Mechanism of the Magnetic and Speciﬁc-heat Anomalies in Rare-earth Dodecaborides RB12 (R=Tb-Tm): an Effect of Crystal-ﬁeld-splitting Order Parameter

doi:10.15541/jim20200623

Abstract

Abstract:

Rare-earth dodecaborides RB₁₂ (R=Tb, Dy, Ho, Er, Tm) are all characterized by a controversial and unresolved magnetic and speciﬁc-heat anomaly at low temperature (T_C≈3-22 K) except LuB₁₂ with closed f-shell. Although the bump feature in magnetic susceptibilities resembles that of antiferromagnetically ordered R³⁺ ions, no deﬁnite magnetic structure was identiﬁed by either neutron scattering or Mössbauer spectra. The anomalies in susceptibilities, entropy, and low temperature neutron diffraction pattern all pointed to the amplitude-modulated nature of complex magnetic structure. In view of the rather small crystal-field-splitting energies of the order of meV, we propose to treat crystal-field-splitting (CFS) energy as an order parameter rather than a quantum mechanical quantity. In this way, we found that not only the magnetic and speciﬁc-heat anomalies can be explained properly by a gradual quenching of R orbital moments, but also the low temperature satellite peaks of neutron scattering spectra can be understood in terms of the spontaneously (111) dimerised structure and inelastically absorbed rattling phonon modes.

Key words: rare-earth compound, magnetism in solid, crystal-electrical-splitting, order parameter

CLC Number:

TM28

HU Jingsan, GU Jianfei, ZHANG Weiyi. Mechanism of the Magnetic and Speciﬁc-heat Anomalies in Rare-earth Dodecaborides RB₁₂ (R=Tb-Tm): an Effect of Crystal-ﬁeld-splitting Order Parameter[J]. Journal of Inorganic Materials, 2021, 36(8): 865-870.

Figures/Tables 6

References 28

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RB₁₂	TbB₁₂	DyB₁₂	HoB₁₂	ErB₁₂	TmB₁₂
a/(0.1 nm)	7.503	7.500	7.491	7.483	7.475
$\langle {{r}^{4}}\rangle $/(×10^-4, nm⁴)	0.1295	0.1180	0.1081	0.09959	0.09206
$\langle {{r}^{6}}\rangle $/(×10^-6, nm⁶)	0.1505	0.1328	0.1181	0.1058	0.09530
$\text{ }\!\!\Delta\!\!\text{ }_{1}^{0}$/meV	7.53	6.36	6.36	5.90	5.49
$\text{ }\!\!\Delta\!\!\text{ }_{2}^{0}$/meV	14.22	12.99	11.97	11.09	10.31

RB₁₂	TbB₁₂	DyB₁₂	HoB₁₂	ErB₁₂	TmB₁₂
a/(0.1 nm)	7.503	7.500	7.491	7.483	7.475
$\langle {{r}^{4}}\rangle $/(×10^-4, nm⁴)	0.1295	0.1180	0.1081	0.09959	0.09206
$\langle {{r}^{6}}\rangle $/(×10^-6, nm⁶)	0.1505	0.1328	0.1181	0.1058	0.09530
$\text{ }\!\!\Delta\!\!\text{ }_{1}^{0}$/meV	7.53	6.36	6.36	5.90	5.49
$\text{ }\!\!\Delta\!\!\text{ }_{2}^{0}$/meV	14.22	12.99	11.97	11.09	10.31

RB₁₂	${{\theta }_{\text{D}}}$/K	$\text{ }\!\!\Delta\!\!\text{ }_{1}^{0}$/meV	$\text{ }\!\!\Delta\!\!\text{ }_{2}^{0}$/meV	${{T}_{\text{C}}}(\text{Cal}.)$/K	${{T}_{\text{C}}}(\text{Exp}.)$/K^[12]
TbB₁₂	377	10.66	20.21	22.69	22.05
DyB₁₂	375	9.42	17.81	16.61	16.35
HoB₁₂	374	7.63	14.38	10.69	7.38
ErB₁₂	372	6.24	11.74	6.52	6.65
TmB₁₂	371	5.07	9.51	3.51	3.28

RB₁₂	${{\theta }_{\text{D}}}$/K	$\text{ }\!\!\Delta\!\!\text{ }_{1}^{0}$/meV	$\text{ }\!\!\Delta\!\!\text{ }_{2}^{0}$/meV	${{T}_{\text{C}}}(\text{Cal}.)$/K	${{T}_{\text{C}}}(\text{Exp}.)$/K^[12]
TbB₁₂	377	10.66	20.21	22.69	22.05
DyB₁₂	375	9.42	17.81	16.61	16.35
HoB₁₂	374	7.63	14.38	10.69	7.38
ErB₁₂	372	6.24	11.74	6.52	6.65
TmB₁₂	371	5.07	9.51	3.51	3.28

RB₁₂	$\Delta \chi (\text{Exp}.)$	$\Delta \chi (\text{Cal}.)$	$\Delta C/R(\text{Exp}.)$	$\Delta C/R(\text{Cal}.)$
TbB₁₂	-	2.39	1.4	2.46
DyB₁₂	3.89	4.15	1.2	1.72
HoB₁₂	5.65	6.91	-	1.43
ErB₁₂	6.91	10.56	1.1	1.41
TmB₁₂	4.77	15.58	2.0	2.16

Mechanism of the Magnetic and Speciﬁc-heat Anomalies in Rare-earth Dodecaborides RB₁₂ (R=Tb-Tm): an Effect of Crystal-ﬁeld-splitting Order Parameter

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