Showing 1–3 of 3 results for author: Olmos, R

Pressure-induced magnetic properties of quasi-2D Cr2Si2Te6 and Mn3Si2Te6

Authors: Rubyann Olmos, Po-Hao Chang, Prakash Mishra, Rajendra R. Zope, Tunna Baruah, Cedomir Petrovic, Yu Liu, Srinivasa R. Singamaneni

Abstract: Recently, the pressure has been used as external stimuli to induce structural and magnetic phase transitions in many layered quantum materials whose layers are linked by van der Waals forces. Such materials with weakly held layers allow relatively easy manipulation of the superexchange mechanism and lead to novel magnetic behavior. Using the hydrostatic pressure as a disorderless means to manipula… ▽ More Recently, the pressure has been used as external stimuli to induce structural and magnetic phase transitions in many layered quantum materials whose layers are linked by van der Waals forces. Such materials with weakly held layers allow relatively easy manipulation of the superexchange mechanism and lead to novel magnetic behavior. Using the hydrostatic pressure as a disorderless means to manipulate the interlayer coupling, we applied pressure on two quasi-2D sister compounds, namely, Cr2Si2Te6 (CST) and Mn3Si2Te6 (MST), up to ~1 GPa. Magnetic property measurements with the application of pressure revealed that the ferromagnetic transition temperature decreases in CST while the opposite trend occurs for the ferrimagnet MST. In MST, the magnetization decreases with the increase in the pressure, and such trend is not clearly noticed in CST, within the pressure range studied. Theoretical calculations showed the overall pressure effect on layer separation, bond angle, and exchange coupling, strongly influencing the change in subsequent magnetic characteristics. Exchange coupling in Mn3Si2Te6 is strongly frustrated and the first nearest neighbor interaction is the most dominant of the components with the strongest pressure dependence. Whereas, in Cr2Si2Te6, the exchange coupling parameters exhibit very little dependence on the pressure. This combined experimental and theoretical work has the potential to expand to other relevant quantum materials. △ Less

Submitted 6 February, 2023; originally announced February 2023.

Pressure dependent magnetic properties on bulk CrBr3 single crystals

Authors: Rubyann Olmos, Shamsul Alam, Po Hao Chang, Kinjal Gandha, Ikenna C. Nlebedim, Andrew Cole, Fazel Tafti, Rajendra Zope, Srinivasa R. Singamaneni

Abstract: The van der Waals class of materials offer an approach to two-dimensional magnetism as their spin fluctuations can be tuned upon exfoliation of layers. Moreover, it has recently been shown that spin-lattice coupling and long-range magnetic ordering can be modified with pressure in van der Waals materials. In this work, the magnetic properties of quasi two-dimensional CrBr3 are reported applying hy… ▽ More The van der Waals class of materials offer an approach to two-dimensional magnetism as their spin fluctuations can be tuned upon exfoliation of layers. Moreover, it has recently been shown that spin-lattice coupling and long-range magnetic ordering can be modified with pressure in van der Waals materials. In this work, the magnetic properties of quasi two-dimensional CrBr3 are reported applying hydrostatic pressure. The application of pressure (0 - 0.8 GPa) shows a 72 % decrease in saturation magnetization with small decrease in the Curie temperature from 33 to 29 K. Density functional theory calculations with pressure up to 1 GPa show a reduction in volume and interplanar distance as pressure increases. To further understand magnetic properties with applied pressure, the magnetocrystalline anisotropy energy (MAE) and exchange coupling parameter (J) are calculated. There is minimal decrease in MAE and the first nearest neighbor interaction (J1) (U = 2.7 eV and J = 0.7 eV), shows an increase in J1 with respect to pressure. Overall, CrBr3 displays ferromagnetic interlayer coupling and the calculated exchange coupling and MAE parameters match well with the observations from the experimental work. △ Less

Submitted 30 November, 2021; originally announced December 2021.

Critical phenomena of the layered ferrimagnet Mn3Si2Te6 following proton irradiation

Authors: Rubyann Olmos, Jose A. Delgado, Hector Iturriaga, Luis M. Martinez, Christian L. Saiz, L. Shao, Y. Liu, C. Petrovic, Srinivasa R. Singamaneni

Abstract: We examine the magnetic properties of the quasi 2D ferrimagnetic single crystal Mn3Si2Te6 (MST) through critical phenomena and magnetic entropy analysis in the easy axis (H || ab) as a function of proton irradiance. Employing a modified asymptotic analysis method, we find that upon proton irradiation the critical exponents do not fall into any particular universality class but lie close to mean fi… ▽ More We examine the magnetic properties of the quasi 2D ferrimagnetic single crystal Mn3Si2Te6 (MST) through critical phenomena and magnetic entropy analysis in the easy axis (H || ab) as a function of proton irradiance. Employing a modified asymptotic analysis method, we find that upon proton irradiation the critical exponents do not fall into any particular universality class but lie close to mean field critical exponents (γ = 1, \b{eta} = 0.5). The presence of long-range interactions can be safely assumed for the pristine and irradiated cases of MST examined in this work. Further analysis on the effective spatial dimensionality reveal that MST remains at d = 3 under proton irradiation transitioning from an n = 1 spin dimensionality to n = 2 and n=3 for 1 x 10^15 and 5 x 10^15 H+/cm^2, indicating an XY interaction and a Heisenberg interaction, respectively. The pair (spin-spin) correlation function reveals an increase in magnetic correlations at the proton irradiance of 5 x 10^15 H+/cm^2. In conjunction, the maximum change in magnetic entropy obtained from isothermal magnetization at 3 T is the largest for 5 x 10^15 H+/cm^2 with a value of 2.45 J/kgK at T = 73.66 K, in comparison to 1.60 J/kgK for pristine MST at T = 73 K. Magnetic entropy derived from zero-field heat capacity does not show large deviations across the proton irradiated samples. This suggests that the antiferromagnetic coupling between the Mn sites is stable even after proton irradiation. Such result implies that magnetization is enhanced through a strengthening of the super-exchange interaction between Mn atoms mediated through Te rather than a weakening of the AFM component. Overall, our study finds that the magnetic interactions are manipulated the greatest when MST is irradiated at 5 x 10^15 H+/cm^2. △ Less

Submitted 13 April, 2021; originally announced April 2021.