Phase transitions and exchange interactions in the SmCr₃(BO₃)₄crystal

Abstract

Abstract. Spectroscopic investigation and specific heat and magnetic susceptibility measurements of SmCr3(BO3)4 crystals were performed. The spectra of the Sm 3+ and Cr 3+ ions in samarium chromium borate were calculated and parameters of the exchange interactions between the nearest chromium ions, chromium and samarium ions were determined. Three phase transitions were observed at the temperatures T1= 7.8 ± 0.5 К, T2 = 6.7 ± 0.5 К, and T3 = 4.3 ± 0.2 К, their nature is discussed. The crystal structures with different space symmetry groups R32 and C2/c were found to coexist in а SmCr3(BO3)4 single crystal.Samarium chromium borate SmCr3(BO3)4 is a member of a large family of rare-earth (RE) borates with structural type of the natural mineral huntite. These compounds are described by a general formula RM3(BO3)4, where R is Y or La-Lu and М is Al, Ga, Fe, Cr, or Sc. The compounds are actively investigated due to their interesting physical properties and a promising application potential. However, RE chromium borates are not so well studied. It is known that NdCr3(BO3)4 is an easy-plane antiferromagnet below the temperature 8.0K [1] and that EuCr3(BO3)4 undergoes an antiferromagnetic phase transition at TN ≈ 9 К [2]. A phase transition at 5 К was supposed to occur in SmCr3(BO3)4 [3].We succeeded to prepare a big oriented single crystal of SmCr3(BO3)4 and to perform magnetic measurements on it. It follows from the temperature dependences of the magnetic susceptibility that the magnetic moments of chromium and samarium ions (samarium ions are polarized by the exchange field) are ordered in the ab-plane. However, as this sample was not preserved, heat capacity and optical spectra measurements were carried out on other samples. Crystal characterization by X-ray diffraction and infrared (IR) spectroscopy revealed a polytypic nature of SmCr3(BO3)4. The crystals can be rhombohedral (space group R32) or monoclinic (C2/c), depending on growth conditions. Moreover, domains of both structural phases can coexist in one single crystal. For measurements we chose the crystals with a predominant content of the R32 phase. The temperature dependence of the

Features of magnetic and magnetoelectric properties, H-T phase diagram of GdCr3(BO3)4

“…However, the intrachain interaction (J/k = -6.8 K) for GdCr3(BO3)4 found in Ref [25], differs substantially in comparison with the data for NdCr3(BO3)4 (4 K) [21], EuCr3(BO3)4 (4.6 K) [22], SmCr3(BO3)4 (2.8 K) [24], and TbCr3(BO3)4 (3.2 K) [37]. Thus, it is important to determine the value of the exchange integral characteristic of the Cr 3+ ions in sharing edge oxygen octahedra for the range of dCr-Cr mentioned above.…”

“…Some data on magnetic properties of the samarium chromium borate have been reported in Refs. [23,24]. For SmCr3(BO3)4, three phase transitions were observed at temperatures TN = 7.8 K, T2 = 6.7 K, and T3 = 4.3 K. In the single crystal studied, coexistence of the rhombohedral (R32) and monoclinic (C2/c) structures with domination of the rhombohedral one was found.…”

“…For SmCr3(BO3)4, three phase transitions were observed at temperatures TN = 7.8 K, T2 = 6.7 K, and T3 = 4.3 K. In the single crystal studied, coexistence of the rhombohedral (R32) and monoclinic (C2/c) structures with domination of the rhombohedral one was found. The constants of the intrachain (J/k = 2.8 K) and interchain (J΄/k = -0.75 K) Cr-Cr exchange interactions and of the Cr-Sm interactions (JCr-Sm/k = -0.13 K) have been estimated [24].…”

Crystallochemical Design of Huntite-Family Compounds

“…The space group C2/c is known for the LnAl 3 (BO 3 ) 4 with the Ln = Pr, Nd, Sm, Eu, Tb, Ho (the structure is refined, for example, in [97]); LnFe 3 (BO 3 ) 4 with the Ln = Nd; LnCr 3 (BO 3 ) 4 with the Ln = La, Pr, Nd, Sm, Tb, Dy, Ho; LnSc 3 (BO 3 ) 4 with the Ln = La, Ce, Pr ( Table 1). The centrosymmetry was determined by spectroscopic studies using a factor-group analysis of vibrations (for the LnAl 3 (BO 3 ) 4 with the Ln = Pr [42], Nd [42,45]; LnFe 3 (BO 3 ) 4 with the Ln = Nd [45]; LnCr 3 (BO 3 ) 4 with the Ln = La (Figure 10), Pr, Tb, Dy, Ho [70,71], Nd [26,45,70,71], Sm [70,72]). The LnSc 3 (BO 3 ) 4 crystals with the Ln = La, Ce, obtained by the Czochralski method, crystallize in the centrosymmetric space group C2/c), according to a study of their nonlinear optical properties [35].…”

Crystal Growth of Multifunctional Borates and Related Materials

“…The space group C2/c is known for the LnAl 3 (BO 3 ) 4 with the Ln = Pr, Nd, Sm, Eu, Tb, Ho (the structure is refined, for example, in [97]); LnFe 3 (BO 3 ) 4 with the Ln = Nd; LnCr 3 (BO 3 ) 4 with the Ln = La, Pr, Nd, Sm, Tb, Dy, Ho; LnSc 3 (BO 3 ) 4 with the Ln = La, Ce, Pr (Table 1). The centrosymmetry was determined by spectroscopic studies using a factor-group analysis of vibrations (for the LnAl 3 (BO 3 ) 4 with the Ln = Pr [42], Nd [42,45]; LnFe 3 (BO 3 ) 4 with the Ln = Nd [45]; LnCr 3 (BO 3 ) 4 with the Ln = La (Figure 10), Pr, Tb, Dy, Ho [70,71], Nd [26,45,70,71], Sm [70,72]). The LnSc 3 (BO 3 ) 4 crystals with the Ln = La, Ce, obtained by the Czochralski method, crystallize in the centrosymmetric space group C2/c), according to a study of their nonlinear optical properties [35].…”