largest ZEB reported so far, while for La1.5Ca0.5CoMnO6 the exchange bias field (HEB) is one order of magnitude smaller. Here we show that La1.5Ba0.5CoMnO6 also exhibits a pronounced shift of its magnetic hysteresis loop, with an intermediate HEB value with respect to Ca- and Sr-doped samples. To figure out the microscopic mechanisms responsible for this phenomenon, these compounds were investigated by means of synchrotron x-ray powder diffraction, Raman spectroscopy, muon spin rotation and relaxation, ac and dc magnetization, x-ray absorption spectroscopy (XAS), and x-ray magnetic circular dichroism (XMCD). The parent compound La2CoMnO6 was also studied for comparison as a reference of a non-ZEB material. Our results show that the Ba-, Ca-, and Sr-doped samples present a small amount of phase segregation, and that the ZEB effect is strongly correlated to the system's structure. We also observed that mixed valence states Co2+/Co3+ and Mn4+/Mn3+ are already present at the La2CoMnO6 parent compound, and that Ba2+/Ca2+/Sr2+ partial substitution at the La3+ site leads to a large increase of Co average valence, with a subtle augmentation of Mn formal valence. Estimates of the Co and Mn valences from the L-edge XAS indicate the presence of oxygen vacancies in all samples (0.05≤δ≤0.1). Our XMCD results show a great decrease of Co moment for the doped compounds, and they indicate that the shift of the hysteresis curves for these samples is related to uncompensated antiferromagnetic coupling between Co and Mn.