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Magnetic anisotropy, unusual hysteresis and putative "up-up-down" magnetic structure in EuTAl4Si2 (T = Rh and Ir).

Maurya A, Thamizhavel A, Dhar SK, Bonville P - Sci Rep (2015)

Bottom Line: Surprisingly, the magnetization does not return to origin when the field is reduced to zero in the return cycle, as expected in an antiferromagnet.Instead, a remnant magnetization 1/3 M0 is observed and the magnetic loop around the origin shows hysteresis.This suggests that the zero field magnetic structure has a ferromagnetic component, and we present a model with up to third neighbor exchange and dipolar interaction which reproduces the magnetization curves and hints to an "up-up-down" magnetic structure in zero field.

View Article: PubMed Central - PubMed

Affiliation: Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India.

ABSTRACT
We present detailed investigations on single crystals of quaternary EuRhAl4Si2 and EuIrAl4Si2. The two compounds order antiferromagnetically at TN1 = 11.7 and 14.7 K, respectively, each undergoing two magnetic transitions. The magnetic properties in the ordered state present a large anisotropy despite Eu(2+)being an S-state ion for which the single-ion anisotropy is expected to be weak. Two features in the magnetization measured along the c-axis are prominent. At 1.8 K, a ferromagnetic-like jump occurs at very low field to a value one third of the saturation magnetization (1/3 M0) followed by a wide plateau up to 2 T for Rh and 4 T for Ir-compound. At this field value, a sharp hysteretic spin-flop transition occurs to a fully saturated state (M0). Surprisingly, the magnetization does not return to origin when the field is reduced to zero in the return cycle, as expected in an antiferromagnet. Instead, a remnant magnetization 1/3 M0 is observed and the magnetic loop around the origin shows hysteresis. This suggests that the zero field magnetic structure has a ferromagnetic component, and we present a model with up to third neighbor exchange and dipolar interaction which reproduces the magnetization curves and hints to an "up-up-down" magnetic structure in zero field.

No MeSH data available.


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Heat capacity Cp and entropy Smag as a function of temperature in EuTAl4Si2 and nonmagnetic LaTAl4Si2 for (a) T = Ir and (b) Rh. The horizontal line depicts the high temperature limit (R In 8) of the magnetic entropy for an S = 7/2 spin system.
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f3: Heat capacity Cp and entropy Smag as a function of temperature in EuTAl4Si2 and nonmagnetic LaTAl4Si2 for (a) T = Ir and (b) Rh. The horizontal line depicts the high temperature limit (R In 8) of the magnetic entropy for an S = 7/2 spin system.

Mentions: The heat capacity of the two compounds is shown in Fig. 3. We have also plotted the heat capacity of the corresponding La analogs, which serves as a measure of the phonon contribution assuming that the phonon spectra in the La and corresponding Eu compound are identical. In EuIrAl4Si2, an extremely sharp peak with a peak value of nearly 60 J/mol K and peak position of 14.7 K (Fig. 3(a)), indicative of a first order phase transition from the paramagnetic state to an intermediate magnetically ordered state, is followed by a second transition near 13.2 K marked by a small anomaly at that temperature. The heat capacity of EuRhAl4Si2 (Fig. 3(b)) is apparently marked by only one peak at 11.7 K which is relatively less sharp and has a lower peak height. However, a small kink at 10.4 K is discernible; both are marked by arrows in the figure. The 151Eu Mössbauer spectra, to be described below, also show the presence of two magnetic transitions in both compounds. The magnetic contribution to the heat capacity, Cmag, was obtained by subtracting the normalized heat capacity of the corresponding La compound, following the procedure described in Ref. 3. The entropy Smag calculated by integrating Cmag/T against the temperature is also shown in Figs. 3(a,b). Nearly 75% of the full entropy R In 8 is recovered at the transition temperature, and the remaining by 40 K.


Magnetic anisotropy, unusual hysteresis and putative "up-up-down" magnetic structure in EuTAl4Si2 (T = Rh and Ir).

Maurya A, Thamizhavel A, Dhar SK, Bonville P - Sci Rep (2015)

Heat capacity Cp and entropy Smag as a function of temperature in EuTAl4Si2 and nonmagnetic LaTAl4Si2 for (a) T = Ir and (b) Rh. The horizontal line depicts the high temperature limit (R In 8) of the magnetic entropy for an S = 7/2 spin system.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4496665&req=5

f3: Heat capacity Cp and entropy Smag as a function of temperature in EuTAl4Si2 and nonmagnetic LaTAl4Si2 for (a) T = Ir and (b) Rh. The horizontal line depicts the high temperature limit (R In 8) of the magnetic entropy for an S = 7/2 spin system.
Mentions: The heat capacity of the two compounds is shown in Fig. 3. We have also plotted the heat capacity of the corresponding La analogs, which serves as a measure of the phonon contribution assuming that the phonon spectra in the La and corresponding Eu compound are identical. In EuIrAl4Si2, an extremely sharp peak with a peak value of nearly 60 J/mol K and peak position of 14.7 K (Fig. 3(a)), indicative of a first order phase transition from the paramagnetic state to an intermediate magnetically ordered state, is followed by a second transition near 13.2 K marked by a small anomaly at that temperature. The heat capacity of EuRhAl4Si2 (Fig. 3(b)) is apparently marked by only one peak at 11.7 K which is relatively less sharp and has a lower peak height. However, a small kink at 10.4 K is discernible; both are marked by arrows in the figure. The 151Eu Mössbauer spectra, to be described below, also show the presence of two magnetic transitions in both compounds. The magnetic contribution to the heat capacity, Cmag, was obtained by subtracting the normalized heat capacity of the corresponding La compound, following the procedure described in Ref. 3. The entropy Smag calculated by integrating Cmag/T against the temperature is also shown in Figs. 3(a,b). Nearly 75% of the full entropy R In 8 is recovered at the transition temperature, and the remaining by 40 K.

Bottom Line: Surprisingly, the magnetization does not return to origin when the field is reduced to zero in the return cycle, as expected in an antiferromagnet.Instead, a remnant magnetization 1/3 M0 is observed and the magnetic loop around the origin shows hysteresis.This suggests that the zero field magnetic structure has a ferromagnetic component, and we present a model with up to third neighbor exchange and dipolar interaction which reproduces the magnetization curves and hints to an "up-up-down" magnetic structure in zero field.

View Article: PubMed Central - PubMed

Affiliation: Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India.

ABSTRACT
We present detailed investigations on single crystals of quaternary EuRhAl4Si2 and EuIrAl4Si2. The two compounds order antiferromagnetically at TN1 = 11.7 and 14.7 K, respectively, each undergoing two magnetic transitions. The magnetic properties in the ordered state present a large anisotropy despite Eu(2+)being an S-state ion for which the single-ion anisotropy is expected to be weak. Two features in the magnetization measured along the c-axis are prominent. At 1.8 K, a ferromagnetic-like jump occurs at very low field to a value one third of the saturation magnetization (1/3 M0) followed by a wide plateau up to 2 T for Rh and 4 T for Ir-compound. At this field value, a sharp hysteretic spin-flop transition occurs to a fully saturated state (M0). Surprisingly, the magnetization does not return to origin when the field is reduced to zero in the return cycle, as expected in an antiferromagnet. Instead, a remnant magnetization 1/3 M0 is observed and the magnetic loop around the origin shows hysteresis. This suggests that the zero field magnetic structure has a ferromagnetic component, and we present a model with up to third neighbor exchange and dipolar interaction which reproduces the magnetization curves and hints to an "up-up-down" magnetic structure in zero field.

No MeSH data available.


Related in: MedlinePlus