Interparticle interactions mediated superspin glass to superferromagnetic transition in Ni-bacterial cellulose aerogel nanocomposites

Abstract

The interparticle interactions in a magnetic nanocomposite play a dominant role in controlling the phase transitions -superparamagnetic to superspinglass to superferromagnetic. These interactions can be tuned by controlling the size and number density of nanoparticles. Aerogel composites, 0.3 Ni-BC and 0.7 Ni-BC, consisting of Ni nanoparticles distributed in bacterial cellulose have been used as model systems to study the effect of interparticle interactions with increasing fraction of Ni in the composite. Contrary to conventional approach, the size of Ni nanoparticles is not controlled and was allowed to form naturally in the bacterial cellulose template. The structural characterization using x-ray diffraction and electron microscopies indicates the presence of only Ni and cellulose with no other phases. Thermogravimetric analysis shows that the Ni content in the two aerogels is 78 % and 83.8 % respectively. The uncontrolled growth of Ni in cellulose matrix results in the formation of nanoparticles with 3 different size distributions -< 10 nm particles mainly distributed along the length of fibrils, 50 nm particles present in the intermediate spaces between the fibrils and > 100 nm particles present in voids formed by the reticulate structure. The magnetic behavior of these composites as a function of temperature, magnetic field and frequency shows that different magnetic states can be accessed at different temperatures. At room temperature the composites exhibit a weakly ferromagnetic behavior with a coercivity of 40 Oe which increases to 160 Oe at 10 K. The magnetization at both the temperatures however is found to be non-saturating even at fields as high as 20 kOe. The transition from weakly ferromagnetic state at room temperature to a superferromagnetic state at low temperatures is mediated via a superspinglass state at intermediate temperatures.Both the superspinglass state and the superferromagnetic state are found to be sustained by the interparticle interactions aided by the presence of small nanoparticles along the length of cellulose fibres. A temperature dependent microstructural model has been developed combining the structural and magnetic results obtained from the two composite aerogels. *satish.vitta@iitb.ac.in

Cellulose Aerogels: Synthesis, Applications, and Prospects

“…Then, they prepared a new cellulose derivative aerogel by modifying cellulose aerogel with chloroacetic acid, dimercaprol, and Au(ш) to get an efficient heterogeneous catalyst in the oxidation reactions of aliphatic, benzyl alcohol, and ethylbenzene [233]. Thiruvengadam and Vitta prepared a Ni–BC aerogel nanocomposite with thermally sensitive magnetic behavior [234]. The Yao group developed an aerogel consisting of pressure-sensitive conductive material Ag/CNF by combining a silver mirror reaction with ultrasonic treatment [235].…”

Flexible bacterial cellulose / permalloy nanocomposite xerogel sheets – Size scalable magnetic actuator-cum-electrical conductor

“…Hence the FeNi 3 particles can be treated as isolated nanoparticles in a non-active matrix. The critical size, d sp for such particles above which they can sustain a stable magnetic moment against thermal demagnetization at any given temperature T is given by; 22,23 d sp ≈ 2 10k B T K u 1 3 (1) where k B is the Boltzmann constant and K u the effective magnetocrystalline anisotropy energy constant. The anisotropy energy constant K u depends on the chemical composition as well as crystal structure of the alloy.…”

“…Hence the FeNi3 particles can be treated as isolated nanoparticles in a nonactive matrix. The critical size, dsp for such particles above which they can sustain a stable magnetic moment against thermal demagnetization at any given temperature T is given by; 22,23…”

The interplay between single particle anisotropy and interparticle interactions in ensembles of magnetic nanoparticles

“…Upon cooling the system, the progressive ''blocking'' from the largest to the smallest particles can induce a progressive shift from a pure SPM to an SSG state and finally a complete chainlike SFM ordering even for purely dipolar interacting particles. 19 It should be underlined that concentrated ensembles of individually responding magnetic entities are required for several applications (e.g., magnetic recording, drug delivery, magnetic hyperthermia), where interparticle interactions cannot be neglected. 20 In this context, the magnetic behavior of an ensemble of nanoparticles can be described as a complex interplay between the single particle anisotropy (SPA) and the interparticle interactions (II).…”