DCMPMS Seminars

Study of magnetic anisotropy and spin reorientation transition in some rare-earth transition-metal permanent magnets

by Dr. Santosh Kumar (Department of Physics, University of Warwick, U.K.)

Friday, January 24, 2020 from to (Asia/Kolkata)
at AG80
The microscopic origin of permanent magnetism is magnetocrystalline anisotropy which is generally explained in terms of ferromagnets. However, the best performing rare-earth and transition-metal based permanent magnets are ferrimagnets comprising various magnetic sublattices. The application of a magnetic field may lead to canting between the sublattices and therefore the standard theoretical approach of ignoring the applied magnetic field is not consistent with real experiments. To solve this problem, we have introduced a first principles approach [1] to calculate the magnetization vs field (FPMVB) curves mirroring the experiments actually used to determine the anisotropy. In this talk, I will be discussing about our new experimental results [1] obtained on the single crystals of two of the permanent magnets YCo5 and GdCo5 grown using optical floating zone technique [2]. Our experimental findings[1] are found to be in excellent agreement with the FPMVB approach. The magnetic anisotropy of different magnetic sublattices in some permanent magnets may favor different easy axes of magnetization. Consequently, the material system undergoes a change in easy axis with temperature, known as the spin reorientation transition(SRT). The magnetic anisotropy constants in this transition regime can be significantly higher and interesting phenomena such as giant rotating magnetocaloric effect can be observed here [3].At the end of this talk, I will be discussing in brief about our experimental study[4]of this transition in a permanent magnet NdCo5using torque magnetometry, a technique rarely been applied to understand the SRT. We have also investigated the effects of applying pressure on the SRT in this compound[5]. 

1.	C. E. Patrick, Santosh Kumar et al. Phys. Rev. Lett. 120, 097202 (2018).
2.	C. E. Patrick, Santosh Kumar et al. Phys. Rev. Mater. 1, 024411 (2017).
3.	Nikitin et al.,Phys. Rev. Lett.105, 137205 (2010).
4.	Santosh Kumar et al.,manuscript under review in J. Phys.:Condens. Matter.
5.	Santosh Kumar et al.,manuscript under review in Appl. Phys. Lett.