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 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 intermediate HEB value in respect to Ca-and Sr-doped samples. In order to figure out the microscopic mechanisms responsible for this phenomena, 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 Co 2+ /Co 3+ and Mn 4+ /Mn 3+ are already present at the La2CoMnO6 parent compound, and that Ba 2+ /Ca 2+ /Sr 2+ partial substitution at La 3+ 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 indicate that the shift of the hysteresis curves for these samples is related to uncompensated antiferromagnetic coupling between Co and Mn. arXiv:1909.05287v1 [cond-mat.mtrl-sci]

In this work the physical properties of the intermetallic compound TbRhIn 5 were investigated by means of temperature-dependent magnetic susceptibility, electrical resistivity, heat-capacity, and resonant x-ray magnetic diffraction experiments. TbRhIn 5 is an intermetallic compound that orders antiferromagnetically at T N = 45.5 K, the highest ordering temperature among the existing RRhIn 5 ͑1-1-5, R = rare earth͒ materials, which in contrast to what is expected from a de Gennes scaling along the RRhIn 5 series. The x-ray resonant diffraction data have allowed us to solve the magnetic structure of TbRhIn 5 . Below T N , we found a commensurate antiferromagnetic structure with a propagation vector ͑1/2,0,1/2͒ and the Tb moments oriented along the c axis. Strong ͑over two orders of magnitude͒ dipolar enhancements of the magnetic Bragg peaks were observed at both Tb absorption edges L II and L III , indicating a fairly high polarization of the Tb 5d levels. Using a mean-field model including an isotropic first-neighbor exchange interaction ͑J R-R ͒ and the tetragonal crystalline electrical field ͑CEF͒, we evaluate the influence of the CEF effects in the physical properties of TbRhIn 5 . The results reported here seem to corroborate a general trend of CEF-driven effects on T N along the RRhIn 5 series.

We discuss the evolution of the magnetic properties and magnetic structures along the series of intermetallic compounds RmMIn3m+2 (R=Ce, Nd, Gd, Tb; M=Rh, Ir; and m=1,2). The m=1,2 are, respectively, the single layer and bilayer tetragonal derivatives of their cubic RIn3 relatives. Using a mean field model including an isotropic first-neighbors Ruderman-Kittel-Kasuya-Yoshida interaction (K) and the tetragonal crystalline electrical field (CEF), we demonstrated that, for realistic values of K and CEF parameters, one can qualitatively describe the direction of the ordered moments and the behavior of the ordering temperature for these series. The particular case, where the rare-earth ordered moments lie in the ab plane or are tilted from the c axis and TN can be reduced by tuning the CEF parameters, revealed an interesting kind of frustration that may be relevant to the physical properties of complex classes of materials such as the RmMIn3m+2 (M=Rh, Ir, and Co; m=1,2) heavy-fermion superconductors.

Resonant x-ray diffraction measurements on Gd 2 IrIn 8 reveal an antiferromagnetic structure below T N ϭ40.8 K with wave vector ϭ(1 2 ,0,0) and the Gd moments lying in the tetragonal ab plane, indicating partly frustrated exchange interactions. Strong ͑over three orders of magnitude͒ dipolar resonant enhancements of the magnetic reflections were observed at both Gd L II and L III edges, indicating a relatively high magnetic polarization of the Gd 5d levels. Three-dimensional magnetic fluctuations are evidenced below T N , while measurements taken slightly above T N are consistent with two coexisting length scales for the magnetic correlations. Implications of these results for the physics of Ce n M m In 3nϩ2m (M ϭCo, Rh, or Ir͒ heavy-fermion superconductors are discussed.

Electron spin resonance ͑ESR͒ experiments at different fields or frequencies ͑4.1Յ Յ 34.4 GHz͒ in the Kondo lattice ͑T K Ӎ 25 K͒ YbRh 2 Si 2 single-crystal compounds confirmed the observation of a single anisotropic Dysonian resonance with g Ќc Х 3.55 and no hyperfine components for 4.2Շ T Շ 20 K. However, our studies differently reveal that ͑i͒ the ESR spectra for H Ќc show strong-field-dependent spin-lattice relaxation, ͑ii͒ a weak-field and temperature-dependent effective g value, ͑iii͒ a dramatic suppression of the ESR intensity beyond 15% of Lu doping, and ͑iv͒ a strong sample and Lu-doping ͑Յ15%͒ dependence of the ESR data. These results suggest a different scenario where the ESR signal may be associated to a coupled Yb 3+ -conduction electron resonant collective mode with a strong bottleneck and dynamiclike behavior.

The magnetic structure and fluctuations of tetragonal GdRhIn 5 were studied by resonant x-ray diffraction at the Gd L II and L III edges, followed by a renormalization group analysis for this and other related Gd-based compounds, namely Gd 2 IrIn 8 and GdIn 3 . These compounds are spin-only analogs of the isostructural Ce-based heavy-fermion superconductors. The ground state of GdRhIn 5 shows a commensurate antiferromagnetic spin structure with propagation vector τ = (0, antiferromagnetic (AFM) interactions. While a large J 1 /J 2 ratio favors an antiparallel alignment along the three directions (the so-called G-AFM structure), a smaller ratio favors the magnetic structure of GdRhIn 5 (C-AFM). In particular, it is inferred that the heavy-fermion superconductor CeRhIn 5 is in a frontier between these two ground states, which may explain its non-collinear spiral magnetic structure. The critical behavior of GdRhIn 5 close to the paramagnetic transition at T N = 39 K was also studied in detail. A typical second-order transition with the ordered magnetization critical parameter β = 0.35 was experimentally found, and theoretically investigated by means of a renormalization group analysis. Although the Gd 4f 7 electrons define a half-filled, spherically symmetrical shell, leading to a nearly isotropic spin system, it is argued that a significant spin anisotropy must be claimed to understand the second order of the paramagnetic transition of GdRhIn 5 and the related compound Gd 2 IrIn 8 .

Pressure- and temperature-dependent heat capacity and electrical resistivity experiments on Sn- and La-doped CeRhIn5 are reported for two samples with specific concentrations, Ce(0.90)La(0.10)RhIn5 and CeRhIn(4.84)Sn(0.16), which present the same TN=2.8 K. The obtained P-T phase diagrams for doped CeRhIn5 compared to that for the pure compound show that Sn doping shifts the diagram to lower pressures while La doping does exactly the opposite, indicating that the important energy scale to define the pressure range for superconductivity in CeRhIn5 is the strength of the on-site Kondo coupling.

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