Magnetic ordering of Ho and its role in the magnetization reversal and coercivity double peaks in the Ho3Fe5O12 garnet

Rare-earth based garnet system, Ho3Fe5O12 shows magnetization compensation phenomenon at T-comp = 138 K and a magnetic transition at 50 K. In the present work, we reveal the physics of these low temperature magnetic transitions by carrying out detailed dc magnetization, ac susceptibility, neutron depolarization, and neutron diffraction studies. Interestingly, our dc magnetization study under low (less than or similar to 50 Oe) magnetic fields has shown a previously unknown sign reversal of magnetization (below the T-comp) that persists down to 5 K, the lowest measured temperature. Magnetic measurements under moderate fields between 50 Oe and 1 kOe reveal two compensation temperatures (in the range of 105 - 150 K depending upon the applied field value) leading to double magnetization reversals. Interestingly, for magnetic fields >= 1 kOe, these two compensation temperatures merge to a single T-comp (=138 K). A modified Stoner-Wohlfarth model has been used to explain the asymmetrical nature of double peak around the T-comp in the temperature dependent coercivity data. The ac susceptibility study supports the existence of both the transitions with an evidence of deep minimum at the T-comp (138 K) and a broad peak at 50 K. Mesoscopic neutron depolarization study has revealed a zero domain-magnetization state at the T-comp. Temperature dependent neutron diffraction study has revealed that Ho carries an induced moment above the T-comp due to polarizing effect under the internal magnetic field of the two magnetically ordered Fe sublattices at 567 K, whereas a single umbrella type ordering of Ho sublattice moments appears below the T-comp, resulting in the distortion of magnetic unit cell from cubic to rhombohedral symmetry. However, below 50 K, Ho3+ sites are divided into two inequivalent magnetic sublattices, having different moments and canting angles, and it leads to double umbrella type magnetic structure. Neutron diffraction study has revealed an asymmetric variation of the tetrahedral, octahedral, and dodecahedral sublattice moments resulting in a magnetization reversal at similar to 138 K which is very well supported by the mean field theory calculations. In the present study, we have resolved the ambiguity of magnetic ordering of the rare-earth (Ho3+) sublattice and its role in multiple magnetic transitions. The utility of such compensated ferrimagnetic materials in spin polarizers/analyzers and fast switching memory devices has been emphasized.

Automated summary

Through detailed investigations including dc magnetization, ac susceptibility, neutron depolarization, and neutron diffraction studies, the physics of low temperature magnetic transitions in Ho3Fe5O12 have been revealed. The study showed a previously unknown sign reversal of magnetization below T-comp under low magnetic fields, as well as double compensation temperatures under moderate fields leading to double magnetization reversals. A modified Stoner-Wohlfarth model was used to explain the asymmetrical nature of the temperature dependent coercivity data around T-comp. The findings support the existence of two transitions at 138 K (T-comp) and 50 K, with evidence of a deep minimum and a broad peak, respectively.