Ex) Article Title, Author, Keywords
New Phys.: Sae Mulli 2022; 72: 96-99
Published online February 28, 2022 https://doi.org/10.3938/NPSM.72.96
Copyright © New Physics: Sae Mulli.
Mariam OMRAN1, Joonyoung CHOI1, Younjung JO1*, Mi Kyung KIM2,3, Changyoung KIM2,3
1Department of Physics, Kyungpook National University, Deague 41566, Korea
2Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Korea
3Department of Physics and Astronomy, Seoul National University (SNU), Seoul 08826, Korea
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Magnetic anisotropy is an important phenomenon driven by a strong electron correlation. It is defined as the magnetization tendency of magnetic material in a particular crystallographic direction. In this paper, we investigated the magnetic anisotropy of CoS2 single crystal. Here, torque magnetometry was used to determine the magnetocrystalline anisotropy of the crystal. The angle dependence of torque τ(θ) for CoS2 was measured at several temperatures above and below the ferromagnetic order transition Tc. To verify the effect of surface morphology on magnetic properties, we compared the τ(θ) of uncleaved and cleaved pure CoS2. Results show that two-fold symmetry was equally dominant in both. Furthermore, we compared higher orders of magnetic anisotropy to track the intrinsic and shape anisotropies. All amplitudes showed the same behavior for cleaved and uncleaved samples, but the higher orders were more dominatant in the cleaved sample.
Keywords: Torque magnetometry, Ferromagnet, Magnetic anisotropy
Magnetic anisotropy is an important phenomenon driven by a strong electron correlation. It is a factor that influences the magnetization tendency of materials, implying the dependency of magnetic properties on the direction of the applied field [1-4]. Magnetic anisotropy can be classified into crystal (magnetocrystalline), shape, and exchange anisotropies. Additionally, external factors such as annealing and irradiation can create anisotropy. Crystal anisotropy is a force that maintains the magnetization in a specific crystallographic direction, known as the easy direction of magnetization, and consequently regulates the magnetization strength. Applying the magnetic field in an easy direction of ferromagnet requires only a few tens of Oersteds to achieve saturation. However, when the field is applied in a hard axis direction, the domain movement structure changes and domain rotation occurs in the high field instead. Anisotropic interactions heavily depend on the crystal morphology, symmetry, and content of the magnetic substance. Furthermore, robust magnetic anisotropy dependence on crystal cleavage has been reported.
CoS2 belongs to ferromagnetic materials with a cubic pyrite structure, with its ferromagnetic transition temperature
In our study, we verified out-of-plane (OOP) magnetic anisotropy before and after the ferromagnetic transition of cleaved and uncleaved CoS2 single crystals. Furthermore, higher-order anisotropic contributions have been evaluated and compared for both cases. Results show that compared with the uncleaved sample, the cleavage sample showed a larger higher-order anisotropic constant and a significant contribution to the torque signal.
The crystal structure of CoS2 has a cubic structure with cut corners a cross-section, as shown in the inset of Fig. 4(b). The length of each side is approximately 1 mm. To verify the effect of surface morphology on magnetic properties, we compared the torque signal of uncleaved and cleaved CoS2. Cleaved CoS2 was prepared by parallelly cutting the crystal plane with a razor. The thickness is about 0.3 mm, and the shape of the shortened cross-section is shown in the inset of Fig. 2(b). Torque measurement for CoS2single crystal was performed using the membrane-type surface stress (MSS) device. CoS2 was mounted on the MSS using vacuum grease by aligning the crystal direction. Moreover, the torque change was measured through the change in the resistance of the piezo material comprising a Wheatstone bridge circuit. This is a non-destructive and reliable technique for detecting spin alignment. Here, the magnetic field direction with respect to the crystal axis was controlled using a rotator. We measured the OOP torque while rotating the field through angle
We performed the angle-dependent torque
Since CoS2 has a cubic crystal structure, the rotating plane on which
where A2, A4, and A6 are the coefficients of sin 2
In Fig. 2(a), the red lines indicate the fitted result of
Based on the fitted curves, the amplitudes of the higher-order corrections were extracted. The
To validate the surface shape influence of the crystal on their characteristics, an uncleaved CoS2 single crystal was measured via the same procedure.
Figure 4(a) illustrates the fitted torque curves for the uncleaved CoS2. The fitting curve fits reasonably well for all
To summerize the effect of crystal cleavage on CoS2 magnetic anisotropy, all the extracted amplitudes from the fitted data at
This research was supported by Kyungpook National University Research Fund, 2019