Magnetic study of Ni2Fe0.5In0.5VO6 solid solution

Magnetic study of

Ni Fe In VO solid solution

₂

_0.5

_0.5

₆

1 1 1 2 2

Janusz Typek , Marta Bobrowska , Grzegorz Zolnierkiewicz , Elzbieta Filipek , Agnieszka Paczesna

1

Institute 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

-80 -40 0 40 80 120-0.2 -0.1 0.0 0.1 0.2 -1000 0 1000 -10 -8 -6 -4 -2 0 2 4 6 8 10 T=300 K M a g n e ti z a ti o n [e m u /g ]

Magnetic field [Oe]

T=2 K -60 -40 -20 0 20 40 60 -40 -20 0 20 40 2K 10K 20K 70K 170K 300K M a g n e ti z a ti o n [e m u /g ]

Magnetic field [kOe]

0 50 100 150 200 250 300 0.0000 0.0002 0.0004 0.0006 0.000 0.004 0.008 0.012 0.016 0.020 Temperature [K] FC70kOe ZFC70kOe M a g n e ti c s u s c e p ti b ilt y M /H [e m u /( g · O e )] FC50Oe ZFC50Oe 0 50 100 150 200 250 300 0.000 0.002 0.004 0.006 0.008 0.010 0 10 20 30 40 0.000 0.002 0.004 0.006 0.008 0.010 M a g n e ti c s u s c e p ti b ilt y M /H [e m u /( g · O e )] 70 kOe 10 kOe 3 kOe 500 Oe Temperature [ K] 50 Oe M a g n e ti c s u s c e p ti b ilt y [e m u /( g · O e )] 70 kOe 10 kOe 3 kOe 500 Oe Temperature [ K] 50 Oe 0 30 60 90 120 150 180 210 240 270 300 0 2 4 6 0.0 0.5 1.0 1.5 0 1 2 3 In te g ra te d in te n s it y [a rb . u n it s ] Temperature [K] L in e w id th [k G ] line 1 line 2 line 3 line 4 R e s o n a n c e fi e ld [k G ] -2 -1 0 1 2 3 -4 -2 0 2 4 6 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -3 -2 -1 0 1 T=250 K E P R s ig n a l [a rb . u n it s ] T=90 K Magnetic field [kG] T=10 K 0 1 2 3 4 5 6 7 E P R s ig n a l [a rb . u n it s ] Magnetic field [kG] 7 K 17 K 40 K 70 K 100 K 150 K 200 K 250 K 290 K

· Magnetism of iron ions in a high-spin state forming diverse magnetic nanocomplexes plays a central role in formation of magnetic properties of Ni Fe In VO .2 0.5 0.5 6

· Involvement of nickel ions in iron complexes in In-Fe-V layers through superexchange paths can explain higher than expected effective magnetic moment of Ni Fe In VO formulae unit.2 0.5 0.5 6

· Dc magnetization (static properties) and magnetic resonance (dynamics in microwave frequency range) show very different faces of complicated Ni Fe In VO magnetism.2 0.5 0.5 6

· Presence of at least three different types of magnetic nanocomplexes is evidenced in magnetization and magnetic resonance measurements.

· Thermal behaviour of the low temperature ferromagnetic complex closely resembles magnetization changes in FM nanoparticles. This suggests that the sizes of magnetic complexes in Ni Fe In VO solid solution might be in a nanometric range2 0.5 0.5 6

Conclusions

· Magnetization measurements revealed a step-like temperature dependence, demonstrating the presence of a few different types of magnetic entities confined to separate layers of trivalent indium and iron ions as well as possible vanadium ions in different valence states and nickel ions in neighbouring layers.

· Isothermal magnetization of Ni Fe In VO2 0.5 0.5 6 registered at six different temperatures has shown no saturation - 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)+áH, where L(x)=coth(x)-(1/x) is the S

Langevin function and x=(ì H)/(kT). That form of M(H) was often used e.g. in the superparamagnetic phase of magnetic p

nanoparticles.

· In magnetization of Ni Fe In VO2 0.5 0.5 6 in weak magnetic fields the hysteresis is observed. It is remarkable that even at room temperature the loop is detected. The remanent magnetization (remanence) and the coercive field (coercivity) determined from the loop decrease strongly with temperature increase. The dependence between these two hysteresis loop parameters is nearly linear.

· Strong magnetic resonance signal that has been registered in the whole investigated temperature range is typical for strongly coupled system of iron ions. High temperatures spectrum is composed from few components. On cooling the sample from RT the amplitude and the linewidth increased and the lineshape become very asymmetrical. An attempt was made to fit the spectrum with the sum of simple Lorentzian or Gaussian lines and that procedure was successful if at least three Lorentzian lines was used. Temperature dependence of the resonance field, linewidth and integrated intensity of each component line has been investigated.

Powder sample of Ni Fe In VO , that belongs to the two-component system 2 0.5 0.5 6

built by the isostructural compounds Ni InVO and Ni FeVO , was obtained by 2 6 2 6

traditional calcination method. Magnetization studies were carried on Quantum Design Magnetic Property Measurements System MPMS XL-7 with a superconducting quantum interference device magnetometer in magnetic fields up to 70 kOe and in 2–300 K temperature range. Magnetic resonance spectra of Ni Fe In VO in powder form were recorded on a conventional X-band Bruker 2 0.5 0.5 6

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.

Results

Experimental

A possible configuration of magnetic (filled circles) and nonmagnetic ions (open circles) in Ni Fe In VO in 2 0.5 0.5 6

(a,b) plane of the ilmenite structure. The lines indicate the Fe-O-Fe superexchange paths.

The side view (left) and the top view (right) of ilmenite structure (FeTiO )3 Proposed magnetic structure of Ni FeVO

2 6

The series of investigated Ni Fe In VO compounds2 x 1-x 6

Temperature dependence of dc magnetic susceptibility in ZFC mode in different magnetic fields

Temperature dependence of magnetic susceptibility M/H in ZFC and FC modes in two different external magnetic fields: H=50 Oe (upper panel) and H=70 kOe (lower panel).

Isothermal magnetization M of Ni Fe In VO as a 2 .5 0.5 6

function of an external magnetic field registered at six different temperatures.

Central part of hysteresis loop registered at 2 K (left panel) and 300 K (right panel).

SEM picture of the investigated powder sample of Ni Fe In VO 2 0.5 0.5 6

Temperature dependence of the magnetic resonance parameters.

Fitting of the spectra with Lorentzian lines.

Magnetic resonance spectra of Ni Fe In VO2 .5 0.5 6 solid solution recorded at few different temperatures.