THz ESR Study of Peculiar Co Pyrochlore System GeCo2O4 Using Pulsed High Magnetic Field

• Published in: Applied magnetic resonance Vol. 52; no. 4; pp. 411 - 424
• Main Authors: Okubo, Susumu, Ohta, Hitoshi, Ijima, Tatsuya, Yamazaki, Tatsuya, Zhang, Wei-min, Hara, Shigeo, Ikeda, Shinichi, Oshima, Hiroyuki, Takahashi, Miwako, Tomiyasu, Keisuke, Watanabe, Tadataka
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01-04-2021; Springer Nature B.V
• Subjects: Antiferromagnetism; Atoms and Molecules in Strong Fields; Behavior; Cobalt; Coupling; Critical field (superconductivity); Electron paramagnetic resonance; Electron spin; Electrons; High temperature; Laser Matter Interaction; Lattice vibration; Magnetic fields; Neutrons; Organic Chemistry; Original Paper; Physical Chemistry; Physics; Physics and Astronomy; Pyrochlores; Sensors; Single crystals; Solid State Physics; Spectroscopy/Spectrometry; Spin resonance; Temperature dependence; Terahertz Spectroscopy; Ultrasonic imaging
• ISSN: 0937-9347; 1613-7507
• DOI: 10.1007/s00723-020-01295-x

THz electron spin resonance (ESR) measurements of the spinel compound GeCo
2
O
4
, which consists of the Co
2+
pyrochlore structure, were performed. The temperature dependence measurements revealed new antiferromagnetic phases, AF
1
and AF
2
, below
T
N
. Moreover, a wide magnetic field range of ESR study using a single crystal at 1.8 K also revealed various field-induced phases due to the competition between the spin–lattice coupling and the spin frustration. Critical field resonances were observed at 5.0 T, 8.6 T, and 11.0 T for
B
//[111] and 5.1 T, 7.7 T, 11.2 T, and 13.0 T for
B
//[110] at 1.8 K. Although it became difficult to observe ESR above 86 K, the
g
-values of Co
2+
ions were estimated to be
g
[111]
 = 3.34 and
g
[110]
 = 3.27 for [111] and [110], respectively, from the observed ESR mode above the saturation field at 1.8 K. Detailed frequency-field diagrams of the ESR modes at 1.8 K suggested the existence of spin–lattice coupling energy of 250 GHz (= 1.03 meV = 12 K) at the critical field resonances. The spin gap mode in the frequency-field diagram at 1.8 K showed excitation energies of
E
[111]
 = 1004 GHz (= 4.15 meV = 48 K) and
E
[110]
 = 1044 GHz (= 4.32 meV = 50 K) for [111] and [110], respectively. These results will be discussed in connection with the di-tetramer model suggested previously.