Magnetism of Ni Fe In VO
2
x
1-x
6
(x=0.00; 0.10; 0.25; 0.50) solid solutions
1 1 1 2 2
Janusz Typek , Marta Bobrowska , Grzegorz Żolnierkiewicz , Elżbieta Filipek , Agnieszka Pacześna
1Institute of Physics, West Pomeranian University of Technology, Szczecin, Al. Piastow 48, 70-311 Szczecin, Poland
2
Department of Inorganic and Analytical Chemistry, West Pomeranian University of Technology, Szczecin, Al. Piastow 42,
71-065 Szczecin, Poland
Experimental
EPR measurements
Powder samples of Ni Fe In VO , that belong to the two-component system built by 2 x 1-x 6
the isostructural Ni InVO and Ni FeVO compounds, were obtained by traditional cal-2 6 2 6 cination method. Magnetisation studies were carried on Quantum Design Magnetic Property Measurements System MPMS XL-7 with a superconducting quantum inter-ference device magnetometer in magnetic fields up to 70 kOe and in the 2–300 K tem-perature range. Magnetic resonance spectra of Ni Fe In VO were recorded on a con-2 x 1-x 6 ventional X-band Bruker ELEXSYS E 500 spectrometer operating at 9.5 GHz with 100 kHz magnetic field modulation. The first derivative of the absorption spectra has been recorded as a function of the applied magnetic field. Temperature dependence of the EPR spectra of solid solutions under studies in the 4–300 K temperature range was recorded using an Oxford Instruments ESP helium-flow cryostat.
SEM picture of the investigated powder sample of Ni InVO2 6 SEM picture of the investigated powder sample of Ni Fe In VO2 0.5 0.5 6
Magnetisation measurements revealed a step-like temperature dependence, demonstrating the presence of a few different types of magnetic entities. Three different magnetic ions could be involved in creation of magnetism of these compounds:
2+ 8 3+ 5 4+ 1
Ni (d ), Fe (d ), and V (d ). The magnetic structure is believed to contain different magnetic phases existing at the same tem-perature.
M(T) curves in 20 – 300 K range were fitted with the function ,
where M (0) is the magnetisation at T=0 K, α is a fitting parameter, and T is critical temperature of the i-th component (i=1,2,3).i i i In the high temperature range ferromagnetic (FM) complexes and paramagnetic complexes with FM interactions determine the magnetic properties. In the intermediate temperature range antiferromagnetic (AFM) complexes start to dominate the magnetic response as FM complexes freeze out. At the lowest temperatures the freezing of the AFM nanoclusters causes diminishing of
3+ 2+
magnetisation with temperature decrease. In samples with small amounts of Fe , Ni magnetic ions play a dominating role with AFM transition at low temperature.
Isothermal magnetisation of Ni Fe In VO registered at three different temperatures (T=2, 10, 290 K) has shown no saturation 2 0.5 0.5 6 - even in the strongest available field (70 kOe), what is typical for paramagnetic, superparamagnetic and AFM phases.
The best result of fitting M(H) was achieved by using modified Langevin function, M=M ·L(x)+αH, where L(x)=coth(x)-(1/x) is the s
Langevin function and x=(μ H)/(kT). Here M is the saturation magnetisation, μ is the particle magnetic moment, k is the p s p Boltzmann constant and α is a linear susceptibility. That form of M(H) was often used e.g. in the superparamagnetic phases of magnetic nanoparticles.
EPR spectra of Ni Fe2 0.25In0.75VO recorded at different temperatures was fitted by three Lorentzian lines. The presence of three 6 components was especially required to properly fit the observed spectra taken below 200 K. At low temperatures magnetisation and EPR measurements have shown the presence of AFM and FM complexes. The low temperature FM complex displays ther-mal behaviour that closely resembles FC and ZFC magnetisation changes in FM nanoparticles. This suggests that the sizes of magnetic complexes in the investigated samples might be in the nanometric range.
Results
0 2 4 6 8 10 12 0 1 2 3 4 5 0 50 100 150 200 250 300 0,0 0,2 0,4 0,6 0,8 • x=0.50 x=0.25 x=0.10 x=0.00 ZFC H=4 kA/m Mass susceptibility [ 10 -5 m 3 /kg ] H=240 kA/m Temperature [K] H=5 570 kA/m 4 8 12 16 0 4 8 12 16 0 1 2 3 4 5 6 7 0,0 0,4 0,8 1,2 Mass magnetisation [Am 2 /mol ] T=2 K T=10 K Magnetic field [T] T=290 K x=0.10 x=0.25 x=0.50 x=0.00 0 2 4 6 0 2 4 6EPR amplitude [arb. units]
EPR amplitude [arb. units]
Magnetic field [kOe]
90 K 150 K 200 K 250 K 290 K 289 K 353 K 401 K 443 K 493 K 0 2 4 6 8 10 12 14 0 1 2 3 4 5 6
EPR amplitude [arb.units]
EPR amplitude [arb.units]
Magnetic field [kG] 290 K 250 K 200 K 100 K 35 K 17 K 8 K 4 K x=0.10 290 K 200 K 150 K 65 K 25 K 17 K 14 K 4 K x=0.00 x=0.5 290 K 250 K 200 K 150 K 100 K 70 K 40 K 17 K Magnetic field [kG] 7 K x=0.25 290 K 250 K 180 K 120 K 100 K 70 K 41 K 16 K 4 K 0 2 4 6 8 10 12 14 0 1 2 3 4 5 6 0 10 20 30 40 50 60 70 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0 5 10 15 20
Reciprocal integrated intensity [a.u.]
EPR integrated intensity [a.u.]
Temperature [K] x=0.10 T=5.8 K 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 80 90 100 0.00 0.05 0.10 0.15 0.20 0.25 0.30
EPR integrated intensity [a.u.]
x=0.00
Reciprocal integrated intensity [a.u.]
Temperature [K]
T=14 K
Dc magnetisation measurements
Conclusions
Ni Fe In VO solid solution system is a very interesting case of frustrated magnetism.2 x 1-x 6
Randomness in distribution of magnetic ions causes formation of different types of spin clusters.
The presence of at least three different kinds of magnetic entities is evidenced in magnetisation and magnetic
resonance measurements.
Similarities of the observed magnetic behavior of the investigated samples with magnetic nanoparticles suggest that
the sizes of magnetic clusters in Ni Fe In VO might be in nanometric range.2 x 1-x 6
0 1 2 3 4 5 6 7 -3 -2 -1 0 1 2 3
EPR amplitude [arb. units]
Magnetic field [kOe]
T=90 K
