期刊
PHYSICAL REVIEW B
卷 106, 期 13, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.106.134418
关键词
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资金
- FIST program of the Department of Science and Technology, India [SR/FST/PSII-020/2009, SR/FST/PSII-037/2016]
- Ministry of Education (MoE), Government of India through the Prime Minister's Research Fellowship (PMRF) May 2021 scheme
- Council of Scientific and Industrial Research (CSIR), Ministry of Science and Technology, Government of India [09/0731(13216)/2022-EMR-I]
- Swedish Research Council (VR) [2017-05030, 2021-03675]
- Central Instrument Facility (CIF) of the Indian Institute of Technology Guwahati
- North East Centre for Biological Sciences and Healthcare Engineering (NECBH) of the Indian Institute of Technology Guwahati
- Ministry of Education (MoE), Singapore [MOE2019-T2-1-058]
- National Research Foundation (NRF) [NRF-CRP212018-0003]
- Swedish Research Council [2021-03675] Funding Source: Swedish Research Council
A study on the ferrimagnetic properties of Ni4Nb2O9 reveals that it is caused by two inequivalent Ni2+ ions with different magnetic moments. Experimental results and theoretical analysis of the temperature and magnetic field dependence of the magnetization, ac-magnetic susceptibility, and heat capacity provide new insights into the nature of the ferrimagnetism in Ni4Nb2O9.
Ferrimagnetism in orthorhombic Ni4Nb2O9 below its Neel temperature, T-FN similar to 76K is reported to result from two inequivalent Ni2+ ions having different magnetic moments. However, a clear understanding of the temperature variation of its magnetization [M(T)] for T > T-FN and T < T-FN in terms of a single set of exchange parameters is still lacking. In this work, experimental results obtained from a detailed analysis of the temperature and magnetic field dependence of magnetization [M(T, H)], ac-magnetic susceptibility [chi(ac)( f, T, H)], and heat-capacity [C-P(T, H)] measurements are combined with theoretical analysis to provide new insights into the nature of ferrimagnetism in Ni4Nb2O9. X-ray diffraction/Rietveld analysis of the prepared sample yielded the structural parameters of the orthorhombic crystal in agreement with previous studies, whereas x-ray photoelectron spectroscopy confirmed the Ni2+ and Nb5+ electronic states in Ni4Nb2O9. Analysis of chi(ac)(T) shows the paramagnetic-to-ferrimagnetic transition occurs at 76.5 K (T-FN), which increases with applied field H as T-FN proportional to H-0.35 due to the coupling of the ferromagnetic component with H. For T > T-FN, the chi(dc) versus T data are fitted to the Neel's expression for ferrimagnets, yielding the g-factors for the two Ni2+ ions as g(A) = 2.47 and g(B) = 2.10. Also, the antiferromagnetic molecular field constants between the A and B sublattices were evaluated as N-AA = 26.31, N-BB = 8.59, and N-AB = 43.06, which, in turn, yield the antiferromagnetic exchange parameters: J(AA)/k(B) = 4.27 K, J(BB)/k(B) = 1.40 K, and J(AB)/k(B) = 6.98 K. For T < T-FN, the M versus T data clearly show the magnetic compensation point at T-COM similar to 33 K. The mathematical model presented here using the magnitudes of NAA, NBB, and NAB correctly predicts the position of T-COM as well the temperature variation of M both above and below T-COM. The data of C-P(T) versus T shows a lambda-type anomaly across T-FN. After subtracting the lattice contribution, the C-P(T) data are fitted to C-P = A(T - T-N)((-alpha)) yielding the critical exponent alpha = 0.14(0.12) for T < T-FN (T > T-FN), which is a characteristic of second-order phase transition. Magnetic entropy changes determined from the M-H isotherms shows that the applied field H enhances the magnetic ordering for T > T-FN and T < T-COM, but for T-COM < T < T-FN, the spin disorder increases with the increase in H. The temperature variation of the measured coercivity H-C(T) and remanence M-R(T) from 1.9 K to T-FN initially show a decreasing trend, becoming zero at T-COM, then followed by an increase and eventually becoming zero again at T-FN.
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