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Betancourth, D., V. F. Correa, J. I. Facio, Fernández J., V. Vildosola, R. Lora-Serrano, J. M. Cadogan, A. A. Aligia, P. S. Cornaglia, and García D.J. "Magnetostriction reveals orthorhombic distortion in tetragonal Gd compounds." Physical Review B 99 (2019): 134406.
Abstract: We report detailed thermal expansion and magnetostriction experiments on GdCoIn5 and GdRh(In1−xCdx )5
(x = 0 and 0.025) single-crystal samples that show a sudden change in the dilation at a field B for temperatures
below the Néel transition temperature TN . We present a first-principles model including crystal-field effects,
dipolar and exchange interactions, and the dependence of the latter with lattice distortions in order to fully
account for the magnetostriction and magnetic susceptibility data. The mean-field solution of the model shows
that a transition between metastable states occurs at the field B. It also indicates that two degenerate phases
should coexist at temperatures below TN , which may explain the lack of observation, in high-resolution
x-ray experiments, of an orthorhombic distortion at the Néel transition, even though the experimentally
determined magnetic structure breaks the tetragonal symmetry and the magnetoelastic coupling from our model
is significant. These conclusions could be extended to other tetragonal Gd-based compounds that present the
same phenomenology.
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Carreras Oropesa, W. G., S. Encina, P. Pedrazzini, V. F. Correa, J. G. Sereni, V. Vildosola, García D.J., and P. S. Cornaglia. "Minimal model for the magnetic phase diagram of CeTi1-xScxGe, GdFe1-xCoxSi, and related materials." Journal of Magnetism and Magnetic Materials 503 (2020): 166614.
Abstract: We present a theoretical analysis of the magnetic phase diagram of CeTi1-xScxGe and GdFe1-xCoxSi as a function
of the temperature and the Sc and Co concentration x, respectively. CeScGe and GdCoSi, as many other RTX
(R=rare earth, T=transition metal, X=p-block element) compounds, present a tetragonal crystal structure
where bilayers of R are separated by layers of T and X. While GdFeSi and CeTi0.75Sc0.25Ge are ferromagnetic,
CeScGe and GdCoSi order antiferromagnetically with the R 4f magnetic moments on the same bilayer aligned
ferromagnetically and magnetic moments in nearest neighbouring bilayers aligned antiferromagnetically. The
antiferromagnetic transition temperature TN decreases with decreasing concentration x in both compounds and
for low enough values of x the compounds show a ferromagnetic behavior. Based on these observations we
construct a simplified model Hamiltonian that we solve numerically for the specific heat and the magnetization.
We find a good qualitative agreement between the model and the experimental data. Our results show that the
main magnetic effect of the Sc→Ti and Co→Fe substitution in these compounds is consistent with a change in
the sign of the exchange coupling between magnetic moments in neighbouring bilayers. We expect a similar
phenomenology for other magnetic RTX compounds with the same type of crystal structure.
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Correa, V. F., A. G. Villagrán Asiares, D. Betancourth, S. Encina, P. Pedrazzini, P. S. Cornaglia, García D.J., J. G. Sereni, B. Maiorov, N. Caroca-Canales et al. "Strong magnetoelastic effect in CeCo1−xFexSi as Néel order is suppressed." Physical Review B 100 (2019): 184409.
Abstract: A very strong magnetoelastic effect in the CeCo1−xFexSi alloys is reported. The strength of the magnetostrictive
effect can be tuned upon changing x. The moderate low-temperature linear magnetostriction observed at low
Fe concentrations becomes very large (L
L (16T, 2K) = 3 × 10−3) around the critical concentration xc ≈ 0.23 at
which the long-range antiferromagnetic order vanishes. Upon increasing doping through the nonmagnetic region
(x > xc), the magnetostriction strength gradually weakens again. The interplay between magnetic order and the
Kondo screening appears to cause an enhanced valence susceptibility slightly changing the Ce ions valence,
ultimately triggering the large magnetostriction observed around the critical concentration. Previous studies
of the evolution of the lattice parameters with x as well as magnetization and x-ray absorption spectroscopy
measurements support this hypothesis.
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Facio, J. I., D. Betancourth, N. R. Cejas Bolecek, G. A. Jorge, P. Pedrazzini, V. F. Correa, P. S. Cornaglia, V. Vildosola, and García D.J. "Lattice specific heat for the RMIn5 (R=Gd, La,Y; M=Co, Rh) compounds: Non-magnetic contribution subtraction." Journal of Magnetism and Magnetic Materials 407 (2016): 406–4011.
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