Crystal structure and magnetic properties of potassium erbium double tungstate KEr(WO₄)₂

Abstract

Results of structural, magnetic and specific heat investigations of the potassium erbium double tungstate, KEr(WO 4 ) 2 , are presented. Potassium erbium doubletungstate KEr(WO 4 ) 2 single crystals have been grown by the top-seeded solution growth method (TSSG) and modified Czochralski techniques. It crystallizes in the monoclinic crystal structure (C2/c space group). The unit cell contains four formula units and is described by parameters a = 10.615(2) Å, b = 10.316(2) Å, c = 7.534(2) Å, β = 130.73(3) • . From the x-ray diffraction measurements the fractional atomic coordinates, displacement parameters and interatomic distances have been determined.The specific heat C(T ) of the KEr(WO 4 ) 2 crystal has been measured over a temperature range of 0.6-300 K. The susceptibility has been studied at T = 0.25-4.0 K. The magnetic phase transition was observed at a temperature of 0.48 K. The magnetization has been measured in the temperature region from 4.2 to 60 K and in magnetic field up to 1.6 T. A strong anisotropy of magnetic properties was found. The temperature and field dependences of susceptibility and magnetization data were used for both elucidation of character of the magnetic ordering and calculation of the exchange and dipole-dipole interaction energies as well as for determination of the possible magnetic structure of KEr(WO 4 ) 2 .

Magnetic phase transition in KGd(WO4)2 double tungstate

“…They were found to be equal to α ≈ 0 103 ± 0 018 (T < T N ) and α ∼ 0 116 ± 0 007 (T > T N ). Similar behaviour of the specific heat was observed for other double tungstates, for example: at 0.6 K for KDyW [14], at 0.82 K for RbDyW [8][9][10][11][12][13][14][15] and at 0.48 K for KErW [4]. The magnetic nature of the phase transition occurring at 0.42 K (for KGdW; this paper) will be verified by planned measurements of the magnetization at ultralow temperatures.…”

“…At present, the AReW tungstates with low-symmetric (e.g., monoclinic) crystalline structure and atomic arrangements in the form of chains or layers are intensively studied. Structural, optical and magnetic investigations of the KDyW, KHoW, KErW and RbDyW compounds have been performed previously [2][3][4][5][6]. Many of them show complicated structural phase transitions (SPT), caused by the cooperative Jahn-Teller effect (CJTE), and magnetic phase transitions.…”

The magnetic properties of potassium holmium double tungstate

“…4 we can see that for D/|J i (0)| > -3.7 and the magnetic ordering in system is absent. For KHo(WO 4 ) 2 we obtain D/|J z (0)| = -2.47 > -3.7, i.e., magnetic ordering does not appear. The D/|J(0)| is close to the critical value -3.7.…”

“…A very low temperature phase transition to antiferromagnetic (AF) state is the characteristic property of these low-symmetry systems and indicates that the exchange interactions are weak. For example, the Néel temperature T N is equal to 0.6, 0.7, 0.82 and 0.85 K for KDy(WO 4 ) 2 , KTb(WO 4 ) 2 , RbDy(WO 4 ) 2 and KEr(WO 4 ) 2 , respectively [1][2][3].…”

“…So far, in the double tungstates KLu(WO 4 ) 2 and KGd(WO 4 ) 2 doped with holmium ions the laser emission was observed [4,5]. The results of spectroscopic studies of KHo(WO 4 ) 2 , KLu(WO 4 ) 2 and KGd(WO 4 ) 2 :Ho 3+ were presented in Refs. 6-8.…”