Lattice dynamics and a magnetic-structural phase transition in the nickel orthoborateNi3(BO3)2

Abstract

Nickel orthoborate Ni3(BO3)2 having a complex orthorhombic structure Pnnm (#58, Z=2) of the kotoite type is known for quite a long time as an antiferromagnetic material below We performed the symmetry analysis of the phonon modes at the center of the Brillouin zone.The structural parameters and phonon modes were calculated using Dmol3 program. We report and analyze results of infrared and Raman studies of phonon spectra measured in all required polarizations. Most of the even and odd phonons predicted on the basis of the symmetry analysis and theoretical calculations were reliably identified in the measured spectra. A clear evidence of the spin-phonon interaction was found for some particular phonons below TN. Unexpected emergence of several very narrow and weak phonon lines was observed in the infrared absorption spectra exactly at the magnetic ordering temperature TN. Moreover, anomalous behavior was found for some Raman phonons. Emergence of new phonon modes in the infrared and Raman spectra exactly at TN proves existence of a magnetostructural phase transition of a new type in Ni3(BO3)2. A possible nature of this transition is discussed.

Super‐Superexchange Influence on Magnetic Ordering in Ni3B2O6 Kotoite

“…In ref. , there was also a magnetic cell – a monoclinic one with doubling of the primitive cell relative to the paramagnetic phase (2 a , − b , a + c , 0.0.0). In both papers, it is mentioned that the ribbons are ferromagnetically ordered.…”

“…If we estimate the energies of these magnetic structures using only the resulting Ni‐O‐Ni exchange interactions, the ferromagnetic structure will be most beneficial, but if we take into account all types of exchange interactions, including the super‐superexchange Ni‐O‐B‐O‐Ni interactions, then the most favorable is the ordering shown in Figure c, which is consistent with the magnetic ordering found in refs. .…”

“…The emergence of new phonon modes in the IR and Raman spectra at the magnetic transition temperature, according to the authors of ref. , indicate the existence of a new type magnetostructural phase transition in Ni 3 B 2 O 6 . In a magnetically ordered state, ferromagnetically ordered chains are oriented antiferromagnetically relative to each other.…”

“…In article, the lattice dynamics was investigated by experimental and theoretical methods. Anomalous behavior of some Raman phonons was discovered in the region of the magnetic transition.…”

Экспериментальное исследование и анализ спектров поглощения ионов Ni-=SUP=-2+-=/SUP=- в ортоборате никеля Ni-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-2-=/SUB=-

“…Анализ температурной зависимости магнитной восприимчивости позволил установить, что Ni 3 (BO 3 ) 2 является коллинеарным антиферромагнетиком (T N = 46 K) [14]. Методы оптической спектроскопии (инфракрасная спектроскопия и спектроскопия комбинационного рассеяния света) были использованы ранее только в исследовании динамики решетки Ni 3 (BO 3 ) 2 [15]. На основании анализа температурных зависимостей частот фононов был сделан вывод о магнитоструктурном характере наблюдаемого в Ni 3 (BO 3 ) 2 антиферромагнитного фазового перехода.…”